Structure and common features of volcanoes
Volcanoes can be described by their shape or type - shield or composite.
Both types of volcanoes have common features:
- A region under the surface of the Earth where hot molten magma collects. - this is where the molten rock is stored beneath the ground at great heat and pressure
- The thin narrow pipe in the middle of a volcano that connects the magma chamber to the crater. - this is the channel through which Molten rock that is found within the Earth. rises to reach the Earth's surface
- The thin narrow pipe at the side of a volcano formed when the main vent is blocked. - some magma may escape through the side of the volcano, particularly if the main vent becomes blocked
- The hole at the top of a volcano where lava and ash escape. - this is found at the top of the volcano and the magma usually erupts from here
- The shape of a volcano. - this is formed from the material ejected during eruptions and grows in size with each eruption
When a volcano erupts there can be lava, ash, steam or gaseous emissions. Sometimes eruptions are explosive and lava is thrown out as volcanic bombs.
Composite volcanoes
- Composite volcanoes are made up of alternating layers of lava and ash.
- They are usually found at When two tectonic plates move towards one another. The oceanic crust is forced to sink back into the mantle, whilst the continental crust rises above. Volcanoes and earthquakes are found here..
- Eruptions are infrequent, but mostly violent and can include volcanic bombs.
- The eruptions from these volcanoes may be a A current of hot gas and rock that flows downhill at high speed.. This is a deadly mixture of hot steam, ash, rock and dust. It moves at very high speeds and has high temperatures (400掳C).
- They are steep-sided as the thick and heavy lava doesn't flow very far before it cools.
Examples of composite volcanoes are Mt Unzen in Kyushu, Japan, and Mt Etna in Sicily, Italy.
Shield volcanoes
- Shield volcanoes are usually found at An area where two tectonic plates are moving away from one another. or over a A hotspot occurs when there is intense heat in the mantle which rises towards the crust. When the melted rock (magma) reaches the surface it creates volcanoes, eg the Hawaiian islands..
- They have gently sloping sides because the lava is thin and runny so it moves far before it solidifies.
- Eruptions tend to be often or continuous and mostly gentle.
An example of a shield volcano is Kilauea, in Hawaii.
Hotspots
Hotspots are places where the magma rises up through the crust. They are caused by a static source of magma, often away from plate margins. As the plate moves away from the hotspot, a new volcano island will form.