Lake Toba, Sumatra

Lake Toba, Sumatra Supervolcano

Country:	Indonesia
Subregion Name:	Sumatra (Indonesia)
Volcano Number:	0601-09=
Volcano Type:	Caldera
Volcano Status:	Holocene
Last Known Eruption:	Unknown
Summit Elevation:	2157 m	7,077 feet
Latitude:	2.58°N	2°35'0"N
Longitude:	98.83°E	98°50'0"E
The 35 x 100 km Toba caldera, the Earth's largest Quaternary caldera, was formed during four major Pleistocene ignimbrite-producing eruptions beginning at 1.2 million years ago. The latest of these produced the Young Toba Tuff (YTT) about 74,000 years ago. The YTT represents the world's largest known Quaternary eruption, ejecting about 2500-3000 cu km (dense rock equivalent) of ignimbrite and airfall ash from vents at the NW and SE ends of present-day Lake Toba. Resurgent doming forming the massive Samosir Island and Uluan Peninsula structural blocks postdated eruption of the YTT. Additional post-YTT eruptions include emplacement of a series of lava domes, growth of the solfatarically active Pusukbukit volcano on the south margin of the caldera, and formation of Tandukbenua volcano at the NW-most rim of the caldera. Lack of vegetation suggests that this volcano may be only a few hundred years old (Chesner and Rose, 1991).

One of the largest known volcanic eruptions took place only 74,000 yrs ago, when over 2500 cubic kilometers of magma was ejected from Toba - a volcano-tectonic depression that is often referred to as Earth's largest Quaternary caldera. The caldera is 18 x 60 miles (30 by 100 km) and has a total relief of 5,100 feet (1700 m).Over what was probably a two-week span, thousands of cubic kilometers of debris spewed from Toba Caldera on northern Sumatra. Pyroclastic flows (fast-moving clouds of hot gas, rock fragments, and ash) buried at least 20,000 square kilometers around the caldera. As far away as India, ash from the Toba eruption lies in layers up to 6 meters (about 20 feet) thick; on Samosir Island, the ash layer is more than 600 meters (more than a quarter mile) thick.

Lake Toba, Sumatra Supervolcano

Image courtesy of NASA/GSFC/MITI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team.

Following the eruption, the ground collapsed, leaving the modern caldera, which filled with water to make Lake Toba. Samosir Island is a resurgent volcanic dome, a mound of rock uplifted by pressure from un-erupted magma in the chamber beneath the volcano. The Pusukbukit Volcano on the western shore of the lake also formed after the catastrophic eruption.

Lake Toba, Sumatra Supervolcano

credit: http://www.rpi.edu/~warkd/toba/toba_geology.html

The caldera probably formed in stages. Large eruptions occurred 840,000, about 700,000, and 75,000 years ago. The eruption 75,000 years ago produced the Young Toba Tuff. The Young Toba Tuff was erupted from ring fractures that surround most or all of the present-day lake.

credit: NASA, The Discovery Channel, The Smithsonian Institute, USGS