Is Yellowstone a Volcano?

A volcano by definition is a vent in the earth’s crust through which molten lava, ashes and gases are ejected or a mountain formed by the materials ejected from a volcano. Typical volcanic mountains have a crater from which there has been a massive explosion, side vents that let off steam, layers of ash and lava, and fissures where from lava flows. A super volcano is one that is capable of producing ash and lava of at least 240 cubic miles (1000 cubic kilometers) in volume.

Yellowstone’s volcanism is caused by a theorized hot spot, a huge pocket of magma that stays in place while the North American tectonic plate migrates southeast. Calderas have been plotted all along the path of the hot spot. Over the past 17 million years there have been at least 142 calderas formed from the hotspot. Along the path of the most recent eruptions earthquakes on both sides of the hotspot are still measured. The path of the eruptions forms a parabola, or bow shape, similar to bow waves made by a boat as it travels through water.By the definitions above, Yellowstone would qualify as a super volcano. Calderas are formed when lava spews from a volcano so fast that the land below collapses into a crater-like depression. Island Park Caldera, occupying about 2320 square miles of Yellowstone, was formed from a volcanic eruption 2.1 million years ago. Its super eruption spewed 2500 cubic kilometers of ash and lava from California to Mississippi, making the 1980 Mt. St. Helens eruption look like a small firecracker. Nested inside Island Park Caldera is Henry’s Fork Caldera, formed when 280 cubic kilometers of ash and molten rock were spewed 1.3 million years ago. Yellowstone Caldera formed 640,000 years ago, occupies about 1530 square miles of the park and was formed when 1000 cubic kilometers of ash and lava were spewed.

The Snake River Valley in Idaho was formed as this hot spot moved under the continent. A significant amount of evidence can be found of the Yellowstone hot spot moving through Idaho in Craters of the Moon National Monument west of Idaho Falls. Several Buttes appear throughout the valley as well. The most prominent on the drive to Yellowstone’s West entrance from Idaho Falls is referred to as “R” Mountain in Rexburg, Idaho.

It has been 70,000 years since the latest lava flowed from the Yellowstone hotspot, but the volcano remains active. Yellowstone’s thermal features are caused by heat from the hotspot. Hot springs are formed from hot water coming up from channels below the earth. Thermophiles, or heat-loving microorganisms, give the hot springs color. Geysers are hot springs that erupt due to superheated water that gathers in tight channels until the pressure pushes it up, making a spectacular show of a rising column of boiling water. Fumaroles are vents that let off steam, sometimes making a hissing sound. Mudpots are hot areas in which sediment saturated with water, somewhat like clay, erupts with rising steam.

Last year witnessed a swarm of earthquakes, but scientists at the Yellowstone Volcano Observatory (YVO) do not think that an eruption is imminent. If the volcano were likely to erupt, the Observatory would issue warnings via telephone and internet systems. Anyone who feels an earthquake within the park is asked to report it to the YVO at

It is fun to note though that scientists have observed the volcano is pushing the ground up in areas of the park. A large bulge has been found on the bottom of Lake Yellowstone, and since 2004 the ground has risen almost 3 inches in some locations in the park from pressure created by the Yellowstone volcano.

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