Calderas are formed when volcanoes collapse, usually after much of the material in the magma chamber has been blown out. Calderas formed at the summit of stratovolcanoes may range in depth from a few hundred feet to several thousand feet. Formation of a caldera usually takes place late in the history of the volcano and often follows a long pause in activity during which the cone of the volcano may become deeply eroded. The caldera results not from explosive decapitation of the mountain, but when partial drainage of an underlying magma chamber removes support from beneath the top of the mountain, causing it to collapse.

Although the destructive effects of volcanism (volcanic action or activity) are obvious, volcanoes also provide many benefits to mankind. They are the major contributors to the building of continents. All oceanic islands owe their origin directly or indirectly to volcanism. Over the billions of years of Earth's existence, volcanoes and hot springs near volcanic intrusions have released hot water from the earth's interior. This steam and hot water can be used to produce geothermal energy. Geothermal energy produces electricity inexpensively and with low environmental impact.

Lava provides fertile soil in which crops such as pineapples, sugar cane, and coffee thrive. Lava erodes quickly in areas with adequate rainfall. In some cases, revegetation can begin in less than one year after the eruption. Lava flows are very fertile, especially if covered by ash. The fine ash particles retain water within reach of plant roots and release minerals, such as potassium, which plants need. Vegetation destroyed by falling ash often returns in a more luxuriant form. However, in areas where there is little rainfall, the erosion and breakdown of lava flows to form fertile soils can take thousands of years.¹