<P> On May 18 , 1980 , a major volcanic eruption occurred at Mount St. Helens , a volcano located in Skamania County , in the state of Washington , United States . The eruption ( a VEI 5 event ) was the most significant volcanic eruption to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California . It has often been declared as the most disastrous volcanic eruption in United States history . The eruption was preceded by a two - month series of earthquakes and steam - venting episodes , caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain 's north slope . </P>
<P> On May 18 , 1980 , a major volcanic eruption occurred at Mount St. Helens , a volcano located in Skamania County , in the state of Washington , United States . The eruption ( a VEI 5 event ) was the most significant volcanic eruption to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California . It has often been declared as the most disastrous volcanic eruption in United States history . The eruption was preceded by a two - month series of earthquakes and steam - venting episodes , caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain 's north slope . </P>
what happened after the mt st helens eruption
what happened after the mt st helens eruption
The eruption was preceded by a two - month series of earthquakes and steam - venting episodes , caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain 's north slope .
The eruption was preceded by a two - month series of earthquakes and steam - venting episodes , caused by an injection of magma at shallow depth below the volcano that created a large bulge and a fracture system on the mountain 's north slope .