Question

What triggered the pyroclastic flow during Mount St. Helens' 1980 eruption?

A) Landslide movement
B) Gaseous magma pressure drop
C) Volcanic gas release
D) Superheated groundwater

Answer 1

The pyroclastic flow during Mount St. Helens' 1980 eruption was triggered by a landslide movement caused by an earthquake.

Step-by-step explanation:

The trigger for the pyroclastic flow during the 1980 eruption of Mount St. Helens was A) Landslide movement. On the morning of May 18, 1980, an earthquake caused the mountain's unstable north flank to collapse. This resulted in a massive landslide that directly led to the explosive release of the pyroclastic flow, devastating the northern side of the mountain and the surrounding forests. After the landslide, additional volcanic activity continued, including the emission of volcanic ash and the formation of a vertical eruption column.