Friday, January 21, 2011

Volcanoes in Kamchatka I

Kamchatka is a 1,250 km (~775 mi) long peninsula on the far eastern end of Russia separating the northern Pacific Ocean and Bering Sea from the Sea of Okhotsk.

Image from FlashEarth

As we can see in this image from Google Earth, just to the east of Kamchatka, on the ocean floor, lies the 10.5 km (34,450 ft) deep Kuril Trench.

This deep seafloor trench exists because the crust (lithosphere, technically) of the Pacific Ocean is sliding down that trench and subducting beneath the Sea of Okhotsk.

The plate tectonic interactions in this part of the world are somewhat complex.  As you can see in the diagram at left from Wikipedia, the Pacific Plate is sliding down the Kuril Trench (shown as a blue-barbed line east of the southern part of the Kamchatka Peninsula) underneath the small Okhotsk Plate.

The arrow shows the direction and rate of plate movement here.  The Pacific Plate is moving toward the northwest at a rate of 92 mm/yr (9.2 cm/yr or 3.6 in/yr).

Off the east coast of the central part of the Kamchatka Peninsula, things get complicated because there's a triple junction here.  The blue barbed line coming in from the west is the Aleutian trench which is just south of the arc of the Aleutian Islands coming off of Alaska.  The Pacific Plate is also subducting down the Aleutian Trench but here it's moving under the North American Plate with extends under the Bering Sea and into Asia.

Off the northern east coast of Kamchatka, the seafloor of the Bering Sea (the North American Plate) is subducting beneath the Okhotsk Plate.

All of this is a small part of the so-called Ring of Fire, the chains of active earthquake zones and volcanoes extending around the rim of the Pacific Ocean due to plate subduction down into deep seafloor trenches.

 Image from USGS This Dynamic Earth

What happens during subduction is that the descending slab of oceanic crust begins to melt as it sinks into the Earth's mantle providing magma for overlying volcanoes.  The subducting plate also sticks and slips as it slides down into the mantle causing frequent large earthquakes in such areas.

Now that I've given some background, I want to share the incredible satellite image that was the impetus for this post.

This image was taken from the the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on the Terra satellite on October 11, 2010.  Terra is an Earth-observing satellite NASA runs in partnership with the aerospace agencies of Canada and Japan.

This image shows three volcanoes in Kamchatka - Klyuchevskaya, Bezymianny, and Shiveluch.  Klyuchevskaya and Shiveluch were currently erupting when this image was made.  These eruptions are from magma rising up through the crust and derived from the melting of the subducting Pacific Plate as explained above.

Click here to see the awesome 6277 x 8892 pixel image in all its glory.  In tomorrow's post I'll show a few close-ups and point out a number of interesting volcanic and fluvial (stream-related) features in this image.

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