Topic 6 of 92: Plate Tectonics: The Physical Dynamics of The Crust
Sat, Jul 10, 1999 (19:52) |
Marcia (MarciaH)
As one ocean widens the other narrows: Coming apart at the seams The physical dynamics of the Crust
142 responses total.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 1 of 142: Marcia (MarciaH) * Thu, Jul 15, 1999 (00:14) * 0 lines
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 2 of 142: Gi (patas) * Tue, Jul 27, 1999 (08:28) * 2 lines
...And is this where we'll reshape the earth?;-)
See topic #1 for details...
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 3 of 142: Marcia (MarciaH) * Tue, Jul 27, 1999 (12:28) * 1 lines
This would be the place, indeed. I think for the basic shape, we should retain the sphere (no matter how oblate) so we spin fast enough to keep us from flying off into space. Other than that...feel free to move about.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 4 of 142: Marcia (MarciaH) * Tue, Jul 27, 1999 (12:30) * 1 lines
Unless, that is, you want to reshape the entire place, which would mean moving the discussion to Orogeny and Diastrophism down the list.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 5 of 142: Marcia (MarciaH) * Mon, Oct 11, 1999 (16:36) * 5 lines
PLATE BOUNDARIES
EARTHQUAKES (COMPARE TO MAP ABOVE)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 6 of 142: MarkG (MarkG) * Tue, Oct 12, 1999 (09:47) * 1 lines
Just too fantastic, Marcia! Love these maps
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 7 of 142: Marcia (MarciaH) * Tue, Oct 12, 1999 (12:03) * 1 lines
You have made my day with your comments. Thanks! It is difficult to be inspired to post goodies I find without any input from readers. I really appreciate it!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 8 of 142: Marcia (MarciaH) * Tue, Oct 12, 1999 (12:07) * 1 lines
What I find fantastic about these maps is I personally know the people who created them - they work at the Hawaii Volcanoes Observatory overlooking the main Caldera of Kilauea Volcano. What a splendid place to work!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 9 of 142: Wolf (wolf) * Tue, Oct 12, 1999 (19:33) * 1 lines
nice graphics!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 10 of 142: Marcia (MarciaH) * Tue, Oct 12, 1999 (19:46) * 1 lines
Thanks!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 11 of 142: Gi (patas) * Thu, Oct 14, 1999 (14:07) * 1 lines
Marcia, the tectonic plates map is just what I had asked you for, thank you!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 12 of 142: Marcia (MarciaH) * Thu, Oct 14, 1999 (14:19) * 1 lines
It took me a while, but as soon as I saw it, I knew I had to post it for you!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 13 of 142: Gi (patas) * Thu, Oct 14, 1999 (14:24) * 1 lines
big [] and :-)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 14 of 142: Marcia (MarciaH) * Fri, Oct 15, 1999 (22:42) * 1 lines
*happy smile*
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 15 of 142: Marcia (MarciaH) * Thu, Oct 28, 1999 (22:05) * 5 lines
This map give some indication of the dynamics involved with crust subduction (as in Taiwan) where the Pacific Plate is being dragged under the Asian Plate:
From http://wwwneic.cr.usgs.gov/neis/qed/19991020064658.HTML
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 16 of 142: Marcia (MarciaH) * Thu, Oct 28, 1999 (22:08) * 1 lines
On the above map, the yellow line is the plate boundary. each little colored circle represents an earthquake. The deepest ones are on the left and the shallowest ones are on the right. People living there must have rubber dishes and drinking vessels rather than china and glassware!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 17 of 142: Gi (patas) * Sat, Oct 30, 1999 (03:33) * 1 lines
And if I were them, I'd live in tents!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 18 of 142: Marcia (MarciaH) * Sat, Oct 30, 1999 (13:31) * 1 lines
If I were them...I'd live somewhere else!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 19 of 142: Gi (patas) * Mon, Nov 1, 1999 (12:36) * 1 lines
Right! If possible...
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 20 of 142: Marcia (MarciaH) * Tue, Feb 1, 2000 (16:03) * 1 lines
I know "if wishes were horses, beggars would ride"...but, I wish I could see my graphics...*sigh*
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 21 of 142: Marcia (MarciaH) * Mon, Feb 7, 2000 (19:37) * 7 lines
The single best place on the Web for Plate Tectonics made easy to understand:
http://earth.usc.edu/~stott/Catalina/platetectonics.html
Here's how they think it happened:
http://pubs.usgs.gov/publications/text/historical.html
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 22 of 142: Marcia (MarciaH) * Mon, Feb 7, 2000 (23:14) * 3 lines
The way it looks now
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 23 of 142: Ginny (vibrown) * Tue, Feb 8, 2000 (09:47) * 5 lines
Great links!
So it sounds like no one really knows what actually causes the plates to move?
Does anyone know what causes "hot spots" like the one under Hawaii?
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 24 of 142: Marcia (MarciaH) * Tue, Feb 8, 2000 (12:03) * 3 lines
About the hot spot first...Nope! We are the only one still in evidence the way the earth is configured right now. There are all sorts of places which will tell you how it operates, but no one seems to know WHY it exists in the first place.
There is a subtle current driven by convection and subduction which powers the plates around, but it is not that simple. Some are moving away from and toward others in patterns which do not reflect this simple dynamic. I shall keep up on the literature and let post it as soon as there is a better idea out there.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 25 of 142: Gi (patas) * Tue, Feb 8, 2000 (15:12) * 2 lines
I like this map.
What's a hotspot? Or should I say the hotspot, since you say there's only Hawaii.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 26 of 142: Marcia (MarciaH) * Tue, Feb 8, 2000 (17:02) * 44 lines
Ah, The Hot Spot. Glad you asked. I wondered when this would come up, because there isn't a very good explanation of why we are here!
http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/description_plate_tectonics.html
Located in the middle of the Pacific Plate, the volcanoes of the Hawaiian Island chain are among the largest on
Earth. The volcanoes stretch 2,500 kilometers across the north Pacific Ocean and become progressively older to
the northwest. Formed initially above a relatively stationary "hot spot" in the Earth's interior, each volcano was
rafted away from the hot spot as the Pacific Plate moves northwestward at about 9 centimeters per year. The
island of Hawaii consists of the youngest volcanoes in the chain and is currently located over the hot spot.
From: Tilling, Heliker, and Wright, 1987, Eruptions of Hawaiian Volcanoes: Past, Present, and Future: Department of the Interior/U.S.Geological Survey Publication I know these people and there are no better informed on the subject of Hawaiian volcanoes and the "hot spot" theories:
The great majority of the world's earthquakes and active volcanoes occur near the boundaries of the Earth's shifting
plates. Why then are the Hawaiian volcanoes located near the middle of the Pacific Plate, more than 2,000 miles
from the nearest plate boundary? In 1963, J.Tuzo Wilson, a Canadian geophysicist, provided an ingenious
explanation within the framework of plate tectonics by proposing the "Hot Spot" hypothesis. Wilson's hypothesis
has come to be accepted widely, because it agrees well with much of the scientific data on the Pacific Ocean in
general, and the Hawaiian Islands in particular.
According to Wilson, the distinctive linear shape of the Hawaiian-Emperor Chain reflects the progressive movement
of the Pacific Plate over a deep immobile hot spot. This hot spot partly melts the region just below the overriding
Pacific Plate, producing small, isolated blobs of magma. Less dense than the surrounding solid rock, the magma
rises buoyantly through structurally weak zones and ultimately erupts as lava onto the ocean floor to form volcanoes.
Over a span of about 70 million years, the combined processes of magma formation, eruption, and continuous
movement of the Pacific Plate over the stationary hot spot have left the trail of volcanoes across the ocean floor
that we now call the Hawaiian-Emperor Chain. Scientists interpret the sharp bend in the chain, about 2,200 miles
northwest of the Big Island, as indicating a change in the direction of plate motion that occurred about 43 million
years ago, as suggested by the ages of the volcanoes bracketing the bend.
Part of the Big Island, the southeasternmost and youngest island, presently overlies the hot spot and still taps the
magma source to feed its two currently active volcanoes, Kilauea and Mauna Loa. The active submarine volcano,
Loihi, off the Big Island's south coast, may mark the beginning of the zone of magma formation at the southeastern
edge of the hot spot. The other Hawaiian islands have moved northwestward beyond the hot spot, were
successively cut off from the sustaining magma source, and are no longer volcanically active.
The progressive northwesterly drift of the islands from their point of origin over the hot spot is well shown by the
ages of the principal lava flows on the various Hawaiian Islands from northwest (oldest) to southeast (youngest),
given in millions of years: Kauai, 5.6 to 3.8; Oahu, 3.4 to 2.2; Molokai, 1.8 to 1.3; Maui, 1.3 to 0.8; and Hawaii,
less than 0.7 and still growing.
Even on the Big Island alone, the relative ages of its five volcanoes are compatible with the hot-spot theory. Kohala,
at the northwestern corner of the island, is the oldest, having ceased eruptive activity about 60,000 years ago. The
second oldest is Mauna Kea, which last erupted about 3,000 years ago; next is Hualalai, which has had only one
historic eruption (1800-1801), and lastly, both Mauna Loa and Kilauea have been vigorously and repeatedly active
in historic times. Beacuase it is growing on the southeastern flank of Mauna Loa, Kilauea is believed to be younger
than its huge neighbor.
The size of the Hawaiian hot spot is not know precisely, but it presumably is large enough to encompass the
currently active volcanoes of Mauna Loa, Kilauea, Loihi, and, possibly, also Hualalai and Haleakala. Some
scientists have estimated the Hawaiian hot spot to be about 200 miles across, with much narrower vertical
passageways that feed magma to the individual volcanoes.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 27 of 142: Marcia (MarciaH) * Tue, Feb 8, 2000 (17:27) * 9 lines
For a general discussion and great graphics concerning Hot Spots, please see
http://pubs.usgs.gov/publications/text/hotspots.html
The map below shows Hawaii is far from being the only hot spot on earth.
