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.
