Sunday sand: a few of my favourite grains

Since I’m on the road, a short, but I hope visually enjoyable, post today. Several years ago now, an old geologist friend and fellow sand-enthusiast sent me a wonderful set of samples to begin my collection, and his ongoing encouragement contributed to my actually completing the book. We share Indonesian experiences, and several of the samples included sands from various parts of the huge archipelago – including these, which have remained some of my favourite grains, simply for their stunning photogenicity.

They come from the shores of Sumatra’s LakeToba and their beauty belies their catastrophic origins. They are pure quartz grains, weathered out of the Toba tuffs, great thicknesses of volcanic material blown out of one of the planet’s most devastating eruptions of the last couple of million years. The effects were globally destructive and nearly caused a premature end to the human race, so they are of considerable interest to archaeologists as well as geologists. Oxford University runs one of the projects investigating the story, and introduces it as follows:

The Toba super-volcano has erupted explosively a number of times over the past 1.2 million years. By far the largest and most destructive of these occurred around 74,000 years ago, and it is this ‘Youngest Toba Tuff’ or YTT eruption that forms the focus of this research project. At least 2800 cubic kilometres of volcanic material was ejected during this super-eruption, dwarfing historical eruptions such as Krakatoa and Pinatubo.

The YTT explosion instantly destroyed all life in its immediate area, with intensely hot flows comprised of billions of tonnes of ash and rock, accompanied by a deafening noise and powerful tsunamis. It also sent hundreds of cubic kilometers of ash and gases high into the atmosphere, even as the volcano itself collapsed inwards to form a huge sunken caldera (now Lake Toba). The gases, including sulfur, circled the globe on air currents, while the ash spread out to the north and west fanned by prevailing winds. When the ash began to fall, it covered the Indian subcontinent and rained down into oceans from the Arabian Sea in the west to the South China Sea in the east… Gradually the earth cooled as the sun’s heat was reflected by the suspended gases, affecting rainfall and climates across the globe. Around this time the earth slipped rapidly into a dramatically cold portion of the ice ages, and while this was underway before Toba’s eruption, the super-volcano undoubtedly had an important influence.

At the time of the Toba eruption 74,000 years ago, humans shared the Earth with a number of similar species, including the cold-adapted Neanderthals and the dwarf Homo floresiensis. All these species made stone tools, gathered plants and hunted animals for their livelihood, and all survived the eruption and its after-effects. Nevertheless, when palaeo-climatic records are combined with genetic data that may indicate an abrupt decline in the number of humans (a genetic ‘bottleneck’) at about the time of Toba’s super-eruption, the possibility that we were driven to the edge of extinction deserves investigation.

There’s much hype and mongering of various kinds about “super-volcanoes,” but Toba certainly qualifies for our close attention.

And just as these sand grains are benign witnesses to these events, so is the apparently tranquil Lake Toba: