Volcanoes and Climate
Mt. Ste. Helens
History of Climate Changes Induced by Volcanic Eruptions
It's been a while since a volcano, has changed our climate, even by the smallest amount. The last noteworthy episode occurred in 1991, when Pinatubo volcano in the Philippines went off, eventually lowering atmosphere temperatures by a whole degree centigrade. This effect wore off in a year or two, but still it is important to note the relationship between volcanic eruptions and climate.
On a grander scale, there were two very large volcanoes in the nineteenth century that were able to change the weather in a manner greater than the Filipino explosion that rocked the Pacific island in the last decade of the twentieth century. These monsters were named Krakatoa (1883) and Tambora (1815), and by chance they were both located within the island nation of Indonesia. Because the two are located close together in time and place, the aftereffects from each one often gets confused. But for the record, Tambora was the stronger and bigger eruption, and also the one that brought the most profound climate changes.
The Valley of Ten Thousand Smokes
An Alaskan Giant Goes Off
Pinatubo was not the biggest volcano to go off in the 20th century, for that honor belongs to the Novarupta volcano located on the Aleutian Penninsula of Alaska. In June 1912, this Alaskan monster underwent a V.E.I. 6 eruption that lasted for several days. Approximately, 36 cubic miles (30 times more than Mt. Ste. Helens) of debris was ejected into the atmosphere, but because of its northern location, this volcano had a lesser global effect than Pinatubo.
A Slight Drop in Temperature
During its spectacular eruption in 1991, Pinatubo ejected about three and a half cubic miles of material into the stratosphere. To atmospheric scientists, the most important portion of this event was not the ash, but the huge cloud of sulfur dioxide (SO2), which was emitted from the mouth of the volcano. It is estimated that the culprit cloud was 22 miles high, 684 miles long and weighed 17 megatons. The ash quickly descended back to earth, but the sulfur dioxide stayed airborne as an aerosol. Furthermore, it is this mass of SO2 that was largely responsible for the one degree temperature drop that occurred in the following year.
The Biggest Cooling Factor
By far, the biggest cooling factor in a volcanic eruption is the release of sulfur, which travels high into the stratosphere in the form of SO2 (sulfur dioxide). After its ejection from the mouth of the volcanic, the sulfur dioxide molecule combines with water to form sulfuric acid (H2SO4). The newly formed sulfuric acid exists in tiny droplets, which form a natural kind of aerosol spray which effectively reflects sunlight away from earth, thus creating a cooling effect. Eventually, the drops coalesce and then fall back to earth. Nonetheless, in a large volcanic eruption this cooling effect can last for several years.
Fire and Ice
There is another scientific scenario, currently under discussion, which suggests that rising temperatures in the earth's atmosphere can effect a volcano that is covered in ice. This recently-developed line of thought applies mainly to places like Iceland, Alaska and eastern parts of Russia, where many active volcanoes lie buried underneath an ice sheet.
It is suggested that if the layer of frozen precipitation is not too thick, then the melting of this mini ice cap might erase a natural plug to the volcano. The result could be a minor or middling volcano, which spreads ash and lava from the mouth of the volcano.
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