Topic 73 of 92: Volcanoes from Birth to Extinction
Tue, Apr 23, 2002 (13:52) |
Marcia (MarciaH)
How they work, why they are there and why they change and, eventually, die.
16 responses total.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 1 of 16: Marcia (MarciaH) * Tue, Apr 23, 2002 (14:20) * 5 lines
The modern science of volcanism evolved from the work of Dr Thomas A. Jagger who was a professor at Massachusetts Institute of Technology (MIT). He had travelled to Martinique just after Mount Pelée erupted killing all but 2 inhabitants of the capital city of St Pierre. The devastation motivated him to search for a safe volcano to study for the prediction of future eruptions with the aim of lives being saved. After considerable travel and study he found that Kilauea volcano on the Island of Hawaii was ideal for his studies.
In 1912, Dr Jagger supervised the digging of foundations and the erection of the first modest buildings which would later become Hawaii Volcanoes Observatory. HVO currently attracts volcanologists from all over the world to study the events leading up to the eventuality of a volcanic eruption. The proof of their work was the successful prediction of the eruption of Mt Pinatubo in the Philippines. The successful evacuation of surrounding towns and of Clark Air Force Base saved many thousands of lives.
The following discussion will describe the process which creates and builds volcanoes and eventually destroys them recycling them into the mantle to become new rock. The Earth has been in the recycling business since the very beginning. Grab your rock hammer and sample bag and come along on the great adventure.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 2 of 16: Julie (cascadeclimber) * Tue, Apr 23, 2002 (14:40) * 1 lines
EXCELLENT topic Marcia!! I think I shall post my paper now. I wrote a paper for my English class defining the word volcano. It will give you a VERY brief overview on how volcanoes work.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 3 of 16: Julie (cascadeclimber) * Tue, Apr 23, 2002 (14:42) * 24 lines
Volcanoes are one of nature’s most awesome forces. These natural vents and fissures erupt molten rock and gases from deep inside the earth. Most people think of volcanoes as destroyers, but volcanoes are also creators. The lakes, rivers, groundwater, and oceans, where life began, are all made from volcanic steam that was produced during countless eruptions millions and even billions of years ago. When most of us think of volcanoes we think of the ones in Hawaii, where lava erupts fluidly in an amazing display of fountains and flows. But there are many other types of volcanoes around the world that behave very differently and erupt different materials. One must first explore the ground beneath our feet, as well as above it, to learn what volcanoes are and how they form and shape our planet.
Someone once said to me, “Volcanoes don’t have snow on them.” Indeed, some do though. Snow covered volcanic peaks are often carpeted in lush green plants with moss-covered forests and cascading waterfalls. Some of these snow caped peaks can cause deadly eruptions that rain down their terrors on cities near and far. No one would ever suspect a beautiful mountain, like Mt. Shasta or Mt. Hood, to be capable of blowing up and ejecting molten material from the bowels of the earth. Volcanoes are like glowing cones of silence and screams that spew up geologic history from the bottoms of the earth.
Volcanoes may not be interesting to you, but there is something about them that I find fascinating. I don’t know what it was about the barren, gray, and lifeless crater that grabbed my interest. Maybe it was the reality of how much force was required to cause a mountain to blow its top and blast out its remains into river valleys and our atmosphere. Or maybe it is the fact that a volcano, looking so lifeless and quiet, could easily come to life at any moment, without warning.
Suddenly, at 8:32a.m on Sunday, May 18, 1980, the 9,677-foot summit of Mt .St Helens erupted with a fury few will ever forget. Everything happened in thirty seconds or less as an earthquake shook loose the northern flanks of the volcano, which rushed down hill. Then, the pressure of the molten rock that had increased beneath the bulging crater blasted out in a huge deadly explosion, known as a pyroclastic flow, which tore down the mountain at unimaginable speeds. The avalanche of snow, ash, rock, ice, soil, and other debris raced down the volcano at speeds of one-hundred-fifty miles an hour wiping out everything in its path. After the initial blast, Mt. St. Helens, now a gray and deformed volcano with half of its volcanic cone missing, now rose a mere 8,365 feet into the bright blue sky.
