Volcano Case Study Mount St Helens

Volcano case studies

You should make sure you are familiar with 2 case studies:
Either: Nyiragongo, Democratic Republic of Congo - Poor Country or Montserrat, Caribbean - Poor Country
Either: Mount St. Helens, USA - Rich Country or Iceland - Rich Country

Key terms:

Primary effects: the immediate effects of the eruption, caused directly by it
Secondary effects: the after-effects that occur as an indirect effect of the eruption on a longer timescale
 Immediate responses: how people react as the disaster happens and in the immediate aftermath 
Long-term responses: later reactions that occur in the weeks, months and years after the event


The video below contains more information on the primary and secondary effects of a volcano

On 17th January 2002 Nyiragongo volcano in the Democratic Republic of Congo (DRC) was disturbed by the movement of plates along the East African Rift Valley. This led to lava spilling southwards in three streams.

The primary effects - The speed of the lava reached 60kph which is especially fast. The lava flowed across the runway at Goma airport and through the town splitting it in half. The lava destroyed many homes as well as roads and water pipes, set off explosions in fuel stores and powerplants and killed 45 people 

The secondary effects - Half a million people fled from Goma into neighbouring Rwanda to escape the lava. They spent the nights sleeping on the streets of Gisenyi. Here, there was no shelter, electricity or clean water as the area could not cope with the influx. Diseases such as cholera were a real risk. People were frightened of going back. However, looting was a problem in Goma and many residents returned within a week in hope of receiving aid.

Responses - In the aftermath of the eruption, water had to be supplied in tankers. Aid agencies, including Christian Aid and Oxfam, were involved in the distribution of food, medicine and blankets.

Montserrat - Poor country case study

Mount St Helens - Rich country case study

Mount St. Helens is one of five volcanoes in the Cascade Range in Washington State, USA. The volcano erupted at 8:32am on 18th May 1980. 

Effects - An earthquake caused the biggest landslide ever recorded and the sideways blast of pulverised rock, glacier ice and ash wiped out all living things up to 27km north of the volcano. Trees were uprooted and 57 people died.

Immediate responses - helicopters were mobilised to search and rescue those in the vicinity of the catastrophic blast. Rescuing survivors was a priority, followed by emergency treatment in nearby towns. Air conditioning systems were cleaned after by clogged with ash and blocked roads were cleared. Two million masks were ordered to protect peoples lungs.

Long-term responses - Buildings and bridges were rebuilt. Drains had to be cleared to prevent flooding. The forest which was damaged had to be replanted by the forest service. Roads were rebuilt to allow tourists to visit. Mount St. Helens is now a major tourist attraction with many visitor centres.

Iceland - Rich country case study

Iceland lies on the Mid-Atlantic Ridge, a constructive plate margin separating the Eurasian plate from the North American plate. As the plates move apart magma rises to the surface to form several active volcanoes located in a belt running roughly SW-NE through the centre of Iceland. Eyjafjallajokull (1,666m high) is located beneath an ice cap in southern Iceland 125km south east of the capital Reykjavik

The Eruption:
In March 2010, magma broke through the crust beneath Eyjafjallajokull glacier. This was the start of two months of dramatic and powerful eruptions that would have an impact on people across the globe. The eruptions in March were mostly lava eruptions. Whilst they were spectacular and fiery they represented very little threat to local communities,
However, on 14th April a new phase began which was much more explosive. Over a period  of several days in mid-April violent eruptions belched huge quantities of ash in the atmosphere.

Local impacts and responses:
The heavier particles of ash (such as black gritty sand) fell to the ground close to the volcano, forcing hundreds of people to be evacuated (immediate response) from their farms and villages. As day turned to night, rescuers wore face masks to prevent them choking on the dense cloud of ash. These ash falls, which coated agricultural land with a thick layer of ash, were the main primary effects of the eruption.
One of the most damaging secondary effects of the eruption was flooding. As the eruption occurred beneath a glacier, a huge amount of meltwater was produced. Vast torrents of water flowed out from under the ice. Sections of embankment that supported the main highway in Southern Iceland were deliberately breached by the authorities to allow floodwaters to pass through to the sea. This action successfully prevented expensive bridges being destroyed. After the eruption, bulldozers were quickly able to rebuild the embankments and within a few weeks the highway was reconstructed.

Local impacts:
800 people evacuated
Homes and roads were damaged and services (electricity & water) disrupted
Local flood defences had to be constructed
Crops were damaged by heavy falls of ash
Local water supplies were contaminated with fluoride from the ash

National impacts:
Drop in tourist numbers - affected Iceland's economy as well as local people's jobs and incomes
Road transport was disrupted as roads were washed away by floods
Agricultural production was affected as crops were smothered by a thick layer of ash
Reconstruction of roads and services was expensive

International impacts:
Over 8 days  - some 100,000 flights were cancelled
10 million air passengers affected
Losses estimated to be £80 million
Industrial production halted due to a lack of raw materials
Fresh food could not be imported
Sporting events such as the Japanese Motorcycle grand prix, Rugby leagues challenge cup and the Boston Marathon were affected

International impacts and responses:
The eruption of Eyjafjallajokull became an international event in mid-April 2010 as the cloud of fine ash spread south-eastwards toward the rest of Europe. Concerned about the possible harmful effects of ash on aeroplane jet engines, large sections of European airspace closed down. Passenger and freight traffic throughout much of Europe ground to a halt.
The knock-on effects were extensive and were felt across the world. Business people and tourists were stranded unable to travel in to or out of Western Europe. Industrial production was affected as raw materials could be flown in and products could not be exported by air. As far away as Kenya, farm workers lost their jobs or suffered pay cuts as fresh produce such as flowers and bean perished, unable to be flown to European supermarkets. The airline companies and airport operators lost huge amounts of money.
Some people felt that the closures were an over-reaction and that aeroplanes could fly safely through low concentrations of ash. However, a scientific review conducted after the eruption concluded that under the circumstances it had been right to close the airspace. Further research will be carried out as a long-term response to find better ways of monitoring ash concentrations and improving forecast methods.

