Detailed notes on both the types and structure of volcanoes.

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Helena Bonici Geography 21/06/2011
13EA2 Plate Tectonics
The form, or shape, of a volcano is governed by the composition of erupting
magma and type of erupted products (volcaniclastic products of various kinds such as pyroclastic and
autoclastic fragments or effusive lava). Their shapes are determined in large part by the explosivity of
eruptions, and volume of water that interacts with magma.
The fissure volcano: a long crack in the earth's surface through which magma erupts. These cracks may
form as two tectonic plates pull apart. They are found mainly near mid-ocean ridges.
The shield volcano: This is a broad, shallow volcanic cone, which arises because the running lava, which is
fluid and hot, cools slowly.
The dome volcano: This one has a steep, convex slope from thick, fast-cooling lava
The ash-cinder volcano: Throws out - besides lava - much ash into the air. Through this the volcanic cone
is built up from alternate layers of ash and cinder.
The composite volcano: These are also built up from alternate
layers of lava and ash but, besides its main crater, it has many little
craters on its slope.
The caldera volcano: An older volcano with a large crater which
can be 62 miles(100km) wide. In this crater many little new craters
are formed.

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Helena Bonici Geography 21/06/2011
13EA2 Plate Tectonics
Type of lava flow types:
1. Low water, low silica - runny lava flows (not viscous)
2. Low water, high silica (very viscous) - pasty lava - often building domes
3. High water, low silica (not viscous) - fountain of runny lava
4. High water, high silica (very viscous) - explosion
The silica levels are dependent upon the type of lava which are: basaltic, intermediate and rhyolitic.…read more


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