The Giant Caldera Hidden Beneath Taal Lake

Long before Taal Lake as we know it today existed, in fact all the way back to prehistory, a massive volcano towered over the landscape of what is now the Province of Batangas¹. It stretched from the cliffs of Mount Maculot all the way to the arc of Tagaytay Ridge, forming a single volcanic structure far larger than anything visible today. The lake and the small Volcano Island are only the surviving fragments of this ancient mountain.

Scientists describe this lost volcano as a caldera‑forming system², meaning it once produced eruptions powerful enough to make the ground collapse into the emptied magma chamber below. A caldera is a wide, bowl‑shaped depression created when so much molten rock, or magma, is released that the surface above can no longer support its own weight. Geological studies estimate that the collapse of the original Taal dome happened sometime between 140,000 and 5,000 years ago³.

Many researchers narrow this window to roughly 27,000 to 5,000 years ago⁴, based on the age of volcanic deposits found around the lake. These eruptions were far stronger than anything recorded in modern history. They emptied a large portion of the magma chamber, causing the entire center of the old volcano to sink.

AI-imagined giant volcano that might have once towered over Taal Lake.

This previous mountain that towered over what is now Taal Lake is often mistaken to have been a supervolcano⁵, but this is not accurate. A supervolcano is defined as a volcano capable of producing a VEI‑8 eruption, the highest level on the Volcanic Explosivity Index. VEI‑8 eruptions release more than 1,000 cubic kilometers of material and can affect global climate for years.

Famous examples include Yellowstone in the United States and Toba in Indonesia⁶. Taal has never reached this scale. Its largest known eruptions are classified around VEI‑6, which are extremely powerful but still far below supervolcano levels.

This is why geologists describe Taal not as a supervolcano but as a caldera‑forming volcano — a volcano capable of producing major explosive eruptions strong enough to collapse its own structure, but not strong enough to qualify as a supervolcano. Over time, water accumulated inside the collapsed basin. At one point, the basin even had a natural channel that connected it to Balayan Bay⁷.

This connection allowed seawater to enter the lake, making it brackish. But in 1754, Taal erupted for nearly seven months, releasing so much volcanic debris that the channel was eventually blocked⁸. With the passage to the sea cut off, the lake slowly turned freshwater.

This freshwater, fed by springs around the basin and by rainfall, nurtured fish like the tawilis, maliputo, and muslo that Batangueños know well today⁹. Tawilis is especially unique because it is the only known freshwater sardine in the world, a species that adapted to the lake after it became isolated from the sea. Volcano Island, the small landmass in the middle of the lake, is not the original peak of the ancient volcano¹⁰.

It is only a surviving fragment of the old structure that remained above water after the giant mountain collapsed. What appears to be a small island today once sat deep inside the heart of a much larger volcano. The eruptions we see in modern times come from vents within this island, which now serves as the active center of the entire system¹¹.

Its eruptions in 1911, 1965, 1977, and 2020 are reminders that the forces beneath the lake remain active. The collapse of the old volcano’s dome and the formation of the caldera and lake also shaped Batangas Province’s history¹². It was in communities that grew around the lake that the Spaniards built among the first pueblos in Luzon.

From these pueblos would evolve the geopolitical units that are familiar in the present day: Lipa, Taal, Tanauan, and Bauan. These settlements grew around the lake’s resources, its fertile soil, and its strategic location. The landscape may look calm today, yet it carries the memory of eruptions powerful enough to reshape an entire province.