December 26, 2012

Sarychev Peak Eruption seen from the International Space Station

Sarychev Peak Eruption

A fortuitous orbit of the International Space Station allowed the astronauts this striking view of Sarychev Volcano (Kuril Islands, northeast of Japan) in an early stage of eruption on June 12, 2009. Sarychev Peak is one of the most active volcanoes in the Kuril Island chain, and it is located on the northwestern end of Matua Island. Prior to June 12, the last explosive eruption occurred in 1989, with eruptions in 1986, 1976, 1954, and 1946 also producing lava flows. Ash from the multi-day eruption has been detected 2,407 kilometers east-southeast and 926 kilometers west-northwest of the volcano, and commercial airline flights are being diverted away from the region to minimize the danger of engine failures from ash intake.

This detailed astronaut photograph is exciting to volcanologists because it captures several phenomena that occur during the earliest stages of an explosive volcanic eruption. The main column is one of a series of plumes that rose above Matua Island on June 12. The plume appears to be a combination of brown ash and white steam. The vigorously rising plume gives the steam a bubble-like appearance.

In contrast, the smooth white cloud on top may be water condensation that resulted from rapid rising and cooling of the air mass above the ash column. This cloud, which meteorologists call a pileus cloud, is probably a transient feature: the eruption plume is starting to punch through. The structure also indicates that little to no shearing wind was present at the time to disrupt the plume. (Satellite images acquired 2-3 days after the start of activity illustrate the effect of shearing winds on the spread of the ash plumes across the Pacific Ocean.)

By contrast, a cloud of denser, gray ash—probably a pyroclastic flow—appears to be hugging the ground, descending from the volcano summit. The rising eruption plume casts a shadow to the northwest of the island (image top). Brown ash at a lower altitude of the atmosphere spreads out above the ground at image lower left. Low-level stratus clouds approach Matua Island from the east, wrapping around the lower slopes of the volcano. Only about 1.5 kilometers of the coastline of Matua Island (image lower center) are visible beneath the clouds and ash.

Image Credit: NASA
Explanation from: http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=38985

9 comments:

  1. I have this photo from the year that it occurred. I always thought that the white dome on top is not steam rising. It is a phenomenon of a supersonic shock wave travelling through humid air. The shock wave is an expanding, spherical wave that has an N shaped pressure gradient, where the leading edge is intensely high pressure, with a very low pressure spike following just millimeters behind it. In this low pressure causes any water vapor to condense into visible "steam" for a less than a millisecond, before returning to ambient pressure. The reason why it appears to persist and remain visible, is that even at this altitude and time elapsed after the initial blast, there is still a supersonic shock wave expanding from the site and still propagating through the atmosphere, condensing an ever expanding shell of water vapor in its wake. I've seen this happen when jets break the sound barrier, but since a pressure wave diminished as a cube root of the radius to the source, usually lasting less than 1 second, and heard as a "sonic boom", this is one extremely loud event. That white dome is travelling over Mach 1 and would deafen you miles away.
    The explanation of the white dome as a pileus cloud makes sense, since it is well above the explosion's source. Is there any merit to my explanation? Or did I make a fool of myself on Google+?

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    1. You certainly did not make a fool of yourself. Your'e explanation has my vote.

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  2. How loud would that be from a distance of 1km at sea level?
    My guess is 210dB.

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  3. https://www.youtube.com/watch?v=1oHVMOWsVXk

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  4. I am sixty seven and still learning!

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