West of Yellowstone, in eastern Oregon and Washington, sit the vast basalt canyonlands of the Columbia River. In this basin, about 16 million years ago, fissures in the crust opened up and, over the course of 1 million to 2 million years, oceans of magma poured out onto the surface from a source hundreds of miles inside the earth. Piling up in pancake-like layers, the basalt reached a depth of nearly 10,000 feet in some places. The accompanying ash and gas would have blocked some of the sun's rays, drastically lowering temperatures worldwide. But the Columbia River "flood basalts" were dwarfed by two earlier basalt outpourings in India and Siberia. Those events, one occurring 248 million years ago and the other 65 million years ago, radically altered the earth's climate and may have played a role — possibly along with meteorite impacts — in the mass extinctions of dinosaurs and other animals.
Such calamities are almost beyond comprehension. Easier to grasp are the great eruptions of recent times, minuscule by comparison but still awesome in their destructive power. In the past 225 years alone, volcanic eruptions have killed at least 220,000 people. Only a handful died in lava flows; the rest perished in ways that do not readily come to mind. In 1783, in Iceland, the earth was split by a 17-mile volcanic fissure, which gushed ash, lava, and gases for several months. Nobody died in the actual eruption, but the poisonous fluorine gas that rushed out of the vents blanketed the countryside and killed half of the nation's cattle and three quarters of its sheep. In the ensuing famine 9,300 people died, one fifth of Iceland's population.
In 1815, in what was probably the largest eruption of the last 10,000 years, Tambora exploded on the island of Sumbawa in Indonesia. About 12,000 people died immediately, either incinerated by speeding clouds of gas and ash, known as pyroclastic flows, or drowning in huge volcano-induced waves, known as tsunamis. Later, at least 44,000 people — some say as many as 100,000 Л perished of famine and disease on neighboring islands when thick layers of ash ruined crops and killed livestock. Volcanic aerosols and dust in the stratosphere made temperatures drop around the world, causing "the Year Without a Summer" in New England and creating the vivid red sunsets painted by the English artist J.M.W. Turner.
In 1883, also in Indonesia, Krakatau erupted, its blast heard as far as Rodrigues Island in the Indian Ocean, 2,900 miles away. An estimated 36,000 people died, most of them in towering tsunamis that swept the island of Sumatra.
Nineteen years later, in 1902, Mont Pelée erupted on the island of Martinique, unleashing a pyroclastic flow that sped down the mountain at 100 miles an hour and, in minutes, killed 27,000 people in the city of St. Pierre.
In 1985 a small eruption at Nevado del Ruiz in Colombia melted glaciers at the volcano's summit and created a mudflow that swept through the town of Armero, killing 23,000 people in several hours. Two days later I was on the scene, measuring the gases streaming out of Ruiz and flying over the entombed town. Scientists from both Colombia and the United States had warned of such a disaster but were ignored by local civil defense officials.