USGS logo


Aerial view of the Mono-Inyo Craters Volcanic Chain, California. Several eruptions occurred along both chains as receltly as about 550 to 600 years ago. (Photograph by C. Dan Miller.)

Restless calderas

 The largest and most explosive volcanic eruptions eject tens to hundreds of cubic kilometers of magma onto the Earth's surface. When such a large volume of magma is removed from beneath a volcano, the ground subsides or collapses into the emptied space, to form a huge depression called a caldera. Some calderas are more than 25 kilometers in diameter and several kilometers deep.

Calderas are among the most spectacular and active volcanic features on Earth. Earthquakes, ground cracks, uplift or subsidence of the ground, and thermal activity such as hot springs, geysers, and boiling mud pots are common at many calderas. Such activity is caused by complex interactions among magma stored beneath a caldera, ground water, and the regional buildup of stress in the large plates of the Earth's crust. Significant changes in the level of activity at some calderas are common; these new activity levels can be intermittent, lasting for months to years, or persistent over decades to centuries. Although most caldera unrest does not lead to an eruption, the possibility of violent explosive eruptions warrants detailed scientific study and monitoring of some active calderas.

 Mono-Inyo Craters

Maintained by John Watson
Updated 06.24.97

back start of book next page