Lake Toba, Indonesia

Lake Toba, the largest volcanic lake in the world, was created after the catastrophic volcanic eruption of Mount Toba in Indonesia approximately 74,000 years ago.

The world ended around seventy thousand years ago–or that’s how it would have seemed for any creature within a few thousand miles of what is now the province of North Sumatra, Indonesia. Scientists estimate that roughly 74,000 years ago, Mount Toba erupted in one of the largest volcanic events in the past two million years. The explosive eruption deposited ten billion tons of ash into the atmosphere, an amount 10,000 times greater than was ejected during the eruption of Mount St. Helens in Washington State in 1980 and more than 100 times than what the famous Krakatoa eruption spewed forth in 1883.

People, animals, and plants within a few thousand kilometers of the Toba eruption were wiped out completely, and nearly all humans from Java to the southern border of modern-day Iran were likely killed. To the north, all of India was covered in a minimum of 15 cm (6 inches) of ash, with some areas seeing ash deposits of up to 6 meters (20 feet). Ash deposits in the vicinity of the eruption were as thick as 600 meters (2,000 feet). Sulfates from the Toba explosion have been detected in ice cores taken from as far north as Greenland and as far south as the Antarctic. These sulfates would have lingered in the upper atmosphere for years leading to a rapid cooling of the planet by 4°C (7°F) that would have sparked a decade-long volcanic winter. Such dramatic cooling would have resulted in widespread ecological disaster and significantly reduced food availability as plant and animal species that were unable to adapt to the sudden climatic change died off.

There is some debate among scientists regarding the effect the eruption had on early human populations. Some speculate that there were only about 85,000 humans in total on the planet at the time, centered mainly in Africa with some beginning to migrate into the Asian continent. The so-called “bottleneck” theory holds that the eruption and its aftermath reduced the overall human population on earth to fewer than 5,000 individuals and that all people alive today are descendants of this narrow band of lucky survivors. In essence, the eruption acted as a kind of reset button for the human population, with devastating consequences for those living in Asia and the South Pacific. It was, according to some researchers, the closest humans have come to extinction that we know of.

However, new research conducted over the past decade has resulted in a reevaluation of the genetic bottleneck theory. Some scientists have suggested that the devastation caused by the eruption was not uniform, and that in fact certain pockets of human habitation, most notably in southern Africa, were spared the worst of the impacts. Paleoanthropologists working in South Africa found an ash layer that corresponds to the Toba eruption, but evidence examined from just above, within, and below this layer does not indicate a reduction in human activity. Rather, researchers found more than 400,000 artifacts left behind by humans, ranging from heat-treated stone tools to animal bones and signs of fire. This indicates that modern human populations on the South African coast thrived after the eruption, remaining at the site for thousands of years, indicating that these African populations were not significantly impacted–much less wiped out–by the force of the blast. It is possible that this area acted as a kind of refuge from the worst effects of the eruption, perhaps because South Africa’s east coast provided adequate fishing and foraging stocks to sustain a sizable human population.

As cataclysmic as the Toba eruption was, it had a silver lining from a scientific perspective. The layer of ash it left behind–across nearly the entire surface of the planet–serves as a kind of temporal line in the sand (quite literally) whereby scientists are able to connect human activity in Africa and Asia with climate indicators and biological activity elsewhere around the world within a remarkably narrow timeframe. Since the eruption lasted an estimated ten to fourteen days, with ash raining down across the globe shortly thereafter, it is possible for scientists to connect weather events or animal populations or human activity in one part of the world with those anywhere else the ash layer is unearthed. While the exact year of the Toba event may never be known, the presence of Toba ash provides an unprecedented window of simultaneity into world events at the time of the eruption.

