Calderas and Crater Lakes
- Caldera of Tengger in Java,
Indonesia
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- Calderas
are huge bowl-shaped craters, usually formed by volcanic activity.
Some of the earliest geologists thought the calderas are formed
when violent volcanic eruptions blew the tops off the volcano.
However, few calderas are formed this way.
- Calderas
are formed because eruptions of huge volumes of pyroclastic materials
had left the roof of the magma chamber unsupported, causing it to fracture
and fall downwards into the chambers. Magma is also being drained
from the chamber through fissures at depth. Collapse of the cone
occurs, as it becomes a jumble of enormous blocks, some of which sink
through the magma. This process is termed cauldron subsidence.
This process may take a long time to complete and often happens in an
extinct volcano. An example is the caldera of Tengger in
Java, Indonesia.
- Crater lakes
are formed when a caldera becomes filled with water sometime
after it is formed. An example is the Crater Lake in Oregon,
America. It is nine kilometers in diameter whose floor is 600
meters in depth, while the surrounding 6800-year-old caldera
walls rise steeply 600 meters above it.
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- Crater Lake, Oregon.
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