Introduction For five hours, multiple avalanches of hot ash, pumice, and gases poured out of the crater. During explosive eruptions, fiery, pyroclastic flows travel down slope from a volcano. The Mount St. Helens pyroclastic flow spread as far as five miles north of the crater. The hot lava flows and suffocating ash falls destroying plant and animal life. The eruptions are over, but consequences go on. What happens to the surrounding environment after such an eruption? The Earth repairs itself from the destructive effects of the lava, gases and ash spewed by the eruption of Mount St. Helens.
It is he short-term hazards posed by volcanoes that are balanced by benefits of volcanism and related processes over geologic time. A factor that influenced the recovery of different areas around the volcano was the variety of ways they were impacted by the explosion Volcanic mudflows, also known as lahars, scoured and buried much of the landscape, killing most of the plant and wildlife in their path, though some survived along the edges of these flows. How the pyroclastic flow exploded out of the volcano at speeds of up to 125 mph and temperatures up to 1,200 degrees. This flow created a pumice rock plane of about 6 square miles.
In the once barren area, where the pumice reached up to 131 feet thick, no remnants of the former forest. It now shows plant life, Prairie lupine. Ash poured down on the landscape for hundreds of miles away from the volcano, carried by the prevailing winds, coating trees and other plants and accumulating in deposits along the ground. These varying effects created by the explosions established different landscapes in the area that suited some species better than others did. It also set in motion different types of recovery at varying rates. Even with all of its destruction, these and other components play a role in the Earth’s reconstruction.
Mount St. Helens, located in southwestern Washington about 50 miles northeast of Portland, Oregon, is one of several lofty volcanic peaks that dominate the Cascade Range of the Pacific Northwest; the range extends from Mount Garibaldi in British Columbia, Canada, to Lassen Peak in northern California. Geologists call Mount St. Helens a stratovolcano or composite, a term for steep sided, often- symmetrical cones constructed of alternating layers of lava flows, ash, and other volcanic debris. Stratovolcanoe’s tend to erupt explosively and pose life threatening danger and property destruction.
Mount St. Helens, other active Cascade volcanoes, and those of Alaska form the North American segment of the Pacific “Ring of Fire,” a notorious zone that produces frequent, often destructive, earthquake and volcanic activity. Work done by geologist in the 1950s used methodical studies of the volcanic deposits, laboratory investigations of rock and ash samples, they also used radiocarbon (carbon-14) dating of plant remains buried in and beneath the ash layers and other volcanic debris has allowed them to reconstruct a complete record of the prehistoric eruptive behavior of Mount St.
Helens. Historical Stages Volcanologists have named four stages of volcanic activity, Ape Canyon, Cougar, Swift Creek, and Spirit Lake. These stages are separated by dormant intervals. Little is known about the Ape Canyon stage (300-35 thousand years ago) (ka). During this stage, lava domes in two distinct periods, one from 300 to 250 thousand years ago (ka) and a second from 125-35 ka. Geologists have found layers of ash and rocks that were changed hydrothermally, indicating that an extensive hydrothermal system existed during the latter part of this stage.
The Cougar stage (23 to 17 ka) offers a better record of early Mount St. Helens volcanism is preserved in the Cougar-age debris avalanche and in glacial deposits and lahars in the Lewis River Valley. In the Cougar stage, Mount St. Helens was actively producing lava domes and flows along with explosive eruptions that ejected large volumes of ash and generated pyroclastic flows. The debris avalanche is composed primarily of Ape Canyon-age rocks and was the most devastating event of the stage. The debris avalanche deposited 600 to 900 feet thick on the south flank of the volcano.
This avalanche, which was at least twice as large as the huge debris avalanche that triggered Mount St. Helens’ 1980 eruption, dammed the Lewis River. Downcutting of the dam caused flooding downstream as far as the Columbia River and filled the lower Lewis River Valley with volcanic debris at least 200 feet thick. The Cougar debris avalanche was followed by a large explosive eruption producing pyroclastic flows that buried the avalanche deposits with a 300- foot-thick sheet of pumice. The Cougar Stage culminated with the eruption of the largest lava flow in the history of Mount St. Helens.
The Swift Creek stage (13-11 ka) had explosive eruptions that created widespread layers of ash and three massive ans of volcanic debris that were place from growing and unbalanced Dacite lava domes. These were made of pyroclastic flows and volcanic mudflows, which buried the cougar aged deposit sitting on the south flank of Mount St. Helens. On the west flank, lava domes produced pyroclastic flows, 600 feet thick. The Cedar flats fan filled the valley of Pine creek, overflowed into the Lewis River. The collapses of lava dome dominated mostly by lahar mixed in with pyroclastic matter that was at least 300 feet thick.
