A quiet period of 123 years was ended when an earthquake measuring 4.0 on the Richter scale occurred, on the 20th of March 1980. In the next five days, an earthquake swarm occurred with around 47 tremors measuring 3.0 or more on the Richter scale, with their focuses just 2 km below the north flank of the volcano. The swarm was a result of magma pushing up to the surface. 1 day later hazard warnings went out to the public as geologists studied and monitored the volcano closely. A new 70 m crater appeared and the next day brought steam emissions just after half-past twelve in the afternoon. Local authorities lowered the water level by 8m as a precaution just in case snowmelt causes floodwaters after an eruption. On the 29th of March, a second crater appeared and from then the summit gradually collapsed. During the next day many small eruptions of steam and ash occurred. Lava from the previous eruptions had turned into a solid. This forced the current liquid magma to divert to the north flank of the mountain. When the mountain refused to erupt and took long before anything was actually felt, the media and a whole host of scientists left the site leaving just one lone geologist to monitor the events.
On the 3rd of April, harmonic tremors were recorded which tell geologists that there were movements of magma underneath the volcano. A lava dome also started to swell on the north flank of the mountain growing by about a meter a day. This was due to the diverted magma. In 9 days time it had grown be 2 km in diameter, and stuck out by over 100m. This was directly above the Earthquake swarm focus and the source of the harmonic tremors, and acted as a lid for the lava pressure. By the end of April 1980, all the summit craters become one big one, measuring 500m wide and 200m in depth. This lead to a 30 km radius ‘danger zone’ was erected, angering thousands of sightseers from across the world.
On the 7th of May the steam and ash eruptions began once again. Two days later, USGS scientists said that the town of Toutle, 25 km away from the volcano, “Instead of a huge slide where the whole north side of the mountain would come down at once … a series of smaller landslides is more probable.” 1 day later the bulge at the north flank of the mountain was growing at an amazing 1.5m a day, with several earthquakes measuring 4.0 on the Richter scale. Between the 15th and 17th of March more earthquakes were recorded and the bulge continued to grow.
The day the world had been waiting for, for 123 long years finally came as the volcano finally gave way to the years of pressure of lava that had built up under it. At 8.30 am a gigantic surge of magma caused a 5.0 earthquake. 30 seconds later a massive landslide – one of the largest ever recorded – resulted from the failure of the north flank of the volcano. Ten seconds later came the blast, resembling about 1 Hiroshima bomb every second. The avalanche continued to crash down the valley and along the Toutle river carrying ice, water and debris, around 200m thick. The unexpected disclosure of the volcanoes vent produced a simultaneous blast of high temperature steam, gases pumice and ash directly upwards and outwards, in a northerly direction. The mixture moved at speeds of up to 300 km/h devastating over 360 km2 of vegetation and other life forms in its path. At explosion was heard 70 miles away.
The magma was about 900 degrees once it exited the volcano and in a matter of seconds the heat melted the snow and the ice cap of the volcano, causing huge mudflows to roar down rivers. In about 4 minutes of the blast around 360 km2 had been devastated. The mudflows grew to be 50m deep and 1 km wide in some places. Everything in its path was destroyed indefinitely and before clogging up valleys with its mud, rock debris, and shattered timber. Deposits by the mudflows were at one point about 200m thick in the northern valleys of the river Toutle. The ash left by the volcano reached heights of 20000m and covered parts of northwestern USA.
Once the air had started to clear up a bit a few days later, it was then clear to see what had really happened. The blast had blown of the top of the mountain reducing the height of it by nearly 500m. A week later ash eruptions still continued to occur. The blast had also destroyed all life in an area of some 180 km2.
The destruction of the earthquake was massive but could not really have been prevented as we cannot do anything to stop nature take its cause. Warnings could have prevented 57 people dieing but who was to now when it was going to happen.
