When people hear the term "supervolcano", they tend to think of fictional disasters movies which
portray a sensationalized large volcanic eruption. However, supervolcanoes are real and a number of
them are present around the globe. On average, a supervolcano erupts once every 50,000 to 100,000
years. None of these supervolcanoes are as famous as the Yellowstone Caldera in Wyoming.
Although a large caldera forming eruption is unlikely in the near future, volcanic eruptions
that are many orders of magnitude smaller are quite likely in the next several thousand
years. This series of videos on Yellowstone will discuss this unique volcanic system,
the odds of a future eruption, and what hazards it could pose in the future.
This first video in the series will focus on the background information on this volcano, as well as
the older geologic history of the yellowstone hotspot, and why it exists in Wyoming today.
For this video, we are defining an active volcano as any volcano or volcanic field which
has erupted in the last 10,000 years. Although 10,000 years may seem like a long timeframe,
this is the definition used by the global volcanism program. The Yellowstone volcano
has experienced 4 eruptions during the last 10,000 years, so it is classified as active.
The Yellowstone Caldera is one of three recent supervolcanoes present in the United States.
This begs the question, what is considered to be a supervolcano?
The typical definition given for a supervolcano is any volcano which has produced an explosive
eruption that created at least 1,000 cubic kilometers or 240 cubic miles of tephra in one
or more of its eruptions. To understand how large this truly is, let me compare it to another famous
explosive eruption. In 1980, Mount Saint Helens violently erupted in an eruption which caused the
volcano to lose 1300 ft in elevation. It produced ash that fell as far away as Oklahoma. However,
this eruption only produced 1 cubic kilometer of tephra. In other words, a supervolcanic eruption
is the equivalent of 1000 or more Mount Saint Helens sized eruptions occurring at the same time.
Today, the Yellowstone caldera supervolcano can be found in northwest corner of Wyoming
within the present day Yellowstone National Park. Unlike the majority of volcanoes in the United
States, this volcano did not form directly due to a subduction zone like the cascade mountains did.
Rather, it formed due to the presence of a large mantle plume or hotspot which is present in the
mantle, and has moved over time. The Yellowstone caldera simply describes the three most recent
sites of a caldera forming eruption from this hotspot. With this being said, this hotspot has
produced far more than 3 calderas. Just like in the Hawaiian island chain, the hotspot has not
moved. However, over many millions of years, the north american tectonic plate above the hotspot
HAS moved to the southwest. This gives the hotspot the appearance of slowly moving to the northeast.
We are not truly sure what caused the yellowstone hotspot to form. What we do know is that activity
from this feature started in what is today southeast Oregon and northwest Nevada.
About 16 million years ago, it formed the first in a series of many calderas as the result of
one or more very large explosive eruptions. This first caldera it formed is today referred to as
the McDermitt caldera. This caldera is between 22 and 28 miles wide, depending on the orientation of
which you measure the length of the caldera. As the north american plate moved to the
west-southwest, the hotspot next erupted near the tristate border of Nevada,
Idaho, and Oregon. I must note that the lines I drew on google earth are approximate edges of the
various calderas, although the exact boundaries of many older calderas are still debated.
You can look on satellite for yourself to see the approximate boundaries of these
calderas as they created rather prominent rims. Over the next several million years, the hotspot
moved northeastward along the snake river plain in Idaho. One caldera forming eruption took place
10.8 million years ago and encompassed what is today the city of Twin Falls. 500,000 years later,
another caldera formed to northeast. Part of this caldera is now overlain by recent volcanism
from the Craters of the Moon volcanic field. The last caldera in the series which is not
considered to be part of the Yellowstone calderas formed 6.65 million years ago. This feature,
known as the Heise caldera, is part of the geography of the Idaho Falls metropolitan area.
Eventually, the hotspot reached what is now northeast idaho and northwest Wyoming. Over
a period of 2.1 million years, this hotspot formed three calderas which today are referred
to as the Yellowstone calderas. The next video in this series on
the Yellowstone supervolcano will focus on these three geologically recent calderas,
and the eruptions which formed them. I hope that you enjoyed this video!
Part two will be posted tomorrow. Once it is released, a link will appear on screen right here!