The 6 x 7 km island of Savo consists of a forested andesitic-to-dacitic stratovolcano with a shallow, elliptical 1 x 1.5 km wide summit crater. Lava domes of historical age are located on the crater floor and its NE rim, and older domes occur on the flanks of the volcano. Pyroclastic flows and mudflows traveled down valleys from the summit crater to form debris fans along the coast. Thermal areas located in the summit crater, the south to SE flanks, and offshore include areas of steaming ground, fumaroles, small geysers, and hot springs. Spanish explorers arrived in 1568 during the first historical eruption of Savo. Pyroclastic flows during the climactic phase killed almost all inhabitants of the island, and oral traditions also note the expansion of the island on the northern side. Other eruptive episodes occurred during the mid-17th century and during the 1830s to 1840s.