This summary specifically focuses on volcanoes and tsunamis, which are important parts of Chapter 9.1 (CIE A-Level Geography 9696) The information in the summary covers all the content the exam board could ask pupils about volcanoes and tsunamis, such as volcanic hazards, hazards associated with vo...
Volcanoes
● Most volcanoes are found at plate boundaries, although some like the
volcanoes of Hawaii, occur over hotspots (isolated plumes of magma)
● About ¾ of the world’s 550 historically active volcanoes lie along the Pacific
Ring of Fire
● At subduction zones, volcanoes produce more viscous lava and tend to erupt
explosively and produce much ash
● Volcanoes found at mid-ocean ridges and hotspots tend to produce more
basaltic lava, as in the case of Iceland and Hawaii
Volcanic hazards
● Lava flows
● Ballistics and tephra clouds
● Pyroclastic flows and ash fallout
● Gases and acid rain
● Lahars (mud flows)
● Glacier bursts
Pyroclastic flows Atmospheric ash fallout Destruction of settlements
Volcanic bombs Landslides Loss of life
Lava flows Tsunamis Loss of farmland and forests
Ash fallout Acid rainfall Destruction of infrastructure,
roads, ports and facilities
Volcanic gases Lahars (mudflows)
Glowing clouds Disruption of communications
Earthquakes
● Ash and debris falls steadily from the volcanic cloud, covering the ground with
deposit known as pyroclastic flow
● A pyroclastic flow is a fast-moving cloud of extremely hot gas, ash and rock
fragments, which can reach temperatures of about 1000°C and travel at
speeds of up to 700 km/h
● Ash can be quite dangerous as the fine ash particles can damage people’s
lungs by potentially causing silicosis or asthma and due to the fact that they
, are quite heavy and a small layer can be enough to cause a building to
collapse
● Pyroclastic flows are strong enough to knock down trees and leave a trail of
destruction
● Some of them are extremely hot and can reach up to 700 C
● Lahars are another hazard associated with volcanoes
● A combination of heavy rain and unstable ash increases the hazard of lahars
● Close to the volcano, people are at risk of large fragments of debris, ash falls
and poisonous gases
● Further away, pyroclastic flows may prove to be hazardous and lahars and
debris flows may have an impact on more distant settlements
● Volcanoes can lead to tsunamis and famine
● The ash fallout in Iceland in April 2010 caused widespread disruption to
European air travel, no one was killed in the eruption but the economic cost
was great
● It had a global impact, as the countries that traded with the EU were badly
affected
Volcanic strength
● The Volcanic Explosive Index (VEI) measures the strength of a volcano
● This is based on the amounts of materials ejected in the explosion, the height
of the cloud it creates and the amount of damage caused
● Any explosion above level 5 is considered to be very large and violent
● A VEI 8 refers to a supervolcano
Predicting volcanoes
Volcanoes are easier to predict than earthquakes because there are certain signs:
● There are seismometers that record swarms of tiny earthquakes that occur as
the magma rises
● The use of chemical sensors to measure sulphur levels
● Lasers to detect the physical swelling of the volcano
● Ultrasound to monitor low-frequency waves in the magma, resulting from the
surge of gas and molten rock
● Direct observation
● Since 1980, scientists have correctly predicted 19/22 of Mt St Helens’
eruptions
● However, it’s not always possible to predict when an eruption will occur
● The US geological survey predicted the eruption of Mt Pinatubo in 1991 and
successfully evacuated the area
● However, it was unsuccessful at predicting a volcanic eruption at Mammoth
Mountain Ski Area in California and the false prediction led to reduced visitor
numbers to the resort and caused economic distress to local business owners
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