After Tambora

Mount Tambora, a volcano on the Indonesian island of Sumbawa, was once similar in stature to Mont Blanc or Mount Rainier. But in April 1815 it blew its top off in spectacular fashion. On the 10th and 11th it sent molten rock more than 40 kilometres into the sky in the most powerful eruption of the past 500 years. The umbrella of ash spread out over a million square kilometres; in its shadow day was as night. Billions of tonnes of dust, gas, rock and ash scoured the mountain’s flanks in pyroclastic flows, hitting the surrounding sea hard enough to set off deadly tsunamis; the wave that hit eastern Java, 500km away, two hours later was still two metres high when it did so. The dying mountain’s roar was heard 2,000km away. Ships saw floating islands of pumice in the surrounding seas for years… Alan Robock, an expert on links between volcanoes and climate at Rutgers University, notes a particularly intriguing initial condition that could have influenced the world’s response to Tambora. There had been another large eruption- larger than Pinatubo- just six years before. No one knows where this 1809 eruption was, but its signature can clearly be seen in the Greenland and Antarctic ice sheets. The sulphur put into the stratosphere by volcanoes shows up quite clearly in the year-by-year records of what was going on in the atmosphere that climate scientists extract from polar ice cores. These records make it possible to give dates to large eruptions in the past even if no one recorded the event at the time.