A thick blue haze stretches over the South Pacific archipelago of Vanuatu on the morning of 12 April 2010. The haze is volcanic fog – vog – emitted by the Gaua and Ambrym Volcanoes. Both are known for producing volcanic plumes rich in sulfur dioxide. This gas reacts with moisture in the air to create small droplets (called aerosols) of sulfuric acid, which scatters blue light, coloring the plume. This overview image shows the plume extending for thousands of kilometers to the northwest (upper left) and southeast (lower right) of the islands. Photo courtesy of NASA.