A volcano erupts through the build-up and release of pressure, whether that pressure is of its underlying magma, water or both. This release can be explosive, as it was in the famous eruption of Mt. Vesuvius that destroyed Pompeii, or it can be slow and effusive, as it is in the ongoing formation of the Hawaiian islands.Continue Reading
An eruption that is caused solely by pressures underneath the Earth is a magmatic eruption. In a phreatic eruption, underground water heated by magma forms compressed steam, fracturing and weakening the surrounding rock and ultimately resulting in an violent explosive eruption. A phreatomagmatic eruption is caused by the interaction of magma and water; as the water cools the magma, the resulting stress fractures destabilize the volcano, leading to an eruption.
Explosive eruptions are marked by the violent release of compressed gas, including steam and sulfuric compounds. An effusive eruption, on the other hand, contains little compressed gas and is marked by the gradual flow of lava to the surface. These are two extremes of a sliding scale, with rare Plinian and Ultra Plinian eruptions as the most explosive and continuous Hawaiian eruptions as the least. In general, the more frequent a volcanic eruption is, the less violent and explosive it is.Learn more about Volcanoes
A caldera forms as a volcano's magma chamber empties, resulting in a loss of support for the earth above it. These bowl-shaped depressions can range in size from a few hundred meters to several kilometers wide. They are generally caused by large volcanic eruptions.Full Answer >
A volcanic neck forms when lava inside a caldera cools after magma stops feeding the mountain, and then the outside of the extinct volcano erodes after millions of years. The cooled lava remains intact because it is harder than the surrounding rock that eroded. Perhaps the most famous volcanic neck in the United States is Devil's Tower in Wyoming.Full Answer >
A volcano forms when magma pushes up through the Earth's crust from below, depositing lava on the surface. This lava cools, creating volcanic rock. Over time, repeated eruptions of lava build a cone-shaped mountainous structure, producing a volcano.Full Answer >
The chief difference between a volcano and a mountain is that a volcano forms around a vent that allows magma to reach the surface of the Earth, while a mountain can be formed by a variety of different geological processes. Most mountains form as the result of plate tectonics, although some were formed by magma welling up from the mantle without breaking through the surface.Full Answer >