Saturday, January 22, 2011

Volcanoes in Kamchatka II

In yesterday's post (Volcanoes in Kamchatka I), I discussed the reason why there are volcanoes on the Kamchatka Peninsula (subduction of seafloor crust from the Pacific and North American Plates under the Kamchatka Peninsula which is on the Okhotsk Plate).

Today, I wanted to say a few words about the image above taken by the Terra satellite last October.  Click here to embiggen and see a lot of neat details.  The location of this image on the Kamchatka Peninsula is shown below.  That little island on the lower-right edge of the image is Attu, the westernmost point of the Aleutian Islands coming off Alaska.

As you can see from the image I showed yesterday, these volcanoes are located near that triple junction between the North American, Pacific, and Okhotsk tectonic plates.

By the way, see those islands coming southward off Kamchatka toward Hokkaido Island in the north of Japan?  Those are the Kuril Islands and just today (January 22 at 1247 UTC) they experienced a 4.7 magnitude earthquake due to the constant subduction of the Pacific Plate down the Kuril Trench at 92 mm/yr.

Let's look more closely at some of the features visible in the Terra satellite image above.  The first is Klyuchevskaya volcano (also spelled Kliuchevskoi) in the lower-left part of the image.

This image was taken on October 11, 2010, at 1237 UTC (12:37 pm local time).  Note that the volcano is actively erupting a plume of ash.  The white on the flanks of the volcano are a mix of snow and ash and patchy white clouds are also visible.  Look carefully on the left side of the crater, see the little river of red?  That's a lava flow being picked up by the infrared sensors on the satellite (infrared radiation is emitted from hot objects).  Here's a close-up:

Klyuchevskaya is a stratovolcano and the highest peak on Kamchatka at 4,750 m (15,584 ft).  This volcano has erupted more than 50 times since it was first recorded in 1697 (and there's radiocarbon evidence of eruptions going back six thousand years).  That constant eruptive activity is actually a good thing in some ways - volcanoes that are constantly erupting like this are generally well-behaved and not too dangerous (although the ash plumes rise to 26,000 feet or more and can disrupt air traffic).  It's also a great place for volcanologists to study volcanic processes - the Kamchatka Volcanological Station was established at its base in 1935.

Klyuchevskaya from Global Volcanism Program

Another volcano seen in the image is Bezymianny (lower-left), which is just to the south of Klyuchevskaya volcano.  Note the shadow of the volcano indicating the Sun is to the south (expected in Kamchatka in October) and the plume rising from the crater.  This is just a steam plume (meltwater seeping into fractures and heating into steam due to the hot rock at depth) as no explosive activity was recorded at this time.

Bezymianny from Global Volcanism Program

Bezymianny was once though to be extinct, until it violently erupted in 1955-1956 and blew out the east-southeast side of the volcano leaving behind a horseshoe-shaped crater (very similar to the way Mt St Helens erupted in Washington State back in 1980).  A large lava dome now exists in the crater with intermittent explosive activing and pyroclastic flows.

The third major volcano in the Terra satellite image is Shiveluch which is located in the northeastern part of the Terra satellite image.  Shiveluch is one of the most active stratovolcanoes in Kamchatka and was erupting a plume of ash when this image was taken (crater is circled in red).

Shiveluch has been active for at least 65,000 years with dozens of major eruptions and uncounted minor ones.  The eruptions are characterized by the collapse of lava dome complexes leading to debris avalanches and lahars (flows of ash and water).  The last major eruptions of Shiveluch were in 1854 and 1964.

The large circular area seen is a 9 km (5.6 mi) diameter caldera that is breached on its southern side.  The 1964 eruption formed the area of brown debris flows seen in the lower part of the image.

Scrolling around the large Terra satellite image, you can see a lot of other volcanic features (in some places, it almost looks like the area was struck by a storm of meteorites).  There's also a curious horsehoe-shaped structure near the center of the image.

It's an old volcanic caldera, breached to the southeast.  Extinct now, but once the site of a powerful explosive eruption that would have killed anything living within miles in that direction.

The river flowing north-south through the central part of the image also shows some neat features. It's a meandering river channel which is typically of a mature river in a relatively flat area.  The landscape, however, shows a number of scars indicating how the river channel has changed position over the years.

This is very similar to what's seen in the area of lower Mississippi River.  Meanders form loops in the river and the loops get cut off because rivers preferentially erode the outside bend of curves.  These loops then get left behind as horseshoe-shaped lakes called oxbows (note the oxbow to the left of the main river channel.  Eventually these oxbows stagnate into swamps and then fill in with sediments (as seen in the numerous scars in the image).

Another type of fluvial (stream-related) feature is seen in the river flowing east-west across the image.  There, we don't see meanders so much as we see a braided (anastomosing) channel.  These are typical of sediment-laden streams in flat areas typically draining off glaciers.

There are also some signs of life in this image with cultivated fields, a road, an airstrip and a town (right of the airstrip) in this incredibly remote place to live surrounded by constantly erupting volcanoes.

This is why Earth scientists like satellite image.  You can obtain a lot of information about an isolated area like this relatively easily.

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