islands

Lakes on Islands in Lakes: Toba and Taal in Indonesia and the Philippines

Article-Grid, GeoNotes, Islands, Physical Geography / By

For those interested in geographical superlatives pertaining to islands and lakes, Elburz.org has an interesting list, beginning with the world largest island (Greenland) and largest lake (Caspian Sea). It continues with the largest lake on an island (Nettilling Lake on Baffin Island in Canada), the largest island in a lake (Manitoulin Island in Lake Huron in Canada), the largest island in a lake on an island (Samosir in Lake Toba on Sumatra in Indonesia), the largest lake on an island in a lake (Lake Manitou on Manitoulin Island in Lake Huron in Canada), the largest lake on an island in a lake on an island (Crater Lake on Volcano Island in Taal Lake on Luzon in the Philippines), the largest island in a lake on an island in a lake (unnamed island in Mindemoya Lake on Manitoulin Island in Lake Huron in Canada), and the largest island in a lake on an island in a lake on an island (Vulcan point in Crater Lake on Volcano Island in Taal Lake on Luzon in the Philippines).

Two of the lakes in question were formed in volcanic craters, Taal in the Philippines and Toba in Indonesia. Massive volcanic explosions in the past produced the depressions that eventually formed these lakes, while subsequent volcanism built up the islands within them. The Toba Event—the supervolcanic eruption of the Toba volcano that occurred some 69,000-77,000 years ago—is believed by some scientists to have plunged much of the world into a decade-long volcanic winter that reduced the global human population to a mere 1,000-10,000 breeding pairs.

Past eruptions of Taal Volcano were never as devastating as the Toba Event, but Taal is still counted as one of the world’s sixteen most potentially deadly volcanoes. Taal Lake is of note mostly for its biological oddities. Taal was once a salt-water bay; after it was separated from the sea, it turned fresh gradually, allowing a number of oceanic species time to adjust to freshwater conditions. Taal thus supports freshwater sardines as well as a freshwater sea snake. It once had bull sharks as well, but they were exterminated by local fishermen in the 1930s. Bull sharks live in freshwater environments elsewhere in the world, including Lake Nicaragua.

René-Levasseur: The World’s Second Largest Island in a Lake?

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The Wikipedia’s list of the world’s largest islands in lake has some intriguing features. Four of the top seven positions are occupied by islands in North America’s Great Lakes: Manitoulin Island in Lake Huron (or Lake Michigan-Huron, which is actually a single lake), Isle Royale in Lake Superior, St. Joseph Island in Lake Huron, and Drummond Island, also in Lake Huron.

While Manitoulin is clearly the world’s largest lake island, the second position entails some ambiguity. Until the turn of the millennium, Vozrozhdeniya Island in the Aral Sea was the second largest island in a lake, but the shrinkage of the Aral subsequently turned it into a peninsula then caused to disappear completely as a geographical feature. Currently René-Levasseur Island in Quebec’s Lake Manicouagan occupies the second slot. Lake Manicouagan, however, is an artificial reservoir, created by the damming of the Manicouagan River in the 1960s. Unique among large lake islands, René-Levasseur is larger than the lake that surrounds it; the island covers 2,020 km2 (780 sq mi), whereas the area of the lake is 1,942 km2 (750 sq mi).  

         Together, René-Levasseur Island and Lake Manicouagan make an interesting geographical feature, easily discernable from space. Due to the near circularity of both the lake and the island, they are sometimes called the “eye of Quebec.” Such circularity derives from the feature’s origin as an asteroid impact crater some 214 million years ago. The crater was originally around 100 kilometers wide, but erosion and sedimentation gradually reduced the depression to a width of around 72 kilometers. Until the damming of the Manicouagan River, two crescent-shaped lakes occupied the periphery of the depression. Once the dam was completed, the two lakes merged together to form what is now Manicouagan reservoir.