Toward the end of the Swift Creek stage, Mount St. Helens had dacite domes ith elevations up to 7,000 feet. The last stage, Spirit Lake (3. 9 ka to the present) is subdivided into six erupted periods, Smith Creek (3. 9-3. 33 ka), Pine Creek (2. 9-2. 55 ka), castle creek (2. 55-1. 985 ka), sugar Bowl (A. D. 850-900), Kalama (A. D. 1479-1720), and Goat Rocks (A. D. 1800-1857). The preservation of deposits gave geologists numerous ages detailed through tree-ring and radiocarbon dating. Volcanism was sporadic. In the early stages, eruptions were mostly dacite, but enough amounts of basalt and andesite were found to take notice.
In the Smith Creek period volcanic ctivity resulted in ash eruptions. There was a major eruption around 3. 5 to 3. 3 ka that huge lahars tumbled it way down the Toutle River even reached the Columbia River. This eruption was roughly four times larger than the 1980 eruption. These ash- producing eruptions did little to change the volcano’s shape. The next period (Pine Creek) had ash eruptions and produced pyroclastic flows and dacite domes. On the south side of the volcano hot growing lava domes repeatedly collapsed.
These lava domes produced a widespread fan of volcanic debris that was as much as 600 feet thick. On the opposite side, similar deposits were found as downstream to the town of Toutle. Dacite domes were found in the walls of the carter after the 1980 eruption show that at the end of this period the volcano was a cluster of lava domes with a maximum elevation of about 7000 feet”. (Michael A. Clynne, 2005) In the Sugar Bowl, Mount St. Helens gave way to three more lava domes and produced two lateral blasts that had a small affect on the area, about one tenth of the 1980 eruption.
This period was short lived and again did little to change the appearance. A very active Kalama eriod is broken into three stages early, middle and late . In the early phase in 1479 was filled with activity of huge amounts of pyroclastic flows that gave a layer of dacite ash. In 1482 another small eruption which produced another layer of ash. This early phase also had lava domes tha grew inside the crater which were distrubed by the eruptions. The middle phase opened around 1510 with an eruption of andesite as pyroclastic flows that made hot lahars, a few lava flows, and ash.
This period tops out in 1535 with numerous thick andesite lava flows that can be found on all flanks of Mount St. Helens and ended in 1570. The late Kalama phase saw the large growth a dacite dome at the summit ( Summit Dome ) “The Summit Dome took nearly 100 years to grow (1620 to 1720) and gave Mount St. Helens its pre-1980 form. During growth, it shed material as pyroclastic flows and lahars on all flanks of the volcano. Mount St. Helens acquired its pre- 1980 cover of glaciers as a result of growth of the Summit Dome. ” (Michael A.
Clynne, 2005) The Goat Rock period was short and small. In 1800 an explosive eruption produce a layer of ash, then a year later an andesite ava flowed on the north side of Mount St. Helens. Eruptions from 1831-1857 were observred as ash and small fan of volcanic debris and lahars. Again these eruption did not have much of an affect on the apperance of volcano. These are Just some of the events that lead up to the devesting eruption of Mount St. Helens in 1980. The 1980 Pre-Eruption Thursday, March 20 1980 an earthquake measured 4. 0 on the Richter scale was recorded.
It appeared to oringinate directly under Mount St. Helens. As usual aftershocks followed the next day. What was unusal was the aftershocks continued nto Saturday and Sunday with more frequent aftershocks and the epicenter seems to be rising toward the surface. “By Monday March 24, the number of earthquakes had Jumped to more than one per minute, some as strong as 4. 0 on the Richter scale”. (Carson, 2000, p. 29) As experts gathered in the region with local and state athourites they decieded to close part of the mountian off above the timberline as a precaution.
A local radio traffic reporter looking for a new story angle about the mountian, flew near the summit and saw steam and black ash discharging from a hole in the snow. This was hidden from a ground veiw because of overcast skies. When the plume subsided and the skies cleared aerial observers saw a new crater 200 feet in diameter and 150 feet deep opend on the top of the mountianalong with cracks up to three miles long running east to west near the summit, indicating that the north side of the peak was starting to droop. Later on March 30 Mount St. elens had 93 small eruptions of steam and ash that spewed from the summit. In April seimometers recorded tremors that were rhytmic and continous which indicate magma moving beneath the Earth’s surface. Geolgist’s knew that Mount St. Helens would explode but when was everyones question. During the last weeks of April and early May the steam and ash that had been shooting out of the mountian had settle down. It appears that Mount St. Helens would not erupt after all. During those weeks it was calm on the outside , but deep below the surface there still was plenty of activity.
