environmental hazards

Question 1

what was the cause of the Mount St Helen’s eruption?

Answer 1

It lies near a destructive plate boundary. Here the Juan De Fuca Plate is being forced beneath the North American Plate into the mantle. As the Juan De Fuca plate descends it melts. As it melts, molten rock rises into the crust. On the 18th May 1980 the magma found its way into the magma chamber of Mt St Helens. The pressure became too much causing the volcano to erupt.

Question 2

what was the impact on landscape and people?

Answer 2

 400 million tonnes of ash rose 20km into the air. Some rose so high, it never came down
 There was a tremendous blast from the eruption, which could be heard 300km away.
 A mudflow of rock, melted ice and ash hurtled down the mountain side at 250km/h. The heat from the eruption had melted ice and snow on the mountain, releasing millions of litres of water.
 The eruption of ash blew away the top of the mountain. In seconds it changed from a mountain of 2950 m high to 2560 m high. At the top, a crater 500 m deep was formed.

Question 3

what aid was used before the mount st helens eruption?

Answer 3

 The state authorities evacuated people from the exclusion zone, which saved many lives.
 A few residents, scientists, reporters and cameramen refused to leave.
 Unfortunately the authorities were given inaccurate advice from the scientists, so there were still people living and holidaying in the area which was devastated by the eruption.

Question 4

why was short term aid essential for the mount st helens eruption?

Answer 4

– 198 stranded people were rescued and the fallen ash was removed. The authorities were able to mobilise many people and equipment quickly to help in these operations.
– The above gave employment to many of the 200,000 people temporary put out of
work by the eruption.
– Over 1 million tons of ash was removed from roads, buildings and airports. In one
town, Yakima, the removal of ash alone took ten weeks and cost over £1 million.

Question 5

why was long term aid essential for the mount st helens eruption?

Answer 5

– It was concerned with returning the area to what it was like before the eruption and
this took several years.
– Millions of trees replanted
– Compensation given to farmers
– Channel dredged to allow ships to pass
– New tourist facilities built Major
– repairs undertaken and new highway built Money given to rebuild
– Money given to redevelop the salmon hatcheries

Question 6

how do you predict a volcano?

Answer 6

Seismographs can detect small earthquakes which can indicate the movement of magma towards
the surface.

Question 7

why was the reaction for the eruption so beneficial but what did they miss?

Answer 7

 Mt St Helens had given clear warnings that it might erupt explosively. From March onwards here were minor earthquakes and small eruptions of ash and steam. These gradually became more severe.
 As a result, the authorities worked out an exclusion zone based on a previous eruption and evacuated residents, tourists and forestry workers. Emergency services, including helicopters and aeroplanes were placed on high alert. Many lives were saved due to these actions.
 However scientists could not give a precise date for the eruption. Even the day before the eruption, scientists were stating that the eruption might still be a few weeks away. Nor did the experts predict that the blast from the eruption would be from the north side. Due to this they miscalculated the exclusion zone and as a result out of the 61 people killed, 90% lost their lives outside this zone.