Volcano 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
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
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
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
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.
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
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
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.
Earthquake Monitoring at Mount St. Helens
Due to the eruptions of 1980-86 and 2004-2008, Mount St. Helens has had the best seismic monitoring network of all volcanoes in the Cascade Range. It is also the most seismically active volcanoes in the Washington and Oregon Cascades. In an average month, 22 events are located by the Pacific Northwest Seismic Network (PNSN), with the number going far higher during eruptive periods. Although a few seismic stations were installed near Mount St. Helens in the 1970s, the first complete network of stations was installed in 1980 in response to unrest starting in March of that year. Since then millions of earthquakes, as well as other non-earthquake signals (e.g., rockfalls, explosions, avalanches, glacier quakes, helicopters) have been recorded. The PNSN earthquake catalog encompasses periods of precursory activity (preceding eruptions in 1980-1986 and 2004), seismicity associated with episodic explosive eruptions (1980) and dome growth (1980-1986 and 2004-2008), and times of relative quiet between eruptions (1987 - 2004 and 2008 to present). Seismic data recorded by this network have been used in many studies, including:
- forecasting eruptions and detecting explosions
- determining eruption dynamics
- developing models of the magmatic system beneath Mount St. Helens
- determining the on-the-ground processes responsible for various types of seismic signals
- detecting repetitive events (or earthquake families), including the first published study of repetitive events in a volcanic setting.
One of the intriguing aspects of volcano seismology is trying to determine the cause, volcanologic or otherwise, of a particular earthquake. This is illustrated by reviewing a plot of earthquake depths over time (right).
The May 18, 1980, eruption is marked by a vertical streak of earthquakes extending down well below 15 km (9.3 miles). Scientists believe that these earthquakes occurred when the May 18 eruption drained magma from deeper parts of the magmatic system, leaving voids of unsupported rock that then failed and produced earthquakes.
In contrast, the 1981-1986 time period was dominated by shallow earthquakes, mainly less than 2 km (1.2 mi) deep. These earthquakes occurred primarily as precursors to individual dome-building eruptions, and are thought to have occurred as a result of stress accumulations associated with magma movement.
Although eruptions stopped after 1986, earthquakes continued to occur, including several years- long dense groups (swarms) of "deep" earthquakes (depths greater than 3 km, or 1.9 mi), which hadn't been seen since 1980. Scientists think these particular "deep" earthquakes probably occurred when new magma entered the system from below and caused the pressure to increase on the system. In contrast, shallow earthquakes from 1987-2004 probably occurred due to a combination of factors: magma left- over from the 1980-86 eruptions cooled, contracted, and created earthquakes; heated groundwater (hydrothermal fluids) circulated and added stress to the volcanic structure; and magma potentially accumulated below 3 km (1.8 mi), which added stress to the system.
The 2004-2008 eruption produced many earthquakes, with well over one million occurring in association with the construction of a new lavadome complex. A notable phenomena observed during the eruption was the occurrence of very regularly spaced patterns of small earthquakes, which were dubbed "drumbeat" earthquakes. These consistently spaced seismic events accompanied the steady eruption of lava spines as they emerged from the Mount St. Helens conduit, and have since been reported at other volcanoes (e.g., Augustine Volcano in 2006).
Owing to the robust seismic data set for Mount St. Helens, scientists understand the character of typical eruptive and non-eruptive earthquake patterns at this volcano. These perspectives are vital assets when interpreting the significance of earthquake activity at the volcano, and they can help scientists to determine when a future eruption may occur. The PNSN's website is an excellent resource for viewing and mapping earthquakes at Mount St. Helens.
In addition to earthquakes that occur due to volcanic processes, seismicity at Mount St. Helens also occurs along tectonic faults, which are associated with motion in the crust and not with volcanic processes. Many of these earthquakes occur along the Mount St. Helens seismic Zone (SHZ), which extends north-northwestwards to Morton, Washington and south-southeastwards to past the Swift Reservoir. Three to four earthquakes per month occur along the SHZ, including a number of events that have been large enough to be felt in nearby communities. The largest event ever recorded on the SHZ (a magnitude 5.2) located near Elk Lake on February 14, 1981. The most recent felt event was a magnitude 4.3 on February 14, 2011, that was felt as far away as Vancouver, Washington. In contrast to earthquakes beneath Mount St. Helens, earthquakes occurring in the area surrounding the volcano, including the SHZ, are all thought to be normal "tectonic" earthquakes caused by tectonic forces that also produce earthquakes throughout western Washington and northwestern Oregon.