National 5 Geography

Global Issues- Environmental Hazards- Case Study

Volcano: Mount Saint Helens 1980

Cause

Mount Saint Helens Erupted on the 18th May 1980.

The volcano is located in the Rocky Mountains, near the west coast of the USA, in the state of Washington.

Mount Saint Helens lies above the boundary of two tectonic plates, at a destructive plate boundary. The small, oceanic Juan de Fuca plate and the continental North American plate move towards each other, causing the heavier oceanic plate to be pulled beneath the North American plate in a process known as subduction. This creates friction, preventing the plates from moving. Eventually, the build up of pressure is too great and the oceanic plate is pushed downwards, causing the crust to melt. Some of this new molten rock is then forced to the surface, forming a volcano.

The volcanic eruption was triggered by an earthquake, measuring 5.0 on the Richter Scale, which occurred at 8:32am. This caused a bulge on the north side of the volcano to become unstable, and fall as an avalanche. The volcano then went on to erupt ash and pyroclastic flow.

Impact

Negative

People

57 people were killed

Around two hundred people had to be rescued

15cm of ash fell, causing airline and traffic chaos (in some areas, ash was as deep as 2 feet)

Ash damaged car engines and farm machinery and destroyed crops, costing farmers £100 million

Electricity supplies and telephone lines were knocked out

Tourists no longer visited the area, damaging the local economy

The timber industry was destroyed as trees were flattened

Buildings, bridges, railway lines and roads were destroyed

Landscape

The eruption blew away the top of the mountain, reducing its height by 400 metres

A crater 500 metres deep formed

Every form of plant and animal life, for a distance of 25 kilometres north of the volcano, was killed

Approximately 7000 animals died and every tree within 30km of the volcano was flattened

The mudflow choked rivers with sediment, killing all fish and water life and completely filling Lake Spirit

12 million salmon died

The harbour at Portland was completely clogged up as the mud emptied itself into it

Positive

People

Five visitor centres were built

A sediment retention dam to prevent ash and sediment from flowing, while still allowing water to pass, was built to prevent the harbour at Portland from becoming clogged up after any future eruptions

A new earthquake and eruption proof road was built, allowing access to Mount Saint Helens

The blast zone was declared a National Volcanic Monument by President Ronald Reagan, creating 110,000 acres dedicated to research, recreation and education

This also created many new jobs and boosted the economy

Landscape

120 new lakes formed

America's youngest glacier formed in the crater of Mount Saint Helens
The roots of plants were still alive beneath the ash, so many plants grew back naturally

Gophers were underground at the time of the eruption, so survived. They mixed old soil (containing seeds and roots) with ash, facilitating germination

Where ash had been washed away, sprigs of roots began to resprout

The ground was cold and wet, and there was snow on the mountain as it was May. This vital timing meant that plants were dormant, so survived

Management

Prediction

From March 1980, there had been several minor earthquakes, which were recorded

The earthquakes increased in frequency and intensity as time went on

Small eruptions of ash and steam indicated that an eruption was imminent

A bulge developed on the north side of the volcano and it increased in size at a rate of five feet per day

Planning
Authorities set up an exclusion zone, based on a previous eruption
Residents, tourists and forestry workers were strongly advised to evacuate the area, but not everyone took the advice
Emergency services, including helicopters and aeroplanes were on stand by, ready for the eruption
However, scientists could not give a precise date for the eruption, so some people did not leave their homes
Short Term Aid
Stranded people rescued
Shelter was provided for those who had lost their homes
Medical supplies were provided to the injured
One million tonnes of ash was removed from roads, buildings and airports
Electricity was restored
The clean up operation gave work to 200,000 people who had been temporarily put out of work by the eruption
However, due to the extent that the landscape had changed due to the eruption, maps were no longer accurate, which slowed down rescue efforts
Long Term Aid
Millions of trees were replanted to restore the timber industry, which suffered a loss of $300 million
Farmers were provided with compensation, as they lost an estimated $70 million
New tourist facilities were built, to provide the area with an income. Now, 3 million tourists visit Mount Saint Helens annually
A channel on the Columbia river shipping channel was dredged to remove logs and a sediment retention dam was built to prevent the Portland Port from becoming clogged up after any future eruptions
Major repairs, including the construction of a new highway, were undertaken to rebuild the 250km of roads, and 25km of railways that were damaged
The government provided money to the owners of the 200 homes that were destroyed
Money was given to redevelop salmon hatcheries as 12 million baby salmon died

	Erstellt von Mhairi McCann vor fast 10 Jahre

Case Study of Mount Saint Helens 1980 Volcanic Eruption National 5 Geography- Global Issues- Environmental Hazards