There I stood, only a half mile from the crater of Mt. St. Helens, looking into her fiery mouth of mysterious, awesome, and unimaginable powers. All was quiet, but I knew all to well that deep underneath the cracked lava dome, magma was churning. If for any reason, the pressure underneath the lava dome began to build, it would increase like a soda can shaken up to its limit until suddenly….BOOM!
The force is tremendous, unlike anything you have ever seen or heard. The ground will begin to shake and quiver and the earth will explode, as molten rock, ash, and gas are ejected out of the volcano. From far away, the blast will look like it’s moving in slow motion, but move closer and you will feel the scorching heat, suffocating gas, and glowing embers as it rushes down the slopes and heads straight towards you at unimaginable speeds.
According to the theory of Plate Tectonics, the earth’s outer layer, known as the lithosphere, is composed of a mosaic of rigid plates, which float on the asthenosphere, a layer of hot partially molten rock located below the lithosphere. These plates move slowly in response to the currents generated by the flow of heat of the asthenosphere below them. When plates are pushed together, a process known as subduction, the heavier plate goes beneath the lighter and more buoyant plate melting parts of both and sending magma to the surface. This is how most typical composite cone volcanoes are formed. When plates are pulled apart, creating a rift zone, an upwelling of magma extends over their edge. A good example of this would be Iceland located directly on top of the Mid Atlantic Ridge, which is a rift zone. Iceland is home to some of the most active volcanoes in the world.
There are also areas on the earth called hot spots, which are thermal plumes that can form in the middle of a plate. Magma rises from these plumes and forms volcanoes. Hawaii is right in the middle of the Pacific plate and is above a hot spot. The active volcano right now is Kilauea, which is located on the Big Island. However, the Big Island of Hawaii will eventually move northwest as the Pacific Plate moves, just as all the other islands in the Hawaiian chain have done and then a new volcano will arise over the hotspot and form a new island.
Volcanoes are categorized into three stages: Dormant, active, and extinct. A dormant volcano is one that is not currently erupting, but is considered likely to do so in the near future. Mt. Shasta in California is a dormant volcano. Its last eruption was about 1786. An active volcano is one that is currently erupting or has erupted in recent history. Mt. St. Helens last erupted in 1980 and is still considered active. Kilauea, in Hawaii, is also an active volcano because it is continuously erupting lava. An extinct volcano is one that is not expected to erupt again. It is very difficult to classify a volcano as extinct though, because sometimes not enough information is known about it.
There are five main types of volcanoes. Composite cones, also known as strato-volcanoes, are built up by alternating layers of lavas and pyroclastic deposits. Pyroclastic deposits are volcanic rock fragments produced by explosive eruptions. Some good examples of a composite cone would be most of the volcanoes in the Cascade Range, such as Mt. St. Helens and Mt. Rainer. Composite cones are known to form long chains like those in the Cascade Range and the Andes. A shield volcano is a broad gentle sloping volcanic cone in a flat dome-like shape. Shield volcanoes usually cover several tens or hundreds of square miles in extent and are composed mainly of overlapping lava flows. Kilauea, on the Big Island of Hawaii, is a shield volcano. Lassen Peak, in the Cascade Range of California is a lava dome, a dome shaped mountain of solidified lava in the form of many individual lava flows. A caldera is a large basin shaped volcanic depression that is formed by the collapse of a volcano, the collapse of the magma
hamber underneath the volcano, or a huge catastrophic eruption where a volcano blows itself to bits. Crater Lake in Oregon is a good example of this. Crater Lake used to be a huge composite cone called Mt. Mazama that probably reached a height of about 16,000 feet. About 6,900 years ago, there was a violent eruption, and the magma chamber below the crater collapsed and emptied out. After many years, the empty basin began to fill with snowmelt and rainwater to form what is now Crater Lake. Last but not least are cinder cones, which are cone-shaped hills formed by the accumulation of cinders and other pyroclastic deposits around a volcanic vent. Sometimes cinder cones form in big clusters like Sunset Crater in Arizona with more than six hundred other cinder cones near by.
