describe the build up of this eruption that you just mentioned
On March 20, at 3:45 p.m. Pacific Standard Time, a shallow magnitude 4.2 earthquake centered below the volcano's north flank, signaled the volcano's return from 123 years of hibernation. A gradually building earthquake swarm saturated area seismographs and started to climax at about noon on March 25, reaching peak levels in the next two days, including an earthquake registering 5.1 on the Richter scale. A total of 174 shocks of magnitude 2.6 or greater were recorded during those two days
1980 eruption of Mount St. Helens
Mount St. Helens remained dormant from its last period of activity in the 1840s and 1850s until March 1980. Several small earthquakes, beginning on March 15, indicated that magma might have begun moving below the volcano. On March 20, at 3:45 p.m. Pacific Standard Time (all times will be in PST or PDT), a shallow magnitude 4.2 earthquake centered below the volcano's north flank, signaled the volcano's return from 123 years of hibernation. A gradually building earthquake swarm saturated area seismographs and started to climax at about noon on March 25, reaching peak levels in the next two days, including an earthquake registering 5.1 on the Richter scale. A total of 174 shocks of magnitude 2.6 or greater were recorded during those two days.

Shocks of magnitude 3.2 or greater occurred at a slightly increasing rate during April and May with five earthquakes of magnitude 4 or above per day in early April, and eight per day the week before May 18. Initially there was no direct sign of erup
what happened after the mt st helens eruption An earthquake which caused the entire weakened north face to slide away, creating the largest landslide recorded when was the last time it erupted? January 2008 and before that? October 2004 and before that? Between 1980s to 1991 which was the deadliest eruption? March 27, 1980 eruptions
wiki:20190485
1980 eruption of Mount St. Helens [SEP] Build-up to the eruption
Mount St. Helens remained dormant from its last period of activity in the 1840s and 1850s until March 1980. Several small earthquakes, beginning on March 15, indicated that magma might have begun moving below the volcano. On March 20, at 3:45 p.m. Pacific Standard Time (all times will be in PST or PDT), a shallow magnitude 4.2 earthquake centered below the volcano's north flank, signaled the volcano's return from 123 years of hibernation. A gradually building earthquake swarm saturated area seismographs and started to climax at about noon on March 25, reaching peak levels in the next two days, including an earthquake registering 5.1 on the Richter scale.