[JOAN CARTAN-HANSEN] In 1980 Mount St. Helens in Washington state erupted sending 540 million tons of ash over 22,000 square miles. The ash was so heavy in some places it blotted out the sun. These pictures were taken during the day. The wind carried the ash far to the east. More recently Mount St. Helens started erupting again and has remained more or less active ever since. Scientists now monitor Mount St. Helens to learn how volcanoes work and what has happened since the 1980 eruption.

[SCIENTIST] Because it erupted in 1980 it did not remove all hazard so I can show you as comparison here between 1980 and 2000. And so you can see as I flicker that on and off, the dome grows and the increase within the crater in the horseshoe shape around the dome of the snow and ice and rock that is accumulating. And so that's a fairly quick period of time for this glacier to develop. Eventually what this will do is fill up And then who knows how many years from now eventually we'll have another mountain like it looked prior to the 1980 eruption. And it will erupt again some day.

[JOAN] Scientists know volcanoes can be deadly. They hope by learning more about them they can some day predict when an eruption might occur and save lives.

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