Using the Hawaiian Islands as a model here is the dynamics of a hot spot:
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 28 of 142: Ginny (vibrown) * Wed, Feb 9, 2000 (13:09) * 5 lines
I am still amazed that the eruption I saw in 1988 is still going on today, and actually started in 1983!
Which brings me to another question. How are "episodes" of an eruption defined?
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 29 of 142: Marcia (MarciaH) * Wed, Feb 9, 2000 (13:20) * 3 lines
An epidsode of an eruption ends when magma ceases to feed the chambers and lava output stops. The oneset of another eruption is preceeded by harmonic tremors as seen in this map made just before the latest episode commenced.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 30 of 142: Marcia (MarciaH) * Wed, Feb 9, 2000 (13:24) * 1 lines
Do you remember the campground whose bathrooms were locked when we were down at Waha'ula where the lava was flowing? Nothing is left of it. In fact, David asked me to hurry down and photograph it before it all disappeared, which I did with some remarkable results and near near-prostration. I photographed and watched as the lava crept over the existing structures, beach, trees, grassy area and into the sea. Incredible experience!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 31 of 142: Cheryl (CherylB) * Wed, Feb 9, 2000 (16:18) * 1 lines
Are some of the older islands (extinct volcanoes) of the Hawaiian chain now submerged? Having eroded back into the Pacific?
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 32 of 142: Marcia (MarciaH) * Wed, Feb 9, 2000 (17:17) * 3 lines
Some are merely atolls - rings of coral (the original rim of the caldera uponm which many generations of coral have grown)with water inside (Lagoon) and outside. Midway Island is one such, as are several others to the west of the main inhabited islands. Kure is the last island in the group considered an island though the Hawaiian ridge continues northwest from Kure and heads toward Japan. Actually, there are extinct volcanoes on most islands which fit the definition: The volcano has eroded down past the level of the original magma chamber.
Cheryl, did you note the graphics I managed to find in the last two days since I got my place on Spring's new hard drive working?!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 33 of 142: Cheryl (CherylB) * Wed, Feb 9, 2000 (17:27) * 1 lines
Graphics have been duly noted. They look great.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 34 of 142: Marcia (MarciaH) * Wed, Feb 9, 2000 (17:56) * 6 lines
I just found the greatest one of all but it is way too big (1,060 KB)to put here and it would slow down the loading significantly. But, go look at it. Very pretty globe, but they need to work on the rotation.
http://www.muohio.edu/tectonics/ATglobe.GIF
Thanks for looking at the graphics. I was being a bit snippy with an inside joke on my paleo lad assistant who insisted it was Laurelasia and not Laurasia. Oh well, guess you had to be there...!
Check Geo2 where volcanoes are discussed first hand! I live on the world's most active one, actually!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 35 of 142: Marcia (MarciaH) * Wed, Feb 9, 2000 (17:57) * 1 lines
(lab assistant...some day, Marcia...!)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 36 of 142: Marcia (MarciaH) * Wed, Feb 9, 2000 (18:11) * 5 lines
Since I cannot put the one I love on Spring (and those of you looking into it, wait till it all loads before you make any judgments. It takes off wonderfully when fully loaded and is a really wonderful gif.)...I offer our globe as Pangaea
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 37 of 142: Marcia (MarciaH) * Fri, Feb 11, 2000 (17:12) * 0 lines
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 38 of 142: Marcia (MarciaH) * Fri, Feb 11, 2000 (17:21) * 0 lines
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 39 of 142: Marcia (MarciaH) * Fri, Feb 11, 2000 (17:28) * 9 lines
Warren's Theory regarding the Juan de Fuca Plate:
I'm gonna make like Casey and make a prediction. If you want to know when the big California quake, and its dropping off into the Pacific, will occur, watch the Juan de Fuca plate around Seattle. This little remnant of an older plate is
caught between the Pacific plate and the North American plate. When this little one subsides enough under the Pacific plate, I think the San Andreas will let go. My point was simply that with the NA plate pushing west and the Pacific plate pushing south/southeast, the little Juan de Fuca plate seems to be sitting in between these two giants, almost in a linchpin position. My thought is that the "Big One" in California might just come when the Juan de Fuca plate finally lets go and slips quickly under the Pacific plate, allowing the North American plate to move in quickly to fill the void. And we all know how nature abhors a void.
The dynamics of his Theory:
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 40 of 142: Marcia (MarciaH) * Fri, Feb 11, 2000 (17:29) * 1 lines
Whew! Only took me three tries because I had renamed the file and not refreshed my ftp list...and tried to post a non-existant file...*sigh*
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 41 of 142: Cheryl (CherylB) * Sat, Feb 12, 2000 (14:55) * 1 lines
Interesting theory on the effect the subduction of the Juan de Fuca Plate will have on the San Andreas Fault. I am a bit familiar with one that suggests that California will breaking off from North America from roughly south to north. The evidence for this being the Gulf of California. The theory is that Baja California was once attached to the rest of Mexico, and that the Gulf of California is a rift splitting off a section of land, similar to the workings of the Great Rift in Africa.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 42 of 142: Marcia (MarciaH) * Sat, Feb 12, 2000 (15:22) * 3 lines
Indeed, both rifts are zones of expansion. Subduction makes all the fun, though.
The cascades are fed by the molten rock pushed into them as the JdF plate dives under the NA plate. I should repost the Volcanic Islands graphic again. In this case the area on that island is being subducted on the western side and expanded on the eastern side. Each little round colored dot represents an earthquake caused by the expansion and subduction going on there.
![]()
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 43 of 142: Marcia (MarciaH) * Sat, Feb 12, 2000 (15:24) * 2 lines
Sorry about that...try again (if I could telnet I could see what I did wrong)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 44 of 142: Cheryl (CherylB) * Sat, Feb 12, 2000 (15:27) * 1 lines
When California does seperate from North America, the effect might be something like Vancouver Island.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 45 of 142: Marcia (MarciaH) * Sat, Feb 12, 2000 (15:30) * 1 lines
Yes, could very well be! Have you ever checked the islands in the San Francisco Bay? Some, like Alcatraz Island, are rock of a very different sort from the rest of the terrain. It came from far away and down deep! I'd like to read about this stuff, not experience it, thanks. It's gonna be some temblor!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 46 of 142: Marcia (MarciaH) * Sat, Feb 12, 2000 (18:03) * 4 lines
A rather pretty - though not all that informative - map of the World's Plates:
See also http://tvnight.org/yapp-bin/restricted/read/geo/26.3 for the comparison of earthquake incidents and plate boundaries. It is not coincident.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 47 of 142: Cheryl (CherylB) * Wed, Feb 16, 2000 (17:29) * 1 lines
You're absolutely right, it's much better to read about massive geophysical events. RE: The remark about earthquake incidents and plate boundaries, the worst earthquake(s) in US History occurred in near New Madrid, MO in 1812-1813. The bed of the Mississippi River was moved several miles in that area, and that part of the river ran backwards (a whirlpool?) for a few days. I think what that means is the flow was temporarily from south to north. Fortunately, that area was not heavily settled then. The point is Missouri is nowhere near a continental plate boundary.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 48 of 142: World Builder (MarciaH) * Wed, Feb 16, 2000 (17:36) * 1 lines
Yup! Thanks for bringing that up in here. It was discussed off-topic in Geo somewhere with KarenR...probably Geo 7....
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 49 of 142: Cheryl (CherylB) * Sun, Feb 20, 2000 (14:07) * 1 lines
Nothing much is happening here in Plate Tectonics, on this board I mean not the Earth. As I type this North America, upon which I sit, is headed west, mostly. Marcia, on your intro to this board you note that as one ocean grows another gets smaller. So it is. The Atlantic which at one is believed to have looked something like the Dead Sea, is now a large expanse of open water. The Meditteranean Sea was once an ocean, now it's a land locked sea. Lastly, the great ancient world girdling ocean Panthalassa is now the Pacific and Indian Oceans. The Pacific is still formidable, being the largest physical feature on the Earth, covering about 1/3 of the surface.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 50 of 142: World Builder (MarciaH) * Sun, Feb 20, 2000 (14:41) * 1 lines
Good points, Cheryl...and I seem to be sitting out here on a comparatively miniscule bit of rock which has poked itself above the surface of the world's greatest ocean (actually, they are all one continuous, are they not?!) The spreading of the mid-Atlantic ridge is expanding that ocean, and the subduction of the Pacific plate is making this vast body of water smaller little by little. Hawaii is being dragged inexorably northwestward over that hotspot. One day we will be a suburb of Tokyo, but it won't be there when we arrive...!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 51 of 142: Gi (patas) * Wed, Feb 23, 2000 (06:58) * 1 lines
Marcia, great discussion. I like the hotspot theory. And the map on post #27 is another for my collection. If you ever need it ;-)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 52 of 142: World Builder (MarciaH) * Wed, Feb 23, 2000 (10:08) * 1 lines
Thanks, Gi. The beautiful thing about the internet is just when it occurs to me that I need an illustration of whatever I am talking about, someone has just posted exactly what I needed.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 53 of 142: Gi (patas) * Wed, Feb 23, 2000 (10:17) * 1 lines
OT: The "list of the most recent posts" is working again! I am so excited. Thank you, Master Programmer! :-)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 54 of 142: Marcia (MarciaH) * Wed, Feb 23, 2000 (12:06) * 1 lines
*grin* The Magician has done masterful work this morning. We are all pretty again. I also like the lists of the recent posts though I got used to using my main hotlist.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 55 of 142: Gi (patas) * Wed, Feb 23, 2000 (22:03) * 1 lines
Oh, I admit I use it to see who's online when I am =)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 56 of 142: Marcia (MarciaH) * Wed, Feb 23, 2000 (22:12) * 1 lines
You do, as well?! *grin*
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 57 of 142: Cheryl (CherylB) * Thu, Feb 24, 2000 (16:36) * 3 lines
I sorry. I can't help myself. I have the urge to post a bad pun -- we love the Earth in spite of its faults.
