May 12, 2014 - Track from Mount Michael volcano, South Sandwich Islands (false color)
The South Sandwich Islands, in the far southern Atlantic Ocean often lie under thick cloud cover. When clouds are thick, false-color imagery can help distinguish features which would be hidden from view in true-color images.
On May 1, 2014 the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite flew over the South Sandwich Islands and captured this false-color image of the volcanic track from Mount Michael volcano. This view is a combination of middle infrared, infrared and visible (red) light (MODIS bands 7,2 and 1). This combination was chosen to help distinguish clouds from snow and ice – and from warm volcanic plumes.
Six islands can be seen in this image, four of which lie under a heavy cloud cover. Two (Thule Island and Cook Island) can be seen at the lower edge of the image and appear as light-colored ovals against the ink-colored ocean waters. The clouds are filled with cold water droplets and ice crystals, and appear light turquoise. The ice-covered islands are also turquoise. Those shrouded by cloud can also be spotted by the ship-wave shaped wave cloud fanning out behind each island’s tall peak, looking like the ripples behind a rock in a stream or the waves behind a boat moving through calm water. These wave clouds are formed when a forward-flowing mass of air hits an obstacle, then flows around it.
Near the center of the image a ship-wave shaped cloud fans out from behind Saunders Island, home to the Mount Michael volcano. A white plume rises from the volcano and trails through the turquoise clouds between the turbulent waves. This is a volcanic track, and appears white because the gas, steam and ash in the volcanic plume reflect all three wavelengths of light, making it very light and bright in the image. Researchers have learned that even small eruptions can affect cloud cover and weather. The tiny solid and liquid particles in the plume (aerosols) act as seeds for the formation of cloud droplets. However, those particles and droplets are much smaller than those in other types of clouds, appearing brighter and denser.