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Concept
Explosive eruption
Summary
In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such that expelled lava violently froths into volcanic ash when pressure is suddenly lowered at the vent. Sometimes a lava plug will block the conduit to the summit, and when this occurs, eruptions are more violent. Explosive eruptions can expel as much as per second of rocks, dust, gas and pyroclastic material, averaged over the duration of eruption, that travels at several hundred meters per second as high as into the atmosphere. This cloud may subsequently collapse, creating a fast-moving pyroclastic flow of hot volcanic matter.
An explosive eruption begins with some form of blockage in the crater of a volcano that prevents the release of gases trapped in highly viscous andesitic or rhyolitic magma. The pressure of the magma builds until the blockage is blasted out in an explosive eruption through the weakest point in the cone, usually the crater. (However, in the case of the eruption of Mount St. Helens, the pressure was released on the side of the volcano, rather than the crater.)
The sudden release of pressure causes the gases in the magma to suddenly froth and create volcanic ash and pumice, which is then ejected through the volcanic vent to create the eruption column commonly associated with explosive eruptions. The size and duration of the column depend on the volume of magma released and how much pressure it was under.
Vulcanian eruption
Peléan eruption
Plinian eruption
Phreatic eruption
Phreatomagmatic eruption
Surtseyan eruption
Consequences:
Eruption column
Pyroclastic flow
Pyroclastic fall
Pyroclastic surge
Pyroclastic flows occur toward the end of explosive eruptions, as volcanic gases are depleted and the gas pressure that supports the eruption column declines. When the pressure falls, the eruption column begins to collapse in on itself, and ash and rock fall back to the ground and flow down the slopes of the volcano.
Official source
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