Compared with mountains, which take millions of years to form, volcanoes rise in a geologic instant, in just thousands or even hundreds of years. This quick growth can make volcanoes structurally unstable. When Mount St. Helens erupted in Washington in 1980, entire slopes of the volcano collapsed. Most geologists have assumed that such catastrophic failures would be triggered only by an eruption. But researchers at the Open University in England now have evidence that an eruption need not occur. Even dormant volcanoes, the researchers say, can collapse. And since dormant volcanoes are thought to be relatively safe and are therefore rarely monitored by geologists, this puts many areas all over the world at risk.
Volcanologist Benjamin van Wyk de Vries has been studying Mombacho, a volcano in Nicaragua whose collapse within the last thousand years gave it a jagged profile. His studies have shown that two processes make volcanoes unstable. ...
