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
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.
from Smith and Siegel, 2000
Fortunately, the 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
Scientists evaluate 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.
supervolcano eruption in the US Video From FirstScience.TV
Scientists have revealed that
Yellowstone Park has been on a regular eruption cycle of 600,000
years. The last eruption was 640,000 years ago ... so the next is overdue. The
next eruption could be 2,500 times the size of the 1980 Mount St. Helens
eruption. Volcanologists have been tracking the movement of magma
under the park and have calculated that in parts of Yellowstone the ground has
risen over seventy centimeters this century.
Normal volcanoes are
formed by a column of magma - molten rock - rising from deep within the Earth,
erupting on the surface, and hardening in layers down the sides. This forms the
familiar cone shaped mountain we associate with volcanoes.
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.
The Yellowstone 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 ("fire-broken") 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 Falls Tuff.
The region's 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 Valley,
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 low.
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.
Geologists conclude 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.
Even distant 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
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 460F
(238C) 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).
Much larger 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
Although large 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
Explosive eruptions 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, eruption-the 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
Around The World
Around the world
there are several other volcanic areas that can be considered "supervolcanoes"-
Long Valley in eastern California, Toba in Indonesia, and Taupo in New Zealand.
Other "supervolcanoes" would likely include the large caldera
volcanoes of Japan, Indonesia.