At the western end of the Samoan Island chain lies Savai'i. Stretching over 1,682 sq km (649 sq mi), Savai'i is one of the largest landmasses in Polynesia. The mountainous island is a shield volcano that reaches its highest altitude, 1,858 m (6,095 ft), near the center of the island. The region's tropical, humid climate sustains vegetation that carpets much of the island. A jagged line of small, round volcanic craters extends east-west across the island (top of image). South of this uneven line, two deep, parallel valleys extend toward the south. The semicircular contours of the valleys suggest that they might be the remains of an ancient caldera or collapsed magma chamber that was modified by the later eruption of additional lava. With the exception of a few brown crater rims, and a coastal settlement along the image's left edge, the landscape appears in varying shades of green. Dense rainforests cover the island's rugged interior, and thick vegetation also thrives along the coastal plains. Savai'i has remained volcanically active into historical times, with two eruptions occurring in the early 20th century. The eruptions sent big lava flows to the island's northern coast, destroying several villages. Photo courtesy of NASA.