A group of geologist monitoring the shape of the mountian with laser beams noticed that Mount St. Helens was growing very quickly. With measurements in late April that show an ominous bulge on the north side that was growing at a rate of five feet a day. Parts of the bulge grow 450 feet higher than weeks before, a good indication that magma was being forced through the cracks and fissures in the mountian. Days later on May 18 1980 Mount St. Helens erupted. The Eruption At 8:32 am on May 18 1980 an earthquake of 5. a mile below the mountian caused the bulge to shake loose, weakend by the intrusion of magma and pressurized gases Mount St. Helens collapsed on itself. The collapse of the entire north half of the mountian resulted in largest avalanche in history. “The explosion burst latteral instead of vertical, huling rock, ash and chunks of glacial ice at a elocity aproaching the speed of sound”. (Carson, 2000, p. 39) The blast crushed, incinerated, or blew away almost everything in a fan-shape path of desturction. The path of desturction extended out 17 miles from the carter.
Plume rose 16 miles into the astrosherpe and continued for nine hours. The explostive blast within a few miles vaporized all living things even stripping the soil from underlying rock. Another example of the force behind the eruption was Coldwater Ridge six miles directly in the blast line was a thick forest, afterward the area was sandblasted to bare rock. Beyond the inner blast zone 86,000 acres of trees were flash-burnedand knocked down in what is called blown down zone. In this fan-shape blast another zone called, scorch zone about 14 to 17 miles from the crater the intease heat killed trees, but left them standing.
The intease heat melted 70 percent of the snow on the moutain causing hot mudslides that swept trees, houses and blouders down the moutian. The mudslides drained into the Toutle river causeing the it to rise as much as 60 feet in some places. When the first wave of mud found its way 45 miles away it raise the temputure of the Columbia river to 90 dgrees. This was on the west side of the mountian, the east side had to deal with ash. In about 3 horus the plume had blocked the sun over half of the state. The wind carried the ash over Idaho and Montana and made it to Botson in two days.
The amount of ash that was forced out equaled 540 tons and fell over an area more than 22,000 square miles. The offical total took nearly two years to determine the eruptions statistics: 4. 7 billion board feet of timber destroyed, the moutian shrunk by 1,313 feet and the height of the ash plume 16 miles and the unfortunate death of 57 people. The lost of animal ife on that day is estimated at 15 mountian lions, 1,500 elk, 200 black bears, 5,000 black tailed deer,11,000 hares, 300 bobcats, 27,000 grouse, and 1,400 coyotes. The heavy ash miles away from the crater killed many more.
The heat and ash has wipe out so many birds and insects it is uncountable. The eruption damaged 26 lakes and killed millions of fish. (Michael A. Clynne, 2005) Mount St. Helens rises majestically above surrounding forests in this photo taken on May 17, 1980. In the devastating eruption the following day, 57 people were killed, most of the forest destroyed, and 1 ,300 feet of volcanic rock removed rom the volcano’s edifice, lowering its summit elevation to 8,364 feet (inset photo). During the volcano’s 300,000-year history, dozens of eruptions have repeatedly changed its appearance. IJS6S photos by Harry Glicken and Lyn Topinka. ) Devestation to Life Twenty years after the devestation caused by Mount St. Helens eruption, the natural succession of wildlife and plants has changed the landscape again. By surviving underground the pocket gopher played a big role in starting this natual process. The gopher lives in a maze of underground tunnels and feed off the roots of plants. In the short term, gophers would stash nourishments in their cheeks and in the long term stored provisions in hidden cashes underground. (Carson, 2000) Just about everything died, but a few pocket gophers managed to survive using their burrows as fallout shelters and eating roots of plants that were topless form the blast. Wherever the pocket gopher went it, they left fertilized and cultivated plots where wind blown seeds would land and take root. This is the start of a long process that brings the devestated mountian back to life where today the volcanoe is still active. Recent work by scientists with the IJS6S in cooperation with the U. S. Forest Service is shedding new light on the 300,000-year history of Mount St.
Helens Volcano. The work of these IJS6S scientists is only part of the IJS6S Volcano Hazards Program’s ongoing efforts to protect people’s lives and property in all of the volcanic regions of the United States, including the Pacific Northwest, eastern California, Wyoming, Alaska, and Hawaii. ” (Michael A. Clynne, 2005) References Carson, R. (2000). Mount St. Helens The eruption and Recovery of a Volcano. Seattle: Sasquatch Books. Chernicoff, S. , & Whitney, D. 2007). Geology. Upper Saddle River: Pearson. II, J. K. (Director). 1997). Fire Mountain The Eruption and Rebirth of Mount St. Helens [Motion Picture]. Mauro Rosi, P. P. (2003). Volcanoes. Buffalo: Firefly Books. Michael A. Clynne, D. W. (2005, May twelve). Pre-1980 Eruptive History of Mount St. Helens, Washington. Retrieved February twenty two, 2006, from IJS6S U. S. Survey: http://pubs. usgs. gov/fs/2005/3045/ Mount St, Helens, Washinton. (nd). Retrieved February 05, 2011, from usgs. gov: http:// vulcan. wr. usgs. govNolcanoes/MSH/ Parchman, F. (2005). The Echoes of Fury. Kenmore: Kent Sturgis.