Geologists warned that sliding/movement of the bulge could cause a landslide which might trigger volcanic eruptions.
More than 10,000 earthquakes were recorded prior to 18 May, most occurring 2.6 km under the bulge.
The eruption
On May 18 a 5.1 earthquake, centred beneath the mountain, triggered the largest landslide in recorded history on the north slope of the volcano. This near supersonic lateral blast swept out of the north side of the mountain, travelled at 483 km/h and devastated everything in its path. A 60 km2 destroyed.
fan-shaped area was completely
The massive ash cloud rose 24 km into the atmosphere in just 15 minutes and reached the east coast of America in 3 days. Most of the ash fell within 500 km of the mountain; finer ash circled the earth in 15 days.
The landslide swept down the mountain at speeds of up to 250 km/h into the valley below. Mudflows/lahars of melted snow and ice were created and travelled down the valleys destroying bridges, homes, roadways and railways.
Pyroclastic flows with temperatures of 70 C rolled out of the crater at 1,080 km/h for hours after the eruption. These flows covered 10 km2
o , and they burned and destroyed everything in their path. Fifty-seven people were killed by the pyroclastic flows.