In June, 1991, something surprising happened to the Earth. Mount Pinatubo, in the Philippines, erupted. The first surprise was that it was thought to be a mountain, not a volcano. In fact, pressure built up over centuries beneath this dormant volcano caused the second largest eruption of the 20th Century, spewing vast amounts of white ash and sulphates as high as the stratosphere – 10 km above the Earth’s surface.
