The South Sandwich Islands #

The South Sandwich Islands
Image courtesy of NASA., under PD
The South Sandwich Islands are often shrouded with thick clouds, 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.

This satellite image uses a combination of non-visible (middle infrared and infrared) and visible (red) light 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.

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.