Earthquakes and Mount St. HelensVolcanic eruptions are often preceded by earthquake activi...

Earthquakes and Mount St. Helens

Volcanic eruptions are often preceded by earthquake activity as magma rises upward through the crust underlying the volcano. Examine the graphs of earthquake events averaged per week for 1980 (graph a) and for 1981–1992 (graph b). How did earthquake activity differ for the two intervals?