Mt. St. Helens unexpectedly erupted on the 18th of May 1980. Its eruption was a huge blast; exploding a massive crater in the side of the volcano. As by 1980 it had been inactive for 120 years thus inhabitants did not expect such an eruption. Tephra (volcanic ash) rose 20 kilometres into the air and the volume of ash was so great that within a week, it had encircled the globe. It is located within the Rockies mountain range on the west coast of the U.S.A.
On March 20, 1980, a 4.1 magnitude earthquake struck underneath Mt. St. Helens. The Juan de Fuca plate is subducting under the North American plate causing volcanoes and magma rising to the surface. This was the first warning sign that the volcano had reawakened. Scientists flocked to the area. On March 27, a small explosion blew a 250-foot hole in the mountain and released a plume of ash. This caused fears of injuries from rockslides so the entire area was evacuated. Similar eruptions to the one on March 27 continued for the next month. Though some pressure was being released, large amounts were still building. It reached a point where it bulged 1.5 metres per day and as the pressure built up beneath the plates and magma volume increased in the chamber.
In April, a large bulge was noticed on the north face of the volcano. The bulge grew quickly, pushing outward about five feet a day. Though the bulge had reached a mile in length by the end of April, the plentiful plumes of smoke and seismic activity had begun to dissipate. Thus, as April drew to a close, officials were finding it increasingly difficult to maintain the evacuation orders and road closures due to pressures from homeowners and the media as well as from stretched budget issues.
At 8:32 a.m. on May 18, 1980, a 5.1 magnitude earthquake struck under Mt. St. Helens. Within ten seconds, the bulge and surrounding area fell away in a gigantic, rock avalanche. The avalanche created a gap in the mountain, allowing the release of pent-up pressure that erupted laterally in a huge blast of pumice and ash. The noise from the blast was heard as far away as Montana and California; however, those close to Mt. St. Helens reported hearing nothing.
61 deaths were caused by poisonous gas release which accompanied the blast waves. Electricity and water supplies were disrupted. Communications such as telephone wires and transport were interrupted. Inhabitants in the city of Yakima, 120km away, had to wear masks before going outside. More than 50 homes were covered in ash, tephra and other volcanic material.
Economically the effects of the eruption proved catastrophic. 12% of the farming crop was destroyed by volcanic dust. 250km worth of salmon breeding rivers were lost. Roads and railways were destroyed. Logging camps were destroyed and so were bridges which were destroyed down river, interrupting transport.
Environmentally speaking there was ash that fell into rivers and raised the temperatures, clogged them up and killed fish. Mud filled lakes and rivers. 250 square kilometres of trees were destroyed or flattened in the 25km blast zone. For the scientists and others who were caught in the area, there was no way to outrun either the avalanche or the blast. 57 lives were lost in the blast. It is estimated that about 7,000 large animals such as deer, elk, and bears were killed and thousands, if not hundreds of thousands, of small animals died from the volcanic eruption.A crater 3 km long and 0.5 km deep was created in the side of Mt. St. Helens. 20km of ash plume polluted the air. Aquifers were also flooded very heavily.†
Mt. St. Helens is now only 8,363-feet tall, 1,314-feet shorter than it was before the explosion. Though this explosion was devastating, it will certainly not be the last eruption from this very active volcano.
On March 20, 1980, a 4.1 magnitude earthquake struck underneath Mt. St. Helens. The Juan de Fuca plate is subducting under the North American plate causing volcanoes and magma rising to the surface. This was the first warning sign that the volcano had reawakened. Scientists flocked to the area. On March 27, a small explosion blew a 250-foot hole in the mountain and released a plume of ash. This caused fears of injuries from rockslides so the entire area was evacuated. Similar eruptions to the one on March 27 continued for the next month. Though some pressure was being released, large amounts were still building. It reached a point where it bulged 1.5 metres per day and as the pressure built up beneath the plates and magma volume increased in the chamber.
In April, a large bulge was noticed on the north face of the volcano. The bulge grew quickly, pushing outward about five feet a day. Though the bulge had reached a mile in length by the end of April, the plentiful plumes of smoke and seismic activity had begun to dissipate. Thus, as April drew to a close, officials were finding it increasingly difficult to maintain the evacuation orders and road closures due to pressures from homeowners and the media as well as from stretched budget issues.
At 8:32 a.m. on May 18, 1980, a 5.1 magnitude earthquake struck under Mt. St. Helens. Within ten seconds, the bulge and surrounding area fell away in a gigantic, rock avalanche. The avalanche created a gap in the mountain, allowing the release of pent-up pressure that erupted laterally in a huge blast of pumice and ash. The noise from the blast was heard as far away as Montana and California; however, those close to Mt. St. Helens reported hearing nothing.
61 deaths were caused by poisonous gas release which accompanied the blast waves. Electricity and water supplies were disrupted. Communications such as telephone wires and transport were interrupted. Inhabitants in the city of Yakima, 120km away, had to wear masks before going outside. More than 50 homes were covered in ash, tephra and other volcanic material.
Economically the effects of the eruption proved catastrophic. 12% of the farming crop was destroyed by volcanic dust. 250km worth of salmon breeding rivers were lost. Roads and railways were destroyed. Logging camps were destroyed and so were bridges which were destroyed down river, interrupting transport.
Environmentally speaking there was ash that fell into rivers and raised the temperatures, clogged them up and killed fish. Mud filled lakes and rivers. 250 square kilometres of trees were destroyed or flattened in the 25km blast zone. For the scientists and others who were caught in the area, there was no way to outrun either the avalanche or the blast. 57 lives were lost in the blast. It is estimated that about 7,000 large animals such as deer, elk, and bears were killed and thousands, if not hundreds of thousands, of small animals died from the volcanic eruption.A crater 3 km long and 0.5 km deep was created in the side of Mt. St. Helens. 20km of ash plume polluted the air. Aquifers were also flooded very heavily.†
Mt. St. Helens is now only 8,363-feet tall, 1,314-feet shorter than it was before the explosion. Though this explosion was devastating, it will certainly not be the last eruption from this very active volcano.