Bryson goes out of his way to demonstrate the inadequacies of knowledge where the earth is concerned. We know frighteningly little about even the crust of the planet. Even less about what causes the catastrophic events that leave many people dead and cities ruined such as earthquakes, tsunamis and volcanoes. The latter however can produce more volatile displays of power teamed with rather efficient paths of destruction. So much so that despite us living on one of the more precocious land masses, even in the Pacific, it is not the volcanoes here that one should necessarily worry about.

In 1980 Mt St Helens in Washington State in the US erupted with the force of five hundred Hiroshima –sized atomic bombs. It shot out debris at thousands of kilometre an hour killing people 30 kms away. 600 square kilometres of forest was devastated with a giant column of ash rising to 18 kilometres in less than ten minutes. 48kms away an airplane reported getting pelted by rocks. 130 kms away towns got drenched in ash, up to 1.5 centimetres. So bear this in mind whilst we look at Yellow stone national park in the US, which is the largest volcano on the planet.

It is a caldera volcano, which means it rips open and explodes, without leaving a cone, with a gigantic amount of force. Virtually the whole park, 9000 square kilometres of the US is one huge volcano. The last explosion left a crater 65 kilometres across.

Beneath it lies a superplume of molten rock going down 200 kms and it powers all the geysers and interesting sites contained within the parks borders. Think of Rotorua and it’s fantastical geological displays but fear not as the nearest superplume is the Pitcairns in central Pacific. They sit beneath the ground like a martini glass, thin laval intrusions to the surface where there is a huge collection of molten rock ready to go. Yellowstone is the only one on solid ground, the rest being oceanic.

It first exploded about 6.5 million years ago and has done so in a cycle over a hundred times. The most recent three going back ward in time have been a thousand times bigger than Mt St Helens, 280 times as big and the one before was so big no one knows quite how much. It erupts about every six thousand years or so, and guess what? It’s been just over that since the last time it exploded.

We only have comparisons in the geological database to make to this potential explosion though we know the last eruption here covered most of the western side of the united states with ash, an area now that produces roughly half the world’s cereals. This alone would be pretty catastrophic but the suspected climatic consequences would be the real killer for the rest of the world.

The last really big explosion of a volcano was in Indonesia 74,000 years ago. This event was followed by six years of volcanic winter which brought the population of humans at the time to mere thousands for a long time afterward. It took about 20,000 years to recover according to recent evidence. Now this obviously is not quite as catastrophic as the asteroid situation but would still cause mass extinction and some very hard years, possibly hundreds and thousands of them. Life would most definitely not be the same again.

This eruption could happen at any time with no warning. In 1973 lake Yellowstone began to swell, the water seeping over the banks at the southern end. Ten years later the bulge had exceeded a meter across 100 square kilometres. Though it receded for a couple of years it is swelling again now. The sixty thousand years is up so we may soon see a much quieter USA and a much darker sky.