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 VOLCANOS AND LAVA! Lets start with the Composite Volcano. This volcano is usually tens of miles across and ten thousand or more feet in height. They also have moderately steep sides and sometimes small craters in their summits. Then there is the Cinder Cone Volcano. This volcano consists of loose, grainy cinders and almost no lava. They are small volcanoes, usually only about a mile across. The Shield Volcano can be hundreds of miles across and tens of thousands of feet high. They almost always have craters at their summits. There is also a type of volcano called the Giant Caldera Volcano. Calderas, are simply circular depressions and are found on the summits of many of these volcanoes. A Fissure Volcano has no craters at all--instead, they have giant cracks that open in the ground and expel vast quantities of gases and lava. There are four types of Lava: 1. Low water/ Low silica---This lava is very runny. Not quite like water, but more like warm honey or hot wax. This lava flows for long distances before cooling enough to turn solid. 2. Low water/ High silica--SiO is melted in the lava causing silica molecules to have the tendency to stick together and form long chains. These long chains get tangled together and make it difficult for molecules In the melt to slide past each other. 3. High water/ Low silica--With this lava it oozes slowly out to form a bulbous dome which hardly moves at all. 4. High water/ High silica--This lava has lots of dissolved gases and high viscosity which make it deadly. As the lava oozes to the surface, the gases quickly formed bubbles that turn the lava into a red-hot froth that explodes out of the ground as a searing, grayish cloud of superheated steam and tiny particles called ash. I hope that told you a little about volcanoes and lava! Article posted October 12, 2009 at 10:55 PM • comment (2) • Reads 2019 • see all articles |
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