Mt St Helens Volcanic Eruption 1980 

Volcano Learning Zone > Volcanic eruption Casestudies > Mt St Helens

Where is the volcano?

Mt St Helens (8365 ft , 22,550m) is in the Cascade Volcanic Range in Washington State, USA. The Cascade Range has 160 volcanoes and Mt St Helens is considered the most active, and lies 100 miles south of Seattle and 50 miles from the coast at Portland.

Why is there a volcano here?

Mt St Helens is a stratovolcano within the Cascade Volcanic range in Washington State and had been dormant for 100 years prior to 1980. As an Eastern remant of the Pacific Plate, the Juan da fuca plate,has subducted beneath continental North America the Cascade volcanic chain has formed. The Mt.St.Helens volcano has been active for around 40,000 years but the now damaged cone we see today has formed over the last 2,200 years

Eruption Style

The volcano is highly explosive and erupts in the Plinian style like Vesuvius. Sudden violent explosions are accompanied by towering clouds of hot ash, dust and rocks thrown high into atmosphere. Pyroclastic flows and volcanic mud flows called Lahars flow down the mountain at speed and consume the surrounding landscape. lavas from basalt to andesites have been erupted forming layers of ash and lava. In many stratovolcanoes a central summit crater has dome of dacitic lava which is squeezed out of the main vent , similar to Montserrrat. In 1980 this did not occur and instead a crypto dome formed (crypto means hidden) causing the Northern slope of the volcano to bulge and grow. From mapping the deposits around the volcano it seemes that lateral blasts and side domes were not unprecedented.

Sequence of Events

On May 18 1980 Mt.St.Helens produced an enormous lateral blast which obliterated everything for 20 miles north of the volcano. The summit decreased from 2930m to 2550m and a gaping crater 1.5km wide was created.

The sequence of events that occured had not been witnessed before as until then geologists had always seen volcanoes erupt upwards but this was different this was sideways!

In March 1980 earthquakes and a phreatic(steam) 2km eruption column alerted the USGS that the volcano was certainly waking up. Throughout the spring the mountain continued to splutter and steam the northern side of the mountain was bulging out by 1.5m/day. A 5 miles exclusion zone was placed around the volcano and famously Harry Truman owner, of the Spirit lake lodge resort, refused to leave.

On the morning of May 18 Geologist David Johnson was on a ridge 10km north of the volcano when a 5.1 earthquake struck. Suddenly the bulge on the north side of the volcano slid downwards in a massive landslide at 300km/hour and crashed into Spirit lake causing an enormous wave of water the rest of the landslide ploughed down the Tootle river valley and mixed with vast quantities of lake water and ice . Davids last message was to his colleagues in the nearby Vancouver USGS base ( not Canada) "Vancouver,Vancouver .. this is it!"

The landslide uncorked the magma in the crypto dome and released the pressure. The gas in the magma instantly expanded and shattered the rocks at supersonic speed creating a lateral of blast ash and hot rocks which overtook the landslide at reached speeds of 1,000km/hour (670 miles/hour) . The blasts power has been estimated at 500 times that of Hiroshima. 600km2 of forest was blown away and trees combed down like hair, sap exploded in trees in the intense heat. Trees up to 20 miles away were engulfed in the blast 4 times the distance of the exclusion zone.


The third string to Mt.St.Helens bow was a 19km (12miles) high eruption cloud which powered vertically out of the volcano in a matter of minutes. The cloud turned day to night and ash fall was heavy. Lightning crackled around the cloud.

Mudflows or Lahars formed within minutes of the eruption. lake water,melted glacier ice, hot ash and debris all combined to send hot ( 29-33C) cement like flows down the Toutle river. Pyroclastic flows started to form from the crater just after the blast as fresh magma came into contact with the air. Material appeared to overflow the craters edge and flow down the Toutle valley as a grey turbulent cloud.

Harry Truman and David Johnson along with 55 other people did not survive. Both have had ridges named after then within the Mt.St.Helens national monument. The area within the monument is being left to recover naturally. Within 8km of the volcano all trees were obliterated, from 8km to 30km flattened and outside this dead but left standing. Outside the boundary logging companies have replanted trees.

Mount St. Helens showed significant activity on March 8, 2005, when a 36,000-foot (11,000 m) plume of steam and ash emerged. A new dome is growing and will eventually fill the 1980 crater.

Effects and Aftermath

Rescue helicopters looking for survivors were grounded or could not land due to ash. Ash removal from roofs nad roads was costly and lengthy costing 2 million dollars just in one town(Yakima)

Hazard Management

All volcanoes in the Cascades are monitored by the Cascades Volcanic Observatory CVO part of the United States Geological Survey USGS from their base in Vancouver,not Canada but Washington State USA. On March 27th 1980 a phreatic eruption signalled the begnning of an active phase. The CVO moved in a team of Geologists to monitor the volcano.Small eruptions of steam and ash blasted from the old summit dome continued and attracted attention from the press and tourists. Evacuation plans were prepared and roads closed leading to the volcano. As the mountain swelled with magma, and bulged outwards at a rate of 1.5m/day,it was obvious that the Spirit Lake area to the north of the volcano needed to be evacuated. The Washington State Governor placed a 5 mile red zone around the summit only Harry Truman an 83 year old resort owner refused to move. When the volcano erupted on May 18th the lateral blast extended 20 miles 4 x the exclusion zone.

Try our other Mt St Helens entry , World volcano section or Volcanic Hazards page.


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