In May 1980, Mount St. Helens blew its top. Within a few minutes, a blast 500 times as powerful as the Hiroshima atomic bomb blew 1,500 feet off the side of the mountain. It flattened trees for 15 miles around, and sent ash more than 60,000 feet up into the air and around the world.

Scientists are learning many lessons from the eruption of Mount St. Helens. They have seen how much damage can be done in a short time. They have seen that one layer of lava and one layer of ash does not equal one eruption. Instead, many thick layers can be laid down in just one eruption. They have seen how streams can cut deep valleys in a few days. And they have seen how quickly plants and animals can return to the devastated area.

Although Mount St. Helens was an explosive eruption, it is not the biggest man has ever seen. On April 5, 1815, on the island of Sumbawa in what is now Indonesia, the mountain of Tambora exploded. It blew out 150 times more ash and rock than Mount St. Helens. The blast killed 10,000 people, and 82,000 more people died of the famine and disease that followed.


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