My question was, how do explosions in volcanoes happen? What are the triggers?
The build up of hydrostatic pressure (pressure from magma at higher levels in the system) and the expansion of gas shoot lava high into the air. These lava fountains are commonly a few tens to hundreds of feet (meters) high. Less common are fountains that reach over 1,000 feet (300 m) in height. The highest 1959 lava fountain at Kilauea Iki reached 1,900 feet (580 m) in height. Thats 5 and a half football pitches.
Another example of an explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the point at which it bursts violently through the over mantle of rock. In many cases, the rising magma will contain large quantities of partially dissolved gas. Sometimes a lava plug will block the conduit to the summit, and when this occurs, eruptions are more violent. With the sudden release of pressure following the initial explosion, the gas comes out of solution violently and explosively.
Wettonga tribe, Northern Australia
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