Roughly 700 years of dormancy were broken in about 1480, when large amounts of pale gray dacite pumice and ash started to erupt, beginning the Kalama period. The eruption in 1480 was several times larger than the May 18, 1980 eruption. In 1482, another large eruption rivaling the 1980 eruption in volume is known to have occurred. Ash and pumice piled northeast of the volcano to a thickness of ; away, the ash was deep. Large pyroclastic flows and mudflows subsequently rushed down St. Helens' west flanks and into the Kalama River drainage system.