It is little known
that lying underneath one of The United States largest and most picturesque
National Parks - Yellowstone Park - is one of the largest "super
volcanoes" in the world.
Each year, millions
of visitors come to admire the hot springs and geysers of Yellowstone, the
Nation�s first national park. Few are aware that these wonders are fueled
by heat from a large reservoir of partially molten rock (magma), just a few
miles beneath their feet. As this magma-which drives one of the world�s
largest volcanic systems-rises, it pushes up the Earth�s crust beneath
the Yellowstone Plateau.
Eruptions of the
Yellowstone volcanic system have included the two largest volcanic eruptions in
North America in the past few million years; the third largest was at Long
Valley in California and produced the Bishop ash bed. The biggest of the
Yellowstone eruptions occurred 2.1 million years ago, depositing the Huckleberry
Ridge ash bed. These eruptions left behind huge volcanic depressions called
�calderas� and spread volcanic ash over large parts of North
America (see map). If another large caldera-forming eruption were to occur at
Yellowstone, its effects would be worldwide. Thick ash deposits would bury vast
areas of the United States, and injection of huge volumes of volcanic gases into
the atmosphere could drastically affect global climate.
Yellowstone volcanic system shows no signs that it is headed toward such an
eruption in the near future. In fact, the probability of any such event
occurring at Yellowstone within the next few thousand years is exceedingly low.
The term "supervolcano"
has no specifically defined scientific meaning. It was used by the producers of
The BBC TV show Horizionin 2000 to refer to volcanoes that have generated Earth's largest volcanic
eruptions. As such, a
supervolcano would be one that has produced an exceedingly large, catastrophic
explosive eruption and a giant caldera.
natural-hazard levels by combining their knowledge of the frequency and the
severity of hazardous events. In the Yellowstone region, damaging hydrothermal
explosions and earthquakes can occur several times a century. Lava flows and
small volcanic eruptions occur only rarely�none in the past 70,000 years.
Massive caldera-forming eruptions, though the most potentially devastating of
Yellowstone's hazards, are extremely rare-only three have occurred in the past
several million years. U.S. Geological Survey, University of Utah, and National
Park Service scientists with the Yellowstone Volcano Observatory (YVO) see no
evidence that another such cataclysmic eruption will occur at Yellowstone in the
foreseeable future. Recurrence intervals of these events are neither regular nor
predictable. credit: USGS
however, begin life when magma rises from the mantle to create a boiling
reservoir in the Earth's crust. This chamber increases to an enormous size,
building up colossal pressure until it finally erupts. The explosion would send
ash, dust, and sulfur dioxide into the atmosphere, reflecting the sun's rays and
creating a cold wave lasting several years. Crops in many areas would fail and
many species of animals and plants would face extinction.
region has produced three exceedingly large volcanic eruptions in the past 2.1
million years. In each of these cataclysmic events, enormous volumes of magma
erupted at the surface and into the atmosphere as mixtures of red-hot pumice,
volcanic ash (small, jagged fragments of volcanic glass and rock), and gas that
spread as pyroclastic flows in all directions. Rapid withdrawal of such
large volumes of magma from the subsurface then caused the ground to collapse,
swallowing overlying mountains and creating broad cauldron-shaped volcanic
depressions called calderas.
The first of these
caldera-forming eruptions 2.1 million years ago created a widespread volcanic
deposit known as the Huckleberry Ridge Tuff, an outcrop of which can be viewed
at Golden Gate, south of Mammoth Hot Springs. This titanic event, one of the
five largest individual volcanic eruptions known anywhere on the Earth, formed a
caldera more than 60 miles (100 km) across.
A similar, smaller
but still huge eruption occurred 1.3 million years ago. This eruption formed the
Henrys Fork Caldera, located in the area of Island Park, west of Yellowstone
National Park, and produced another widespread volcanic deposit called the Mesa
most recent caldera-forming eruption 640,000 years ago created the 35-mile-wide,
50-mile-long (55 by 80 km) Yellowstone Caldera. Pyroclastic flows from this
eruption left thick volcanic deposits known as the Lava Creek Tuff, which can be
seen in the south-facing cliffs east of Madison, where they form the north wall
of the caldera. Huge volumes of volcanic ash were blasted high into the
atmosphere, and deposits of this ash can still be found in places as distant
from Yellowstone as Iowa, Louisiana, and California.
