Volcanic Plume Over Southern Atlantic Ocean Revealed
Through False-Color Imagery
The South Sandwich Islands, in the far southern Atlantic Ocean, are often
shrouded with thick cloud, making it difficult to view the region from space.
Sometimes, however, the use of false-color imagery can be used to reveal events
that would otherwise be obscured under cloud cover.
The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite flew over the South Sandwich Islands on April 19, 2014 and acquired
this false-color image of the cloudy scene.
This false-color image uses a combination of non-visible (middle infrared and
infrared) and visible (red) light captured in bands 7, 2, and 1, respectively,
to distinguish clouds from snow and ice. Here the ice-covered islands appear
bright turquoise, the clouds light turquoise and the water in the ocean appears
deep black. Because the volcanic plume is a moist mixture of gas and ash, it
reflects all three forms of light relatively well, so it appears nearly
white.
In the north of this image, a thin plume of white rises from the volcano on
Zavodovski island, the northernmost of the South Sandwich Islands and streams to
the northeast. Further south, a wider white plume can be seen blowing across the
Atlantic Ocean. This plume rises from the Mount Michael volcano, which is a
young and frequently active stratovolcano located on Saunders Island, near the
center of the South Sandwich Island chain.
The white plume from Mount Michael forms a chain of swirling eddies as it
blows to the northeast. To the south, similar eddies can be seen behind three
other islands. These are known as Von Kármán vortices. These vortices can form
nearly anywhere that fluid flow is disturbed by an object. Because the
atmosphere behaves like a fluid, when streaming air hits a blunt object, such as
a mountain peak, the wind is forced around the object. The disturbance in the
flow of the wind propagates downstream in a double row of vortices that
alternate their direction of rotation, much like the eddies seen behind a pier
in a river as water rushes past.
Image Credit: Jeff Schmaltz/MODIS Land Rapid Response Team, NASA
GSFC
NASA
Guillermo Gonzalo Sánchez Achutegui
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