What would happen if the Earth's crust were of one solid piece; would volcanoes pop up all over the place?
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 58 of 142: Marcia (MarciaH) * Thu, Feb 24, 2000 (17:08) * 3 lines
Since we are cooling down slowly, we could not keep from buckling. Imagine a rigid balloon (yeah...right!) or a basketball, even. Now let the air out. It no longer remains a sphere unless there are uniform wrinkles to take up the slack. That is why there is a zone of melting and refilling for volcanoes. Below that it solidifies and above that it solidifies. Clever, this earth, no?!
Love your pun...*appreciative groans*
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 59 of 142: Mike Griggs (mikeg) * Sat, Feb 26, 2000 (12:21) * 1 lines
crust dynamics is my favourite topic :-)) Lithospheric flexure anyone? *grin*
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 60 of 142: Marcia (MarciaH) * Sat, Feb 26, 2000 (12:39) * 4 lines
Hi Mike!! E Komo Mai...*grin* (Welcome in Hawaiian) Wow! Got a real fan of our plastic earth. Think of the problems we would have without flexure! Big time rending of the surface fabric...much better in little pieces and bit by bit than one gigantic stress buckling. Especially with the tides caused by the Sun and Moon not just on water, but also causing lithosphere bulging in their direction with great regularity.
I am delighted out of all proportion to have you post here. Most honored, too.
Thanks! Please return. And, if you find great plate graphics, please feel free to post them or let me know and I'll put them on my space at Spring and I'll post them (more permanent that way.) *Hugs*
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 61 of 142: Mike Griggs (mikeg) * Sat, Feb 26, 2000 (13:44) * 9 lines
Hi Marcia,
Lithospheric flexure was my research title...lots of great pics and stuff like that. Also some fat math, just to make it look good :-)
I'd read up on the hotspot theory before - smart guy that Wilson. You should look at the work of Tony Watts (Oxford University) http://www.earth.ox.ac.uk/~tony/watts/INDEX.HTM
and there's also a more index-like page at http://www.earth.ox.ac.uk/~webmaint/Research/Tectonics.shtml
Lots of Watts' pictures turned up in my dissertation :-)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 62 of 142: Marcia (MarciaH) * Sat, Feb 26, 2000 (14:08) * 3 lines
Cool, Mike! Great Name for your researcg title! I had no idea of what course of study your University tour was pertaining. How fortuitous.(Happy me... jumping up and down gently because we have had earthquake swarms lately and I do not want to cause a really big one - all 116 pounds of me...) It is way beyond the realm of propriety to ask you to your research in little bits of wisdom from time to time, but I hope you might help someone who graduated from college just before they began teaching Plate Tectonics as a given rather than a theory...and to help keep me on the straight and narrow as to my statements. If I am wrong, correct me, please!!! Off to check your lovely links...sigh!
And, he is good looking, too?! Wow!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 63 of 142: Marcia (MarciaH) * Sat, Feb 26, 2000 (14:19) * 0 lines
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 64 of 142: Marcia (MarciaH) * Sat, Feb 26, 2000 (14:21) * 1 lines
Oh yes, about that fat math....that is why I am not a professional Geologist. My son can extrapolate and measure the volume of a magma chamber which is totally invisible. I have no idea how and my mind rebels at any attempt on my part to try to understand it. Bravo, Mike! You da Man!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 65 of 142: Marcia (MarciaH) * Sat, Feb 26, 2000 (14:22) * 1 lines
I closed those teeny tags then scribbled them - better hit the softball field!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 66 of 142: Marcia (MarciaH) * Sat, Feb 26, 2000 (14:45) * 2 lines
OK guys, go look at Mike's URLs and see some really great modelling concerning
Lithospheric flexure. (Mike! Those guys are using your title!) Be happy it exists or Mauna Loa's weight would have punched through long ago!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 67 of 142: Mike Griggs (mikeg) * Sat, Feb 26, 2000 (14:55) * 3 lines
Lithospheric flexure is actually a general term rather than something I can claim to have created :-) My research title of "Numerical Modelling of Lithospheric Flexure at Hawaii" was all mine though...doesn't quite roll of the tongue as well as the former, though *grin*
LF is really fun...stick a big mountain on the planet to bend it and then work out how thick the crust is based on the bendiness :-))
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 68 of 142: Gi (patas) * Sat, Feb 26, 2000 (14:58) * 1 lines
Only you do not stick it, do you? You pull it, rather, I think ;-)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 69 of 142: Mike Griggs (mikeg) * Sat, Feb 26, 2000 (14:59) * 1 lines
i think you push for mountains, actually...
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 70 of 142: Gi (patas) * Sat, Feb 26, 2000 (15:01) * 1 lines
I guess you're right :-)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 71 of 142: Mike Griggs (mikeg) * Sat, Feb 26, 2000 (15:03) * 1 lines
i think you push for mountains, actually...
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 72 of 142: Mike Griggs (mikeg) * Sat, Feb 26, 2000 (15:03) * 1 lines
oops :-) re-posted
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 73 of 142: Mike Griggs (mikeg) * Sat, Feb 26, 2000 (15:04) * 1 lines
or, as with hawaii, you find a hot bit of the earth and run a plate across it, creating your very own chain of private islands
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 74 of 142: Marcia (MarciaH) * Sat, Feb 26, 2000 (20:48) * 1 lines
Mike...When were you in Hawaii? You DO know that I live in Hilo on the slopes of Mauna Loa with Kilauea perking just 30 miles away, did you not? Wow! I am fascinated to know more about your research. My son David is also a Geologist...! Auwe! I did not know... No wonder I put you on my babes list with those Blond Brits which run rampant through my family *grin* Please make yourself at home and feel free to correct my (probably) inumerable errors.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 75 of 142: Marcia (MarciaH) * Sat, Feb 26, 2000 (23:51) * 1 lines
Wish William could join the conversation...
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 76 of 142: Mike Griggs (mikeg) * Sun, Feb 27, 2000 (14:36) * 3 lines
alas I've never made it to Hawaii...my work was purely theoretical. I did have a nice dream about flying over the chain once, though...almost as good as being there :-)
I would post my diss. if I had a computer copy of it...unfortunately, Mr. Broken Hard Disk ate the only computerised copy...if I ever have the time/energy I'll put it all into the computer again. Several of the pictures I used you have above - cool! :-)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 77 of 142: Marcia (MarciaH) * Sun, Feb 27, 2000 (15:13) * 3 lines
Pox on Broken Mr Hard Drive. Scan it in sometime when you have nothing more pracitcal to do - or better still, when it is published, may I have a reprint (or do they not do that anymore?!
I've been to Britain from Hawaii 3 times. It is only s 20-hour flight over what looks exactly like the neatest 3-D topo globe ever. It is your turn to come over here to see how big Mauna Loa can grow before the thickness of the crust limits it - or does it? Or whatever...!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 78 of 142: Mike Griggs (mikeg) * Sun, Feb 27, 2000 (15:31) * 1 lines
I don't think that the crust thickness can limit the size can it? Although I suppose the lithosphere underneath the main load can fracture...still I'm not sure this can cause a size limit. Maybe it can...I can't remember off the top of my head...
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 79 of 142: Marcia (MarciaH) * Sun, Feb 27, 2000 (16:17) * 1 lines
Since you can extrapolate how thick the crust must be to be able to withstand the pressure of mountains of known mass, is it possible to determine what would happen should the mountain mass become heavier than the flex and thickness of the crust can handle? Conversely, does the crust thicken beneath the mountain as it builds greater and greater mass? Has anyone studied this? Is there geological evidence of what happens when the mountain becomes too heavy for the crust and flex to handle? Just curious since I can see the top of Mauna Loa from my yard...!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 80 of 142: GeoLady (MarciaH) * Thu, Apr 27, 2000 (22:58) * 50 lines
Mike, here's one for you!
******************************
Postdoc Position in Leeds
******************************
From: Jurgen Neuberg
THE UNIVERSITY OF LEEDS
SCHOOL OF EARTH SCIENCES
RESEARCH FELLOW IN GEOPHYSICS
This NERC-funded postdoctoral position is available immediately for a
fixed period of three years. Research is primarily in volcano
seismology and will involve numerical simulations of seismic wavefields
in magmatic environments. Work will be centered on the analysis of
seismic as well as other datasets from Montserrat and the development
of computercodes to simulate the time-dependence of magma properties in
order to compare the resulting seismic signature with Montserrat data.
Applicants should have a PhD and research experience in some of the
relevant areas of volcanology and seismology, and scientific
programming in a Unix environment.
Salary will be on the scale for Research Staff Grade 1A, within the
range 15,735-17570 according to qualifications and relevant experience.
Informal enquiries may be made to Dr Jurgen Neuberg by email
locko@earth.leeds.ac.uk or to Dr Brian Baptie bbap@mail.nmh.ac.uk; tel
+44 113 2336769 (J. Neuberg, from May 15)
Application forms and further particulars may be obtained from Mr Bob
Moorcroft, School of Earth Sciences, The University of Leeds, Leeds LS2
9JT UK, tel +44 113 233 5254, fax +44 113 233 5259, e-mail:
earrfm@earth.leeds.ac.uk.
Closing date for applications 31 May 2000.
The University of Leeds promotes an Equal Opportunities Policy.
------------------------------------------------------------------------
Dr Jurgen Neuberg
School of Earth Scienecs
The University of Leeds
Leeds LS2 9JT, United Kingdom
Tel: office +44 113 233 6769
home +44 113 293 9392
Fax: +44 113 233 5259
E-mail: locko@earth.leeds.ac.uk
------------------------------------------------------------------------
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 81 of 142: Ian Greenwood (judgedred) * Sat, Jun 24, 2000 (16:14) * 6 lines
Just found you.
