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TOPIC: Yellowstone caldera


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RE: Yellowstone caldera
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Parts of the collapsed, restless volcano in Yellowstone National Park are swelling faster than has ever been recorded.
Geologists from the University of Utah say two domes inside the Yellowstone caldera have steadily inflated at two to three times the rate as some of the most rapid movements recorded between 1923 and 1984.

"We've gone to this really pronounced, and I would say unprecedented, uplift of the caldera" - Bob Smith, a Utah geologist and one of the leading researchers into Yellowstone's busy volcanic life.

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On October 14th and 15th, there was a swarm of 74 small earthquakes at a location within the Yellowstone Caldera, 12 km NW of Old Faithful. The largest earthquake was local magnitude 2.4. This swarm is modest in size compared with other historic earthquake swarms at Yellowstone.
Park officials said the earthquakes were more likely caused by the underground movement of hot water and gas, rather than the migration of magma.

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Heart Mountain
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A mountain near the Montana-Wyoming border once moved 45 kilometres in a catastrophic scenario that could be repeated elsewhere.

Rock at the summit of Heart Mountain is 250 million years older than at its base. That suggests the top and the bottom have not always been together. The presumed migration to its present home has puzzled scientists for years. They have known the mountain moved, but no one has explained how it happened or how long it took.

A new explanation comes from deep underground, where lava bubbled up to the surface and sent the mountain on its way in surprisingly quick fashion.

heartmountainb
Latitude: 44.664878° Longitude: -109.119133°

Title: Hot water: A solution to the Heart Mountain detachment problem?
Authors: Einat Aharonov, Mark H. Anders

The Heart Mountain block slide of northwestern Wyoming and southwestern Montana is one of the largest slides known to have occurred in Earth's history.
This early Eocene block slide covered an area of over 3400 km2 and moved a minimum of 45 km across open terrain. The initial 2- to 4-km-thick Heart Mountain block slide moved on a slope of about 2°, detaching for half its length on a nondescript bedding plane in the Ordovician Big Horn Dolomite (BHD). Given our current understanding of fundamental mechanics, such a great mass of rock should not have begun sliding on such a gentle slope without some special condition. Here we suggest that a special condition existed during the interval between extensive upper-plate dike injections and the initial movement phase. In our model, the dike injections increased horizontal stresses and heated the surrounding layers. Both the increased stresses and the heat input elevated fluid pressure of water trapped within the BHD. In addition, vertical hydrofracturing was retarded as horizontal stress approached vertical, thus allowing a critical buildup of fluid pressure. Fluid overpressuring is a mechanism that can overcome the mechanical problem of initiating movement on a low-angle surface. Moreover, this mechanism explains the observed fluidised features found along the basal contact of the slide block as well as the observed lack of deformation in the lower plate.

heartmountain2

Extent of Heart Mountain block slide. Compiled from maps by Pierce and Nelson
(1971) and Nelson et al. (1980). CV—Crandall Volcanic Centre. SV—Sunlight Volcanic Centre. Stratigraphic column from Pierce (1957).

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heartmountain
Heart Mountain, seen standing out from its base rock in this satellite image, originally formed with the Absaroka Range, to the West, about 50 million years ago.
Credit: NASA


-- Edited by Blobrana at 23:36, 2006-05-22

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RE: Yellowstone caldera
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A new study has revealed forces brewing deep beneath Yellowstone National Park could be making one of the largest volcanoes on Earth even bigger, .

In the past decade, part of the volcano has risen nearly five inches, most likely due to a backup of flowing molten rock miles below the planet's crust.
The activity may have cracked the crust in the park's famous Norris Geyser Basin (NGB), leading to the formation of new fumaroles—holes that vent smoke and gas—and the reawakening of some of the area's geysers, including Steamboat, the largest geyser in the world.
Yellowstone last erupted about 640,000 years ago, spewing 240 cubic miles of material. Despite the newly discovered activity, researchers don't expect it to erupt any time soon. Eventually, however, it could explode again as a super-volcano that would destroy life for hundreds of miles around.
Radar observations from the European Space Agency's ERS-2 satellite reveal that the jellybean-shaped Yellowstone caldera—a giant depression caused by past volcanic explosions—began to rise in 1995.
Although the caldera floor started to sink in late 1997, part of the north rim, called the north rim uplift anomaly (NUA) continued rising until 2003.
Magma has risen from the Earth's core under Sour Creek dome, a major feature in the eastern section of the caldera. When the magma reaches the mantle layer, six to 12 miles below the surface, it spreads like a pancake before branching off into several tunnels.
Magma flow is controlled by natural valves—one at Sour Creek dome that lets magma enter the system, and others that allow it to flow out. The outflow valve below the north rim uplift anomaly, however, can only pass so much magma at once.

"Magma's always coming up in Sour Creek dome and going through the system. But maybe there are pulses when more comes up. That may be what causes the surface to rise" - Charles Wicks, USGS research geophysicist.

