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Volcanoes, Vog, and Vortices

Volcanoes, Vog, and Vortices

Astronauts aboard the International Space Station oriented the camera specifically to capture this panorama of Hawaii’s Kilauea volcano with long swirls of volcanic gases wafting to the west. Astronauts are trained to take images of hard-to-see atmospheric haze by shooting obliquely to enhance visibility.

The haze, or “vog”—a combination of fog, smog, and volcanic gas—is well known to Hawaiians. Vog is scientifically defined as “a visible haze comprised of gas and an aerosol of tiny particles and acidic droplets, created when sulfur dioxide and other gases chemically interact with sunlight and atmospheric oxygen, moisture, and dust.” (Hawaiian Volcano Observatory).

In this photograph, the vog haze is transported hundreds of kilometers downwind of the volcano; for scale, the Big Island of Hawaii is 137 kilometers (85 miles) long. The vog forms a series of subtle, but distinct alternating swirls known as von Kármán vortices, a favorite subject for astronaut photography. Click here to view an animation of alternating vortices being shed from an island can be seen here. These vortices form under specific conditions of high atmospheric pressure and relatively slow wind speeds. They usually show up in clouds downwind of islands, as shown in this astronaut photo of cloud patterns over the Kuril Island chain. Images of vog haze are captured often by astronauts, but few show the von Kármán phenomenon.

Astronaut photograph ISS042-E-281151 was acquired on February 18, 2015, with a Nikon D4 digital camera using a 78 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 42 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by M. Justin Wilkinson, Texas State University, Jacobs Contract at NASA-JSC.