I am new to Geology, having started a college course last September, being 40, have missed a lot of years.
Live in England but have a special interest in Washington State having a friend in Seattle. Hawaii is also on the favorites list having covered its volcanic activity in class.
Great site, fabulous maps and discussions.
Ian
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 82 of 142: Marcia (MarciaH) * Sat, Jun 24, 2000 (16:27) * 1 lines
Welcome and Aloha! Your name is on my Yahoo IM list...we must have spoken before. I am available most days Hawaii (which means you are having breakfast as I am having dinner - we are 11 hours behind you!) I have a friend who teaches at Central Washington and has a PhD in Geology. More volcanic Hawaiian stuff on Geo topic 2. I live about 30 miles from the ongoing eruption.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 83 of 142: Marcia (MarciaH) * Sat, Jun 24, 2000 (16:34) * 2 lines
Thanks for the kind comments about Geo. It will be my memorial or whatever. I live in here and finding interesting things for it is a true labor of love.
It is nice to have a more mature man amongst us. Happy Me!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 84 of 142: Marcia (MarciaH) * Fri, Oct 6, 2000 (19:57) * 16 lines
Continents in Collision: Pangea Ultima
NASA Science News for October 06, 2000
Creeping more slowly than a human fingernail
grows, Earth's massive continents are nonetheless
on the move. Geologists say that in 250 million
years the Atlantic Ocean could be just a distant
memory while Earthlings will be able to walk from
North America to Africa.
FULL STORY at
http://science.nasa.gov/headlines/y2000/ast06oct_1.htm?list89800
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 85 of 142: Marcia (MarciaH) * Thu, Jan 11, 2001 (19:21) * 7 lines
Ian, this map's for you: http://nmnhwww.si.edu/gvp/volcano/
WORLD VOLCANISM AND PLATE BOUNDARIES - ONE AND THE SAME
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 86 of 142: Marcia (MarciaH) * Wed, Jan 17, 2001 (12:28) * 55 lines
Scientists Find Seismic 'Hot Spots' in California
LOS ANGELES (Reuters) - Future earthquakes could inflict the severest
shaking and greatest damage on a densely populated area of
Southern California that stretches from the skyscrapers of downtown
Los Angeles to the wealthy suburbs of Orange County, according to a
study Tuesday.
"We find that the area extending from approximately the Los Angeles
Memorial Coliseum (in downtown Los Angeles) down toward Anaheim,
centered in a long, trough-like fashion, is an area where we'll probably
having the most extreme shaking in future earthquakes," Thomas
Henyey, the study's lead scientist and director of Southern California
Earthquake Center, said.
The study, conducted by a consortium of universities and the U.S.
Geological Survey, was based on five years of research following the
1994 Northridge quake that rocked Southern California, killing 57
people and causing more than $20 billion in damage.
More than 20 scientists studied major basins in Southern California for
clues to help improve seismic analysis after the quake that registered
a magnitude of 6.7.
Other vulnerable areas include the San Fernando valley northwest of
Los Angeles and parts of Ventura County, extending north and west
from the city, Heyney said.
The sites most vulnerable to hard shaking are valleys and basins
featuring flatter ground, softer surface soil, and thicker layers of
sediment resting atop the hard bedrock that lies below the earth, the
scientists said.
They added that it was no surprise that in the Northridge quake, areas
featuring softer soil, such as portions of the Santa Monica freeway,
were more severely damaged than other areas that were even closer to
the epicenter.
Most earthquake fatalities and damage occur when buildings and other
structures fail during violent shaking caused by seismic waves. Areas of
soft sedimentary rock shake far more than rocky mountainous areas,
said Lucy Jones, scientist-in-charge for the United States Geological
Service.
"If you live up in the mountains you can get away from the
amplification of seismic waves that occur down in the valleys. This is
another piece of information all of us in Southern California can use to
manage the risks in our lives," Jones said.
That doesn't mean Southern California residents should start packing
their bags and heading for the hills, she said.
There are many other factors that determine an area's vulnerability to
quakes -- including distance from a quake's epicenter, the strength of
a quake, and direction in which a fault ruptures, he said. In addition
each new earthquake features unique, unpredictable peculiarities, she
said.
However the new data will make earthquake predicting more accurate.
It will also help insurers make clearer estimates, guide builders as they
bolster new and existing roads and buildings against quakes, influence
public policy, and help other countries interpret their own earthquake
data, Heyney said.
Southern California, the scientists said, is an area that accounts for
half of all U.S. earthquakes and where major earthquakes occur about
every 30 years.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 87 of 142: Marcia (MarciaH) * Wed, Feb 7, 2001 (20:43) * 17 lines
India Earthquake - Please read this! (thanks, Ian)
from: Noerjadi, Andrea
Sent: 2/8/01 5:02 AM
Subject: Click and Donate for the EarthQuake Relief
There is a site called http://www.causeanaffect.org/ which is paid for by corporate sponsors. Every click on its "Save a life" button will
result in donation of food packets for the victims. It will not cost anything to the people clicking on the site, because corporations are paying for the donations. One click per day is counted for donation.
I would appreciate it if you pass it along to the people in your address book.
Regards-
fr
Yahoo! Groups Sponsor
www.
[earthquake] posts replies to all list recipients. earthquake@yahoogroups.com
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 88 of 142: Marcia (MarciaH) * Fri, Mar 23, 2001 (14:16) * 3 lines
Thanks to Ian for the following URL. Bet you haven't heard this one explainatin for the Tunguska Event before:
http://www.geocities.com/olkhov/tunguska.htm
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 89 of 142: Cheryl (CherylB) * Fri, Apr 13, 2001 (13:43) * 1 lines
I've never come across that account for Tunguska before. It does seem entirely plausible. The most bizarre theory I've come across in regard to the Tunguska Event has to do with Tesla and the testing of some "highly secret application of electricl energy". No kidding.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 90 of 142: Rob Glennie (AotearoaKiwi) * Wed, Jun 6, 2001 (00:51) * 5 lines
Hi
I hope you don't mind New Zealand making an extraordinary claim? I lay claim to the land of the New Zealand continent below sea level. I know it is something like 30 times bigger than New Zealand as it is presently known but it all part of our massive continental shelf.
Rob
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 91 of 142: Marcia (MarciaH) * Wed, Jun 6, 2001 (14:00) * 3 lines
Mind? I am delighted that you posted this amazing information here. I definitely need to see a topo map of the entire basin with NZ and surrounding continent in the middle.
I wish I knew what was going on with my PC... I cannot get the National Geographic map to which you referred. I am relying on the New Zealand government map which shows towns and a little topography but none below sea-level. Off I go to hunt up more maps. Rob, could you please send at least the url for where to go. Meanwhile I will use Mapquest to see what I can find.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 92 of 142: Marcia (MarciaH) * Wed, Jun 6, 2001 (14:03) * 1 lines
Rob, have you designed your flag and named your continent? I am curious how your creative mind works. Your scientific one works just fine.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 93 of 142: Rob Glennie (AotearoaKiwi) * Fri, Jun 8, 2001 (04:15) * 7 lines
Hi
I want a flag with the outline of New Zealand in a cup shape shown by two silver ferns whose stems are interlocking in white. It should be on a black backdrop because that is our national colour. The continent should be called Kiwiana based on the name Gondwana.
Mapquest may actually be your best bet because I am not hot on things to do with the internet. I tend to stick to the clubs and groups instead of surfing freely.
Rob
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 94 of 142: Marcia (MarciaH) * Fri, Jun 8, 2001 (12:53) * 5 lines
You have thought about your new land and all that symbolism I can follow most closely. An excellent choice for the country's name, as well. What is the symbolism for having black as New Zealand's national color? If your silver ferns are like ours, they are lacy, pretty, and the undersides of the fronds are covered with silver spores. If you put a little one on your jeans and give is a slap then carefully peel it away, the silvery outline remains on your clothes.
Rob, I am pretty good with hunting stuff up on the internet. Please let me know if I can help you find anything. In fact, that is what I do when not putting stuff in here, internet research has replacead a lot of library research for me.
Next you need a national anthem. (I am still hunting up your NZ national anthem on the web. It is one of the very few I am lacking.)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 95 of 142: Cheryl (CherylB) * Fri, Jun 8, 2001 (15:45) * 3 lines
Kiwiana. A new continent.
Does anyone know how Gondwanaland got its name? I understand Pangea; that means "All Land" in Greek. After Pangea broke into northern and southern contenents, Gondwana or Gondwanaland was the great southern continent. What was the name of the great northern continent? Is it something like Lareasia? I know that's not even close.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 96 of 142: Marcia (MarciaH) * Fri, Jun 8, 2001 (17:01) * 1 lines
It's all back some few hundred posts but let me refresh memories because I have also forgotten. You're right about Pangea. (Kiwiana sounds so lovely)
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 97 of 142: Marcia (MarciaH) * Fri, Jun 8, 2001 (17:26) * 9 lines
http://pup.princeton.edu/chapters/s6276.html
Gondwanaland (meaning "Land of the
Gonds," an indigenous Indian people living in the region where the early convincing
evidence of the existence of the supercontinent was discovered). Gondwanaland once
included Africa, South America, Antarctica, Madagascar, and India, conjoined into a
single mega-continent. The events of the African Rift Valley system over the past 20 million
years simply continue this complex process of fragmentation of the old supercontinent, and
the Okavango Delta is merely the youngest manifestation of its effects.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 98 of 142: Marcia (MarciaH) * Fri, Jun 8, 2001 (17:43) * 7 lines
Very interesting background in this site
http://www.huxley.ic.ac.uk/Local/EarthSciUG/ESSecondYr/GEODYN/cdrift.html
Orogenic belts
There is a striking continuity of fold belts across Laurasia and Gondwana. For example the Appalachian fold belt of western North America seems to be continuous with the Caledonides of NW Europe. Furthermore, sediments within these foldbelts indicate that their source regions existed in what is now ocean. Thus, sediments from the Caledonides of northwest Europe appear to have been derived from the west, while sediments in Guyana in northeast South America were
derived from the east and contain diamonds which appear to be derived from the Sudan.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 99 of 142: Cheryl (CherylB) * Sat, Jun 9, 2001 (10:43) * 1 lines
Many thanks Marcia for the inforamation and the links.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 100 of 142: Marcia (MarciaH) * Sat, Jun 9, 2001 (15:55) * 1 lines
No one is saying why Laurasia was called that (will check a few books on my shelf instead of the learned scholars ont he 'net. )
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 101 of 142: Rob Glennie (AotearoaKiwi) * Mon, Jun 11, 2001 (01:01) * 23 lines
Hi
Marcia, I will spare you the hassle of looking for our anthem on the net.
