(A map of Yellowstone National Park showing the Caldera Rim(Red Circle) , courtesey of USGS)

(One of Yellowstone's many Geysers produced by the magma heat beneath the Caldera, courtesy of USGS)

(Ariel Photograph of Yellowstone with the Caldera visible in the center, courtesy of Earth-Pics)

The Yellowstone Caldera

Yellowstone National Park has been long renowned for its magnificent splendor and beauty since well before President Theodore Roosevelt turned it into our first national park in 1903. The main reason for Yellowstone’s geologic beauty as well as its geysers, hot springs, and bubbling mud pits is that underneath Yellowstone’s relatively serene exterior there exists a giant caldera, remnants of an ancient supervolcano that last erupted 600,000 years ago. This large caldera is the result of a “hot spot” that geologists believe exists directly below the Earth’s crust upon which Yellowstone perches. The existence of this caldera is a very visible and ever present sign of the transformative powers of tectonic processes as well as a possible future danger to the United States and much of the Western Hemisphere.

History of the Yellowstone Caldera

Yellowstone has a long history of volcanic activity. The area erupted in catastrophic explosions 2 million years ago, with a much smaller explosion 1.2 million years ago, and, most recently 600,000 years ago another catastrophic eruption occurred. The first eruption 2 million years ago (the Huckelberry ridge eruption) threw over 600 cubic miles of rock and ash out of the earth, a staggeringly huge amount that is about 24,000 times the amount produced by the 1980 eruption of Mt. St. Helens in Oregon. An eruption this large occurs rarely in Earth's history, this eruption covered much of the Western United States in over a meter of ash. The most recent eruption, called the Lava Creek eruption, was significantly smaller, though still quite massive, emitting about 240 cubic miles of volcanic rock from inside the earth, and creating a 24 by 47 mile caldera that encircles much of the park today. The caldera came into existence as the exploding volcano collapsed, as the ground beneath it sunk due to the emptying of the lava pool beneath the caldera, creating a huge depression encircled by the caldera rim. The existance of a hot magma chamber beneath the caldera has been determined by scientists to be the cuase of the geysers, boiling mudpits, and hotsprings that abound in the park. Also the land itself is moving above the caldera; by as much as 1 inch a year up and down in the park as the pressure built up in the magma chamber increases and decreases in different areas. In the past 50 years the Yellow Creek Dome has risen almost a meter, causing theYellowstone lake to tilt southward, creating larger beaches at the north end and higher water at the southern end. (CVO, 2000; TBIMSU, 2005)

Hot Spots and the Formation of the Yellowstone Caldera

What is the reason that Yellowstone has erupted three times in just over 2 million years with more massive explosions than almost any other volcano in Earth’s long history? The answer is that a geologic “hot spot” exists beneath Yellowstone. Volcanic “hot spots” are an intriguing anomaly in geology as most volcanoes are created by the interaction of the collision and subduction of tectonic plates. The energy that fuels volcanoes is created inside the Earth’s core, and which heats up the mantle and creates a pliable surface that tectonic plates- which are continent sized hardened pieces of rock which have risen up above the mantle and move slowly across it. When two of these plates collide subduction of one plate by the other usually occurs, that is, the heavier plate will be forced beneath the lighter one, pushing it down into the mantle. When this happens volcanoes and earthquakes often occur. “Hot Spots” on the other hand are stationary plumes of exceedingly hot magma that has been heated in the core and risen through of the mantle and the crust of the earth, forming a huge magma pool beneath the surface.This magma pool creates a dome on the surface of the crust as well as ring fractures. On occasion pressure will build to the point that magma erupts out of the crust, resulting in a gigantic explosion of volcanic rock. This situation existed in yellowstone 630,000 years ago before the huge eruption collasped the dome, forming the current caldera. Furthermore, the caldera has shifted in the northeasterly direction with each eruption, this movement occurs because the North American continental plate moves several centimeters in the southwestern direction each year, a “hot spot” though remains still, resulting in a line of caldera that shift in the opposite direction of the plate movement. (USGS, 2005; SDSU)

The Danger of Future Eruptions

There are many dangers that come from having the largest recently active caldera in the world situated near the west coast of the United States. In the event of the eruption all life within several hundred miles would probably perish very quickly. People living in the western part of the United States and neighboring parts of Canada would be seriously threatened with death, depending on the size and speed of the eruption, at the very least the amount of ash deposited over the area would kill all plants and animals there in a short period of time. The great plains of the United States would be unable to grow crops and even the mid-west would be very seriously affected. Not just the United States and Canada would be affected though, the sheer amount of ash that would be thrown in the air would probably block out much of the light from the sun all over the world for several years, creating a worldwide famine due to crop failures. Such an event, even if it were on a scale of the third, smaller, major eruption would be a global disaster of such proportions that it would probably put human civilization, as we now know it, into serious danger. (USGS 2005)

Is This at All Likely?

The prior caldera eruptions occurred on regular intervals at about every 600,000 years, which if one takes that number literally means we are overdue. The problem with looking at it this way is that geologic events such as volcanoes are not regular and can never be accurately predicted far into the future. Furthermore scientists are pretty sure that the caldera will not erupt anytime soon (hundreds to thousands of years), if ever again, as the strength of the eruptions has been on the wane and current geologic evidence, which includes regular small earthquakes, water temperature changes, and dome resurgence, are not considered by geologists as signs of an iminent eruption. With events that occur on a geologic time scale of hundreds of thousands of years there probable impact on humans is negligible due to the huge gaps of time between events. For comparison evolutionary modern homo sapiens have existed for about 100,000 years and human civilization does not stretch back more than about 6,000 years. This is all just the blink of an eye if one looks at geologic time spans of millions of years. Ultimately, worrying about the impending eruption of Yellowstone is not an useful way to spend ones time, and planning for it would be an exercise in futility. (Yellowstone media group, 2003; USGS , 2005)

Literature Cited

Yellowstone Media Group. 2003. Yellowstone national park geology- "calderas". http://www.yellowstonenationalpark.com/calderas.htm, Accessed April 2005.

United States Geologic Survey. 2005 March 30. Volcanic history of yellowstone. http://volcanoes.usgs.gov/yvo/history.html. Accessed April 2005

Cascades Volcano Observatory- United States Geologic Survey. 2000. America's volcanic past- yellowstone national park. http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_yellowstone.html, Accessed April 2005

United States Geologic Survey. 2005 March 17. Path of the yellowstone hotspot. http://volcanoes.usgs.gov/yvo/figures/fig1.html, Accessed April 2005.

Thermal Biology Institute Montana State University. Thermal biology in yellowstone national park. http://tbi.montana.edu/msse/lres580/kelly.html, Accessed April 2005.

San Diego State University Department of Geological Sciences. Yellowstone caldera, Wyoming. http://www.geology.sdsu.edu/how_volcanoes_work/Thumblinks/yellowstone_page.html, Accessed April 2005.

Link to other Student Webpages for 2005 Earlham Physical Geology

Copyright © 2004 Earlham College. Revised April 11, 2005 . Send corrections or comments to parkero@earlham.edu