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    Tuesday, November 13, 2007

     

    Yellowstone Magma Chamber

    Yellowstone Volcano Rises at Unprecedented Rate

    By Andrea Thompson, LiveScience Staff Writer

    posted: 08 November 2007 02:00 pm ET


    Yellowstone’s ancient volcanic floor has been rising since mid-2004 because a blob of molten rock the size of Los Angeles infiltrated the system 6 miles beneath the surface, scientists say, but there is no risk of an eruption.

    Yellowstone National Park is the site of North America's largest volcanic field, which is produced by a hotspot, or gigantic plume of hot, molten rock, that begins at least 400 miles (643 kilometers) beneath Earth's surface and rises to 30 miles (48 kilometers) underground, where it widens to about 300 miles across.

    Occasionally, blobs of magma break away from the top of this plume and rise up to resupply the magma chamber beneath the park's "caldera," a 40-mile by 25-mile bowl-like depression and volcanic leftover whose walls you can see in the northwest part of the park.

    These rising blobs of magma can sometimes push on the caldera floor, causing it to rise. Scientists monitoring the Yellowstone caldera think that's exactly what has caused the caldera floor to rise by almost 3 inches (7 centimeters) per year over the past three years—more than three times faster than it has more typically risen since observations began in 1923.

    "Our best evidence is that the crustal magma chamber is filling with molten rock," said study leader Robert Smith, a seismologist at the University of Utah. "But we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates again."

    Smith and his colleagues, whose work is detailed in the Nov. 9 issue of the journal Science, say that there is no indication that the caldera will produce an eruption anytime soon.

    "There is no evidence of an imminent volcanic eruption or hydrothermal explosion. That's the bottom line," Smith said. "A lot of calderas worldwide go up and down over decades without erupting."

    Other well known calderas include California's Long Valley and Italy's Campi Flegrei, near Naples, which have both been known to rise and subside again for even tens of thousands of years without erupting.

    The recent uplift of the Yellowstone caldera, recorded by GPS and satellite radar measurements, is considerably faster than the previous record of 0.8 inches (2 centimeters) per year from 1976 to 1985.

    Smith and his teams used computer simulations to determine changes in the shape of the magma chamber, which acts as a sponge-like body that holds magma between areas of solid rock. They found that the magma pushing up on the caldera is likely about 38 miles long and 13 miles wide, about the area of the city of Los Angeles, but only tens to hundreds of yards thick.

    The magma that accumulates in the chamber powers Yellowstone's famous geysers and hot springs, the largest hydrothermal field in the world.

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    http://en.wikipedia.org/wiki/Yellowstone_Caldera



    Yellowstone Caldera

    From Wikipedia, the free encyclopedia

    Yellowstone Caldera

    The northeastern part of Yellowstone Caldera, with the Yellowstone River flowing through Hayden Valley and the caldera rim in the distance
    Elevation 10,308 feet (3,142 m) at Mount Sheridan
    Location Wyoming, U.S.
    Range Rocky Mountains
    Coordinates 44°24′N, 110°42′W
    Topo map USGS Yellowstone National Park
    Type Caldera
    Age of rock 70,000 – 2.1 million years
    Last eruption 640,000 years ago
    Easiest route hike/auto/bus

    The Yellowstone Caldera is a volcanic caldera in Yellowstone National Park in the United States. It is located in the northwest corner of Wyoming, measuring about 55 kilometers (34 mi) by 72 kilometers (45 mi). The caldera was discovered based on geological field work conducted by Bob Christiansen of the United States Geological Survey in the 1960s and 1970s. After a BBC television science program coined the term supervolcano in 2000, it has often been referred to as the "Yellowstone supervolcano."


    [ Volcanism

    Yellowstone, like the Hawaiian Islands, is believed to lie on top of one of the planet's few dozen hot spots where light hot molten mantle rock rises towards the surface. The Yellowstone hot spot has a long history. Over the past 17 million years or so, successive eruptions have flooded lava over wide stretches of Washington, Oregon, California, Nevada, and Idaho, forming a string of comparatively flat calderas linked like beads, as the North American plate moves across the stationary hot spot. The oldest identified caldera remnant is straddling the border near McDermitt, Nevada-Oregon. The calderas' apparent motion to the east-northeast forms the Snake River Plain. However, what is actually happening is the result of the North American plate moving west-southwest over the stationary hot spot deep underneath.

