Friday, March 15, 2013

Tao Rusyr – An island within an island

The Kuril Islands are part of one of the most volcanically active areas in the world, activated by the subduction of the Pacific Plate under the Eurasian Plate along a 200 km long deep-sea trench. The remarkable Onekotan Island contains a 7.5 km wide caldera, Tao-Rusyr which formed during a VEI (Volcanic Explosivity Index) 6 eruption around 5500 Before Christ. (For an overview of the VEI, see A caldera forms when the magma chamber under a volcano empties and collapses creating a cauldron-like structure. Caldera’s often fill with water, in case of Tao-Rusyr, Kal’tsevoe Lake.

Not long after the big eruption the magma chamber of Tao-Rusyr filled up again. However, the magma could not move through the solid rock of the caldera floor and thus a new volcanic cone, an island within an island, Krenitzyn Peak formed. At 1325 m high the volcanic cone towers high above Onekotan Island. Also, it has a 350 meter wide and 100 meter deep crater. In 1952, a week after a 9.0 earthquake occurred along the subduction zone a VEI 3 eruption occurred on the east flank of Krenitzyn peak creating a small lava dome.

On the northern end of Onekotan island three much older overlapping calderas make up Nemo Peak. One caldera was created 25,000 years ago, the other two 9500 years ago and more recently. Here, a central cone is surrounded by the crescent shaped Chernoe Lake.

Image: NASA Earth Observatory. The image shows Tao-Rusyr with Krenitzyn Peak on the right and Nemo Peak on the left.

KURILE ISLANDS, ALEXANDER BELOUSOV AND MARINA BELOUSOVA. Institute of Volcanology and Seismology, Petropavlovsk, Russia. THOMAS P. MILLER. U.S. Geological Survey. 2009

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