The elliptical, 10 x 20 km wide caldera of Laguna de Bay is located immediately SE of Manila city, Philippines. It is the largest lake on Luzon Island and its surface is only 1 m above sea level.
Jalajala is a fumarole field on the flank of Mount Sembrano on the shore of Laguna de Bay.
Pre-caldera eruptions formed basaltic to basaltic-andesitic volcanoes, including the extinct Talim Island and Mount Sembrano stratovolcanoes located on opposite sides of the current caldera.
The caldera has formed during at least 2 major explosive eruptions about 1 million and 27,000-29,000 years ago.
Activity after the caldera formation consisted in the formation of explosion craters on the southern end of the Talim Island at the SW rim of the caldera. Some of these maars are young, but their precise ago is unknown.
