Travel

Lake Toba – An Explosive History

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The most cataclysmic event for humans happened right in Malaysia’s backyard. It may have led to a decimation of Homo sapiens, but also may have indirectly resulted in unleashing of the characteristics that make us most human. If you think this event is the 2004 Indian Ocean tsunami, you’ll have to go back a bit further – about 75,000 years further. 75,000 years ago, there were still several subspecies of the Homo genus roaming the planet, most notably Homo neanderthalensis and the recently discovered Homo floresiensis (a ‘hobbit-like’ subspecies found on the Indonesian island of Flores). All were hunters and gatherers, and all could craft and use primitive stone tools.

Of these, perhaps it was only Homo sapiens that might’ve looked up and recognised the ominous dark skies as a potential threat. But even with a brainspan of about 1400cc (equal to our own), Homo sapiens were still a long way from the cognition and creativity of our own subspecies (Homo sapiens sapiens, or ‘very wise man’), but the anatomy was likely sufficient to comprehend the imminent dangers that lay ahead. The skies indeed turned black as 800 cubic kilometres of ignimbrite (compacted pyroclastic rock) all but destroyed everything in its path and 2,000 cubic kilometres of rhyolite ash virtually enshrouded much of the planet. The next thousand years would prove very difficult for our ancestors…

They couldn’t have known what happened, or why, or where this black rain of destruction originated. It was only much later that we began to learn what happened in those fateful weeks. Lake Toba lies about 300km east of Kuala Lumpur, on the Indonesian island of Sumatra. Located at an altitude of 800m, the lake is 100km long and 30km wide, and today is dotted with highland resorts and traditional houses of the Toba Batak people. Samosir Island dominates Lake Toba, and as it’s only about a 5-hour drive from the city of Medan, it’s popular with tourists seeking hiking excursions, a cool break from the tropical climate, or a serene getaway (though check with a tour operator before you plan a trip).

But 75,000 years ago, the area was anything but serene. In 1949 the Dutch geologist van Bemmelen discovered Lake Toba was surrounded by a vast layer of ignimbrite – a telltale feature of past volcanic activity. Since then, rhyolite ash similar in composition has been found in Malaysia – and as far away as India. Lake Toba was undeniably the remains of a past volcano. By today’s definition it was a ‘supervolcano,’ and the most recent in geologic history. The scope of Toba’s fury –ejecting about 3,000 times more material than the 1980 Mount St. Helens eruption – is hard to comprehend even with our modern big brains. (For comparison, I clearly remember volcanic ash falling on my hometown – 1,800km from St. Helens).

The huge eruption is estimated to have lasted two weeks, but it was to have a devastating effect on the planet’s ecosystem for a thousand years. Some scientists estimate the eruption led to a decrease in average global temperatures by 3 to 3.5 degrees Celsius for decades, while others go so far as to say the Toba eruption accelerated the Wisconsinian glaciation (the last major advance of continental glaciers) of the last ice age. Though the Toba eruption’s connection to glaciation is unclear, its link to the population of the Homo genus is supported by a wealth of evidence. In those first decades after the eruption, the population of Homo sapiens declined dramatically, and was most likely broken into small isolated groups.

The evidence that all living humans today are descended from one prehistoric population comes from both mitochondrial DNA coalescence and the relatively small variations in the human Y chromosome seen today. A ‘population bottleneck’ occurred, during a period coinciding to a time immediately following the Toba eruption. A ‘population bottleneck’ (an event witnessed in many natural species) is also seen to increase genetic drift. In layman’s terms, genetic drift means small populations exhibit a larger variation of traits than in a large population. By all scientific evidence, ‘our’ small isolated pocket of Homo sapiens – the one that all living humans descend from – was once decimated to a population of less than 10,000. It’s hard to believe, but humans were once an endangered species.

Other pockets of Homo sapiens populations died out, as eventually did Homo neanderthalensis (30,000 years ago) and Homo floresiensis (12,000 years ago). We were alone to again fan out from Africa and repopulate. But what did this all mean to our Homo sapiens ancestors? Did the added stress of the climate following the Toba eruption, combined with a decimated population, bring humanity from Homo sapiens to our present Homo sapiens sapiens subspecies?

Those are questions that are still hotly debated among palaeo-anthropologists, but it was only after the Toba eruption that evidence shows us beginning to exhibit the traits that make us most human – sapience and sentience, culture and creativity. It should be noted that, as in all true science, the causal relationship between the Toba eruption and the population bottleneck of Homo sapiens, the cause of the spark humanity’s more advanced characteristics, and the subsequent migration of Homo sapiens sapiens out of Africa are only theories that are based on available evidence. Competing theories exist, and none can ever be truly proven. (Even Prof. Stanley Ambrose, major proponent of the Toba catastrophe theory, uses the term “may have caused severe bottlenecks in humans.”)

What is entirely factual, however, is that the evidence exists. 75,000 years ago, a supervolcano erupted that left us the Lake Toba crater and a layer of rhyolite ash that in places is over 3m thick. At about the same time Homo sapiens survived through an extreme population bottleneck, in which the ancestry of today’s worldwide population – less than 10,000 souls – barely squeezed through.

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The debate will rage on amongst scientists, skeptics, and armchair anthropologists about the theories, but the evidence puts Malaysia and this region of the world directly in the spotlight. New discoveries from your ‘home away from home,’ such as that of Homo floresiensis, are adding to our wealth of knowledge about the natural world. Lake Toba is calm today. The skies are clear azure, the air cool and moist. When you look up from your resort chair, or trekking path, or lake canoe, you’ll feel at peace, finely attuned to the bounty of nature around you. And if you listen closely, you might sense that something happened here 75 millennia ago that truly shaped the world – and humanity.

Source: The Expat July 2005 
This artilce was editied for ExpatGomalaysia.com
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