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Showy Swirls Around Jeju Island - NASA Science
science.nasa.gov
On February 19, 2026, a NASA satellite captured a striking image of colorful water and swirling cloud patterns around Jeju Island, which is part of South Korea. The island is located about 100 kilometers south of the Korean mainland in the ocean.
The highest point in all of South Korea is not on the mainland. It is Hallasan, a broad, flat volcano on Jeju Island. This massive volcano rises 1,950 meters (6,400 feet) above the sea. Its last known eruption was about a thousand years ago, in the 11th century.
The swirls in the clouds are known as von Kármán vortex streets. These spirals form when wind or other fluid flows around a tall, solid object that blocks its path. Jeju Island, with its tall volcano, acts like that object in the wind.
Scientists explain that the wind speed must be just right for these patterns to appear. If the wind is too slow, clouds simply drift past the island. If the wind is too fast, it becomes too chaotic for swirls to form clearly. The ideal wind speed is between 18 and 54 kilometers per hour. At this speed, the air flow creates alternating swirls that spin in opposite directions behind the island. In this particular image, the swirls look soft and wispy. At other times, they can form sharper, more defined parallel rows of clouds.
In mid-February 2026, the seas around Jeju Island were also very active. The satellite image shows large areas of colorful, churning water. A prominent brown plume of water can be seen stretching west of the island. This plume is full of sediment, which are tiny bits of rock and soil.
This sediment originated from the coast of China's Jiangsu province. The shallow coastal waters there are always murky and brown. However, very large plumes like this one are especially common during winter. Seasonal changes are the likely reason for this. In winter, ocean currents and the mixing of different layers of water change. These changes can stir up more sediment from the sea floor, creating these large, visible plumes that drift far from the coast.
The image was taken by an instrument called MODIS. MODIS stands for Moderate Resolution Imaging Spectroradiometer. It flies on NASA's Terra satellite, which orbits Earth. This instrument helps scientists monitor and study the planet's land, oceans, and atmosphere.