Before Eyjafjallajokull and Krakatoa there was Tambora

Eruptions and Disruptions: Iceland's volcano pales before giants

Excerpts:

On the evening of April 5, 1815, on the island of Sumbawa in what's now Indonesia, a volcano named Tambora began to rumble and cough. It sputtered on and off for days. Then on the 11th and 12th, eruptions shook houses and boats hundreds of miles away. Over 10 days, Tambora belched 24 cubic miles of lava and pulverized rock (try to imagine a cubic mile of anything), and created a crater more than three miles wide and nearly a mile deep.

Flowing lava, flying rocks and deadly gases killed thousands of people on Sumbawa, which is near the Equator, and nearby islands. Earthquakes and tsunamis killed tens of thousands more. Hundreds of millions of tons of ash and dust filled the sky, turning days into nights and blanketing the nearby island of Bali in a foot of volcanic ash. It smothered vegetation on islands for hundreds of miles around, and carpets of floating pumice covered the seas. An estimated 117,000 people in the region, then known as the Dutch East Indies, eventually died, many from starvation caused by crop failures and epidemics of disease. And that was just the beginning.

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Like a giant cannon, Tambora blew ash, dust and an estimated 400 million tons of sulfurous gases some 27 miles straight up into the stratosphere, high above the weather. This material blew up and through the troposphere—the layer nearest Earth's surface where clouds, wind, rain and 75% of the weight of the atmosphere (nitrogen, oxygen, trace gases and water vapor) reside. The troposphere is 4.8 miles thick at the North and South Poles and 9.6 miles thick at the equator. Tambora blew its load more than 17 miles beyond it, up where the air is super-thin and a layer of ozone protects the Earth from the sun's ultraviolet rays.

There, the pull of the Earth's gravity is very light, so the ash and dust floated and spread into a thin veneer circling the globe. The sulfurous gases mixed with water vapor and ozone to create an aerosol of sulfuric acid. The particles and molecules, under gravity's gentle pull, slowly sank into a layer that blanketed the planet and reflected the sun's warming rays back into space. Over several years, it settled into the troposphere, where winds and rains eventually deposited it on Earth.

Comments:

• WSJ graphic: Major volcanic eruptions in recent history
  
• The Year Without a Summer. Historian John D. Post has called this "the last great subsistence crisis in the Western world"
  
• Krakatoa
  
• Volcanic Explosivity Index