Background The Taal caldera is largely filled by Lake Taal, whose 267 sq km surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and contains several eruptive centers submerged beneath the lake. All historic eruptions took place from the 5-km-wide volcanic island in the northern-central part of the lake. The island is formed by overlapping stratovolcanoes, cinder cones and tuff rings (maars). Historic eruptions have seen the constant change and growth of the island. Taal caused one of the worst volcano disasters in history: its eruption in 1911 killed 1334 people and caused ash fall as far as Manila city. Due to its devastating potential, Taal was declared one of the "Decade Volcanoes" in the Decade Volcanoes program of the 1990s in order to incentive study and monitoring of the volcano. Taal is today one of the most closely monitored volcanoes in the region. An increase in seismic activity under Taal was recorded in November 2006, followed by an increase in hot water springs in the crater in April 2007.