Volcanoes erupt in many different ways. Some eruptions are quiet and may only erupt lava, but others erupt quite violently, blasting materials out into our atmosphere that circulate around the globe. There are four main types of eruptions. “Strombolian” is a type of volcanic eruption characterized by fountains of fluid lava that explode upwards in small bursts from a central crater. Mt. Etna in Italy has experienced many Strombolian eruptions. “Hawaiian” is a type of volcanic eruption that is characterized by spectacular fire fountains and lava flows. Kilauea, in Hawaii is a good example of a Hawaiian eruption. The lava flows may sometimes destroy property, but rarely move fast enough to endanger people. “Effusive” is an eruption dominated by the outpouring of lava onto the ground, typically out of fissures. A good example of an Effusive eruption would be the volcanoes in Iceland. The Laki fissure in Iceland erupted in 1783 spreading almost eight miles of lava in just five months. “Plinian” is a
arge explosive eruption in which a steady, turbulent stream of pyroclastic material is released at high velocity from a vent. This eruption cloud can reach heights greater than six miles into the atmosphere. A great example of a Plinian eruption would be the eruption of Mt. St. Helens in 1980, where the eruption column reached a height of about fifteen miles into the atmosphere. During the eruption of Mt. Pinatubo in the Philippines, the eruption cloud grew to a height of about eighteen miles.
Volcanoes erupt with several different types of lavas. Basaltic lava flows are runny and fluid lava that rarely explodes. This type of lava often forms shield volcanoes like Kilauea in Hawaii. Basaltic lavas branch out into three other kinds. “Aa” is a type of lava flow with a rough and jagged surface. This type of lava can really ruin a pair of hiking boots. Watch your step and don’t fall. Falling on this stuff will really hurt. I have learned from experience. “Pahoehoe” is a type of lava flow with a smooth, glossy, ropy surface and usually much easier to walk on, as long as the surface of the flow is not too thin. “Pillow” lava, just how it sounds, tends to form by the chilling that occurs when lava flows into or under water. Andesitic lavas are moderately fluid being only slightly more viscous than basaltic lavas. This type of lava occasionally explodes and typically forms perfect symmetrical composite cone volcanoes like Mt. Shasta in the Cascades. Dacitic lava is slightly more viscous than an
esitic lava flows and tends to erupt explosively. Lassen Peak in the Cascades has erupted dacitic lavas in its eruptive history. Rhyolitic lava is stiff highly viscous lava that usually piles up around vents of lava domes. When rhyolitic lava makes contact with the atmosphere it is highly explosive. The Inyo and Mono chain volcanoes in central California erupted vast quantities of rhyolitic lavas about 200,000 years ago. If this same thing were to occur today it would be catastrophic.
There are many hazards associated with volcanoes. Two of the deadliest hazards that have claimed the most lives are pyroclastic flows and lahars. A pyroclastic flow is an avalanche of hot ash, rock fragments, and volcanic gases that rush down the side of a volcano sixty miles per hour or more. Pyroclastic flows are common during eruptions of composite cones because they tend to have more explosive and larger eruptions than other types of volcanoes. The reason pyroclastic flows are so deadly is not only because they are fast and destroy everything in their path, but also because they are, at times, unpredictable.
A lahar is a catastrophic mudflow or debris flow consisting of a mixture of rock, ash, water, snow, and pyroclastic materials that originates on the slopes of a volcano. Mt. Rainer, a typical composite cone that overlooks the city of Seattle in the Cascades, has a nasty and unsettling history of lahars. The town of Orting, located about thirty miles from Mt. Rainer, was built on old lahar deposits, and it’s only a matter of time until another lahar comes rushing down, wiping out everything in its path, including the unfortunate little town of Orting.
Lava flows can also become a volcanic hazard as well. One of the most famous ones was during the eruption of Heimaey in Iceland in 1973. The lava flow destroyed the town and threatened to close the economically important harbor, but the citizens fought back, and, with lots of water and a little bit of luck, they were able to divert the lava flow and stop it from destroying their harbor.
