come in all sizes and can cause damage on a local, regional or global
scale. On a local scale lava flows can cause damage to property (Hawaii,
Etna) and mudflows can lead to loss of life/property and can destroy
vital communication links (Ruapehu,NZ). On a regional scale some eruptions
like Mount St. Helens can devastate large areas and disrupt aviation.
On a global scale eruptions that transport material high into the
stratosphere can affect our climate (Pinatubo, El Chichon). Eruptions
at the other side of the world can affect the UK climate.
It has been suggested
that large volume, prolonged volcanic eruptions that punctuate geological
time are in some cases associated with mass extinctions. Such huge
outpourings of lava are found in India, South Africa, Antarctica,
Greenland/Scotland, Yemen-Ethiopia, Washington-Idaho USA etc . Maybe
such volcanic activity contributed to the extinction of the dinosaurs
or was it a meteorite?
molten rock to the surface of the Earth and in so doing provide information
about processes deep within the Earth. If during their passage to
the surface they pick-up fragments of the Earth then these rocks and
minerals provide a unique insight into the nature of the Earth sometimes
at depths of 200-400km. The rocks from 200-400km down in the Earth
contain garnets, pyroxenes and olivines. Kimberlite volcanoes in South
Africa and Canada are renowned for their diamonds some of which are
3,000,000,000 years old (i.e., 3 billion years old).
come in a variety of colours some black (basalt), grey (andesite),
or pink (rhyolite) and they can contain a variety of crystals - quartz
(rhyolites), feldspar (andesites) and olivine (basalts). Volcanic
rocks erupted some 3-4 billion years ago are called komatiites and
they provide vital evidence about the nature of the early Earth.