    Yellowstone sits on top of three overlapping calderas. (USGS)
    Yellowstone sits on top of three overlapping calderas. (USGS)

    Currently, volcanic activity is exhibited only via numerous geothermal vents scattered throughout the region, including the famous Old Faithful Geyser, but within the past two million years, it has undergone three extremely large explosive eruptions, up to 2,500 times the size of the 1980 Mount St. Helens eruption. The three eruptions happened 2.1 million years ago, 1.3 million years ago, and the most recent such eruption produced the Lava Creek Tuff 640,000 years ago and spread a layer of volcanic ash over most of the North American continent. Smaller steam explosions occur every 20,000 years or so; an explosion 13,000 years ago left a 5 kilometer diameter crater at Mary Bay on the edge of Yellowstone Lake (located in the center of the caldera). Additionally, non-explosive eruptions of lava flows have occurred in and near the caldera since the last major eruption; the most recent of these was about 70,000 years ago. Craters of the Moon National Monument in Idaho is the result of volcanic activity between 11,000 and 2,000 years ago.

    The volcanic eruptions, as well as the continuing geothermal activity, are a result of a large chamber of magma located below the caldera's surface. The magma in this chamber contains gases that are kept dissolved only by the immense pressure that the magma is under. If the pressure is released to a sufficient degree by some geological shift, then some of the gases bubble out and cause the magma to expand. This can cause a runaway reaction. If the expansion results in further relief of pressure, for example, by blowing crust material off the top of the chamber, the result is a very large gas explosion.

    [ Volcanic hazard

    A full-scale eruption of the Yellowstone caldera could result in millions of deaths locally and catastrophic climatic effects globally, but there is little indication that such an eruption is imminent. [1] However, the system is not yet completely understood, and the study of Yellowstone is ongoing. Geologists are closely monitoring the rise and fall of the Yellowstone Plateau, which averages +/- 1.5 cm yearly, as an indication of changes in magma chamber pressure.[1][2] Major eruptions of the Yellowstone hotspot appear to occur roughly every 700,000 years. The Lava Creek Tuff eruption 630,000 years ago was last major eruption.

    [ Origin

    Location of Yellowstone Hot Spot in Millions of Years Ago
    Location of Yellowstone Hot Spot in Millions of Years Ago

    The source of the Yellowstone Hot Spot is not without controversy. Some geoscientists theorize that the Yellowstone Hot Spot is the effect of an interaction between local conditions in the lithosphere and upper mantle convection (G.R. Foulger: [2] and [3]). Others prefer a deep mantle origin (mantle plume). (See list of off-line references in mantleplumes.org/CRB.html). No theory is close to airtight. Part of the controversy is due to the rather sudden appearance of the hot spot in the geologic record. Additionally, the Columbia Basalt flows appear at the same approximate point in time, causing speculation about their origin.[4]

    [ See also

    [ Further reading


    [ External links

    Retrieved from "http://en.wikipedia.org/wiki/Yellowstone_Caldera"

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    Sleeping Giant: The Yellowstone Caldera Super Volcano

    By: Justin Reynolds

    Yellowstone National Park is our nation’s oldest, most recognized recreational areas due to its many geysers, thermal pools, mountain views, and a vast array of wildlife, including most of America’s remaining herds of bison. As a result of its popularity, the park attracts nearly 3 million visitors yearly, (www.nps.gov/yell). Yet, what many of these visitors do not realize is that landmarks they came to visit, such as Old Faithful and the park’s other numerous geysers, are fueled by a sleeping giant. Underneath Yellowstone there rests one of the world’s largest, potentially harmful volcanoes known to man, and if historical records prove true, it is due to blow.

    http://volcanoes.usgs.gov/yvo/figures/fig1.html

    The question for geologists is what fuels this volcano and the various geothermal features dotted across Yellowstone? Geologists refer to the phenomenon as the Yellowstone Hot Spot (Francis 197). A hot spot is a location in the Earth’s crust where magma flows up from the magma, forming volcanoes in its wake. The hotspot has been affecting the area for the last 16 million years, yet scientific understanding of its effect on Yellowstone’s formation has only just begun. What is known is that the hotspot is relatively stationary within the depths of Earth, and the North American tectonic plate is moving in a southwest direction over the hotspot at a rate of 4.6 centimeters annually, (Direction). While the North American plate moved southwest over the hotspot, the volcanic formations progressed northeast, beginning in northern Nevada and southeast Oregon 16.5 million years ago and reaching its present day location near Yellowstone National Park 2 million years ago, (Direction). The current location of the Yellowstone hotspot is shown in the figure to the right. The orange outlines are the outlines of the three calderas which have resulted from eruptions during the past 2 million years. Notice how mountains have formed a parabolic shape around the hotspot as the North American plate moves southwest over the hotspot.

