Lake Toba

Lake Toba is a large lake, 100km long and 30km wide, in the middle of the northern part of the Indonesian island of Sumatra.

Geology

In 1949 the Dutch geologist Rein van Bemmelen reported that Lake Toba was surrounded by a layer of ignimbrite rocks, and was a large volcanic caldera. Later researchers found rhyolite ash similar to that in the ignimbrite around Toba in Malaysia and India, 3000km away. Oceanographers discovered Toba ash on the floor of the eastern Indian Ocean and the Bay of Bengal.

Related Topics:
1949 - Dutch - Geologist - Rein van Bemmelen - Ignimbrite - Volcanic - Caldera - Rhyolite - Malaysia - India - Oceanographers - Indian Ocean - Bay of Bengal

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The Toba eruption is dated at 73,000 ± 4000 years ago. It had a Volcanic Explosivity Index of 8, making it the most recent eruption of a supervolcano and probably the greatest eruption in the last two million years.

Related Topics:
Toba eruption - Volcanic Explosivity Index - Supervolcano

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A large area collapsed after the ejection of so much subsurface material, forming a caldera, which filled with water creating Lake Toba. Later, the floor of the caldera uplifted to form Samosir, a large island in the lake. Such uplifts are common in very large calderas, apparently due to the upward pressure of unerupted magma. Toba is probably the largest resurgent caldera on Earth.

Related Topics:
Caldera - Samosir - Magma

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There have been no historic eruptions at Toba, but large earthquakes have occurred, the most recent in 1987 along the southern shore of the lake. The underwater fault off the west coast of Sumatra has had several major earthquakes since 1995, including the ~9.0 2004 Indian Ocean Earthquake and the 8.7 2005 Sumatra earthquake.

Related Topics:
Earthquake - 1987 - 2004 Indian Ocean Earthquake - 2005 Sumatra earthquake

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