Mount Tambora (or Tamboro) is an active stratovolcano which is a peninsula of and the highest peak on the island of Sumbawa in Indonesia. Sumbawa is flanked both to the north and south by oceanic crust, and Tambora was formed by the active subduction zone beneath it. This raised Mount Tambora as high as 4,300 m (14,100 ft), making it one of the tallest peaks in the Indonesian archipelago in the 18th century. After a large magma chamber inside the mountain filled over the course of several decades, volcanic activity reached a historic climax in the eruption of 10 April 1815. This eruption had a volcanic explosivity index (VEI) of 7, the only unambiguously confirmed VEI-7 eruption since the Lake Taupo eruption in about AD 180. (The 946 eruption of Paektu Mountain might also have been VEI-7.)