Calderas

• Calderas are very large craters often two or more kilometers in diameter that form at the top of volcanoes.
• They are often deep extending downwards for a few hundred meters and sometimes, in cases of inactive volcanoes, contain lakes e.g. Lake Bosumtwi in Ghana.
• There are several theories regarding how calderas are formed although it is more likely that each of these theories is applicable in certain instances.

Formation of a caldera. Image by ElateAfrica.

Violent eruption

• A composite volcano may sometimes explode violently that its top is blown off and disintegrates into a mass of rocks and ashes
• Leaving the crater at the top of volcanoes greatly enlarged thus forming a caldera.

Subsidence

• A caldera may also be formed as a result of block subsidence (downward displacement of the central block).
• After an eruption the supply of magma is depleted  causing a huge chasm to form beneath the volcano.
• The weight of the cone sometimes causes faults to develop and after some time the whole cone collapses into the chasm beneath.
• Longonot in Kenya may have been formed this way.

Meteor theory

• This theory suggests that solid objects from the space (meteors) fall by gravity and on impact with the earth formed calderas.
• While meteors falling on earth have been known to form craters this theory even if proved true cannot account for all the calderas.

Mountain collapse

• A mountain may collapse if it has a large mass floating on a wetter surface resulting in a caldera.

To access more topics go to the Geography Notes page.