[Geysers] USGS info on Yellowstone supervolcano

[Freund, Udo]

Yellowstone Volcano Observatory (http://volcanoes.usgs.gov/yvo), March
2005 
The docudrama Supervolcano dramatically explores the impact of a large
caldera-forming eruption at Yellowstone. The scale of the portrayed
eruption is similar to the eruption of the Huckleberry Ridge Tuff at
Yellowstone 2.1 million years ago. The movie is realistic insofar as
depicting what could happen if an eruption of this magnitude were to
occur again. Although the drama is set in the future, it does an
acceptable job of addressing some of the issues scientists would grapple
with if Yellowstone showed signs of an impending eruption. The questions
and answers below shed light on issues related to volcanism at
Yellowstone. A much more detailed discussion, including full-color
illustrations, can be found in U.S. Geological Survey Fact Sheet
2005-3024, available online at http://pubs.usgs.gov/fs/2005/3024/.

QUESTION: What is the chance of another catastrophic volcanic eruption
at Yellowstone?	
ANSWER: Although it is possible, scientists are not convinced that there
will ever be another catastrophic eruption at Yellowstone. Given
Yellowstone's past history, the yearly probability of another
caldera-forming eruption could be calculated as 1 in 730,000 or
0.00014%. However, this number is based simply on averaging the two
intervals between the three major past eruptions at Yellowstone - this
is hardly enough to make a critial judgement. This probability is
roughly similar to that of a large (1 kilometer) asteroid hitting the
Earth. Moreover, catastrophic geologic events are neither regular nor
predictable.

QUESTION: What is a "supervolcano"?	
ANSWER: The term "supervolcano" implies an eruption of magnitude 8 on
the Volcano Explosivity Index, meaning that more than 1,000 cubic
kilometers (250 cubic miles) of magma (partially molten rock) are
erupted. The most recent such event on Earth occurred 74,000 years ago
at the Toba Caldera in Sumatra, Indonesia. 
	
QUESTION: What would happen if a "supervolcano" eruption occurred again
at Yellowstone?	
ANSWER: Such a giant eruption would have regional effects such as
falling ash and short-term (years to decades) changes to global climate.
The surrounding states of Montana, Idaho, and Wyoming would be affected,
as well as other places in the United States and the world. Such
eruptions usually form calderas, broad volcanic depressions created as
the ground surface collapses as a result of withdrawal of partially
molten rock (magma) below. Fortunately, the chances of this sort of
eruption at Yellowstone are exceedingly small in the next few thousands
of years. 
	
QUESTION: Is Yellowstone monitored for volcanic activity?
ANSWER: Yes. The Yellowstone Volcano Observatory (YVO), a partnership
between the United States Geological Survey (USGS), Yellowstone National
Park, and the University of Utah, closely monitors volcanic activity at
Yellowstone. The YVO website (http://volcanoes.usgs.gov/yvo)
<http://volcanoes.usgs.gov/yvo> features real-time data for earthquakes,
ground deformation, streamflow, and selected stream temperatures. In
addition, YVO scientists collaborate with scientists from around the
world to study the Yellowstone volcano. 

QUESTION: Do scientists know if a catastrophic eruption is currently
imminent at Yellowstone?	
ANSWER: There is no evidence that a catastrophic eruption at Yellowstone
is imminent, and such events are unlikely to occur in the next few
centuries. Scientists have also found no indication of an imminent
smaller eruption of lava. 
	
QUESTION: How far in advance could scientists predict an eruption of the
Yellowstone volcano?	
ANSWER: The science of forecasting a volcanic eruption has significantly
advanced over the past 25 years. Most scientists think that the buildup
preceding a catastrophic eruption would be detectable for weeks and
perhaps months to years. Precursors to volcanic eruptions include strong
earthquake swarms and rapid ground deformation and typically take place
days to weeks before an actual eruption. Scientists at the Yellowstone
Volcano Observatory (YVO) closely monitor the Yellowstone region for
such precursors. They expect that the buildup to larger eruptions would
include intense precursory activity (far exceeding background levels) at
multiple spots within the Yellowstone volcano. As at many caldera
systems around the world, small earthquakes, ground uplift and
subsidence, and gas releases at Yellowstone are commonplace events and
do not reflect impending eruptions. 
	
QUESTION: Can you release some of the pressure at Yellowstone by
drilling into the volcano?	
ANSWER: No. Scientists agree that drilling into a volcano would be of
questionable usefulness. Notwithstanding the enormous expense and
technological difficulties in drilling through hot, mushy rock, drilling
is unlikely to have much effect. At near magmatic temperatures and
pressures, any hole would rapidly become sealed by minerals
crystallizing from the natural fluids that are present at those depths. 
	
QUESTION: Could the Yellowstone volcano have an eruption that is not
catastrophic?	
ANSWER: Yes. Over the past 640,000 years since the last giant eruption
at Yellowstone, approximately 80 relatively nonexplosive eruptions have
occurred and produced primarily lava flows. This would be the most
likely kind of future eruption. If such an event were to occur today,
there would be much disruption of activities in Yellowstone National
Park, but in all likelihood few lives would be threatened. The most
recent volcanic eruption at Yellowstone, a lava flow on the Pitchstone
Plateau, occurred 70,000 years ago. 
	
QUESTION: Because Yellowstone is so geologically active, are there other
potential geologic hazards in Yellowstone?
ANSWER: The heat and geologic forces fueling the massive Yellowstone
volcano affect the park in many ways. Yellowstone's many geysers,
hotsprings, steam vents, and mudpots are evidence of the heat and
geologic forces. These hydrothermal (hot water) features are mostly
benign, but can rarely be the sites of violent steam explosions and pose
a hydrothermal hazard. Earthquakes, another example of active geologic
forces, are quite common in Yellowstone, with 1,000 to 3,000 occurring
annually. Most of these are quite small, although significant
earthquakes have shaken Yellowstone, such as the 1959 magnitude 7.5
Hebgen Lake quake, the largest historical earthquake in the
intermountain region, and the 1975 magnitude 6.1 quake near Norris
Geyser Basin. The many earthquakes and steam explosions in the past
10,000 years at Yellowstone have not led to volcanic eruptions. 	
Udo Freund