What do shaking a can of soda and a volcanic eruption have incommon? Yes, both make a mess, but theres more. Scientists arekeeping a watchful eye on Mount St. Helen's as plumes of steam andash continue to spew from the awakened volcano. Steve Spangler usessome simple experiments with soda and Alka-Seltzer to betterexplain the underground science.
Volcanoes form when chambers of magma, or hot molten rock, boil to the surface. These magma chambers often remain sealed for hundreds of years between eruptions until the pressure builds sufficiently to break through a vent, which is a crack or weak spot in the rock above. A considerable amount of gas is also mixed in with the molten rock which accounts for the build-up in pressure.
Think of the magma as the soda inside a 2-liter plastic bottle (the magma chamber). Give the bottle a few shakes and then twist open the cap. Its no surprise that soda spews everywhere. The same holds true for a volcano. The built-up pressure in the magma chamber breaks through a crack or weak spot and the gases force the molten rock out of the chamber. The blast creates a crater where lava and ash spill out, forming the cone. On some volcanoes, the magma chamber collapses after a violent eruption and a caldera forms, which is just a large, bowl-shaped crater.
In order to understand the build-up of pressure caused by the gases in the magma, try the following experiments:
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