At Yellowstone and some other volcanoes, some
scientists theorize that the earth's crust fractures and cracks
in a concentric or ring-fracture pattern. At some point these
cracks reach the magma “reservoir,” release the pressure,
and the volcano explodes. The huge amount of material released
causes the volcano to collapse into a huge crater—a caldera.
The Hydrothermal System of Geyser Basins
Yellowstone's hydrothermal features wouldn't exist
without the underlying magma body that releases tremendous heat.
They also depend on sources of water. In the high mountains surrounding
the Yellowstone Plateau, water falls as snow or rain and slowly
percolates through layers of porous rock. Some of this cold water
meets hot saline brine that is directly heated by the shallow magma
body. The water's temperature rises well above the boiling point
but the water remains in a liquid state due to the great pressure
and weight pushing down on it from overlying rock and water. The
result is superheated water with temperatures exceeding 400 degrees
Fahrenheit.
The superheated water is less dense than the colder,
heavier water sinking around it. This creates convection currents
that allow the lighter, more buoyant, superheated water to begin
its slow journey back to the surface following the cracks, fissures,
and weak areas through rhyolitic lava flows. As hot water travels
through the rock, high temperatures dissolve some silica in the
rhyrolite.
While in solution underground, some of this silica
deposits as geyserite, coating the walls of the cracks and fissures
to form a nearly pressure-tight seal. This locks in the hot water
and creates a "plumbing system" that can withstand the
great pressure needed to produce a geyser.
Select How Geysers Work to see an animation of the
process (138K).
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Theories | Yellowstone's Hotspot | Anatomy
of a Geyser | Anatomy of a Hot Spring
| How Geysers Work (138K)