Water cycle

Classified in Geology

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The magmas that are the most liquefied erupt quietly and flow from the vent to form sloping shield volcanoes, a name that is conceived because they look like the shields of ancient German warriors. The lava that flows from shield volcanoes is usually only one to ten meters thick, but the lava may extend for great distances away from the vent. The volcanoes of Hawaii and Iceland are typical shield volcanoes.
Magma with high gas contents and high viscosities are usually more explosive than the lava that flows from shield volcanoes. This gas-rich lava in many occurrences is blown very high into the air during an eruption.

Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. They are estimated to account for 75% of annual magma output. The vast majority are located near areas of tectonic plate movement, known as ocean ridges. Although most are located in the depths of seas and oceans, some also exist in shallow water, which can spew material into the air during an eruption.

The gas-filled lava in the reservoir is now under great pressure from the weight of the solid rock around it. The pressure causes the gas to blast or melt a channel in a fractured or weakened part of the rock. The magma now moves through the channel to the surface. When the magma gets near the surface, the gas in the magma is released. The gas and magma blast out an opening called the central vent.

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