Caldera

From TheBestLinks.com

This article is about volcanic calderas. Caldera Systems is also the former name of SCO Group.

A caldera is a volcanic crater which usually has a flat surface at the bottom, formed by a volcano collapsing into itself, usually because of low pressure in the magma chamber below or because of a violent eruption. Calderas are often filled with water, creating crater lakes.

A common mistake is to assume that calderas are not as powerful as other volcanos. In fact, a caldera eruption will have several thousand times the explosive force as a normal volcanic eruption, and will eject considerably more debris. When Mount St. Helens erupted, it released 1.2 cubic kilometers of ejecta, but when Yellowstone Caldera erupted 600,000 years ago it released 1000 cubic kilometers of material, covering half of North America in up to two meters of debris. The ecological effects of a volcanic eruption of this size can be seen in the record of the Lake Toba eruption in Indonesia. About 75,000 years ago, this volcano released 2800 cubic kilometers of ejecta. In the late 1990s, archeologist Stanley Ambrose [1] (http://www.anthro.uiuc.edu/faculty/ambrose/) proposed that a volcanic winter induced by this eruption reduced the human population to a few thousand individuals, resulting in a population bottleneck (see Toba catastrophe theory).

In the Tertiary period of the geologic timescale, intense volcanism in southwest Colorado led to the formation of several large calderas. Today, the remnants of these calderas form the San Juan Mountains.