Question: On what date did the 1980 eruption of Mount St. Helens, in which "Crater Glacier" was formed, occur?
Sentence (from "1980 eruption of Mount St. Helens"): The eruption (a VEI 5 event) was the only significant volcanic eruption to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California.
Relevant evidence: No