Often regarded as the southeastern border of Europe, the Caucasus Mts stretch from the Black Sea (left) to the Caspian Sea (right). The mountain range spans 1,125 km (700 mi), forming part of the southern Russian border, and crossing Georgia, Armenia, and Azerbaijan from left to right respectively. With a snowline of approximately 3,350 m (11,000 ft) and many peaks over 4,500 m (14,760 ft), much of the snow seen in this image is present year round. Also visible in this photo are apparent phytoplankton blooms in the Caspian Sea, marked by blue-green swirls. Image credit: NASA.