What causes explosive volcanic eruptions?

Explosive volcanic eruptions occur when gas dissolved under pressure inside viscous magma violently froths into volcanic ash as pressure drops suddenly at the vent. These violent events can expel thousands of kilograms of material per second high into the atmosphere, sometimes creating fast-moving pyroclastic flows. When lava plugs block a summit conduit, the resulting eruptions become even more destructive.

What we know

• Explosive eruptions happen when gas dissolved under pressure in viscous magma froths into volcanic ash upon a sudden pressure drop at the vent. [1, 2]
• Explosive eruptions can expel as much as 1,000 kg per second of rocks, dust, gas, and pyroclastic material reaching speeds of several hundred meters per second. [2]
• The blockage of a summit conduit by a lava plug can make explosive eruptions significantly more violent. [2]
• An eruption column can collapse to create a fast-moving pyroclastic flow consisting of hot volcanic matter. [2]

Where to go next

• compared withHow does an effusive eruption differ?
• a case in pointWhat happens during a lateral blast?
• how it workedHow does magma interact with water to cause explosions?
• the bigger pictureWhat are the wider categories of volcanic eruptions?
• what followedWhat are the effects of a pyroclastic flow?
• an unexpected connectionHow can rising magma cause a sideways eruption?Magma does not always erupt upward from the crater, as it can diverge toward the flanks and cause a lateral blast when the expanding flank breaks.

Sources

• [1]explosive eruption (Wikidata Q1321886) · CC0 1.0
• [2]Explosive eruption · CC BY-SA 4.0
• [3]Phreatomagmatic eruption · CC BY-SA 4.0
• [4]Effusive eruption · CC BY-SA 4.0
• [5]Lateral eruption · CC BY-SA 4.0