Phillip Larson
Geology 330
9.11.2005
Yellowstone and Super-Volcanoes
Yellowstone National Park, which encompasses 3,472 square miles, is larger then
both Delaware and Rhode Island combined (Lowenstern). It is presently home to 10,000
geothermal features, including 300 geysers. The park was established in 1872 by, then
President Ulysses S. Grant, who declared, “This Park will be forever dedicated and set
apart as a public park or pleasuring ground for the benefit and enjoyment of the people
(USGS).” Today, Yellowstone is one of the most visited natural sites in the world with
hundreds of thousands of tourists visiting every year. You may ask yourself, as many
tourists do, why is this spot so unlike anything else in the world? Why is all this
geothermal activity concentrated in one large area such as this? The answer to this lies
behind the natural beauty of Yellowstone. Yellowstone is one of the world’s largest
volcanoes and at some time in the future could pose a threat not only to the area but to all
life on Earth. Although the likelihood of such a large scale eruption is minute, the
consideration must be given as to the likelihood of future eruptions. The goal of this
paper is to inform not only of this likelihood of future eruptions and its consequences, but
to examine the past geologic record in order to better understand the nature of the
Yellowstone Super-Volcano.
What is Yellowstone?
The Hotspot:
First an understanding of the driving mechanism must be recognized in order to
understand what the nature of the Yellowstone volcanic system truly is. The Yellowstone
Super-Volcano originates from a hotspot which lies in the mantle where hot, molten rock
rises to the Earth surfaces which in-turn heats the ground underneath thus causing the
geothermal activity we see today. A hotspot is a volcanic center that has been
persistently active for at least a few tens of millions of years. It causes a break in the
Earth’s surface due to a rising mantle plume, not always directly associated with volcanic
arcs or oceanic ridges (Bates and Jackson). It is believed that the Yellowstone hotspot is
stationary within the Earth. It’s apparent motion is due to the North American Plates
southwestwardly movement at a rate of about 4.6 cm per year over the Yellowstone
hotspots lifespan of a little over 16 million years.
The Super-Volcano:
This hotspot has been responsible for several eruptive episodes which will be
discussed in detail later, but has presently found itself in the Northwest corner of
Wyoming and has created an enormous volcanic caldera known as a Super-Volcano. A
Super-Volcano is a term used to describe a volcanic area of immense size and capable of
enormous eruptions, the largest known on Earth. Using this term implies eruptions of a
magnitude 8 on the Volcano Explosivity Index. This would mean that 1,000 plus cubic
kilometers of magma and partially molten rock would be erupted. This scale eruption
would be over 2 to 3 thousand times the size of the Mount St. Helens eruption of 1980.
There are many such Super-Volcanoes across the Earth’s surface. There is evidence to
support 7 known Super-Volcanoes including the Yellowstone volcanic system. The
United States alone is home to three of these Super-Volcanoes located in Yellowstone,
Long Valley California, and Valles Caldera in northern New Mexico. Super-Volcanoes
also exist in many other places worldwide. The four known Super-Volcanoes outside the
United States and last eruptive episodes are; Aira Japan, which last erupted on a very
small scale (for a Super-Volcano) 22,000 years ago, Lake Taupo New Zealand, 26,500
years ago, The Siberian Traps of Siberia, 251 million years ago, and Lake Toba in
Sumatra, Indonesia which had the last major Super-Volcanic eruption 74,000 years ago.
It is interesting to note that the massive Toba eruption is thought to have nearly caused
the extinction of the homo-sapien species as well as many others. The Siberian Trap
eruptions were also thought to be a primary suspect for the Permian Extinctions 251
million years ago (O’Hanlon).
The Yellowstone Hotspot History
There have been numerous eruptive episodes along the Yellowstone Hotspot track
(see figure 2). The Yellowstone Hotspot originated roughly 16.6 million years ago along
the Nevada-Oregon border. This started as an outpouring of basaltic lava in the
Columbia Plateau and rhyolitic centers developing to the south (Perkins and Nash).
Along its track there are thought to have been 6 caldera forming events along what today
is known as the Snake River Plain. These episodes have occurred approximately 16.6-15
ma, 15-13 ma, 12-10.5ma, 10.5-8.6ma, 10-7ma, and 6.5-4.3ma until it reached its present
day location where many more eruptive episodes have occurred. This apparent path is
well marked along the 650 km path of the Snake River Plain. Evidence for this hotspot
track has been determined through careful examination of silica ash fall records which
seem to provide the best space-time transgression of the hotspot (UND.edu).
