Nightingale Island and the adjacent smaller Middle (or Alex) and Stoltenhoff Islands and associated small islets are the southernmost of the Tristan da Cunha island group.  The heavily eroded Nightingale Island consists of early and late stage ash and agglomerate units with intervening massive trachytic intrusions and lava flows.  Volcanic rocks were K-Ar dated at between 0.4 and 0.15 million years, and a radiocarbon date of about 39,000 yrs BP was obtained from an ash layer overlain by a lava flow.  An earthquake swarm lasting 6 hours beginning on July 29, 2004 was followed by observation of large blocks of floating phonolitic pumice that washed up on Tristan da Cunha.  The event was considered to have originated from an eruption associated with an earthquake swarm 37-53 km SSE of Tristan da Cunha on the submarine SE flank of Nightingale Island.