22.214.171.124 Tectonic processes Human response to volcanic hazards Syllabus: Understand the variation in response to risk in terms of probability of hazard occurrence and level of economic development Assess the costs and benefits of living near areas of volcanic activity. Use case studies to look at hazards and to illustrate the benefits including minerals, fertile soils, geothermal power and tourist attractions.
Aim to deviate and slow down a torrent of lava e.g. threatening villages on Etna’s lower slopes
‘ Eruption began 42 days ago at 2368m. Since then millions of tonnes of lava have gushed out of a small crater and covered the mountainside with immense tongues of molten rock some of them up to 6km long. 1 hotel, 3 restaurants, 25 houses and numerous orange groves destroyed. Then the main crater at summit 3423m began to erupt.
The lava pouring out from the side of the mountain has carved out a channel about 6m wide and 4.5m deep with ridges of solidified lava forming on either side of its course. The lava races along at an average speed of about 16km / hr. The intention is to blow up a section of the solidified ridge and channel the molten lava along a new path. The lava will burst into a man made canal after the explosion then run into an ancient crater and down the mountainside parallel to the present flows.’
Workers have used more than 70 bulldozers in a desperate attempt to pile up enough earth to divert the lava away from the station. Lava halts as Etna battle continues
1. Building and structure design can do little to resist lava, pyroclastic flows and lahars as the hazards will destroy any structures in their path.
2. Ash fallout has the largest spatial impact and design may help reduce its impact. The weight of ash on roofs especially if wet can be enough to cause roof collapse. Roofs need to be strong and designed to shed ash with steep sloping sides .
Most volcanic events are preceded by clear warnings of activity from the volcano. If the community is prepared in advance many lives can be saved.
1. Evacuation of the area can save lives, but preparation and management structures to organise the evacuation, temporary housing food etc are needed.
The length of time of the evacuation may be long term. 5 000 residents of Montserrat were evacuated three times between Dec 1995 and Aug 1996 for periods of up to three months to avoid pyroclastic flows and ashfalls.
In 1995 officials drew up an emergency evacuation plan for the 600 000 people at risk from an eruption of Vesuvius. The operation is large scale and involves removing some people to safety by ship.
2. People need to be clear about the risk and not panic during an event.
Evacuations have been successful in recent years and are the most common hazard management strategy.
The Galunggung eruption of 1982 Java involved 75 000 evacuees and a small fatality of 68. 1985 eruption of Nevado del Ruiz – Colombian government did not have a policy in place for monitoring volcanoes or for disaster preparedness.
3. Communications between the scientists monitoring volcanoes and government officials must be clear, consistent and accurate .
4. If an eruption is expected, scientists monitor the activity and produce hazard maps .
If there is a lack of communication and indecision this leads to disaster – the Colombian government had more serious and immediate problems – economic crisis, political instability and narcotic cartels to deal with.
City of Kagoshima with half a million people lies close to Sakurajima volcano
The Japanese meteorological agency and Kyotos University’s Sakurajima Volcanological observatory use the latest technology to monitor events.
Events that appear to signal the build up to a volcanic eruption:
A gradual swelling of land around the volcano as magma astarts to build up. At Sakurajima this is marked by a rise in the seabed of northern Kagoshima Bay with consequent change in tide levels on the Sakurajima shore relative to those around Kagoshima city.
1. With magma coming closer to the surface, earthquakes will become more frequent.
Groundwater levels may change , the temperature of hot spring waters may rise
The chemical composition and the amount of gases released may alter . The ratio of hydrogen chloride to sulphur dioxide gas emitted from the volcano’s active crater increases during earthquake swarms and shortly before an eruption. Remote sensing is used to monitor gases .
4. As an eruption approaches a tiltmeter measures minute movements of the mountain.
Seismometers detect earthquakes which occur immediately beneath the crater, signalling the onset of the eruption. They occur 1 to 1.5 seconds before the explosion at the crater bottom.
The violence of the eruption may correlate with the length of the preceding dormant period but also with the viscosity of the underground magma. The harder it is for the gases to escape, the more violent it is when the pressure is finally released. Magma is blasted skywards, cooling and solidifying as it moves through the air
Magma is blasted skywards, cooling and solidifying as it moves through the air. It can vary in size from a fine dust to boulders, or bombs that fly at speeds of up to 300kmph. Most of the released magma forms pyroclastic flows.
Secondary – temperature change, lahars, landslides, acid rain ,
Select one volcanic hazard and referring to one or more examples, describe and explain its effect on people and the environment (6 marks)
Answers state how both people and the environment are affected.
S marks description of effects, 2 marks for explanation 2 marks for one or more examples. Ash can contaminate water supplies, destroy vegetation, cause people to suffocate and result in collapsed roofs or ruined crops.
To what extent can the impact of volcanic hazards be reduced? (10 marks)
Answers should consider prediction of volcanic hazards as a possible method of reducing impacts. Review some of the ways that volcanoes are monitored, including the importance of eruptive types and histories. The possibility of modifying the event should also be considered in the light of attempts that have been made to divert or halt lava flows.
Responses to the hazard could include building modifications such as strengthening roofs to prevent collapse during ash falls, hazard mapping and subsequent land use planning, evacuation plans, provision of emergency services, education to promote awareness and international cooperation
Little can be done to control a volcanic eruption. attempts are made to control lava flows by spraying water as a coolant to stop the flow (Iceland 1973 Eldafell) or by use of explosives to divert lava (Etna 1983)
The construction of earth barriers to divert lava (Etna 2001) and the use of barrier dams to reduce the secondary hazard of lahars in Japan and Indonesia.
Other structures used to protect the community could include the provision of strong roofs against ash and tephra accumulation or the construction of houses that can be moved in areas at high risk from lava flows.
Responses should note that a hazard risk map is essential to enable communities to avoid having settlements, farmland, roads, power and water supplies in areas of high risk. The success of such a strategy depends upon the willingness of the community to accept some economic loss.
Not all countries have good records of past eruptions making effective land use planning difficult.
Evacuation procedures to save lives include the organization of temporary housing, food and water supplies. This is essentially the job of governments. E.g. Montserrat 1995, 1996
The difficulties of providing rapid emergency relief could be mentioned. Efforts are more likely to be successful in MEDCs were capital and resources are more readily available, communications are effective and warning systems are more reliable. Responses may also refer to the planned involvement of outside aid agencies such as the Red Cross and the UN.
National pride might make some countries reluctant to ask for help
Political problems may affect the flow of relief aid from other countries.
Using examples, examine how different types of volcanic eruption have different impacts on people
Both the primary and the secondary hazards associated with tectonic activity are more predictable and therefore less serious in MEDCs than in LEDCs. Examine the validity of this statement with reference to either earthquakes or volcanoes that you have studied
Discuss the idea that volcanic activity is more harmful than beneficial to humans