Tephrochronology and radiocarbon dating indicate that Glacier Peak eruptions occurred in 1700 AD ± 100 years , 1300 AD ± 300 years , 900 AD ± 50 years , 200 AD ± 50 years , 850 BC , 3150 BC , and in 3550 BC . The Volcanic Explosivity Index ( VEI ) for three of these was 2 to 4 , small compared to the 5 of the 1980 eruption of Mount St. Helens . They were characterized mainly by a central vent eruption , followed by an explosive eruption . These eruptions varied in outcome ; some produced lahars , some pyroclastic flows , and others lava domes
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
Glacier Peak