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Crater lakes form as the created depression, within the crater rim, is filled by water. The water may come from precipitation, groundwater circulation (often hydrothermal fluids in the case of volcanic craters) or melted ice. Its level rises until an equilibrium is reached between the rates of incoming and outgoing water.
A colloid of volcanic gas and magma can form as a density current called a pyroclastic flow. This occurs when erupted material falls back to the surface. The colloid is somewhat fluidised by the gas, allowing it to spread. Pyroclastic flows can often climb over obstacles, and devastate human life. [3]
When it does reach the surface, however, a volcano is formed. Thus subduction zones are bordered by chains of volcanoes called volcanic arcs. Typical examples are the volcanoes in the Pacific Ring of Fire, such as the Cascade Volcanoes or the Japanese Archipelago, or the eastern islands of Indonesia. [16] [2]
Science wrestled with the ideas of the combustion of pyrite with water, that rock was solidified bitumen, and with notions of rock being formed from water . Of the volcanoes then known, all were near the water, hence the action of the sea upon the land was used to explain volcanism .
Some of the eruptive structures formed during volcanic activity (counterclockwise): a Plinian eruption column, Hawaiian pahoehoe flows, and a lava arc from a Strombolian eruption. Several types of volcanic eruptions—during which material is expelled from a volcanic vent or fissure—have been distinguished by volcanologists.
A volcanic eruption is essentially the only natural way for short-lived – less than a few years – gases like sulfur dioxide and water vapor to make it into the stratosphere.
The presence of water can greatly alter the characteristics of a volcanic eruption and the explosions of underwater volcanoes in comparison to those on land. For instance, water causes magma to cool and solidify much more quickly than in a terrestrial eruption, often turning it into volcanic glass. The shapes and textures of lava formed by ...
During the eruption, the heat of the lava from the subglacial volcano melts the overlying ice. The water quickly cools the lava, resulting in pillow lava shapes similar to those of underwater volcanoes. When the pillow lavas break off and roll down the volcano slopes, pillow breccia, tuff breccia, and hyaloclastite form.