Photoglossary

Calderas and Craters   A caldera is a bowl-shaped depression which forms when the summit of a volcano collapses into its upper magma chamber after the material inside of it has been removed. Calderas can form from either violent volcanic eruptions or as magma slowly drains away during relatively quiet eruptions. At the top of a volcano is a vent which leads down to a subsurface magma chamber or reservoir. As volcanic material escapes the vent, the walls of the volcano lose their structural support. This causes the walls to collapse into the magma chamber, thereby forming the caldera. The best-known caldera in North America is Crater Lake in Oregon which is 10 km (6 miles) across and 600 meters (2,000 ft) deep. The calderas that have formed from volcanic activity on Mauna Loa and Kilauea in Hawaii are approximately 3 to 5 km (1.5 to 3 miles) wide and several hundred meters (yards) deep. The largest caldera in North America is La Ganita in Colorado, which is 32 km (19 miles) wide and 80 km (50 miles) long. The terms crater and caldera are often used interchangeably to describe a volcanic depression. Caldera, however, is the term generally used to describe a collapsed volcanic summit. Crater is the term most often associated with impact craters which form from the bombardment of a planetary body by meteorites.   Photo Credit: D.W. Peterson, USGS     Io Home Page Photoglossary Home Page