Types of Volcanoes

Cinder Cone

Cinder Cones  - Cinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world.
Calderas - Calderas, are simply circular depressions, are found on the summits of many volcanoes. "Giant" calderas are the largest of these: huge craters up to many tens of miles across. Giant Calderas form by collapse (see animation) in gigantic eruptions that spew volcanic rocks out hundreds or even a thousand miles in all directions. Sometimes the calderas are so filled with lava and volcanic ash that there is no recognizable depression at all. These can only be found by carefully locating the big fractures or "faults" in the ground that mark the edges of the cauldera. One such cauldera  lava dome nearly fills Yellowstone National Park.



Fissure - Fissure volcanoes are flat surface areas which are hard to detect  until they erupt. The lava flow is very close to the surface of the earth with a deeper dome of lava below. In this type, there is no central crater at all. Instead, giant cracks (fissures) open in the ground and expel vast quantities of lava that spread far and wide to form huge pools that can cover almost everything around. When these pools of lava cool and solidify, the surface remains mostly flat.
Shields - Another easily recognized volcano which is familiar is the Shield volcano. This type of volcano can be hundreds of miles across and many tens of thousands of feet high. The individual islands of the state of Hawaii are simply large shield volcanoes. Mauna Loa, a shield volcano on the  island of Hawaii, is the largest single mountain in the world, rising over 30,000 feet above the ocean floor and reaching almost 100 miles across at its base. Shield volcanoes have low slopes and consist almost entirely of frozen lavas.



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03/12/03 09:20 PM