[1] The caldera forms the middle lobe of Laguna de Bay, bound by the Morong Peninsula and Talim Island to the west, and the Jalajala Peninsula to the east.

The caldera may have formed in two stages about 1 million and 27,000-29,000 years ago, during which time at least two major explosive eruptions took place.

[1] Deposits from the caldera form thick ignimbrite sheets in Rizal, Metro Manila, Laguna, and Bulacan.

[2] Remnants of volcanic activity include undated maars at the southern end of Talim Island and a solfatara field on nearby Mount Sembrano.

[1] Given the current shape of the lake and the caldera, and how it was once connected to Manila Bay as evidenced by its ground drill geology, its formation is speculated to have been a result of an even earlier cataclysmic eruption, pointing to a possibility that it was once a volcano of considerable elevation that exploded, similar to Krakatoa.