The Rockpile

May 2003, by Will Gray

Yellowstone National Park, World's Largest Active Volcanic Caldera

Catastrophic volcanic eruptions of large volumes of rhyolite magma have occurred three times in Yellowstone National Park, forming large calderas. These eruptions occurred 2 million, 1.3 million and 600,000 years ago. These calderas are basins formed when the surface collapses after the eruption of great amounts of volcanic rock that leave a void beneath the earth's surface. The last of these giant eruptions was 10,000 times as large as the Mount St. Helens eruption in Washington State in 1980. The Yellowstone eruption formed a caldera 53x28 miles across. The pyroclastic flow of pumice and ash had a volume of 240 cubic miles-- enough to cover the entire lower 48 states with a layer five inches thick. The volcanic cloud of ash and gases circled the earth many times, reducing the solar radiation that reached the earth and had great effect on the earth's climate. No volcanic eruption of this magnitude has ever occurred in human history.

The magma chamber below the caldera is still active and is the source of more than 10,000 hot springs, pools, geysers and bubbling mudpots. The latest caldera is buried by several rhyolite lava flows that erupted between 75,000 and 150,000 years ago. A survey was made in the caldera in the Yellowstone Lake area in 1923. When the survey was repeated in 1985 it was found that the ground near the center of the caldera had risen over three feet. Since 1985 the ground has subsided six inches.

The source of the volcanic activity in Yellowstone National Park is a "hot spot" in the mantle beneath the North American Plate. Catastrophic eruptions have occurred from this hot spot over the past 17 million years. The North American Plate is moving southwestward at about 2 ½ centimeters per year and calderas are strung out like beads over a distance of 300 miles from Idaho to Yellowstone National Park. The hot spot will be at the Canadian border in approximately 20 million years.

The last volcanic eruption of the magnitude of the Yellowstone eruption occurred at Toba Caldera in Indonesia 75,000 years ago. Scientist studying DNA of the human race found what they believe showed that the world's population nearly became extinct 70-80,000 years ago. Some suggest that this was the result of the eruption of the Toba volcano in Indonesia. No one is sure what effect the eruption of one of these super volcanoes would have on the world's population today. Since the Yellowstone super volcano has erupted approximately every 700,000 years, another eruption is expected within the next 100,000 years.

References:
Dzurisin, D.; Christiansen, R.L.; Pierce, K.L. Volcano Hazards Fact Sheet: Yellowstone: Restless Volcanic Giant: USGS Open-File Report 95-59.
Smith, R.B., Braile, L.W. 1994, "The Yellowstone hotspot: Journal of Volcanology Geothermal Research, v. 61, pages 121-187.


THE ROCKPILE
The Rockpile is a new section for the DAPL website. Every month we will have a new article on some aspect of geology. These articles are not meant to be highly technical, but instead are written with the Landman in mind. We hope to give you an oversight of a particular area or geological subject. Will Gray, who graduated with a Masters Degree in Geology from the University of Oregon, has kindly agreed to write a monthly article. Will began his career with Texaco, and later worked for British American Petroleum and Sinclair. He has been an independent for the last thirty years. Thanks, Will!
We will be happy to publish submissions by other geologists and engineers - contact the webmaster if you would like to volunteer to write an article for the DAPL.

Click here for previous Rockpile Articles

May 2003, by Will Gray Yellowstone National Park, World's Largest Active Volcanic Caldera Catastrophic volcanic eruptions of large volumes of rhyolite magma have occurred three times in Yellowstone National Park, forming large calderas. These eruptions occurred 2 million, 1.3 million and 600,000 years ago. These calderas are basins formed when the surface collapses after the eruption of great amounts of volcanic rock that leave a void beneath the earth's surface. The last of these giant eruptions was 10,000 times as large as the Mount St. Helens eruption in Washington State in 1980. The Yellowstone eruption formed a caldera 53x28 miles across. The pyroclastic flow of pumice and ash had a volume of 240 cubic miles-- enough to cover the entire lower 48 states with a layer five inches thick. The volcanic cloud of ash and gases circled the earth many times, reducing the solar radiation that reached the earth and had great effect on the earth's climate. No volcanic eruption of this magnitude has ever occurred in human history. The magma chamber below the caldera is still active and is the source of more than 10,000 hot springs, pools, geysers and bubbling mudpots. The latest caldera is buried by several rhyolite lava flows that erupted between 75,000 and 150,000 years ago. A survey was made in the caldera in the Yellowstone Lake area in 1923. When the survey was repeated in 1985 it was found that the ground near the center of the caldera had risen over three feet. Since 1985 the ground has subsided six inches. The source of the volcanic activity in Yellowstone National Park is a "hot spot" in the mantle beneath the North American Plate. Catastrophic eruptions have occurred from this hot spot over the past 17 million years. The North American Plate is moving southwestward at about 2 ½ centimeters per year and calderas are strung out like beads over a distance of 300 miles from Idaho to Yellowstone National Park. The hot spot will be at the Canadian border in approximately 20 million years. The last volcanic eruption of the magnitude of the Yellowstone eruption occurred at Toba Caldera in Indonesia 75,000 years ago. Scientist studying DNA of the human race found what they believe showed that the world's population nearly became extinct 70-80,000 years ago. Some suggest that this was the result of the eruption of the Toba volcano in Indonesia. No one is sure what effect the eruption of one of these super volcanoes would have on the world's population today. Since the Yellowstone super volcano has erupted approximately every 700,000 years, another eruption is expected within the next 100,000 years. References: Dzurisin, D.; Christiansen, R.L.; Pierce, K.L. Volcano Hazards Fact Sheet: Yellowstone: Restless Volcanic Giant: USGS Open-File Report 95-59. Smith, R.B., Braile, L.W. 1994, "The Yellowstone hotspot: Journal of Volcanology Geothermal Research, v. 61, pages 121-187.

© Website 2001 by Denver Assn of Petroleum Landmen © Content by individual contributors