God Defend New Zealand (the part we sing)
God of nations at thy feet
In the bonds of love we meet
Hear our voices we entreat
God defend our free land
Guard Pacific's triple star
from the shafts of strife and war
Make her praises heard afar
God defend New Zealand
Or are you looking for the whole thing. Given a couple minutes I can find the Maori verse as well and post it.
I was thinking about insurance policies and stuff like that. Would it not be pretty difficult to get insurance against the wrath of Nature if you build in the zones where lava flows HAVE BEEN KNOWN to go. I have this idea in my head
that California (earthquakes), Florida (hurricanes), and Texas (tornadoes), should be actively discouraging economic activity in those zones as the risk of a earthquake/hurricane/tornado is too high to ignore.
Rob
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 102 of 142: Marcia (MarciaH) * Mon, Jun 11, 2001 (13:28) * 3 lines
Add too that list of places not to build, the Mississippi River flood plain. Or, any other mighty river, for that matter. Hawaii has declared some places off limits for building by zoning them for non-inhabitation only due to the liklihood of further lava flows occurring there.
Rob, the words are lovely. Now I must hunt down the music to which it is sung. Have you chosen an anthem for Kiwiana? Please, no English drinking songs. Ours is just about unsingable! I have learned the Hawaiian National Anthem and the Hilo March in Hawaiian by singing them phoenetically whilst vacuuming. That way my awful singing is drowned out and I finally memorize them. I'd love to see yours in Maori. Is it sung in both languages as a matter of course? The Hawaiian one is sung ONLY in Hawaiian, as is the Hilo March.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 103 of 142: Marcia (MarciaH) * Mon, Jun 11, 2001 (13:51) * 1 lines
Alright, Rob! I downloaded bpth the Maori and English versaons of New Zealand's Anthems. Sung by a female pop singer wiht a lovely voice, but not the original way I wish to have it, so I will continue my search. It is lovely, though. Simeple, dignified and says it all in a few words. It is very special, indeed!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 104 of 142: Marcia (MarciaH) * Mon, Jun 11, 2001 (13:53) * 1 lines
It is remarkable how much sung Maori sounds like Hawaiian! I would imagine spoken, they would also resemble one another!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 105 of 142: Marcia (MarciaH) * Mon, Jun 11, 2001 (14:00) * 46 lines
God of nations! at Thy feet
In the bonds of love we meet,
Hear our voices, we entreat,
God defend our Free Land.
Guard Pacific's triple star,
From the shafts of strife and war,
Make her praises heard afar,
God defend New Zealand
Men of ev'ry creed and race
Gather here before Thy face,
Asking Thee to bless this place,
God defend our Free Land.
From dissension, envy, hate,
And corruption guard our State,
Make our country good and great,
God defend New Zealand.
Peace, not war, shall be our boast,
But, should foes assail our coast,
Make us then a mighty host,
God defend our Free Land.
Lord of battles in thy might,
Put our enemies to flight,
Let our cause be just and right,
God defend New Zealand.
Let our love for Thee increase,
May Thy blessings never cease,
Give us plenty, give us peace,
God defend our Free Land.
From dishonour and from shame
Guard our country's spotless name
Crown her with immortal fame,
God defend New Zealand.
May our mountains ever be
Freedom's ramparts on the sea,
Make us faithful unto Thee,
God defend our Free Land.
Guide her in the nations' van,
Preaching love and truth to man,
Working out Thy Glorious plan,
God defend New Zealand.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 106 of 142: Marcia (MarciaH) * Mon, Jun 11, 2001 (14:01) * 12 lines
God Defend New Zealand
Thomas Bracken wrote his poem in the early
1870s, and offered a prize of 10 guineas for the best
musical setting. This was won by Otago
schoolteacher John Joseph Woods. In 1940, on the
recommendation of the NZ Centennial Council, the
Government declared God Defend New Zealand to
be the National Hymn, and bought the copyright. In
1977, with the Queen's consent, God Defend New
Zealand was given equal status with God Save the
Queen as one of New Zealand's national anthems.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 107 of 142: Marcia (MarciaH) * Mon, Jun 11, 2001 (14:12) * 46 lines
AOTEAROA
1. E Ihoa Atua,
O nga Iwi! Matoura,
Ata whakarongona;
Me aroha roa.
Kia hua ko te pai;
Kia tau to atawhai;
Manaakitia mai
Aotearoa.
2. Ona mano tangata
Kiri whereo, kiri ma,
Iwi Maaori Pakeha
Repeke katoa,
Nei ka tono ko nga he
Mau e whakaahu ke,
Kia ora marire
Aotearoa.
3. Tona mana kia tu!
Tona kaha kia u;
Tona rongo hei paku
Ki te ao katoa
Aua rawa nga whawhai,
Nga tutu a tata mai;
Kia tupu nui ai
Aotearoa.
4. Waiho tona takiwa
Ko te ao marama;
Kia whiti tona ra
Taiawhio noa.
Ko te hae me te ngangau
Meinga kia kore kau;
Waiho i te rongo mau
Aotearoa.
5. Tona pai me toito;
Tika rawa, pono pu;
Tona noho, taha tu;
Iwi no Ihoa.
Kaua mona whakama;
Kia hau te ingoa;
Kia tu hei tauira;
Aotearoa.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 108 of 142: Marcia (MarciaH) * Mon, Jun 11, 2001 (14:22) * 3 lines
I should create a national anthem topic in Music, as if I did not have enough up and running here and there already. This most dignified of the 4 versions I managed to copy off the internet (NOT Napster) is by the New Zealand Symphony orchestra http://nz.com/NZ/Culture/Music/Audio/natanth.au
Nations are part of Geo, perhaps I should do it here. They won't let me create my own topics in music, I fear. If that is the case... I shall work around them.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 109 of 142: Marcia (MarciaH) * Fri, Jun 22, 2001 (23:19) * 8 lines
http://www-seismo.hannover.bgr.de/ermos.html
Worldwide earthquakes with magnitude M> = 5.0 during the last 12
months
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 110 of 142: Marcia (MarciaH) * Fri, Jun 22, 2001 (23:24) * 4 lines
Does anyone doubt the plate boundaries are the most active? Check the post just above this one. It seems to be a remnant plate in the Pacific on
which I am, and ROB!!! Do you have to be in the place with the most shaking going on?! Actually, you appear to be at the base of the Indonesian arc.
The New Madid fault in the central eastern part of the US has been notably quiet. This is a bit distressing. It is not done with its moving mountains.
Or St. Louis, for that matter. Shall the Mississippi again change course? It is just a matter of time.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 111 of 142: Cheryl (CherylB) * Mon, Jul 2, 2001 (18:12) * 1 lines
Have you ever noticed when flying over the Mississippi that you can see the old riverbeds. It seems that "Old Man River" gets restless from time to time.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 112 of 142: Marcia (MarciaH) * Fri, Jul 6, 2001 (18:32) * 20 lines
Mahalo Liam... This is fascinating!
Discovery of stagnant lithosphere says less mixing occurs in Earth
CHAMPAIGN, Ill. The discovery of a large amount of subducted lithosphere beneath the Fiji Islands suggests that the mixing of Earth s mantle caused by plate tectonics occurs less than previously thought, so large volumes of primordial mantle may still exist, University of Illinois researchers say. According to plate tectonics, hot material rises to Earth s surface where it cools and eventually sinks back down to be recycled, a process called subduction. But fundamental questions remain such as how fast this cycle occurs, and to what extent the material is mixed.
"Wholesale penetration of subducted lithosphere would destroy the primordial mantle," said Wang-Ping Chen, a UI professor of geophysics and a researcher at the Mid-America Earthquake Center. "Mixing isn t as severe as once thought: A lot of material may never enter the deep Earth."
As reported in the June 29 issue of the journal Science, Chen and doctoral candidate Michael Brudzinski used seismic wave speeds and earthquake ruptures to investigate the nature of subducting lithosphere and deep earthquakes near Fiji. At this region, the cold Pacific plate is plunging beneath the Indo-Australian plate at nearly 20 centimeters per year five times faster than movement along the San Andreas fault in California.
In addition to the usual pattern of deep earthquakes along most subduction zones, the researchers identified a group of deep earthquakes off to the side. "This expansive cluster of earthquakes extended hundreds of kilometers above and to the west of the active subduction zone," Chen said, "making it difficult to connect these outboard earthquakes with the actively subducting lithosphere." The most plausible explanation, Chen said, is a large slab no longer attached to the subducting lithosphere. "This detached slab may be from a previous episode of subduction along a nearby trench about 5 to 8 million years ago. The subduction zone then shifted its geometry, leaving behind a large remnant."
If similar slabs exist elsewhere, a substantial amount of subducted material may never penetrate deep within Earth, thereby preserving a significant primordial component of the mantle, Chen said. "We are not saying that subducted lithosphere never goes to great depth but the extent of such deep recycling is much less than some researchers believe."
Chen and Brudzinski also pointed out that seismic wave speeds, alone, are an inadequate indicator of the temperature of the material through which the waves pass. The chemical composition and crystal structure of the rocks also must be carefully considered.
