Big Blast

In October of 1815, a ship near the coast of India encountered an amazing sight: a “raft” that stretched for miles across the Indian Ocean. It consisted of ash, topsoil, dead trees, and other debris from a volcano that blew its top six months earlier — the most powerful eruption of the past 2,000 years or more. It killed almost a hundred thousand people, and altered the climate across much of the planet.

Mount Tambora is on an Indonesian island northwest of Australia. It was built by a clash between two of the plates that make up Earth’s crust. They meet at the bottom of the Indian Ocean. One plate plunges below the other, melting its rock. Some of this molten rock pushes through the layers above it, building volcanoes.

At two-and-a-half miles, Tambora was one of the tallest. But on April 10th, 1815, it blasted its upper 4,000 feet to bits. Rock and hot gas raced down Tambora’s flanks, killing thousands. Tsunamis killed thousands more. Ash and sulfur destroyed crops and livestock and fouled lakes and rivers, eventually killing tens of thousands. And volcanic ash in the upper atmosphere cooled the entire planet, causing 1816 to be remembered as “the year without a summer.”

Although Mount Tambora lost its top, volcanic domes are building inside the crater that was the mountain’s base, and steam squirts through cracks in its floor. So this one-time killer is not dead yet.