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Physical
Lava Dome Growth
Lava dome growth is the slow piling up of thick, sticky lava into a round mound over a volcano's vent.
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The idea
A lava dome is a round, mound-shaped pile that forms when thick, sticky lava is slowly pushed out of a volcano. The lava is so viscous that it cannot flow very far, so it piles up around the vent instead of spreading out. Lava becomes this thick when its magma contains a lot of silica or when its dissolved gas has escaped. Around 6% of eruptions on Earth form lava domes.
Domes can grow slowly and steadily for months, years or even centuries. Some reach heights of several hundred meters, and their sides are made of unstable rock debris. Gas pressure can build up inside, so a growing dome may suddenly explode. If part of a dome collapses and exposes pressurized magma, it can send out pyroclastic flows, fast-moving currents of hot gas and rock.
Lava domes are one of the main structural features of many tall, cone-shaped stratovolcanoes around the world. Scientists use the average rate of dome growth as a rough sign of how much magma is arriving, though it does not tell them when a dome will explode. Some domed shapes on the Moon, Venus and Mars may be lava domes too.
Check yourself
Question 1 of 2
About what share of eruptions on Earth form lava domes?
Composition
what it's made of
- Viscous Lava — Thick, sticky lava, often rich in silica, that cannot flow far.
- Vent — The opening in the volcano that the lava is slowly pushed out of.
- Rock Debris — The loose, unstable rock that makes up a dome's sides.
- Lava Spines — Spikes of lava that can grow on top of a dome and make it less stable.
- Trapped Gas — Gas pressure that builds up inside and can cause explosions.
Connection
how it relates
Under Igneous Rock
Change
how and why it evolves
- Past
- Before the 1980 eruption of Mount St. Helens, a cryptodome, a hidden dome of magma at shallow depth, made the side of the volcano bulge outward until it collapsed. Magma reached the surface of Mount St. Helens about October 11, 2004, and built a new dome until scientists declared the eruption over on July 10, 2008.
- Now
- Since late May 2008, a glacier in the crater of Mount St. Helens has completely surrounded its lava domes.
- Next
- Geologists predict that future eruptions of Mount St. Helens will be more destructive, because the way its lava domes are arranged requires more pressure to erupt.