June 7, 2010

Yellowstone National Park Part II - The Supervolcano, Wyoming

The Yellowstone area is famous for its amazing geological features. It has the highest density of geysers on Earth, in addition to its amazingly colorful hot springs and mud pots. When Yellowstone was first explored by geologists, they did not have a good explanation for the source of this heat. Yellowstone is far from any volcanic mountain ranges or other major tectonic features that release this much heat.

Eventually geologists realized that it must be a volcano. The rocks are rhyolite and dacite, which are clearly volcanic and thick ash layers are found all over. But, how big exactly is this volcano? There was no obvious cone or crater and no evidence of past volcanic eruptions on the surface.

It was not until NASA was testing new 3D camera technology in the 1960's in anticipation for the moon landings did the area get adequately mapped aerially to show the size of the caldera. When they did it, they found it was larger than any volcano known on Earth at that point.

Yellowstone was not just a volcano, but a Supervolcano. It is the result of a hot spot under the North American continent. It produces a line of volcanoes, much like the Hawaiian Islands. But, this ones follows the Snake River valley from Boise all the way to Yellowstone.

Because Rhyolite is full of silica (melted out of the continental crust as the magma plume works its way through the crust), it is so incredibly sticky it can not flow. Thus, enormous quanities of gases build up in the magma chamber and the pressure reaches levels that exceed Mount St. Helens by thousands of times. If it were to go, it would be unlike any eruption the world has ever seen. The devastation would range thousands of miles and the effects would be global.

The last eruption of Yellowstone was 600,000 years ago and buried Nebraska, some 1300 miles away with up to 6 feet of ash. It seems to erupt in cycles of 500,000-1,000,000 years. It takes that long because of the Rhyolites ability to hold the gases in. Mountains with andesite (such of Mount Rainier and Mount St. Helens) have less silica (because they are closer to the ocean and on top of thinner crust) hold less gas and erupt more frequently (usually between every 200-1000 years). In the middle of the ocean, Hawaiian lava has very little silica and is extremely fluid and thus does not erupt violently.

The Grand Canyon of the Yellowstone is carved by the Yellowstone River into these weak Rhyolite layers of rock and ash and decayed by acids such as sulfur dioxide and carbonic acid.

Since silicon dioxide is white (think quartz), the quantity is often noticeable in the rocks. Rhyolite is light beige, Andesite a darker gray, and basalt with no silica black.

These hot acidic volcanic hot springs also have unique ecosystems. There are extremophiles that live only in this intense heat. Instead of using sunlight for energy, these bacteria convert chemicals into energy. Many convert iron sulfide or hydrogen sulfide into metabolites. They are studied by scientists for many reasons including drug manufacturing.

NASA is interested in them because they could be a template for the type of life that may live on other planets.

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