| Big, explosive eruptions can send huge quantities | | | | be seen was a blanket of ash. A |
| of gas and fine debris into the atmosphere. The | | | | horseshoe-shaped crater 1.2 miles across and |
| bigger ones have sent debris high into the | | | | roughly 2460 feet deep replaced the peak. But |
| stratosphere where it spreads around the globe | | | | the most impressive thing was the blowdown |
| and might remain for months or even years. The | | | | zone where huge virgin Douglas firs were snapped |
| debris has the ability to filter out a portion of the | | | | like matchsticks and lay on their sides, covered |
| sun's energy and to lower the earth's | | | | with ash. The U.S. Forest Service estimated that |
| temperature.The most notable cold spell linked to | | | | 10 million trees were felled by the blast.When |
| a volcano was the one that followed the eruption | | | | Mount St. Helens Erupted, there was instant |
| of Mount Tambora in Indonesia in 1815. Many | | | | speculation that it could have major effects on |
| scientists attribute the abnormally cold spring and | | | | climate. For a time the large volume of volcanic |
| summer of 1816 to the clouds of volcanic debris | | | | ash that it emitted had significant effects both |
| put into the atmosphere by Mount Tambora. | | | | locally and regionally. But worldwide cooling was |
| There were other less dramatic effects from | | | | less than 0.2 degrees Fahrenheit.However, studies |
| Kakatoa in 1883 and Mount Agung in 1963. | | | | following the eruption of El Chichon showed a |
| However, it wasn't until the eruptions of Mount St. | | | | worldwide cooling effect on the order of .5 to .9 |
| Helens in the state of Washington in 1980 and El | | | | degrees Fahrenheit. Why, if it was less explosive |
| Chichon in Mexico in 1982 that scientists really got | | | | than Mount St. Helens, did it have a greater |
| to study the volcanic blasts with the use of | | | | impact on global temperatures? The reason is |
| sophisticated satellites and remote sensing | | | | that the material emitted by Mount St. Helens |
| instruments.Prior to 1980, Mount St. Helens, | | | | was fine ash that settled out relatively quickly. El |
| Washington was a steep conical volcanic peak | | | | Chichon, on the other hand, spewed an estimated |
| that rose 9,680 feet, had a snow-capped summit | | | | 40 times more sulfur-rich gases than Mount St. |
| and even a few small glaciers. But on the morning | | | | Helens. These clouds combined with moisture in |
| of May 18th, 1980, the entire north side of the | | | | the stratosphere to produce dense clouds of |
| summit came down - about half a cubic mile of | | | | sulfur acid droplets, which both absorbed and |
| rock and ice. An instant later and enormous | | | | reflected solar radiation. Explosiveness alone is a |
| explosion of expanding steam and volcanic gas | | | | poor instigator of climatic change. For volcanism to |
| rocked the countryside. The gases formed a | | | | impact the climate, you would have to have a |
| ground-hugging black cloud filled with hot, dense | | | | whole bunch of volcanoes going off over a |
| debris that raced over four major ridges and | | | | relatively short period of time. Such an idea was |
| valleys up to 17 miles from the volcanic | | | | once floated as the reason for the ice ages, but |
| summit.For the first couple of miles from the | | | | scientists have other ideas today. |
| summit, everything was obliterated. All that could | | | | |