"Temperature and pressure change the crystal structures of rock below certain depths," Chen said. "We found that seismic waves traveling through the cold, remnant slab have about the same speed as in the surrounding mantle material, which has already changed to a denser crystal structure."
Cold temperature of the subducting lithosphere hinders its transition to a denser material, a mechanism that triggers deep earthquakes in laboratory experiments, Chen said.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 113 of 142: Marcia (MarciaH) * Wed, Sep 19, 2001 (19:56) * 14 lines
Evolution of magma-poor continental margins from rifting to seafloor spreading
R. B. WHITMARSH*, G. MANATSCHAL† & T. A. MINSHULL*
* Southampton Oceanography Centre, European Way, Southampton, SO14 3ZH, UK
† CGS-EOST, Université Louis Pasteur, 1 rue Blessig, 67084 Strasbourg, France
Correspondence and requests for materials should be addressed to R.B.W. (e-mail: rbw@soc.soton.ac.uk).
The rifting of continents involves faulting (tectonism) and magmatism, which reflect the strain-rate and temperature dependent processes of solid–state deformation and decompression melting within the Earth. Most models of this rifting have treated tectonism and magmatism separately, and few numerical simulations have attempted to include continental break-up and melting, let
alone describe how continental rifting evolves into seafloor spreading. Models of this evolution conventionally juxtapose continental and oceanic crust. Here we present observations that support the existence of a zone of exhumed continental mantle, several tens of kilometres wide, between oceanic and continental crust on continental margins where magma-poor rifting has
taken place. We present geophysical and geological observations from the west Iberia margin, and geological mapping of margins of the former Tethys ocean now exposed in the Alps. We use these complementary findings to propose a conceptual model that focuses on the final stage of continental extension and break-up, and the creation of a zone of exhumed continental mantle
that evolves oceanward into seafloor spreading. We conclude that the evolving stress and thermal fields are constrained by a rising and narrowing ridge of asthenospheric mantle, and that
magmatism and rates of extension systematically increase oceanward.
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v413/n6852/abs/413150a0_fs.html&filetype=&_UserReference=C0A804EF4650FE6EBE3BDE4270453BA8F717
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 114 of 142: Marcia (MarciaH) * Fri, Oct 26, 2001 (20:17) * 7 lines
[1]GEOPHYSICS, SEISMOLOGY, & VOLCANOLOGY
* Earth's Auroras Make Rare Joint Appearance in a Feature Film
* Satellites Measure "Bouncing" Landscapes
* Atlantic Floor Destined to Slip Under North American Continent
References
1. http://www.sciquest.com/cgi-bin/ncommerce3/ExecMacro/sci_level3.d2w/report?nav_banner=bio&resource=articles&gateway=S-geophy
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 115 of 142: Marcia (MarciaH) * Tue, Oct 30, 2001 (18:17) * 6 lines
Thanks Terry, if you did not see my email yet (aloha.net is being recalcitrant this evening) this is proof that I am restored to health on Geo and my ftp is working just fine.
This is thanks to John. I rather love it, actually!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 116 of 142: Paul Terry Walhus (terry) * Tue, Oct 30, 2001 (20:09) * 1 lines
Great! Yes, I saw it and just replied to it. The new group/user scheme should solve all your access problems.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 117 of 142: Marcia (MarciaH) * Thu, Nov 1, 2001 (15:19) * 10 lines
Atlantic floor destined to slip under North American continent
.. the floor of the Atlantic Ocean will plunge beneath the North
American continent, forming a deep trench about 2,000 miles long and possibly
generating volcanoes, according to research at the University of
Minnesota and the Swiss Federal Institute of Technology in Zurich.
See article:
http://www.spacedaily.com/news/tectonics-01h.html
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 118 of 142: Marcia (MarciaH) * Mon, Dec 10, 2001 (21:30) * 0 lines
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 119 of 142: Marcia (MarciaH) * Mon, Dec 10, 2001 (21:32) * 17 lines
Iceland Lake Disappearing Into New Crack in Earth
Bijal P. Trivedi
for National Geographic Today
October 1, 2001
Icelanders are accustomed to their land being stretched, split, and torn by violent earthquakes and haphazardly rebuilt by exploding
volcanoes. But everyone was surprised when a large lake began to disappear into a long fissure created by one of last summer's
earthquakes.
The draining lake is an oddity even by Icelandic standards, and has lured hordes of curious onlookers to it barren shores.
The water level of Lake Kleifarvatn has fallen more than four meters (13 feet) within the last year, revealing a barren lake bed with
steaming thermal springs.
"If you put your ear to the ground, you can hear the lake draining," said geologist Amy Clifton of the Nordic Volcanological
Institute in Reykjavik, Iceland. "It sounds like water going down the sink."
more... http://news.nationalgeographic.com/news/2001/10/1001_lostlake.html
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 120 of 142: Marcia (MarciaH) * Mon, Dec 10, 2001 (21:34) * 1 lines
This should have been in the geothermal activity topic, but since Iceland sits atop the Mid-Atlantic Ridge, I put it here.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 121 of 142: Marcia (MarciaH) * Sun, Feb 24, 2002 (17:24) * 11 lines
Prizes reward geophysics and optoelectronics
http://physicsweb.org/article/news/6/2/18
British geophysicist Dan McKenzie of Cambridge University has won this
year's Crafoord prize - worth US$500 000 - for his pioneering studies of
plate tectonics. Awarded by the Royal Swedish Academy of Sciences, the
prize recognizes research in areas not covered by the Nobel Prizes.
Meanwhile, the Rank Prize for Optoelectronics has been awarded to three
groups for the invention of fibre Bragg gratings, optical coherence
tomography and `vertical cavity' lasers.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 122 of 142: Marcia (MarciaH) * Sun, Mar 10, 2002 (17:33) * 9 lines
This matter was brought up earlier - what caused the plates to form. I have found a wonderful page of links and graphics and text explaining much of what I will post elsewhere. But, for here, I post what caused to plate formation;
On an earth time scale, igneous fractionation is responsible for the formation of all the
world's volcanic arcs and continents, the implication being, the earth began without
continents, and the total size of the continents has grown with geologic time. Contemplate
the earth with no continents. It is easy to appreciate the importance of igneous
fractionation to just about everything about the earth.
http://geollab.jmu.edu/Fichter/IgnRx/Introigrx.html
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 123 of 142: Marcia (MarciaH) * Sun, Mar 10, 2002 (18:59) * 3 lines
Scroll down the page of the above link for more detail than you ever wanted to know. I find it fascinating.
Something that has kept me awake nights: When I defined the meaning of Sigma - I defined it as the sum of. Actually it is the summation of what came before. Summation is not the same as adding a to b and getting c.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 124 of 142: Curious Wolfie (wolf) * Mon, Mar 11, 2002 (17:01) * 1 lines
it's like a recap.....
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 125 of 142: Marcia (MarciaH) * Mon, Mar 11, 2002 (19:13) * 1 lines
Yup - if I hunt long enough after posting very convoluted explanations, we will find it simply stated. Too bad we have to warp children's imaginations by teaching them the hard way to do things!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 126 of 142: Curious Wolfie (wolf) * Mon, Mar 11, 2002 (20:50) * 1 lines
yeah, and parents get them in trouble for teaching them an easier/better way...*sigh*
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 127 of 142: Marcia (MarciaH) * Mon, Mar 11, 2002 (22:15) * 1 lines
*SIGH* That is why I value John so highly - he KNOWS the hard way to tell us how things work. He can even do it in several languages. However, happily for us, he is also able to make it understandable for even my eager mind, depite my being math-challenged.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 128 of 142: Curious Wolfie (wolf) * Tue, Mar 12, 2002 (09:50) * 1 lines
yes indeed---for me too!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 129 of 142: Marcia (MarciaH) * Sat, Apr 27, 2002 (01:01) * 11 lines
GEOPHYSICS, SEISMOLOGY, & VOLCANOLOGY
* Himalayan Warming "May Trigger Floods"
* Ancient "Rift Valley" Lakes Covered Gates Pass, Also Whetstone,
Empire Mountains in Southern Arizona
* Condensed Matter Escapes the Lab
References
1. http://www.sciquest.com/cgi-bin/ncommerce3/ExecMacro/sci_level3.d2w/report?nav_banner=bio&resource=articles&gateway=S-geophy
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 130 of 142: Marcia (MarciaH) * Sat, May 4, 2002 (23:58) * 5 lines
EarthScope to Attack Earth's Crust
EarthScope is a pathbreaking proposal to study the entire continental crust of North America in depth and consistent detail. It has passed muster with the science agencies and been in the president's budget request three times. See if you think it's worth lobbying Congress to get it finally started.
http://geology.about.com/library/weekly/aa041600a.htm
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 131 of 142: Marcia (MarciaH) * Tue, May 21, 2002 (23:15) * 31 lines
Scientists discover hundreds of faults off West Coast
CORVALLIS - Five times more mapped faults than previously imaged by scientists apparently cross the fractured Gorda Plate about 125 miles off the Northern California and Southern Oregon coasts.
Preliminary data presented today (Tuesday, May 14) at Oregon State University, reveals more than 340 strike-slip and spreading-center related normal faults or fault segments in the region, said Jason Chaytor, an OSU master's candidate in the College of Oceanic and Atmospheric Sciences.
Chaytor presented the data at the 98th annual meeting of the Cordilleran Section of the Geological Society of America. "Where Plates Collide" is the theme of the conference, which is hosted by the OSU Department of Geosciences.
Researchers had once plotted more than 60 faults spilling out across the Gorda Plate from the Gorda Ridge spreading zone, Chaytor said. But analysis of data collected by NOAA in 1997 imaged more suspected faults, he said. During the past several months, Chaytor, Chris Goldfinger, an OSU associate professor of oceanic and atmospheric sciences and Robert Dziak, an OSU assistant professor of oceanic and atmospheric sciences and research scientist with the National Oceanic and Atmospheric Administration, have studied data collected during mapping of the region.
