I nominate the island of Sumatra as the earth's appendix. (Now that I have your attention.) Stretching from the northwest over a thousand miles to the southeast, and up to 270 miles wide, it is evenly sliced asunder by the equator, and it just keeps rupturing and trying to kill us.
Off its south-eastern tip lies the treacherous 15 mile wide Sunda Strait, in which resides Krakatoa, the volcano whose explosive May 1883 eruption killed at least 36,000 people. In December of 2004, the Java trench just off Sumatra's north-western coast was the epicenter for the 9.3 magnitude earthquake and resulting tsunami that killed 230,000 humans. And in the 12, 000 foot high Barisan Mountains on Sumatra itself, lies Lake Toba, a water filled caldera 18 miles wide by 60 miles long. It was this placid tropical vacation spot which on a December or January day 71,500 years ago – plus or minus 4,000 years – came very close to killing everybody.
On that very bad day 71,500 years ago the once great Mount Toba had a lump of rhyoite stuck in its vent, preventing the magma in its six mile wide reservoir nine miles below the surface from exhaling. The pressures built up until, as it must eventually, something gave. Perhaps it was a minor earthquake along the Sumatra Fault. Perhaps, as at Mount St. Helens, it was a landslide that released the twin beasts beneath the mountain. The initial explosion was big enough, throwing off tens of millions of tons of rock, but also enough to unleash an older, deeper magma chamber just to the north. The co-joined reservoirs were 17 cubic miles across. And the resultant combined explosion lasted a week, and threw ten trillion, trillion with a “T”, ten trillion tons of 1,500 degree Fahrenheit magma, rock and gas into the stratosphere.
This youngest Toba eruption was far greater than the 1815 eruption of yet another Indonesian volcano: this one about a thousand miles to the east, the 14,000 foot high Mount Tambora. This monster killed perhaps 11,000 locally and threw enough sulfuric acid into the stratosphere to turn 1816 into the “Year Without a Summer”, killing another 60,000 in Europe, China and North America through starvation and disease, when crops failed. Mount Toba was 100 times bigger than that, the largest volcanic explosion in the last 2 million years. The Toba ash fell in Greenland. The math says it caused a “volcanic winter” that lasted 6 to 10 years. Global temperatures would have dropped six degrees Fahrenheit. That makes it big enough to have killed almost every human on earth.
Off course it was easier back then, because there were only about 55,000 primates walking around on two legs, divided, like a biblical tale of Cain and Able, into two family tribes; homo Neanderthal and homo Erectus. Like all family stories, this one is more complicated than any mere recitation of names and dates can explain. But what is important to remember is we are talking about fewer humans than there are endangered Gorillas and Chimpanzees today. So killing all the humans on earth was not that big a job.
Erectus was the older brother, and he left his African home first. Taking his innovative hunter-gatherer life style on the road, he enjoyed a population boom as a result. But like an unsuspecting Wall Street investor, the boom was followed by a nasty surprise bust. It was Erectus' far flung prodigy who camped in the shadow of Mount Toba, 71,500 years ago. And according to research by geneticist Lynn B. Jorde at the University of Utah, the genetic markers passed down to us by our ancestors indicate a
“bottleneck” when the number of Erectus was reduced to a mere 10,000 individuals, maybe, even, as low as 40 “breeding pairs”. In other words, 70,000 years ago the total world-wide population of us, could have jointly attended a Sacramento Kings basketball game, with the stadium still left half empty, with the “breeders”, scattered about in the corporate sky boxes.
I should point out that our story has a happy ending. Sixty thousand years after Toba, human populations had not only rebounded, but had grown to more than one million individuals world wide. This was primarily thanks to the invention of agriculture, but it was also a byproduct of the elimination of our competition.
Half a million years before the Toba eruption, the more robust humanoids, named after Germany's Neander River valley where their skeletons were first uncovered, had moved into Europe. And 40,000 after Toba, Homo Neanderthals were extinct. The last survivors discovered so far were a single family group, camped in what is now Spain, and dated to no more than 45,000 years ago. Why did they die out? Their body type required between 100 and 350 more calories per day than the ancestors of Erectus, otherwise known as “us”.
In other words, as any supermodel can tell you, we are a better at surviving starvation, at least better at it than Neanderthal. Hard to believe given the current population of fat assed Big Mac eating, french fry inhaling Americans. But maybe that explains our obsession with “all you can eat”. In any case, by 1804 the population of Homo sapians sapiens had reached 1 billion individuals. And collectively we now weigh 100 times the biomass of any other land animal that has ever walked the earth. Apatosaurus, you should have invented the Whopper. Any chance another super volcanic eruption could kill us all has become extremely unlikely. Not impossible, just unlikely. But then the size of the Toba eruption was unlikely in the first place.
This is one small factual problem with this gloom and doom story. In 2013 archaeologists working at Lake Malawi, at the southern end of the African Rift Valley, discovered a layer of volcanic ash that was part of the Toba eruption, 71,500 years ago. This was to be expected, given that the African Rift Valley was ground zero for human evolution, and our story is about how humans were almost wiped out by Toba. But the herds of wildebeests and antelope in the rift valley humans were feeding off of were more far numerous then, than they are now. And their genetic heritage shows no Toba bottleneck. How could we starve if our food did not?
Well, it could have been that just about the same time Toba really blew its top, that smallpox made its first appearance. Small Pox kills 40% of adults infected and 80% of children. In fact, it is far more likely that a tiny bacteria or an even smaller virus would wipe us out, than a big volcano, as anybody with a runny nose six year old can testify. The Black Death (Yersinia pestis) killed about 200 million people in the 14th century alone – 1/3 of the population of Europe. Or maybe 71,500 years ago the Predator race flew in from their home planet for their first Terrestrial hunting safari.
Add Toba to just about any other disaster and you could have a human ending event. This may explain, at least in part, why it has taken four billion years for a life form on earth to develop the cognitive power stand up on their own two legs and say, “I'll have a Big Mac with fries, please.”
The one thing we know about Toba is, it is going to do it again. Over the last million years, Toba has produced three major eruptions, one 840,000 years ago, a second 700,000 years ago, and the big one 71,500 years ago. The lake that fills the caldera is 1,600 feet deep, but beneath that is another 1,500 feet of sediment.
The lava reservoir beneath the caldera has refilled enough to raise a resurgent dome in the middle of the lake, more than 3,000 feet above the water. It has been named Samosir Island. At 30 miles long, 15 miles wide, and 247 square miles in area, it is the largest island within an island in the world. And it contains two lakes with their own islands. This appendix is reloading to rupture again. Should we be worried?