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article imageNorth America's supervolcano: Yellowstone National Park

By Karen Graham     Nov 7, 2013 in Science
Yellowstone, the world's first National Park was established in 1872. With its subalpine forests, wildlife and geothermal features, it's been a top vacationers destination. But we were unaware of it being a big volcanic crater, a very, very big one.
North America, or to be more precise, the United States and Canada share the rather dubious distinction of living on the same continent with one of the world's largest supervolcanoes. The vast majority of what is left of the volcano, the caldera, or bowl, makes up most of Yellowstone National Park in the northwest corner of Wyoming. The caldera is approximately 34 miles wide by 45 miles in length.
Early history of Yellowstone National Park
It is known from studies and research by archaeologists, geologists and anthropologists that early man lived in and around the area we call Yellowstone as early as 11,000 years ago. They were aware of the geothermal activity, hot springs, geysers and hot mud pools that abounded there.
Members of the Crow Nation. Circa:1840-1843. The Crow Nation s territory included what is now Yellow...
Members of the Crow Nation. Circa:1840-1843. The Crow Nation's territory included what is now Yellowstone Natl. Park
Karl Bodner (1808-1893) Library of Congress
From the early 1800's until 1851, mountain men hunting and trapping in Yellowstone would come back to civilization with fantastic stories of steaming hot water shooting into the sky and sulfurous smelling pools so vile they took one's breath away. They talked wildly of "fire and brimstone," but most people dismissed these tales as myth and yarns.
It was Jim Bridger, in 1859, who when providing written information and very accurate maps of the Yellowstone area, mentioned "vulcanism" for the first time. It wasn't long after the Civil War ended that real exploration of this strange and wonderful place began. But no one suspected how geologically important Yellowstone was.
The Yellowstone caldera and supervolcano
To be precise, the Yellowstone caldera is the volcanic caldera and the supervolcano located within Yellowstone National Park. The caldera was formed during the last of the three eruptions of the volcano. The name "supervolcano" was not used before the year 2000. Before scientists had access to satellite pictures of the earth, they knew about the volcanic caldera, but had no idea as to the actual size, or numbers of them.
Supervolcano became widely used after a BBC documentary called Supervolcano in 2005. The best definition is to say a supervolcano is a "volcanic field that produces extremely large volcanic eruptions." There were three super-eruptions over the last 2.1 million years.
The first is called the Huckleberry Ridge eruption, occurring 2.1.million years ago. The second one is called the Mesa Falls eruption, occurring 1.3 million years ago. The third super-eruption is called the Lava Creek eruption, occurring 640,000 years ago. This third eruption formed the Yellowstone caldera. The Henry's Fork caldera, formed after the second eruption is the only caldera that can be plainly seen today. It covers the Snake River Plain-Yellowstone hotspot.
Yellowstone National Park actually sits on top of four over-lapping calderas.
Yellowstone National Park actually sits on top of four over-lapping calderas.
Kelvin Case
Are we in danger of an imminent eruption of the volcano?
Two stories emerged recently, one being that scientists had discovered the magma pool under Yellowstone was twice as big as when it was last measured in 2004. This new information is attributed to improved data from seismic tomography. This means we now have a way of creating accurate pictures of the pool. With their new knowledge, scientists also found the magma reservoir is only 7 percent full.
Detailed picture of caldera and magma reservoir.
Detailed picture of caldera and magma reservoir.
The second story occurred over a period of six days, from Sept. 10 through Sept. 16, when over 130 small earthquakes were recorded. There were 16 epicenters around the park, and the earthquakes were occurring in clusters, or "swarms."
There are two kinds of clusters. One kind, called the Primary shock-Aftershock, we are all familiar with. We have a large magnitude quake, and then for several hours and days, continue to have weaker and weaker ones until they stop. The second kind is called a swarm. A swarm is a whole bunch of earthquakes, usually of small magnitude, without a major quake preceding them.
There are any number of web pages spewing end of the world stories of how the world is on the brink of an extinction event in the very near future. But saner minds are monitoring the caldera and the magma reservoir that lies 4 to 10 miles underneath. In order to understand what all the excitement was about recently, some background is needed.
Yellowstone is no stranger to earthquakes. On average, 1,000 to 3,000 earthquakes are recorded annually. They range from less than 1.0 on the seismographs to 3.7 or so. Rangers say that most of these quakes are not even felt by visitors. Monitoring goes on daily, as a joint effort by the U.S. Geological survey, the Yellowstone National Park Service and the University of Utah.
What the scientists do know is that geologic activity has remained the same as it has been for the past 30 years, since monitoring first started. They temper this with saying that while it is possible to have an eruption occur, it is highly unlikely of anything happening in the next 10,000 years or more.
A more likely scenario would be to have a lava flow occur. The lave could ooze slowly for months or years, leaving time for further evaluation. But there is no scientific evidence of this happening either. With the advances that have been made in seismology and the forecasting of volcanic activity in the past 25 years, scientists have learned a lot about the Yellowstone caldera.
Yes, Yellowstone supervolcano is an active volcano. As evidence, there are 1,000 to 3,000 earthquakes annually. There is active ground deformation, meaning the ground has risen over the magma dome over the centuries. And, there are over 10,000 thermal features. There is no way an eruption can be prevented. It's beyond man's ability to change that. But an eruption in not seen in the foreseeable future, and that is many thousands of years.
More about Yellowstone National Park, Volcano, magma, caldera, earthquake swarms
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