Volcanos

Mount Saint Helens, just north of the Columbia River.

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Note: Volcanos like Mt. St. Helens can explode. That's because there is water in the lava (remember, the lava came from under the ocean originally). The water is really hot, and when some of the pressure is released, it can turn to steam. That makes its volume much bigger, so the mountain can get blasted into the air. You may recall that there is a big volcano in Hawaii, which doesn't explode. There are two reasons. First, the lava in volcanos like this is a lot less viscous, so water vapor bubbles can more easily bubble up to the surface instead of pushing the lava up. Second, there is less water (0.5% by weight instead of 5%).

Thanks to Prof. K. Cashman for help on this. Take a class from her if you want to learn about volcanos.

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