A volcano is a place where molten rock from deep inside the Earth breaks out through the crust. The molten rock is called magma while it is underground, and lava once it reaches the surface. There are around 1,500 active volcanoes on land today (and thousands more under the ocean), and roughly 20 of them are erupting at any given moment. Volcanoes can be terrifyingly destructive, but over geological time they have built mountains, made islands, shaped continents and (probably) helped create the very atmosphere we breathe.
- Active volcanoes (on land)Approx. 1,500Plus many more under the sea
- Erupting right nowApprox. 20At any given moment
- Tallest volcanoMauna Loa4,170 m above the sea (9 km from base)
- Lava temperature700 to 1,250 °CGlowing red to white-hot
- Famous eruptionMount Vesuvius, 79 ADBuried Pompeii
- Most powerfulKrakatoa, 1883Heard 4,800 km away
What causes a volcano
Most volcanoes form where Earth's tectonic plates meet. When one plate slides under another (a process called subduction), the rock heats up and partly melts, forming magma. Less dense than the surrounding rock, the magma slowly rises towards the surface. Sometimes it cools and hardens underground. Sometimes it breaks through and erupts. The famous Ring of Fire around the Pacific Ocean is where around 90% of all volcanoes are found.
Types of volcano
- Shield volcanoes: wide, gently sloping mountains built from runny lava. Examples: Mauna Loa, Mauna Kea in Hawaii.
- Stratovolcanoes (composite): tall and steep, built from alternating layers of lava and ash. Often very explosive. Examples: Mount Fuji, Vesuvius, Mount St Helens.
- Cinder cones: small steep cones built from blobs of frozen lava. Often form quickly during a single eruption.
- Supervolcanoes: enormous calderas that erupt very rarely but produce far more material than ordinary volcanoes. Yellowstone and Toba are examples.
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