Using multibeam bathymetry, sidescan sonar and seismic reflection data that provide soundings of water depth and echo strength, seafloor imaging programs can interpret depths and echo strengths and allow scientists to create a snapshot of the seafloor.
"Long linear features strongly suggest the faults are more pervasive throughout the Gorda Plate than originally thought," Chaytor said. "A lot of the faults are actually created at the spreading ridge - the Gorda Ridge spreading zone. This isn't unusual. It's quite common to see this many faults in these areas."
The Pacific Coast from northern British Columbia to Punta Gorda, near Cape Mendocino in California's Humboldt County, is the region known to geologists as the Cascadia Subduction Zone, Chaytor said. There, two large slabs of the earth's crust called the Juan de Fuca and the Gorda plates have been diving ponderously down beneath the North American continental plate for millions of years.
The Gorda Plate, now about five million years old at the point where it enters the subduction zone, is a relatively young, hot and thin plate in geologic terms, Chaytor said.
Many researchers believe the Juan de Fuca-Gorda-North America plate system is a likely source for a much-anticipated mammoth earthquake that could threaten Portland, Seattle and parts of northern California.
The Pacific Plate, south of the Gorda Plate, creeps northward about three centimeters a year along the California coast, compressing the Gorda Plate and triggering frequent small to moderately-sized earthquakes within the plate. The geological record shows that deep faults inside the diving plates have generated tremendous quakes with magnitudes of 8.0 to 9.0 every 500 years.
"We will be trying to figure out if more activity on the plates may actually lessen the strain in the subduction and mean less chance of a larger earthquake," Chaytor said.
One curiosity of the region is the peculiar form the faults take on the coastal side of the Gorda Spreading Ridge, he said. Faults that fan out from the ridge on the seaward side exhibit fairly typical and uniform lines. Faults marching shoreward, however are skewed into sharp deviations that resemble question marks, Chaytor said.
Researchers are unsure if there is any significance to the shape of the faults in the region.
"As the northern portion of the zone is spreading faster than the southern part and as the volume is being forced into the continental margin, pre-existing faults are being reactivated," Chaytor said.
"Right now we are just looking at the fundamental science of it all. What it will eventually mean in terms of seismic hazards remains to be seen."
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 132 of 142: Marcia (MarciaH) * Fri, Jul 26, 2002 (14:54) * 134 lines
MORE BLASTS FROM YELLOWSTONE'S PAST
Hotspot Generated 142 Huge Eruptions, 40 Percent More Than Previously Known
July 15, 2002 -- The Yellowstone hotspot, which powers Yellowstone National Park's geysers
and hot springs, produced 142 huge volcanic eruptions during the last 16.5 million years -- far
more than the 100 previously known blasts, University of Utah geologists found.
The cataclysmic explosions -- known as "caldera eruptions" -- typically generated 250 to 600
times as much volcanic ash as the 1980 eruption of Mount St. Helens in Washington state, and
some were up to 2,500 times larger, covering as much as half the continental United States with
inches to feet of volcanic ash.
While geologists Michael Perkins and Barbara Nash identified many more of these catastrophic
eruptions than had been known previously, they also showed the rate of such eruptions has
slowed: about 32 giant eruptions per million years before 15.2 million years ago, slowing to 10 to
20 huge eruptions per million years between 15.2 million and 8.5 million years ago, and then only
2.5 cataclysmic blasts per million years during the past 8.5 million years.
Caldera eruptions have that name because they create giant craters known as calderas that
measure tens of miles wide. They are the most devastating but most rare type of eruption.
The Yellowstone hotspot -- which many scientists believe is a plume-like zone of hot and molten
rising from at least 125 miles beneath Earth's surface -- produced its three most recent caldera
eruptions at or near the present site of Yellowstone National Park 2 million, 1.3 million and
642,000 years ago. The other, earlier eruptions happened as western North America drifted
southwest over the hotspot during the past 16.5 million years, creating a chain of volcanic fields or
centers extending from the Oregon-Nevada-Idaho border northeast across southern Idaho
toward Yellowstone's present location in Wyoming.
Researchers previously identified about 100 caldera eruptions, including the three most recent
ones at Yellowstone. But in a study of distinct volcanic ash layers deposited by each eruption,
Perkins and Nash showed there were at least 142 catastrophic caldera eruptions during the past
16.5 million years, and at least four more in the preceding 500,000 years.
"The most active source of volcanism in the continental United States -- the Yellowstone hotspot
-- was much more active and produced much greater volumes of volcanic material in the last 16
million years than we had thought as it passed from Oregon across Idaho to its present site at
Yellowstone National Park," Nash says.
The study was published in the March 2002 issue of Geological Society of America Bulletin.
Only the hotspot's three most recent caldera eruptions originated from the hotspot's current
location beneath Yellowstone National Park. The 45-by-30-mile-wide Yellowstone caldera,
formed by the caldera explosion 642,000 years ago, is the "new kid on the block," Nash says. To
understand the Yellowstone hotspot's long-term behavior, Perkins and Nash looked for clues left
by the older eruptions from now-inactive calderas.
Nash, a volcanologist, compares the hotspot phenomenon with moving hand over a candle. "If
you move your hand slowly over the flame in one direction, the flame will leave a burn track that
extends in the opposite direction along your hand."
As the hotspot location moved, new calderas were born, matured, and died. The 142 eruptions
were clustered in six or seven volcanic fields or "centers" extending from the
Oregon-Idaho-Nevada border northeast to Yellowstone. There were multiple eruptions from one
or more calderas at each field.
Detecting the locations of these ancient cataclysmic eruptions is difficult because as Earth's crust
drifted over the hotspot, smaller "post-caldera" eruptions covered or destroyed the older volcanic
centers. However, each huge caldera eruption left behind widespread ash deposits, which
researchers have found from the Pacific seafloor off the California coast to the high plains of
Nebraska and south to the Gulf of Mexico.
Perkins and Nash spent a decade finding these ash fall tuffs -- rock beds formed as volcanic ash
settled to the ground and cooled -- studying their chemistry and determining a chronology of the
eruptions that produced them. The age and chemical composition link each tuff to a specific
eruption and to one of the six or seven volcanic centers along the hotspot track.
Scientists date volcanic ashes using the radioactive decay of potassium-40 to argon-40 in a
potassium mineral called sanidine. Because argon is a gas, researchers assume that no argon was
present in the mineral when it was erupted. Argon accumulates in the mineral's crystal lattice as
potassium decays. Thus the amount of argon reveals the age of the ash and the date of the
eruption that produced it. The age of undated ashes can be estimated from the ages of ash layers
above and below them.
The hotspot's history is marked not only by a slowdown in how often big eruptions occur, but by
distinct changes in the compositions and temperatures of the magma, or molten rock, that erupted.
Based on such changes, Perkins and Nash classify the hotspot's activity into three stages of
volcanic activity or "magmatism" in the past 16.5 million years. Nash also hypothesizes about an
earlier period based on ash fall tuffs from four big eruptions not included in the count of 142
because of their different chemical composition. She believes there may have been even more
eruptions from this earlier stage some 17 million years ago.
Magma temperatures from millions of years ago can be deduced using mineral geothermometers.
Some minerals have chemical compositions that vary depending on the temperature at which they
crystallize from molten to solid rock. So the chemical composition of crystals in the ash indicates
the temperature of the magma when it erupted and started to cool.
Not only have caldera eruptions become less frequent over time, the erupting magma has also
become cooler, decreasing from more than 1830 degrees Fahrenheit about 16 million years ago
to as little as 1470 degrees Fahrenheit in the past 7.5 million years.
Yellowstone hotspot caldera eruptions are believed to stem from molten basalt rising from depth,
and then melting and mixing with the overlying granitic crust, which in turn erupts. Nash believes
the decrease in magma temperatures over time means that less high-temperature basalt is
incorporated in the melting process.
The three eruptions at Yellowstone during the past 2 million years were, respectively, 2,500, 280,
and 1,000 times larger than the 1980 Mount St. Helens eruption. Some researchers speculate the
earlier caldera eruptions were "a bunch of little guys," but Nash says some of their ash deposits
were just as thick and widespread, "so we conclude they were large too."
Nash says there are a few possible explanations for why caldera eruptions have become less
frequent. First, the hotspot's heat source within the Earth could be cooling down. Second, as
North America drifts over the hotspot, the crustal rock above the hotspot may be thicker, cooler
and harder to melt, although Nash says there is no persuasive evidence of that.
A third possibility, which Nash believes is most likely, links the hotspot's behavior to two kinds of
motion of the overlying rock: the southwest movement of the North American plate of Earth's
crust, and the east-west stretching apart of the crust in the western United States during the past
17 million years.
Hotspot volcanism occurs when molten basalt rises from Earth's mantle and melts granite in the
crust, feeding caldera eruptions. If the crust remained still instead of moving, caldera eruptions
would continue until the basalt ran out of fresh material to melt. On the other hand, if North
America moved too quickly over the hotspot, then the hotspot wouldn't have time to melt the
overlying crust and there would be no eruptions. Between these two extremes is an optimum plate
speed that allows the maximum amount of crustal melt to be produced, resulting in more frequent
and larger eruptions.
North America drifts southwest at a constant rate of almost 14 miles per million years. But the
east-west stretching of Earth's crust in the West has slowed in the past 8.5 million years. The net
effect, says Nash, is that crustal rock is now moving over the hotspot more slowly than it did prior
to 8 million years ago, so crustal rock melts less efficiently and big eruptions are becoming less
frequent.
"There is no reason to expect any sudden change" in the current rate, which has produced three
caldera eruptions in the past 2 million years, she says. "I anticipate there will be future large-scale
eruptions at Yellowstone, but not in my lifetime or not in the foreseeable future. That doesn't mean
there couldn't be smaller eruptions as there have been during the last 600,000 years -- lava flows,
small eruptions, and steam events."
