Super Volcanoes in the United States: Yellowstone Caldera

The earthquake swarms that occurred around Christmas 2008 beneath the eastern end of Yellowstone Lake have served as a reminder that Yellowstone National Park sits on top of super volcano. This super volcano has erupted in a cycle about every 600,000 years. It was these volcanic eruptions, and their residual evidence that have shaped much of Yellowstone National Park's natural beauty.

The last eruption occurred about 650,000 years ago, and these earthquakes may be a sign that the caldera may becoming more active. It could also be a precursor to a smaller eruption, or simply a more normal occurrence of magma shifting around under the lake. If the super volcano where to erupt, it would bring massive loss of life and tremendous loss, to the United States. It would also have drastic effects an agriculture due to climate change brought about by volcanic ash and dust ejected into the atmosphere.

A caldera ("cooking pot" from Spanish) is a geologic feature that forms from a collapsed volcanic crater that exceeds a one mile diameter. Calderas are formed when the magma chamber underneath the earth collapses after an eruption and lava has flowed out from the the chamber.

Yellowstone's caldera far exceeds the one mile wide criteria. The caldera is so big that it has actually formed Yellowstone Lake. The caldera measures about 35 miles across. Would the weight of the water be enough to keep any magma surging beneath the earth's surface in check? Not hardly. In a full scale eruption the explosive force exerted by the magma thrust would exceed 60 million atom bombs.

Besides Yellowstone Caldera, there are two other active calderas that are located in the lower 48 states. The Long Valley Caldera is located near Mammoth, California is about half the size of Yellowstone Caldera. The last time Long Valley erupted was about 760,000 years ago.

The Long Valley Caldera has been quite active in recent years, and like Yellowstone, has a full time observatory to monitor its geologic conditions. In 1980, an earthquake swarm on the southern end of the valley occurred in association with increased uplift of the caldera. It was shown to rise about 10 inches. Occasional increased bulges have been noted in the caldera at times in the years since and earthquake continues.

The activity that occurred in the 1980s in Long Valley look to be more significant in terms of magnitude and numbers of the earthquakes. A few of the Long Valley earthquakes measured up to 6 in the Richter scale compared to the 3.0 measurements recently made a Yellowstone. It may be that in Yellowstone's case, we may be headed for a more active period in the life cycle of the caldera.

The other active caldera in the lower United Stated is Valles Caldera, located northwest of Santa Fe, NM. This caldera is the smallest of and least active of the three. Up until 2000, it was privately owned. The Valles Caldera National Preserve was then created and government funds purchased the land from the owners to enact increased environmental protections for the area.

The Valles Caldera last erupted about 1.5 million years ago and is not likely to produce another eruption anytime in the near future. The area is still noted for geothermal activity, with an abundance of steam vents and a few hot springs.

Since no super volcanoes have been observed it is tough to say whether eruptions are imminent at our active calderas. However, they can being a wealth of understanding to the geologists who monitor their near daily changes.