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