While the degree of global catastrophe brought about by the eruption remains in dispute, there is no doubting the resulting magnificence of the lake created in its wake. Over the course of the next 1,500 years, rainwater drained into the caldera and created the largest volcanic lake in the world and the second largest lake globally after lake Victoria in Africa. Like many of the world’s largest lakes, it appears more like an ocean than a lake when viewed from the shore. The caldera, easily visible from space due to its size, measures roughly 100 km (62 miles) long and 30 km (19 miles) wide. Once the water levels stabilized, the caldera’s central mound became an island in the middle of the lake with an area equal in size to the country of Singapore.

Samosir Island was formed by upward pressure of magma deep within the caldera that lifted the floor of the crater until, around 30,000 years ago, it broke through the surface of the lake. Lake sediments present on the island indicate that it has risen around 450 meters (1,476 feet) since the eruption and is still growing. (Chances are, at some point in the future, the caldera will erupt again.) This enormous earthen dome, approximately 50 kilometers (30 miles) long and 15 kilometers (10 miles) wide, occupies a large part of the lake’s center and is home to some 100,000 people.

The island is the cultural home of the Toba Batak people, an indigenous group native to North Sumatra. The first Batak village, Sianjur Mulamula, was built on the western shore of the lake and it was from this location that the Batak people fanned out into the surrounding hills and Samosir Island. Early accounts of encounters with the Batak people described their practice of eating the bodies of captured enemy warriors. Notably, Marco Polo’s memoirs mention an indigenous group from Sumatra known to consume human flesh. The first European explorers to reach Lake Toba in the late 18th century also reported witnessing ritual cannibalism among the Batak, although some of these accounts were likely exaggerated for narrative effect. According to Batak religious tradition, consuming the body parts of another allowed for the absorption of the deceased person’s ancestral spirit. Some elders, well into the 20th century, recounted stories of their grandparents eating human remains. Contemporary Bataks no longer engage in the practice, however. The Toba Batak began converting to Christianity in the late 20th century with the arrival of German missionaries, and today the vast majority of Batak practice some form of Christianity.

As is the case with so many lakes and waterways around the world, climate change and human activity have and continue to take a toll on the lake’s ecosystem. Where large volumes of water flow, hydroelectric power usually follows, and Lake Toba is no exception. Water from the lake drains east via a single primary channel–the Asahan River–which, after a series of construction projects in the 1980, hosts a number of hydroelectric power stations that supply electricity to lesser-developed areas of northern Sumatra. Many villages on the shores of the lake farm fish in large floating net cages. There are over 12,000 of these giant submerged fisheries throughout the lake, most of which operate well beyond their rated capacity; a cage that should hold 3,000 to 5,000 fish, for example, will contain upwards of 10,000. The food required to feed this many fish creates an abundance of phosphorus in the water that, combined with raw sewage inflows and agricultural runoff, results in a hyper-eutrophic condition, meaning the water contains excessive nutrients that create dead zones with low oxygen levels. As a result, in 2016 increasing pollution levels in the lake killed off 1,500 tons of fish. In response, the local government in the lakeside village of Sualan sent in 600 military personnel and police to force the dismantling of the cages in a bid to curb pollution. In addition, industrial pollutants and other contaminants enter the lake via 25 rivers that drain into it. Funding for wastewater treatment facilities has been provided in some municipalities by foreign investors, but the lack of underlying infrastructure, namely sewer lines, has made widespread application of sewage treatment a challenge.

And yet, although literally created from the ashes of a global cataclysmic event, Lake Toba has evolved into a scenic and cultural touchstone for the area’s indigenous groups, locals, and tourists. In service of this, the Batak Museum, part of the larger TB Silalahi Center complex, opened to the public in 2011. Dedicated to the preservation of the cultural values and history of the Batak, the museum contains artifacts dating back 500 years, and includes an outdoor mock Batak village featuring three rumahs (houses) and three sopos (storage structures) built in the traditional style.

Is it possible to view a nearly world-ending event in a positive light? Perhaps for the people who were alive to witness it the answer would be “no.” But for those of us here today, who can to a person trace our ancestry back to a few bands of hearty (and perhaps lucky) survivors, the Toba event demonstrates that what may have been a calamity in one era can become a gift for another.


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