Each of Yellowstone's
explosive caldera-forming eruptions occurred when large volumes of rhyolitic
magma accumulated at shallow levels in the Earth's crust, as little as 3 miles
(5 km) below the surface. This highly viscous (thick and sticky) magma, charged
with dissolved gas, then moved upward, stressing the crust and generating
earthquakes. As the magma neared the surface and pressure decreased, the
expanding gas caused violent explosions. Eruptions of rhyolite have been
responsible for forming many of the world�s calderas, such as those at
Katmai National Park, Alaska, which formed in an eruption in 1912, and at Long
If another large
caldera-forming eruption were to occur at Yellowstone, its effects would be
worldwide. Thick ash deposits would bury vast areas of the United States, and
injection of huge volumes of volcanic gases into the atmosphere could
drastically affect global climate. Fortunately, the Yellowstone volcanic system
shows no signs that it is headed toward such an eruption. The probability of a
large caldera-forming eruption within the next few thousand years is exceedingly
More likely in
Yellowstone than a large explosive caldera-forming eruption is eruption of a
lava flow, which would be far less devastating. Since Yellowstone's last caldera-forming
eruption 640,000 years ago, about 30 eruptions of rhyolitic lava flows have
nearly filled the Yellowstone Caldera. Other flows of rhyolite and basalt (a
more fluid variety of lava) also have been extruded outside the caldera. Each
day, visitors to the park drive and hike across the lavas that fill the caldera,
most of which were erupted since 160,000 years ago, some as recently as about
70,000 years ago. These extensive rhyolite lavas are very large and thick, and
some cover as much as 130 square miles (340 km2), twice the area of
Washington, D.C. During eruption, these flows oozed slowly over the surface,
moving at most a few hundred feet per day for several months to several years,
destroying everything in their paths.
From 1,000 to 3,000
earthquakes typically occur each year within Yellowstone National Park and its
immediate surroundings. Although most are too small to be felt, these quakes
reflect the active nature of the Yellowstone region, one of the most seismically
active areas in the United States. Each year, several quakes of magnitude 3 to 4
are felt by people in the park.
Although some quakes
are caused by rising magma and hot-ground-water movement, many emanate from
regional faults related to crustal stretching and mountain building. For
example, major faults along the Teton, Madison, and Gallatin Ranges pass through
the park and likely existed long before the beginning of volcanism there.
Movements along many of these faults are capable of producing significant
earthquakes. The most notable earthquake in Yellowstone�s recent history
occurred in 1959. Centered near Hebgen Lake, just west of the park, it had a
magnitude of 7.5. This quake caused $11 million in damage (equivalent to $70
million in 2005 dollars) and killed 28 people, most of them in a landslide that
was triggered by the quake.
that large earthquakes like the Hebgen Lake event are unlikely within the
Yellowstone Caldera itself, because subsurface temperatures there are high,
weakening the bedrock and making it less able to rupture. However, quakes within
the caldera can be as large as magnitude 6.5. A quake of about this size that
occurred in 1975 near Norris Geyser Basin was felt throughout the region.
earthquakes can affect Yellowstone. In November 2002, the magnitude 7.9 Denali
Fault earthquake struck central Alaska, 1,900 miles (3,100 km) northwest of
Yellowstone. Because this quake�s energy was focused toward the active
Yellowstone volcanic and hydrothermal system, it triggered hundreds of small
earthquakes there. The region's hydrothermal system is highly sensitive to
quakes and undergoes significant changes in their wake. Earthquakes may have the
potential to cause Yellowstone's hot-water system to destabilize and produce
explosive hydrothermal eruptions.
