Volcanoes, Clouds, and Swirling Winds

Volcanoes, Clouds, and Swirling Winds

Zavodovski Island is but five miles wide, uninhabited by humans, and about as remote a place as you can find on Earth. It is the northernmost in the chain of the volcanic South Sandwich Islands, and its dominant feature is Mount Curry volcano. Yet this tiny bud of land can do compelling things to the sky around it.

The natural-color image above shows the interplay of low-level volcanic emissions, clouds, islands, and winds in the far South Atlantic (or Southern Ocean). It was acquired on April 27, 2012, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite.

Previous research has shown that low-level volcanic emissions (as opposed to explosive eruptions) can affect the atmosphere, and that appears to be what is happening here. Mount Curry has been known to emit steady streams of gases and aerosols—tiny solid and liquid particles. Aerosols are key to the formation of clouds, as they provide a nucleus around which water molecules can accumulate to form droplets and, ultimately, clouds.

In the case of Mount Curry and Zavodovski Island, the sulfate aerosols from the simmering volcano are just enough to seed clouds in the air masses passing over the island. Note how the plume stretching north is brighter than the surrounding clouds, a result of the small aerosol particle size and the numerous small water droplets that form around them. The smaller droplets provide more surfaces to reflect light.

To the southeast, Visokoi Island also disturbed the atmosphere in this image. It’s not clear whether gas and aerosols were being emitted from Hodson Volcano—the wider region has rumbled with some earthquakes lately—or if the interesting cloud vortices are created by topography. Like ships streaming through water, islands can create wakes in the cloud patterns above them. Visokoi stands 3,295 feet (1,005 meters) above the water line, and as prevailing sea winds push past, the jut of the island into those low-level marine clouds alters the flow of winds and air masses enough to affect their shape.

NASA image by Robert Simmon, based on data provided by Jeff Schmaltz, LANCE MODIS Rapid Response. Caption by Mike Carlowicz.

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