Transcript Yellowstone National Park in northwest Wyoming is a picturesque

Yellowstone
http://volcanoes.usgs.gov/volcanoes/yellowstone/yello
wstone_multimedia_11.html
Yellowstone National Park in northwest
Wyoming is a picturesque land of geysers, hot
springs, waterfalls, mountains, and lakes. But
just in case you don’t have enough to worry
about, it is also the largest supervolcano in
North America and among the top three largest
in the world. The term “supervolcano” refers
to a measure of volume of material erupted
and explosiveness.
The U.S. Geological Survey (USGS) map below shows the general
setting of the Yellowstone volcano and caldera. Calderas are created
following an eruption when the volcano collapses in on itself.
Example Volcano Volumes from the Image Above
Volcano Name
Lassen Peak
Location
Date (Years ago)
Volume in km3
Northern California 1915
0.006
Wilson Butte Eastern California (1,300)
0.05
Mt St. Helens Washington
0.25
May 18, 1980
Pinatubo
Philippines
1991
5
Novarupta
Alaska
1912
13
Mesa Falls
Yellowstone
(1.3 Million)
Long Valley Caldera Eastern California (760,000)
Lava Creek
Yellowstone
(640,000)
280
580
1000
Huckleberry Ridge Yellowstone (2.1 Million)
2450
Toba
2800
Sumatra
(74,000)
According to the Yellowstone Volcano Observatory, run by the
USGS and the University of Utah, during the past 2 million years
the Yellowstone super volcano has had three of the world’s
largest volcanic eruptions:
Eruption of the >2450 cu km Huckleberry Ridge Tuff about 2.1
million years ago created the more than 75-km-long Island Park
caldera.
The second cycle concluded with the eruption of the Mesa
Falls Tuff around 1.3 million years ago, forming the 16-km-wide
Henrys Fork caldera at the western end of the first caldera.
Activity subsequently shifted to the present Yellowstone
Plateau and culminated 640,000 years ago with the eruption of the
>1000 cu km Lava Creek Tuff and the formation of the present 45
x 85 km caldera. Resurgent doming subsequently occurred at both
the NE and SW sides of the caldera and voluminous (1000 cu km)
intracaldera rhyolitic lava flows were erupted between 150,000
and 70,000 years ago.
http://volcanoes.usgs.gov/volcanoes/yellowstone/yellowstone_gallery_2.html
Pictures of
Yellowstone
Yellowstone is presently the site of one of
the world’s largest hydrothermal systems
including Earth’s largest concentration of
geysers. As such, it could be one of the largest
sources of geothermal-produced electricity, but
that’s not likely to happen.
The USGS map below shows the coverage of
ash deposits from the three major eruptions,
compared to the 1980 eruption of Mount St.
Helens. The map also shows the extent of the
Bishop Tuff which erupted from the Long Valley
volcano in California 760,000 years ago.
The Yellowstone super volcano is the youngest of a series of
such volcanoes that have erupted over the past 17 million
years. The older volcanoes trace a line running up the Snake
River Plain. The graphic below shows the location and age of
these volcanoes. Notice also the parabolic shape of
earthquake epicenters (red dots).
The theory of this volcanic region is that there is a
stationary “hot spot” in the mantle that periodically
breaks the surface with an eruption. Eruptions occur in a
linear pattern showing that the continental crust is moving
over the hot spot at about 2.8 cm/yr at an azimuth of about
247 degrees according to Smith et al. “The Yellowstone
hotspot has been the source of voluminous rhyolite tuffs
and lavas with eruptions often having volumes of
hundreds to thousands of cubic kilometers and
representing some of the largest Quaternary eruptions on
Earth.”
A similar hot spot occurs under Hawaii. In Hawaii, the
magma is basaltic which is very fluid so eruptions are
relatively tame: volcanic explosivity index (VEI) 0 to 1. In
Yellowstone, however, the magma is rhyolitic, very thick
and viscous. That makes for violent explosions (VEI 8,
the maximum) which produces ash rather than lava flows.
What is happening now?
The National Park Service assures us, “There
is no evidence that a catastrophic eruption at
Yellowstone National Park (YNP) is imminent.
Current geologic activity at Yellowstone has
remained relatively constant since earth
scientists first started monitoring some 30
years ago. Though another caldera-forming
eruption is theoretically possible, it is very
unlikely to occur in the next thousand or even
10,000 years. Scientists have also found no
indication of an imminent smaller eruption of
lava.”
National Geographic news of January 19, 2011 reports:
Yellowstone National Park’s supervolcano just took a deep
“breath,” causing miles of ground to rise dramatically,
scientists report.
But beginning in 2004, scientists saw the ground above the
caldera rise upward at rates as high as 2.8 inches (7
centimeters) a year.
The rate slowed between 2007 and 2010 to a centimeter
a year or less. Still, since the start of the swelling, ground
levels over the volcano have been raised by as much as 10 inches
(25 centimeters) in places.
“It’s an extraordinary uplift, because it covers such a
large area and the rates are so high,” said the University of
Utah’s Bob Smith, a longtime expert in Yellowstone’s volcanism.
Scientists think a swelling magma reservoir four to six
miles (seven to ten kilometers) below the surface is driving
the uplift. Fortunately, the surge doesn’t seem to herald an
imminent catastrophe.
“At the beginning we were concerned it could be
leading up to an eruption,” said Smith, who coauthored a paper on the surge published in the
December 3, 2010, edition of Geophysical Research
Letters.
“But once we saw [the magma] was at a depth
of ten kilometers, we weren’t so concerned. If
it had been at depths of two or three kilometers
[one or two miles], we’d have been a lot more
concerned.”
The following is a graphic from Smith, showing
topographic swelling caused by magma pressure at
Yellowstone; rather impressive:
Apparently, all is (relatively) quiet on the western
front, but who knows when the pimple will pop.