Lake Toba is a volcanic lake in North Sumatra Indonesia that measures 100 x 30 square kilometers, making it the largest crater lake in the world. In the middle of the lake there is an island that was formed by resurgent volcanic activity which is called Samosir Island .
Lake Toba has long been one of the main tourist attractions in North Sumatra along with Bukit Lawang and Nias island, and is
visited by both foreign and domestic tourists.
It is estimated that Lake Toba was formed as a result of a volcanic eruption around 73,000 – 75,000 years ago, which constituted the most recent super-volcanic eruption.
Bill Rose and Craig Chesner from Michigan Technological University estimated that volcanic materials that were spewed out of Mount Toba (soon to be Lake Toba) totaled an amazing 2800 cubic kilometers, with 800 cubic kilometers of ignimbrite rock and 2000cubic kilometers of volcanic ash that is estimated to have blown to the west for 2 weeks. This incident caused mass death and destruction and was the cause of the extinction of several species, and the near demise of humans. According to DNA evidence, this event caused a bottleneck in the human population of the planet, shrinking the population down to perhaps 15,000 individuals after the eruption and its after effects.
After this eruption, a caldera was formed that was gradually filled with water, becoming what we know today as Lake Toba .
The pressure from magma below the caldera has led to uplift resulting in the emergence of Samosir Island . Samosir was originally a peninsula attached to the mainland by a narrow isthmus, but the Dutch constructed a 10 meter wide canal which bisected this tiny isthmus, effectively making Samosir a de facto island.