    Volumes of Yellowstone's largest eruptions compared to large historic eruptions.

    http://volcanoes.usgs.gov/yvo/figures/fig2.html

    Map showing the area of the US that was once covered by ash from Yellowstone eruptions.

    http://volcanoes.usgs.gov/yvo/figures/fig3.html

    During the past 2 million years, the volcanic region has been subject to 3 definable cycles of activity, all occurring approximately 600,000 years apart, (Fisher 107). The first occurred about 2 million years ago and produced a massive 2,500 cubic kilometers of volcanic ash. The next happened 1.2 million years ago, resulting in 280 cubic kilometers. The most recent took place 600,000 years ago, resulting in 1,000 cubic kilometers of ash, (Fisher 108). In comparison, the eruption of Mt. St. Helens in 1980 created an enormous amount of destruction while only spewing 2.5 cubic kilometers of erupted ash, (Fisher 108). The diagram to the left shows the immense amount of ash associated with the three eruptions compared to some other notable volcanic eruptions. The first Yellowstone eruption produced 1,000 times the ash alone! To the right is a diagram showing the ash distribution across America as a result of the Yellowstone eruptions compared to the Mt. St. Helens eruption. As the diagram shows, an eruption of such large scale would surely be devastating to the Great Plains and Western states. The eruption which occurred 2 Million years ago provided enough ash to cover or partially cover 20 states. In contrast the St. Helens volcano only partially covered a few regionalized states in 1980.

    The substances present in the magma chamber underneath Yellowstone prior to eruption were composed of ryholite lava and volcanic ash. Ryholite lava is very viscous, meaning that it is very thick and flows slowly due to friction, (Francis 141). It is the opposite of Basalt lava which is less viscous and flows freely. In each case, pressure built up to insurmountable levels due to the thick nature of the ryholite lava present, which led to three of Earth’s largest known pyroclastic-flow eruptions. The eruptions, mentioned previously, were powerful enough to result in a massive blanket of volcanic ash that was deposited as far east as Louisiana, (Ash).

    In the wake of these eruptions, three separate calderas were formed in relation to their eruption, as the top of the magma chamber producing the ryholite lava collapsed due to the lack of structural support provided by the lava. A caldera is a large, more-or-less circular depression surrounded by steep cliffs, and formed when a magma chamber empties out its magma, and the surface above the chamber collapses. (Francis 292). The Yellowstone Caldera is presently 45 km in diameter and 75 km in length. However, it will ultimately take a new form when the next massive eruption occurs.

    Map showing the locations of features in the photogallery.

    http://volcanoes.usgs.gov/yvo/gallery_map.html

    Recently in April of 2004, over 500 earthquakes were recorded in the general Yellowstone region. The largest was just below 3.0 in magnitude, not incredibly large, yet the sheer numbers are somewhat disturbing. At one point, according to seismic recording stations near Yellowstone, over an eleven day period, 465 individual earthquakes were recorded near or at the caldera. In addition, a “bulge” has recently been recorded in the center of the caldera. A recorded rise of 86 centimeters was observed between 1923 and 1984, and then it subsided slightly between 1985 and 1989 until rising again recently, (Fisher 109). The significance of these fluctuations is unknown, but it is believed to be related to the level of the magma present in the underground chambers beneath Yellowstone.

    Could the “bulge” be a sign of future volcanic activity? Scientists are unsure, as there is currently no technology present that is capable of predicting earthquakes. The activity of Yellowstone’s hydrothermal system does not vary much from other similar large calderas, yet historical records of volcanic activity in the region suggest that a potentially cataclysmic eruption should occur in the near future, (Fisher 111). Each of the eruptions that occurred in the past, were spaced about 600,000 years apart, the same amount of time between the last eruption and now.

    Diagram physical and chemical processes of volcanic gas interactions in atmosphere

    http://volcanoes.usgs.gov/Hazards/What/VolGas/SO2Aerosols.html

    When dealing with volcanoes, potential eruptions are always a concern to scientists. What would another eruption of the Yellowstone Caldera mean to the rest of the World? As with previous eruptions, the ash expelled into the stratosphere, would blanket the entire Great Plains. Earth’s most fertile lands would be virtually blanketed in a layer of ash. Crops would fail, and a local and global shortage of grains would develop. The ash would work its way into the Mississippi-Missouri River system, polluting the water and filling in channels from North Dakota to the Gulf of Mexico, (Ash). This ash would also block out the sun light and result in an overall global cooling of a few degrees as shown in more depth above. Essentially, the effects of another eruption of the Yellowstone Caldera would be devastating to our planet and would surely test the resilience of mankind. Yet, by all scientific accounts, the activity that is occurring presently beneath our nation’s oldest national park does not pose an imminent threat towards mankind. But the possibility still remains of a catastrophic eruption in the near future unlike any man has ever seen.

    For more information on current seismic activity in the Yellowstone region see…

    Current Activity: http://volcanoes.usgs.gov/yvo/monitoring.html

    For more information on Yellowstone National Park visit…

    www.nps.gov/yell

    http://volcanoes.usgs.gov/yvo/images/2000-rbs-3.3yellashvolumes_large.jpg


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