Figure 2 Yellowstone Hotspot Track. www.usgs.gov
Yellowstone’s Recent History
Since the Yellowstone Hotspot has been located at its present location there have
three major caldera forming, eruptive episodes. These were again determined by careful
examination of ash-flow tuffs in the areas surrounding and far reaching from the present
calderas. There is thought to be a general sequence of how these caldera forming
episodes occur. First the large area above the hotspot is uplifted which depicts the rise of
rhyolite below the Earth’s crust. This forms a magma chamber which inflates as the
rhyolite beneath continues to rise. This then leads to fracturing and faulting at the surface
and occasionally extrusion of lava from the newly formed fractures. After pressure
continues to build highly pressurized rhyolite magma erupts from the concentric ring
fractures and the top of the magma chamber collapses in on itself. This then produces the
large calderas we noticed on the present landscape (USGS). The first of these episodes,
which was the largest eruption in Yellowstone’s recent history, occurred 2.1-2.3 ma. This
eruption, known as the Huckleberry Ridge eruption, vented 2,450+ km3 of ash and
rhyolitic lava, covered an area of approximately 15,500 km2, and formed a caldera that
was thought to be 75x95 km in size. This caldera is not as clearly evident as the next two
to be noted but is thought to include Big Bend Ridge, Snake River, and Red Mountain
Caldera segments. It was determined through the study of the Huckleberry Ridge Tuff.
The second eruption, which occurred 1.3 ma, was much smaller than the Huckleberry
Ridge eruption. The second major eruption vented 280 km3 of ash and lava, covered an
area of 2,700 km2 with ash and rock, and created the Henry’s Fork Caldera which is
approximately 16km in diameter. This was determined through the study of the Mesa
Falls Tuff. The third eruption occurred 640,000 years ago and was determined through
the studies of the Lava Creek Tuff. During this eruption 1,000 km3 of ash and rock were
erupted which covered an area about 7,500 km2. This created the modern Yellowstone
Caldera which can be seen today and stretches 85x45 km in size (USGS)
Figure 2 Yellowstone Calderas and Post-Caldera Volcanic Rocks. www.usgs.gov
Most often the eruptive episodes at Yellowstone and along its hotspot track are
not eruptive. They most often consist of very thick, sticky, and slow moving rhyolite
lava flows. Since the last eruption 40 such lava flows have occurred.
The Likelihood of Future Eruptions and Its Consequences
This volcanic system has shown that it continually cycles threw eruptive caldera
forming episodes throughout its 16.5 million year existence. This means that it will most
likely erupt again in another explosive event similar to those in the past. The question
then remains what the likelihood of such an eruption would be on human time scale and
what the consequences of such an eruption would be? It has been theorized that
Yellowstone is on a roughly 7-8 hundred thousand year cycle but evidence for this is very
sparse. If this were the case we should be looking at the possibility of another eruptive
event in the making. Most geologists agree that a build up to eruption would signal itself
hundreds, even thousands of years before the event actually occurred (USGS). There
clearly has been no evidence of any kind of abnormally increased activity in any aspect in
the area. And although another catastrophic eruption may be possible there are some
geologists who believe a catastrophic eruption, like those of the past, may never occur
again. It is far more likely that eruptions of lava flows will occur as they have many
times in the Yellowstone Hotspot history. It has been calculated that the odds of this kind
of caldera forming eruption has a likelihood of 1 in 730,000 or .00014% of occurring
which is thought to be equivalent to a 1km asteroid striking the Earth. The overall
unpredictability of any major geologic event adds to this uncertainty (USGS).
If it were to happen the consequences would be devastating not only the United
States but to the world as well. The United States economy would be devastated and the
loss of life could be in the millions within a few weeks of the eruptions. Ash would
blanket most of the country as it has done in past eruptions causing far reaching
devastation to most of the nation. Ash from the last eruption, 640,000 years ago was
found as far away as Iowa, Louisiana, and California (see figure 3 for ash coverage). The
global climate could change drastically due to the debris and gases which would have
been erupted into the atmosphere causing millions to die due to temperature change and
widespread famine. This has been clearly shown by much smaller scale eruptions like
that of Krakatoa in 1883 and Tambora in 1815 which caused global temperatures to
plummet a few degrees C. Both these eruptions were not even close in size to any of
Yellowstone’s three episodes. Other evidence of the devastating affects of SuperVolcanoes is believed to be shown by the near extinction of homo-sapiens due to the
Toba eruption 74,000 years ago and possible the Permian mass extinction due to the
Siberian Traps of 251 million years ago.
Figure 3. UW-Madison. Shows ash fall range of the largest two eruptions.
Conclusion
The Yellowstone Hotspot has existed for around 16.5 million years. It has
exhibited the ability to have large caldera forming eruptions consistent with that of a
Super-Volcano. The three major eruptions in Yellowstone’s recent history have left ash
fall to examine the record of its past and through this examination we can determine the
activity that has lead to Yellowstone’s formation. Yellowstone is undoubtedly a
volcanically active area with many unique features found no where else on Earth. The
likelihood of it ever erupting again is uncertain but it is a very rare occurrence at that. A
future eruption is something that must be considered and continual study must be made to
make sure that we are aware if it does increase its activity. The most likely outcome of
any eruptive episode would be lava flows which have abundantly shown themselves in
the past along the hotspot track and even the likelihood of that on human timescale is
very rare.
