context: On May 18, 1980, a volcanic eruption occurred on Mount St. Helens, a volcano located in the state of Washington, United States. The eruption (level 5 in the Volcanic Explosivity Index) is the only significant eruption that occurred on the mainland of the United States consisting of 48 states since the eruption of the Lassen Peak volcano in California in 1915. [1] The eruption was preceded by a period of two months in the form of earthquakes and steam release, caused by the release of magma in shallow depths under the volcano which created large bulges and burly systems on the northern slope of the mountain. An earthquake that occurred at 8:32:17 a.m. PDT (UTC − 7) on Sunday, May 18, 1980, caused the entire north side of a landslide to make it the largest recorded landslide ever. This also results in the opening of rocks that are half-melted and rich in gas and steam so that they become low pressure. The rocks then react by blowing up a mixture of hot lava and destroying the old rocks which then lead to the Spirit Lake very quickly preceding the landslide north of the mountain.
question: What causes the eruption of Mount St. Dr. Helens on May 18, 1980?
answers.text: the release of magma in shallow depths under the volcano which created large bulges and burly systems on the northern slope of the mountain