The second type may be familiar to you from news reports from Hawaii: the shield volcano. This type of volcano can be hundreds of miles across and 10,000 feet high. A shield volcano is characterized by gentle upper slopes (about 5 degrees) with somewhat steeper lower slopes (about 10 degrees). The shield volcanoes are almost entirely composed of relatively thin lava flows built up over a central vent.
Shield volcanoes have small amounts of pyroclastic material, most of which accumulates near the eruptive vents, resulting from fire fuming events. Thus, shield volcanoes typically form from nonexplosive eruptions of low viscosity basaltic magma.
Stratovolcanoes (Composite Volcanoes)
Many of Earth’s most beautiful mountains are stratovolcanoes—also referred to as composite volcanoes. The stratovolcanoes are made up of layers of lava flows interlayed with sand- or gravel-like volcanic rock called cinders or volcanic ash. These volcano land formations are typically 10-20 miles across and up to 10,000 or more feet tall. This type of volcano has steeper slopes of 6-10 degrees on its flanks and as much as a 30 degree slope near the top.
While ordinary volcanoes can kill thousands of people and destroy entire cities, scientists believe that a supervolcano explosion is big enough to affect everyone on the planet. Although they’re called “super,” most people would have trouble spotting a supervolcano before it erupts. The main feature of supervolcanoes is a large magma chamber, which is an underground reservoir filled with flowing, hot rock under huge pressures. Afer their eruption ash has been blown so far away that no mountain exists, and commonly the area is low and lake-filled.
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