The large magma
reservoir beneath Yellowstone may have temperatures higher than 1,475F (800C),
and the surrounding rocks are heated by it. Because of this, the average heat
flow from the Earth's interior at Yellowstone is about 30 times greater than
that typical for areas elsewhere in the northern Rocky Mountains. As snowmelt
and rainfall seep deep into the ground, they can absorb enough of this heat to
raise the temperature of the ground water close to the boiling point. Geyser
basins and other thermal areas in Yellowstone National Park are places where hot
ground water has risen close to the surface. Research drilling at Yellowstone in
the 1960s confirmed that the ground water beneath many of the park's thermal
areas is very hot. At Norris Geyser Basin, water temperatures as high as 460.F
(238.C) were recorded at depths of only 1,090 feet (332 m).
Because the boiling
point of water increases with increasing pressure and pressure increases with
depth, deep water can be hotter than boiling water near the surface. If the
pressure that confines this deep water is reduced quickly, pockets of water may
suddenly boil, causing an explosion as the water is converted to steam. Such
activity drives the eruptions of geysers, like Old Faithful, which are
repetitive releases of plumes of steam and water. Rarely, steam explosions are
more violent and can hurl water and rock thousands of feet. In Yellowstone's
geologic past, such violent events, called hydrothermal explosions, have
occurred countless times, creating new landscapes of hills and craters.
A recent and notable
hydrothermal explosion occurred in 1989 at Porkchop Geyser in Norris Geyser
Basin. The remains of this explosion are still clearly visible today as an apron
of rock debris 15 feet (5 m) across surrounding Porkchop's central spring. In
the 1880s and early 1890s, a series of powerful hydrothermal explosions and
geyser eruptions occurred at Excelsior Geyser in the Midway Geyser Basin. Some
of the explosions hurled large rocks as far as 50 feet (15 m).
hydrothermal explosions have occurred at Yellowstone in the recent geologic
past. More than a dozen large hydrothermal-explosion craters formed between
about 14,000 and 3,000 years ago, triggered by sudden changes in pressure of the
hydrothermal system. Most of these craters are within the Yellowstone Caldera or
along a north-south-trending zone between Norris and Mammoth Hot Springs.
hydrothermal-explosion crater documented in the world is along the north edge of
Yellowstone Lake in an embayment known as Mary Bay. This 1.5-mile (2.6
km)-diameter crater formed about 13,800 years ago and may have had several
separate explosions in a short time interval. What specifically triggered these
very large events is not firmly established, but earthquakes or a pressure
release caused by melting glaciers or rapid changes in lake level may have been
a significant factor.
These very large and
violent hydrothermal explosions are independent of associated volcanism. None of
the large hydrothermal events of the past 16,000 years has been followed by an
eruption of magma. The deeper magma system appears to be unaffected even by
spectacular steam explosions and crater excavations within the overlying
hydrothermal explosions are a feature of Yellowstone's recent geologic history,
most explosions in historical times have been relatively small and have left
craters at most a few yards across. For example, in early 2003, a long linear
fissure appeared on a hillside above Nymph Lake, north of Norris Geyser Basin,
venting steam and throwing bits of rock onto the surrounding hillside. Although
most hydrothermal explosions in the park are small, their remains can be noticed
by observant visitors and attest to the nearly continuous geologic activity at
are best compared by recalculating the volume of erupted volcanic ash and
pumice in terms of the original volume of molten rock (magma) released
(shown in this diagram by orange spheres). On this basis, the 585 cubic miles
(mi3) of magma that was erupted from Yellowstone 2.1 million years ago (Ma) was
nearly 6,000 times greater than the volume released in the 1980 eruption of
Mount St. Helens, Washington, which killed 57 people and caused damage exceeding
$1 billion. Even the 1815 Tambora, Indonesia, eruptionthe largest on Earth in
the past two centuries was more than five times smaller than the smallest of
Yellowstone's three great prehistoric eruptions at 1.3 Map credit: USGS
Answers on Supervolcanoes, Volcanic Hazards
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 critical 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 (240 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) 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
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
United States Geological Survey, University of Utah, National Geographic,Thomas
Reichert,The Geological Society of London
compiled from The British Antarctic Study, NASA, Environment Canada,
UNEP, EPA and other sources as stated and credited Researched by Charles
Welch-Updated daily This Website is a project of the The Ozone Hole Inc.
a 501(c)(3) Nonprofit Organization http://www.theozonehole.com