Will Mt. St. Helens erupt again?

A volcanic dome growing in the Mount St. Helens crater. Photo courtesy of the U.S. Geological Survey.

Mt. St. Helens still emits steam pretty much every day, but it hasn't had any eruptions since 1985. We can not say if it will erupt again this century, but studies indicate that there is still hot magma under the mountain, so it will probably erupt sometime. Fortunately, Mt. St. Helens is still carefully monitored by volcanologists, so that if or when the mountain begins to become active again, we should have early warning.

Chuck Wood

It is likely that Mt. St. Helens will have one or more small eruptions during your lifetime, but probably unlikely that it will have another big one. At the time of the 1980 eruption there was the weight of the whole volcanic cone available to keep the magma pressure from erupting. This allowed a large amount of pressure to build up and consequently the eruption was large. Now the whole top of the mountain is gone so there is a good deal less weight available as a counter balance to the pressure. This means that eruptions occur after lesser amounts of pressure have built up and the eruptions are therefore smaller. Eventually, of course, Mt. St. Helens will recover its cone-shaped shape by filling in the amphitheater with lava domes and ash. Once this occurs (probably over a period of a few hundred years) it'll be ready to suffer another large 1980-size eruption.

Since the famous 1980 eruption there has been a lava dome growing within the caldera, and every once in a while part of the dome either collapses or is blasted away by either gas or steam explosions. These eruptions seem to be getting less and less frequent but have probably not stopped.

Scott Rowland

Mount St. Helens erupted at least 10 times in the 200 years before the 1980 eruption. It is considered to be the most active volcano in the Cascades. Volcanologists that study Mount St. Helens believe it is likely to erupt again within a few decades or a century at most.

It can be difficult to know when a volcano is dead. Many cinder cones, are monogenetic, erupting only once before the volcano is dead. Stratovolcanoes can erupt many times in only a few centuries, like Llaima in Chile, which has erupted at least 40 times in the last 350 years. Stratovolcanoes can also go many centuries without an eruption, like Newberry volcano in Oregon, which has not erupted in 1,300 years but will probably erupt again. Large volcanic systems, like Yellowstone, can go hundreds of thousands of years between eruptions.

Steve Mattox

Update.