| On locations where tectonic plates diverge or converge, volcanoes can be found. A volcano consists of a deep magma chamber where magma accumulates, pipes that lead to surface vents, and the vents through which lava is emitted during a volcanic eruption. Volcanoes are often known to have a mountain-like shape (see picture). |
Figure 1: layout of a volcano
Volcanoes that have not erupted for some time are dormant, and volcanoes that have not erupted even in the distant past are called extinct. Volcanic activity and volcanic eruption is usually triggered by alterations of tectonic plates, resulting in landslides or earthquakes.
There are different types of volcanic eruptions:
- Phreatic: explosion of steam, water, ash and rock as magma comes in contact with groundwater or surface water
- Rhyolite flow: high-silica lava (>68%)
- Basalt flow: low-silica lava (when the silica content is low, lava usually has a higher magnesium and iron content)
- Pyroclastic flow: fast-moving hot ash, gas and rock
- Lahar: mudflow of pyroclastic material into a river valley
- Carbon dioxide emission
Volcanic eruptions can be extremely damaging to the environment, particularly because of a number of toxic gases possibly present in pyroclastic material. It typically consists mainly of water vapour, but it also contains carbon dioxide and sulphur dioxide gas. Other gases typically found in volcanic ashes are hydrogen sulphide, hydrogen chloride, hydrogen fluoride, carbon monoxide, and volatile metal chlorides.
Carbon dioxide emitted from volcanoes adds to the natural greenhouse effect. Sulphur dioxides cause environmental problems, because they are converted to sulphuric acid in the stratosphere; the main cause of acid rain. Furthermore, sulphate aerosols are formed, which reflect solar radiation and absorb heat, thereby cooling the earth. Sulphate aerosols also take part in chemical reactions, forming ozone destructive material.
An example of a volcanic eruption that caused substantial environmental damage is the Mount Pinatubo eruption in the Philippines.