Hidden in the stormy Furious Fifties, the South Sandwich Islands generate spectacular cloud formations.
Winds sweeping past volcanic peaks create swirling vortex streets, while volcanic emissions brighten passing clouds. These islands, rarely visited by humans, are a natural lab for studying atmospheric and oceanic interactions.
Remote and Rugged Volcanic Peaks
The South Sandwich Islands are a remote chain of eleven volcanic peaks in the southern Atlantic Ocean. Located about 1,000 miles (1,600 kilometers) northeast of the Antarctic Peninsula, they lie within the Scotia Sea – a cold, iceberg-laden expanse shaped by the powerful Antarctic Circumpolar Current.
These steep, conical islands sit in the Furious Fifties, a stormy region known for strong westerly winds and frequent cloud cover. The interaction between these winds and the islands’ rugged terrain creates a variety of striking cloud formations, including wave clouds, volcano tracks, and lenticular clouds.
A Satellite’s View of Swirling Patterns
On February 24, 2025, the VIIRS (Visible Infrared Imaging Radiometer Suite) on the NOAA-20 satellite captured swirling air patterns behind three of the islands: Visokoi, Candlemas, and Saunders. These patterns, known as von Kármán vortex streets, form when wind flows past a tall, stationary object, creating alternating, spiraling eddies.
These vortex streets appear in Earth’s atmosphere when moderate winds, ranging from 18 to 56 kilometers (11 to 34 miles) per hour, push marine stratocumulus clouds past elevated landforms under stable atmospheric conditions. When winds are too weak, clouds move smoothly around obstacles. When they are too strong, the vortices break apart and lose their distinct structure.
A Mathematician’s Legacy in the Sky
The features are named after Theodore von Kármán—an accomplished mathematician, aerospace engineer, and one of the Jet Propulsion Laboratory’s founders. He was the first to describe the oscillating flow features in mathematical terms while working as a graduate assistant in 1911.
Small particles produced by volcanic activity also appear to have slightly brightened the trail of clouds extending from Saunders Island, explained Santiago Gassó, a University of Maryland atmospheric scientist. Gassó has studied how weak volcanic activity from the island’s Mount Michael volcano regularly modifies passing clouds.
How Volcanoes Influence Cloud Behavior
Scientists have observed cloud brightening—also called the Twomey effect—for decades. Clouds with extra particles from volcanic emissions have more and smaller cloud droplets than normal clouds. This means there are more surfaces to reflect light, making volcanically “polluted” clouds appear brighter than others. The same process produces bright ship track clouds over the ocean, except in that case the extra particles come from ship exhaust.
“A volcano track is most noticeable in marine stratus cloud decks when the cloud base is within a few hundred meters from the volcano top,” Gassó said. “That is often the case at Saunders Island and other high-latitude islands. It is less common to see the phenomenon in tropical regions,” he said.
Mount Michael’s Persistent Eruptions
Satellite observations indicate that emissions of sulfur dioxide and other gases are common at Mount Michael, which has a lava lake roiling deep inside its central crater and has been weakly erupting since 2014. Multiple satellite sensors, including the TROPOMI (Tropospheric Monitoring Instrument) on Sentinel-5P, observed enhanced levels of sulfur dioxide on February 24, said Michigan Tech volcanologist Simon Carn.
“The South Sandwich Islands are an excellent ‘natural laboratory’ for studying the impact of volcanic emissions on clouds,” Carn said. “But we have to rely on satellite observations due to the inaccessibility and remoteness of the islands.”
Icebergs in the Scotia Sea
To the west of the island chain, several small icebergs float visibly beneath a thin cloud layer. The Antarctic Circumpolar Current often steers icebergs, which have broken off ice shelves in Antarctica, toward the Scotia Sea—an area known among glaciologists as a place where icebergs go to die as they encounter warmer water and air.
Though the incoming icebergs will not last forever, they may be helping support life in the region. Some research indicates that icebergs drifting into the Scotia Sea are often hotspots of biogeochemical and ecological activity, bringing elevated numbers of phytoplankton, krill, and seabirds with them.
A Penguin Paradise
Should any of these seabirds find their way to Zavodovski Island, they will have company. The island is thought to have one of the largest colonies of chinstrap penguins in the world. The South Sandwich Islands are also frequented by seals, whales, and several types of fish.
NASA Earth Observatory image by Wanmei Liang, using VIIRS data from NASA EOSDIS LANCE, GIBS/Worldview, and the Joint Polar Satellite System (JPSS).
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