Brooke Shiley, a science-writing intern for University of Utah Public Relations, prepared this news release.
http://www.newswise.com/articles/2002/7/HOTSPOT.UUT.html
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 133 of 142: Marcia (MarciaH) * Wed, Dec 11, 2002 (18:09) * 6 lines
RESEARCH OFFERS EXPLANATION FOR EARTH'S BULGING WAISTLINE
---------------------------------------------------------
A team of researchers from NASA's Jet Propulsion Laboratory and the Royal Observatory of Belgium has apparently solved a recently observed mystery regarding changes to the physical shape of Earth and its gravity field. The answer, they found, appears to lie in the melting of sub-polar glaciers and mass shifts in the Southern, Pacific and Indian Oceans associated with global-scale climate changes.
http://spaceflightnow.com/news/n0212/09bulge/
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 134 of 142: Marcia (MarciaH) * Fri, May 23, 2003 (15:40) * 45 lines
Plate Tectonics in a Nutshell
(from: About Geology)
A simple starting point for exploring plate tectonics
Geologists have an explanation—a scientific theory—of how the Earth's surface behaves called plate tectonics. Tectonics means large-scale structure. So "plate tectonics" says that the large-scale structure of the Earth's outer shell is a set of plates. (plate tectonic maps)
Tectonic plates don't quite match the continents and the oceans on the Earth's surface. The North American plate, for instance, extends from the west coast of the U.S. and Canada into the middle of the Atlantic Ocean. The Pacific plate includes a chunk of California as well as most of the Pacific Ocean. This is because the continents and ocean basins are part of the Earth's crust, and the plates are much thicker than the crust. The part of the Earth that makes up the plates is called the lithosphere. It's about 100 kilometers thick, but that varies greatly from place to place. (more on the lithosphere)
The lithosphere is solid rock, as rigid and stiff as steel. Beneath it is a softer, hotter layer of solid rock called the asthenosphere ("es-THEEN-osphere") that extends down to around 220 kilometers depth. Because it's at red-hot temperatures the rock of the asthenosphere can bend slowly in a plastic way, like a bar of Turkish taffy. In effect, the lithosphere floats on the asthenosphere even though both are solid rock.
The plates are constantly changing position. The lithospheric plates move slowly over the asthenosphere. "Slowly" means slower than fingernails grow, no more than a few centimeters a year. The forces that move them are not fully clear, but the plates certainly move—we've measured their movements directly, and geologic evidence shows that they have moved the same way in the past. Over many millions of years, the continents have traveled everywhere on the globe. (more on measuring plate motion)
Plates move with respect to each other in three ways: they move together (converge), they move apart (diverge) or they move past each other. Therefore plates have three types of edges or boundaries: convergent, divergent and transform. In convergence, when the leading edge of a plate meets another plate, one of them turns downward. That downward motion is called subduction. Subducted plates move down into and through the asthenosphere and gradually disappear. (more on convergent margins)
Plates diverge at volcanic zones in the ocean basins, the mid-ocean ridges. These are long, huge cracks where lava rises from below and freezes into new lithosphere. The two sides of the crack continually move apart, and thus the plates gain new material.
Where plates move past each other is called a transform boundary. These are not as common as the other two boundaries. The San Andreas fault of California is a well-known example.
Plate tectonics explains a lot of things:
* On the three different types of boundary, plate movement creates distinctive kinds of earthquake faults. (more on fault types)
* Most large mountain ranges are associated with plate convergence, answering a long-standing mystery. (more on mountains)
* Fossil evidence suggests that continents were once connected that are far apart today; plate movements are responsible.
* The world's seafloor is geologically young because old oceanic crust disappears by subduction. (more on subduction)
* Most of the world's volcanoes are related to subduction. (more on arc volcanism)
Plate tectonics also lets us answer new kinds of questions:
* We can build maps of world geography in the geologic past and model ancient climates.
* We can study how mass extinctions are related to effects of plate tectonics such as volcanism. (more on mass extinction)
* We can examine how plate interactions affected the geologic history of a region.
There are several unanswered questions about plate tectonics itself:
* What moves the plates?
* What creates volcanoes in "hotspots" that are outside subduction zones?
* How rigid are the plates, and how precise are their boundaries?
* When did plate tectonics begin, and how?
* How is plate tectonics connected to the Earth's mantle below? (more on the mantle)
* What happens to subducted plates? (more on the death of plates)
* What kind of cycle do plate materials go through?
Plate tectonics is unique to Earth. But learning about it during the last 40 years has given scientists many theoretical tools to understand other planets, even those that circle other stars. For the rest of us, plate tectonics is a simple theory that helps make sense of the Earth's face.
http://geology.about.com/library/bl/blnutshell_plate-tec.htm
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 135 of 142: Marcia (MarciaH) * Fri, May 23, 2003 (15:42) * 3 lines
They said it more simply than I might have done. This is currently my research involvement in preparation for delivering a paper (my idea of a nervous breakdown). To preserve this information for future use, I post it here.
Thank you to the folks at http://geology.about.com/
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 136 of 142: Cheryl (CherylB) * Fri, May 23, 2003 (15:50) * 1 lines
Thanks for posting that very succinct summation of plate tectonics, Marcia. Good luck in preparing for delivering that paper.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 137 of 142: Marcia (MarciaH) * Fri, May 23, 2003 (15:55) * 20 lines
Thanks for the good wishes. I have an expert on doing this sort of thing even if his field of expertise is in another field. I worry about teaching the teachers about my findings! That is more than a little intimidating to someone like me who assumes everyone but me already knows!
More on where the subducted plates go..... but they fail to mention the lava I found in ancient erosion beds. Definitely from other plates, in my case, and I need to get back into the field to find the specimens which should be there if my theory is correct.
The Death of Plates
What happens to a lithospheric plate after it has been subducted
What happens to plates after they are subducted is hotly debated, and the topic points to the future of plate tectonics itself. The evidence shows that cold descending lithosphere (the slab) sinks until it warms up to the temperature of the surrounding mantle. We detect the presence of the slab in two ways: the cold, rigid rock generates earthquakes as it cracks from the stresses of the deep Earth, and studies of seismic waves show that they speed up as they move across the slab.
By these means we can visualize slabs descending to around 650 kilometers depth in some cases, where there is a major discontinuity separating the upper and lower mantle. Some studies picture a few slabs going through this barrier. Other slabs appear to descend only a few hundred kilometers and level off there. Earthquake evidence at shallow depths is clear, but eventually slabs stop having quakes and we must rely on other clues. That evidence, based on seismic tomography, is subtle and not universally accepted.
Do plates disappear in the mantle, or do they leave permanent traces? Is the deep Earth a mixing machine or a cemetery of old plates? It appears to be something of both. Rocks from the upper mantle have a certain amount of variation, suggesting that distinct bodies of material can be maintained for hundreds of millions, even billions of years. On the other hand, plate tectonics has gone on for nearly 3 billion years, and most of the old oceanic lithosphere has clearly been recycled. (more about the mantle)
Geochemists, seismologists, mineral physicists, paleogeographers, computer modelers and other specialists all bring to the table their own insights into the deep Earth. Tying these insights into a single unified theory of the Earth is a very difficult problem. Some of their assumptions are in conflict, and their definitions of some terms disagree. Facts that one specialty considers tentative are taken as truth by other specialists. And so the great scientific conversation will continue for many years to come.
There's a strong presumption among geologists today that below the plates the whole deep Earth has its own cycle: downwelling of old lithosphere is matched by upwelling of hot plumes from the mantle's base, and everything must be in balance. But in Earth science, we have learned again and again that geologic affairs are not what we presume. We should assume that we cannot presume anything.
A small but growing school of geoscientists concludes that deep plumes are not supported by the evidence. Instead, they look to plate tectonics to explain even more than it does today. With its presumptions removed, says anti-plume leader Don Anderson, "plate tectonics is a much more powerful concept than generally believed." See this introduction to the nonplume hypothesis, or dip into the ferment at the professional level at mantleplumes.org.
http://geology.about.com/library/bl/blnutshell_plated
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 138 of 142: Cheryl (CherylB) * Tue, May 27, 2003 (18:02) * 1 lines
The deep Earth still holds many secrets, including just what does happen to those subducted areas of plates. The lava, and its origins, in the ancient erosion beds sounds fascinating. Hope that you find out more about it.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 139 of 142: Marcia (MarciaH) * Sat, May 31, 2003 (15:44) * 1 lines
The latest theory on what happens to subducted plates is that it is remelt in convection cells and continues to do so until another breach of the crust occurs and it begins life anew as volcanoes broken into the most basic elements. I have many sorts of rocks I have on my "must find" list for the Appalachains. I'll be looking not only for Pahoehoe, but also granite. Will it be potassium or magnesium fledspar gluing the quartz and mica together?!
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 140 of 142: Marcia (MarciaH) * Sat, May 31, 2003 (15:47) * 1 lines
It also occurred to me that all of that part of the mainland west of the Appalachains was once an inland sea, thus the large layers of limestone and fossil reef on my lava specimens. However, since the lava was the topmost layer, the limestone and reef remains have to have been from a prior inland sea. I wonder how far back I'll be able to chase this elusive subject.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 141 of 142: Paul Terry Walhus (paul) * Sun, Jun 13, 2004 (15:10) * 5 lines
Nice link to geos at
http://www2.parkschool.org/~Karen_Manning/tectonics%20outline
Nice of them to point their students to John Volos excellent research.
Topic 6 of 92 [Geo]: Plate Tectonics: The Physical Dynamics of The Crust
Response 142 of 142: Marcia (MarciaH) * Fri, Jun 25, 2004 (19:47) * 1 lines
How excellent of you to comment on that. I think he needs to be emailed about it since he is far too busy at the moment to come here. Thanks, Terry! That is terrific news!
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