Phillip Larson
Geology 330
November 9, 2005
The Yellowstone Super-volcano
In the northwest corner of Wyoming lies one of the most outstanding areas
of nature and beauty in the world. Home to 10,000 geothermal features, including
hot springs and over 300 geysers, Yellowstone National Park, which encompasses
3,472 square miles, is larger then both Delaware and Rhode Island combined
(Lowenstern). The park was established in 1872 by, then President Ulysses S.
Grant, who declared, “this park will be forever dedicated and set apart as a public
park or pleasuring ground for the benefit and enjoyment of the people (USGS)."
Today, Yellowstone is one of the most visited natural sites in the world with tens of
thousands of tourists visiting every year. You may ask yourself, why is this spot so
unlike anything else in the world? Why is all this geothermal activity concentrated
in one large area such as this? The answer to this is what lies behind the natural
beauty of Yellowstone. What lies behind is one of the world’s largest supervolcanoes, which poses a threat not only to the area, but to all life on Earth.
Although the likelihood of such a large eruption is minute, the consideration must
be given as to what could happen and what evidence is there that it will happen
again.
The Past Record
To understand the volcanic system we are looking at and to understand the
likelihood of a future eruption we must first look at the evidence of past volcanic
activity. The park is known to have three calderas which were created by three
eruptions in geologic history. It is important to note at this point that two of these
eruptions were “among the largest individual eruptions known on Earth.” These
three eruptions are believed to have occurred roughly 2.1 million, 1.3 million, and
640,000 years ago (believed now to have an approximate 700,000 year cycle). The
first eruption, known as the Huckleberry Ridge eruption, “vented more than 2,500
cubic kilometers of volcanic debris (enough to bury the state of Texas 12 feet
deep).” This eruption in itself was 6,000 times greater than that of the 1980
eruption of Mount St. Helens (Lowenstern). The eruption which occurred 640,000
years ago created the youngest massive caldera in the park, which measures 45 by
30 miles. This “blasted” more that 1,000 cubic kilometers of volcanic material into
the atmosphere. In relation to Mt. St. Helens, it ejected over 8,000 times more ash
and lava (discovery).
So why is this happening here?
It is believed that Yellowstone National Park lies directly above what is
known as a hotspot. The Yellowstone hotspot is believed to be driven by the
“upwelling of a deep seated mantle plume.” This hotspot has been tracked through
examination silica ash fall records and shows and east, north east movement,
which now places it in the northwest corner of Wyoming. It has “over the past 17
million years or so, had successive eruptions which have flooded lava over wide
stretches of Washington, Oregon, California, Nevada, and Idaho, forming a string of
comparatively flat calderas linked like beads, as the North American plate moves
across the stationary hot spot.” The apparent motion of the hotspot is actually due
to the movement of the North American plate moving to the south-southwest. This
is seen through the existence of the Snake River Plain and it being caused by the
Yellowstone hotspot. “The Snake River Plain extends 400 miles (650 km) westward
from northwest Wyoming to the Idaho-Oregon border. The Snake River Plain is a
broad, flat arcuate depression which is concave to the north and covers one quarter
of the state of Idaho. Elevations on the Snake River Plain decrease from the east
(4,400-5,000 feet; 1,350-1,525 m) to the west (2,950-3,900 feet; 900-1,200 m).
Some features within the Snake River Plain become younger to the east. For
example, calderas become progressively younger from west to east. The
Yellowstone calderas are the youngest and mark the approximate hotspot location.”
(UND.edu)
What is the Likelihood of a Future Eruption and its consequences?
It is without a doubt that this volcanic system will erupt again at some point.
The likelihood of it happening on our timescale is almost non-existent. As
Lowenstern pointed out it is far more likely that a small eruption or lava flow would
take place but nothing as catastrophic as many might think. If, which is highly
improbable, the Yellowstone Caldera were to erupt it would have extraordinarily
devastating consequences. The immediate impact would be thousands, if not
millions dead. The United States economy would be in shambles and much of the
North American species would be wiped out. Evidence of the devastating affects of
a super-volcano eruption has been studied in the most recent eruption of the supervolcano Toba eruption 74,000 years ago. It was believed to have dropped human
populations down to a few thousand people, nearly pushing the human race to
extinction. The resulting ash cloud from an eruption such as this would be blasted
into the high atmosphere and carried around the world by various atmospheric
winds. This would cause global temperatures to plummet and could possibly cause
millions to die due to temperature change and hunger. Evidence of this is seen
when studying the ash fall records of the most recent eruption, where ash has been
found as far away as Iowa, Louisiana, and California (USGS). As mentioned earlier
the United States would find itself in a dire situation with millions dead in the
immediate aftermath of the eruption. The economy would most like collapse and in
turn would devastate much of the global economy. So, understandably there is
some reason to be concerned, but as mentioned earlier the likelihood of such a
blast is highly improbable in any human time scale. Plus, it is believed that a supervolcano eruption would give warning signs up to a thousand years before the event
actually occurred.