Tsunamis may also accompany volcanic eruptions. Tsunamis are great sea waves that are caused by earthquakes, landslides, or volcanic eruptions. During the eruption of Krakatoa in 1883, a series of tsunamis washed away one-hundred-sixty-five coastal villages on the islands of Java and Sumatra killing 36,000 people.
Volcanoes may at times seem to be destroyers throwing deadly clouds of hissing gas, molten rivers of hot rock, and avalanches of snow and ash down their slopes, but they are also the re-builder’s of our planet, releasing new moisture into the atmosphere and creating new land surfaces.
After Mt. St. Helens catastrophic eruption, an area within about twenty miles looked like a barren moonscape. There was no life to speak of what so ever. I was just at Mt. St. Helens in August of 2001, only twenty-one years after the big eruption. Most of the area still looks like a barren moonscape, but it is no longer lifeless. There were blooming flowers, bushes with berries, and tiny tree saplings growing right out of the volcanic ash. Elk, gophers, coyotes, and other mammals are also now seen roaming around their ever-changing home. It will take hundreds of years for Mt. St. Helens to re-grow itself. By that time though, Mt. St. Helens may erupt again, stunning and amazing us with the awesome power and fury of our earth and its mysterious and fascinating volcanoes.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 4 of 16: Marcia (MarciaH) * Tue, Apr 23, 2002 (15:34) * 3 lines
Julie!!! You are fantastic! Anyone who has paid any attention to Geo has seen copious amounts of snow on Mauna Loa and Mauna Kea. Indeed, watching the live webcam of Popocatépetl will show you that active volcanoes sustain snowfalls. So does Ruapehu Webcam in New Zealand.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 5 of 16: Cheryl (CherylB) * Thu, May 9, 2002 (17:02) * 1 lines
Heat mapping of Anarctica has indicated atleast one very hot spot under the. It is theorized to be a volcano over a mile of ice.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 6 of 16: Marcia (MarciaH) * Thu, May 9, 2002 (17:58) * 12 lines
Indeed, Cheryl.
Hotspots in Antarctica---there's a complicated question. The tectonics of Antarctica are not that well understood. There are a few
linear chains of volcanoes but as pointed out in "Volcanoes of the Antarctic Plate and Southern Oceans" by WE LeMasurier and JW
Thomson, there are not age dates available to tell if these are hotspot chains. However, other evidence has shown that that the Antarctic
plate hasn't moved very much over the past 80 million years, so you might not expect to see linear hotspot chains. Most of the volcanism on
the actual continent itself seems to be related to a large continental rift called the West Antarctic Rift. There are some hotspot island
volcanoes on the Antarctic plate, but they are not on the continent itself.
http://volcano.und.nodak.edu/vwdocs/frequent_questions/grp7/antarctica/question679.html
By Scott Rowland to whom I am grateful for my weekly volcano reports.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 7 of 16: Julie (cascadeclimber) * Fri, Jul 12, 2002 (04:17) * 2 lines
Hi Everyone!
I got a very interesting question for you all. I was reading Roadside Geology of Washington a few months ago before I went on my trip to Washington. It explained that most of the Cascade Volcanoes erupted basaltic lavas at their birth and early lives. Then they began to erupt andesitic lavas which many are doing now. At the end of their lives they seem to erupt ryholitic lavas, and finally they have a catostropic ryholitic eruption. If that is true, than that would mean Crater Lake is at the end or near its end of its life cycle because its last eruption was ryholitic and perhaps catastophic. Mt. Rainer's composition is begining to become ryholitic as well. Glacier Peak has already erupted enormous quantities of rhyolitic ash about 12,000 years ago. Could it mean that Glacier Peak and Crater Lake are near the end of their life cycles? Okay....here's the big question.....What makes the chemistry of magma change over time?
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 8 of 16: John Tsatsaragos (tsatsvol) * Fri, Jul 12, 2002 (05:34) * 3 lines
You caught me unread Julie. I wonder if it is true the circle of life for volcanoes.
