A hill or mountain, typically conical, from which substances such as lava, fragmented rock, vapor and other gases are ejected via a crater or vent.
Volcanoes are typically associated with lightning, because they ‘create their own weather’.
- What does it look like?
It looks like a hill or a mountain, cone-shaped, but it has a crater rather than a ‘closed’ peak of a ‘regular’ mountain.
- How is it formed?
It is formed when two tectonic plates converge and the denser, thinner one is subducted underneath; the material there melts as it is closer to the mantle, rises and forms a volcano.
Case Study: Etna and Soufriere
- Where located, and why?
Etna – island of Sicily, southern Italy (boundary of African and Eurasian plate)
Soufriere Hills – Montserrat (Atlantic plate subducting under Caribbean plate)
- Why formed?
Etna – because it lies on the plate boundary of the African and Eurasian plate.
Soufriere – because it lies on the plate boundary of the Atlantic and Caribbean plate, and the Atlantic is oceanic whereas the Caribbean is continental.
- How do they erupt?
Etna – most eruptions occur near the summit, where there are currently six distinct craters; however, there are over three hundred vents on the flanks of the volcano. Eruptions near the summit are highly explosive and visually spectacular. It is a composite volcano.
Soufriere – composite volcano as well. Material builds up and forms domes, before briefly bursting the top of the dome which result in pyroclastic flows, ash and explosive eruptions.
- Why hazardous?
Etna – recent eruptions have been on a very large scale, increasing after each other, plus there was reported to be a huge influx of magma into the cone starting in 1994. In addition, the mountain emits large amounts of sulfur dioxide and is situated close to civilization.
Soufriere – toxic ash clouds, possible probability of lahar flows and landslides.
Because the magma chamber is so deep down, draw a jagged line, then another jagged line to show that there’s a break like a broken axis.
Pointer: we’re expected to be able to draw these from memory.
Fissure volcano; a line, not an ‘eruption’ eruption.
Six types of volcanoes: fissure, shield (Hawaii), dome volcano, caldera (massive pimple!), ash-cinder and composite.
Before looking at the diagram below, label:
- ash cloud + volcanic bombs + pyroclastic flow
- magma chamber
- parasitic cone + side vent
Two main types of lava: ‘runny’ lava and ‘thick’ lava.
Runny (basic): behaves like water, very fluid. Low in silica.
Thick (viscous/acid): slow-moving, thick, ‘gooey’, composed of predominantly silica.
Advantages of Volcanoes: Volcanoes and Humans
- 500 mil people live near volcanoes; major cities are close to active volcanoes too
- Magma contains a deep range of minerals. As the rock cools (lava cools) the minerals rise to the surface and materials such as tin, silver, gold and copper are found. Thus mining flourishes. Also sulphur - Kawah Ijen, people carry up to 90kg multiple times a day.
- Geothermal energy: underground steam can drive turbines and produce electricity, or heat water. 2/3 of Iceland’s electricity is this.
- Although volcanic rock is rich in minerals, fresh rocks do not benefit plants. Once the rocks are weathered down however, they form rich soils. Mount Vesuvius; thick deposits of ash and rocks that have weathered – produces grapes, vegetables, orange/lemon trees, herbs, flowers and is a major tomato growing region.
- Simple reason: tourism! Around this there may be bathing lakes, hot springs, mud pools, geysers (Old Faithful). Creates jobs in hotels, etc. Uganda, region around Mt. Elgon heavily promoted.
- It's home: people aren't willing to move
- People don't have the provisions to move