May 17, 1980
Law enforcement officials escorted about 50 carloads of property owners into the Red Zone to retrieve possessions.
May 7-13, 1980
Small explosions of steam and ash are emitted from the volcano. Intermittent earthquakes up to magnitude 4.9.
April 29, 1980
State officials asked the governor to close a large area around the volcano. The plan called for a Red Zone (no public access) and a Blue Zone (restricted access). Emergency services officials are frustrated because the public appeared to remain unaware of the danger.
March 27 to April 18, 1980
Earthquakes and steam-driven explosions occur off and on during this period.
March 20, 1980
A magnitude 4.1 earthquake, unlike any that had been previously detected in the area, occurred just northwest of the summit of Mount St. Helens. Seismologists were uncertain as to whether or not these first earthquakes were related to volcanic activity. They decided to deploy additional seismometers in order to better monitor future activity.
March 15-19, 1980
A number of very small earthquakes are recorded, but are not recognized as immediate precursors to possible volcanic activity.
Data Source: USGS/Cascades Volcano Observatory. Check out this web site for a much more detailed chronology.