John
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 9 of 16: Curious Wolfie (wolf) * Fri, Jul 12, 2002 (10:08) * 1 lines
do volcanoes actually die or just go into a dormant state?
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 10 of 16: Julie (cascadeclimber) * Fri, Jul 12, 2002 (13:58) * 1 lines
I am not sure about this John, thats why I brought it up because I don't entirly agree with what the book had to say. And Wolfie, from what I know you can never really call too many volcanoes extinct. Some can remain dormant for thousnads and thousands of years and then suddenly....BOOM! Although, ones with heavy glaciation and ones that have been severly eroded over time could be extinct, but not necessarily. You'd be surprised how many times people have been fooled living in the shadow of a ticking time bomb that they thought was dead. I wish I had written down the name of the book that said that Mt. Shasta was an extinct volcano. I would have had fun writting to the publisher and telling them they have some very wrong information in there. Even though I don't really agree with what that Washington book had to say, I am going to post an idea that I have seen in many other books that may explain how volcanoes are born and how they die, but specificly the Cascade Volcanic Range.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 11 of 16: Julie (cascadeclimber) * Fri, Jul 12, 2002 (14:33) * 2 lines
First let's look at the theory of plate tectonics. Plate tectonics is a theory of global tectonics in which the lithosphere is divided into a number of plates whose pattern of horizontal movement causes rigid bodies that interact with one another at their boundaries, causing seismic and tectonic activity along these boundraies. In the case with the Cascade Volcanic Range we have the Juan de Fuca Plate going into the North American Plate. There are two ridges offshore; the Gorda Ridge and the Juan de Fuca Ridge. Both of these ridges have been generating new oceanic crust, which sinks into a trench off the coast. The two ridges are thought to be remenants of an oceanic coast that paralleled the whole west coast of North America about 15 to 20 million years ago. A plate called the Farallon Plate, moved away from the ridge and into a trench that also paralleled the west coast. Finally the last of this plate vanished into the trench as the continuing movement of the North American continent brought the trench a
d ridge together. The only remanat left of the trench and the oceanic ridge of the Farallon Plate is still offshore of the Pacific Northwest. The Pacific Plate now slides north over the San Andreas Fault and the Queen Charlotte Fault which runs along off the coast of British Colombia. Within the next 10 to 15 million years the last remanat of the Farallon Plate will dissapear into the trench and the trench and the ridge will met, connecting the San Andreas Fault to the Queen Charlotte Fault. The Pacific Plate will have moved north to the Aleutian trench forming a single fault that runs from Mexico to Alaska parralelling the entire west coast. When the small plate off the coast of the Pacific Northwest lastly dissapears the trench will be gone and the Casacde Volcanoes will all die out. A new chain of mountains will will appear along the entire coats of Oregon and Washington. And don't forget....this is only a theory.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 12 of 16: Marcia (MarciaH) * Wed, Jul 17, 2002 (19:08) * 1 lines
Julie, search for Bowen's Reaction Series on Google.com. You will find all you need to know about the evolution of magma into whatever rock it becomes. It is a continuous recycling which will see Hawaii subducted under the North American Plate in some distant future.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 13 of 16: Marcia (MarciaH) * Wed, Jul 17, 2002 (19:09) * 1 lines
I wish I had brought my notes with me for this topic. I took a tele course in this from Hawaii FOR Hawaii, but it also applies to all the world. Meanwhile back to the discussion!
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 14 of 16: Marcia (MarciaH) * Wed, Jul 17, 2002 (19:10) * 1 lines
The Cascades will not die out until it has eaten the entire Pacific basin according to my professor.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 15 of 16: Lisa (freddie) * Sat, Nov 30, 2002 (22:20) * 1 lines
Thank you for the information Marcia. My son had a small talk to give on volcanoes and he was able to enhance some of his information from your posts.
Topic 73 of 92 [Geo]: Volcanoes from Birth to Extinction
Response 16 of 16: Marcia (MarciaH) * Tue, Dec 10, 2002 (20:34) * 1 lines
Wish I had taken my notes with me for this topic. There is so much more to tell. Thanks for telling me it was useful. That makes my day and a lot more!
Geo conference 
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