In the Philippines, on the island of Luzon, lies the Taal Lake, which boasts a remarkably rare geological structure. Within this lake is an island, and on this island, there is another lake, containing yet another island. Thus, the innermost island is known as the “island with a lake within a lake within an island,” making it the third layer of islands.
According to a report by Live Science, the island within Taal Lake is called Volcano Island, which is the volcanic crater of Taal Volcano. This crater has formed a lake known as the Main Crater Lake, and within this lake lies a small island called Vulcan Point.
According to the United Nations Educational, Scientific and Cultural Organization (UNESCO), this unique geological structure, formed by early volcanic activities and subsequent eruptions, essentially translates to “an island with a lake, a lake within the island, an island within the lake, and a lake within that island.” From outer to inner layers, they describe Luzon Island, Taal Lake, Volcano Island, Main Crater Lake, and Vulcan Point.
Taal Lake is a volcanic crater lake. Researchers believe that this crater was formed by a series of volcanic eruptions between 140,000 years BC and 5380 BC. However, significant changes in the lake’s topography have occurred since that time.
Taal Lake is a bowl-shaped basin that was formed when the top of Taal Volcano was blown off during a prehistoric volcanic eruption, creating the current volcanic crater lake. It was originally a saltwater lake fed by the sea, but is now fed by the Pansipit River. Early volcanic eruptions also formed Volcano Island near the center of Taal Lake.
UNESCO states that Taal Volcano experienced a major eruption in 1754, which deposited a significant amount of materials into the Pansipit River, isolating Taal Lake from the sea. The University of the Philippines notes that this event led to Taal Lake becoming a rainwater collection area and gradually transforming into a freshwater lake.
After the eruption of Taal Volcano in 1754, species trapped in Taal Lake adapted to the freshwater environment or evolved into new species, according to UNESCO. For instance, Taal Lake is home to the only known freshwater sardine in the world – the Tawilis (Sardinella tawilis), and it also hosts a toxic freshwater sea snake unique to the area – the Semperi Sea Snake (Hydrophis semperi).
UNESCO writes on its website, “The transition of Taal Lake from a saltwater to freshwater environment – in geological terms, a relatively recent event – has facilitated the continued evolution of flora and fauna, providing opportunities for ongoing scientific discoveries.”
Researchers have documented 38 eruptions of Taal Volcano in the last 450 years. The most recent eruption occurred in 2020, leading to the evacuation of residents in nearby towns as volcanic ash covered Volcano Island and its surrounding areas.
Taal Lake is the third largest lake in the Philippines and is part of the Taal Volcano Protected Landscape. However, data from the World Lake Database shows that the lake’s ecosystem is under threat from overfishing, tourism, and water extraction for irrigation purposes.