Early on May 18 , an earthquake measuring 5.1 on the Richter scale struck the region , creating a massive landslide — - of rock that released pressure on the volcano 's crater , causing an ejection of steam . Just seconds later , Mount St. Helens erupted laterally , sending supersonic pyroclastic flows into the forest below
erupted
1980 eruption of Mount St. Helens
Reid Blackburn