The research is detailed in the March 2 issue of the journal Nature.
The pulses might be more than the outflow valve can handle—like trying to squeeze all the toothpaste out of the tube at once. As the molten material pushes out on the surrounding rock, the ground around the valve expands and cracks.
This could explain why the uplift anomaly has risen and the Norris Geyser Basin has become more active. Another explanation is that nearby geothermic changes and seismic activity altered the shape of the valve, perhaps narrowing it. However, previous studies have indicated that no such alterations have occurred, and that changes in flow rate more likely cause these deformations.


A high-resolution version of the radar data. This shows the uplift at NUA and the small-scale areas of uplift in the Norris Mammoth corridor. Active faults are marked with black lines and the approximate caldera rim is marked with a heavy black dashed line.
Credit: USGS


The five-inch increase at the uplift anomaly probably wasn't noticed by many tourists, but the changes in the Norris Geyser Basin were easily spotted by some. After a nine year period of inactivity, Steamboat Geyser erupted in May, 2000, and has erupted five times since. Reaching more than 300 feet in the air, Steamboat produces the highest plumes of any geyser in the world.
Since 1989, Pork Chop geyser was active only as a hot spring, but in the summer of 2003 it reawakened as a geyser. Also that summer, several footpaths near the Norris Geyser Basin were closed because of near-boiling ground temperatures.
And a 250-foot line of new fumaroles, holes venting hot smoke and gases, formed near Nymph Lake to the north of the uplift anomaly.

"But when the (uplift anomaly) quit inflating in 2002 and 2003, the thermal unrest died off too. So we think there's pretty good evidence for tying these events together" - Charles Wicks.

Despite these changes, Wicks doesn't believe that Yellowstone is ready to erupt.

"This is probably an ongoing feature in Yellowstone. We've only been able to study it like this for 10 years, so we're still not sure what's normal and what's not. But there's no evidence yet to suspect an eruption"- Charles Wicks.

Also, the magma pancake serves as a thermal buffer that helps stabilise the volcanic system against potentially dangerous sudden changes in temperature.

Adapted from Source

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RE: Yellowstone lake
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Huge volcanic eruptions that occurred over the past 2 million years formed Yellowstone National Park’s striking landscape.
Two eruptions from 1.2 million and 600,000 years ago ejected more than 1,000 cubic kilometres of material each, making them among the largest volcanic eruptions known in the Earth’s geologic record.
At the same time, the emptying of the magma chambers beneath Yellowstone created large surface depressions called calderas.
The youngest caldera measures nearly 80 kilometres long by 50 kilometres wide. Thought by most geologists to be the current location of a “hot spot” of upwelling, hot material from Earth’s mantle, and the continuing activity of the region is demonstrated by its geysers, hot springs, and boiling mud pots.


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This Astronaut photograph ISS011-E-10575 was acquired July 15, 2005 with a Kodak 760C digital camera with an 180 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Centre.


This astronaut photograph is centred on Yellowstone Lake, a popular camping and fishing location within the National Park. The lake basin includes part of the youngest caldera and has an area of 352 square kilometres.
Due to the rise and fall of resurgent domes (the locations of volcanic vents) located nearby, the lake basin is now tilted southwards, causing beaches to grow along the northern shore and flooding to occur in the southern arms of the lake.
The West Thumb of Yellowstone Lake was formed by an eruption that occurred approximately 150,000 years ago. The resulting relatively small caldera was subsequently filled with water and joined with the larger lake to the east. Numerous geothermal features such as geysers and hot springs are located in the West Thumb area— this is thought to be due to a relatively shallow, local magma source.

A more recent change to Yellowstone’s geography is the area covered by large fire scars— cleared areas burned during the vast 1988 forest fires. The scars are still highly visible 17 years later because the light-coloured cleared regions contrast with the surrounding forest.

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Yellowstone caldera
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The Yellowstone caldera has been classified a high threat for volcanic eruption, according to a report from the U.S. Geological Survey.

Yellowstone ranks 21st most dangerous of the 169 volcano centres in the US, according to the Geological Survey's first-ever comprehensive review of the nation's volcanoes. Kilauea in Hawaii received the highest overall threat score followed by Mount St. Helens and Mount Rainer in Washington, Mount Hood in Oregon and Mount Shasta in California.



Kilauea has been erupting since 1983. Mount St. Helens, which erupted catastrophically in 1980, began venting again in 2004. Those volcanoes fall within the very high threat group, which includes 18 systems. Yellowstone is classified with 36 others as high threat.
Recurring earthquake swarms, swelling and falling ground, and changes in hydrothermal features are cited in the report as evidence of unrest at Yellowstone. The report calls for better monitoring of the 55 volcanoes in the very high and high threat categories to track seismic activity, ground bulging, gas emissions and hydrologic changes.
Volcano Threat Report: PDF





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