What makes a quiet eruption different from an explosive eruption?
Keith D. Lumsden (Earth Sci.Teacher)
Dear Keith,
The main factors are the viscosity of the magma and the amount of gas.
For example, quiet Hawaiian eruptions result from low viscosity (fluid)
magmas in which the gas rises upward very quickly (faster than the rising
magma). When the magma gets to the surface most of the gas has already
escaped and the volcano produces lava flows or small lava fountains. In
contrast, explosive eruptions result from higher viscosity (stickier)
magmas in which the gas rises upward more slowly (essentially trapped in
the rising magma). When the magma gets near the surface the gas expands
and blows the magma apart, producing violent eruptions and lots of ash.
Steve Mattox, University of North Dakota
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