The plates which are about 20 miles thick, make up the earth's crust and are a chief cause of volcanic activity. These plates are always in motion. They move very slowly, however some at times bump in to each other. These movements put a lot of pressure on the surface rock. Volcanoes obtain their energies from such movement and pressure. Volcanoes form at the boundaries of these plate where two types of movement occurs, two plates will collide with each other or the plates will move apart from each other. Some of these plates layers are cooled and are made up of rigid rocks.
The affects on the landscape is lava that releases onto the Earth's surface. When that lava comes to the Earths surface, it is red hot and sometimes the temperature is more than 2012 degrees Fahrenheit. Fluid lava flows swiftly down a volcano's slopes. Sticky lava flows more slowly. As the lava cools, the lava hardens into many different formations on the landscape. Highly fluid lava hardens into smooth, folded sheets of rock called pahoehoe. Stickier lava cools into rough, jagged sheets of rock called aa. Pahoehoe and aa cover large areas of Hawaii, where the terms originated. The stickiest lava forms flows of boulders and rubble called block flows. It may also form mounds of lava called domes.
Volcanoes when exploded, can send ash, millions of rock particles and volcanic gas tens of miles into the air. The resulting ash fallout can affect large areas hundreds of miles downwind. Gas pours out of volcanoes in large quantities during almost all eruptions. The gas is made up particularly of steam, but may also include carbon dioxide, nitrogen, sulfur dioxide, and other gases. Most of the steam comes from a volcano's magma, but some steam may also be produced when rising magma heats water in the ground.
Affects on the living population of the area eruptions pose direct and indirect volcano hazards to people and property, both on... [continues]
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