Volcanoes
Geography: Edexcel A Level, topic 1.1.6
Primary Hazards of Volcanoes
Volcanic eruptions produce a range of hazards - all of which can be devastating. The main primary hazards are:
Ash falls
- Ash fall (tephra) is a solid material of varying grain size (fine ash up to volcanic bombs) ejected into the atmosphere.
- Buildings often collapse under the weight of ash falling on to their roofs.
- Air becomes thick with ash and is very difficult to breathe in and can cause respiratory problems.
- The 2010 eruption of Mount Merapi in Indonesia is an example where volcanic ashfall affected the surrounding area.
Volcanic gases
- Volcanic gases can be poisonous.
- Examples include carbon dioxide, carbon monoxide, hydrogen sulphide, sulphur dioxide and chlorine.
- An example of an eruption that produced a lot of volcanic gases was the 1986 eruption of Lake Nyos, Cameroon.
Pyroclastic flows
- Pyroclastic flows are very hot (800oC), have a high velocity (over 200km/h) and are a mixture of gases and tephra.
- Pyroclastic flows can destroy everything in their paths.
- Examples of eruptions that have produced large pyroclastic flows include:
- The AD79 eruption of Mount Vesuvius in Pompeii, Italy.
- The 1980 eruption of Mount St. Helens in the USA.
Lava flows
- Lava flows are not usually a major threat when they are molten lava as they are slow moving.
- Lava flows create extensive areas of solidified lava.
- Examples of land masses that have been created by lava flows are:
- Hawaii.
- Southwest Iceland.
Secondary Hazards of Volcanoes
The main secondary hazards of volcanoes are:
Lahars
- Lahars are fast mudflows that happen when rain mobilises deposits of volcanic ash.
- In 1985 the Armero tragedy took place when the Nevado del Ruiz volcano erupted in Colombia. Four lahars came towards the town of Armero and around 20,000 people died.
Flooding
- A Jökulhlaup is the name of the flooding that happens when glaciers or ice caps melt. The term originates from Iceland where subglacial outburst floods happen at Vatnajökull.
Test yourself on Volcanoes
Which of the following is true of pyroclastic flows?
Which of the following is a consequence of ash falls?