The 2 x 3.5 km forested island of Blup Blup contains lava flows with well-defined flow fronts. Weak thermal areas are located on the W and N coasts. Most eruptive activity at the andesitic-dacitic volcano originated from a summit crater about 800 m in diameter, although there may be a lava dome on a ridge to the W and a small satellite cone along the SW coast. Reports of eruptions in 1616 and 1830 are erroneous, but there may have been eruptions during the Holocene (Johnson, 1990 p.c.). Blocks from a submarine debris avalanche lie to the NE of the island.