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tapping the magma chamber at lower and lower levels. The result of these fissures was to produce lava flows
reaching some 27 kilometres long and yielding a total of about 220,000 cubic metres of lava that covered an area of nearly 50 square kilometres.
Calderas and crater lakes
Some volcanoes do not rise gracefully to a tall cone with a small crater at the summit. Instead, the top of the cone is missing, and the ‘crater’ is immensely wide. A very large crater is called a caldera. Calderas often contain a large lake, named a crater lake.
The caldera is very large because the top of the cone has collapsed back in on itself. So whereas a crater is simply the top of a vent, a caldera represents the collapsed top of a volcano.
To make a caldera, the magma chamber feeding the volcano has to be quite close to the surface. Then the pressure from the chamber can make the rocks above it crack and weaken. During an eruption some of the contents of the magma chamber are used up, so the chamber is partly empty. Above it lies weak rock, and on top of this is the immense weight of the volcanic mountain.
The weight of the volcano can be enough to collapse the whole centre of the mountain into the chamber below.
(Below) The location of Kilauea on Hawaii.
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(Below) A lava fountain accompanied by ash, Kilauea.
Kilauea
(Below) Lava flowing from Kilauea.
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