The precursor eruptions of Mt. St. Helens in the weeks before 18 May 1980 were primarily unrecognized until subsequent analysis after 18 May 1980. What were the types of eruptions observed?
1) effusive, releasing low-viscosity lava flows
2) phreatic, releasing steam but no fresh magma
3) phreatomagmatic, releasing steam and fresh magma
4) effusive, resulting in dome building