To discuss the effects of primary and secondary volcanic hazards on people and property in Developed Countries, we will use the case study of Mount St. Helens.
Effects of Volcanic Hazards in Developed Countries
Example: Mount St. Helens
Mount St. Helens is a stratovolcano in Washington, the United States of America. The volcano is most famous for its eruption on 18 May 1980, which is the worst volcanic disaster and one of the most significant geologic events in the United States during the 20th century. The actual cost of the destruction wrecked by the eruption remain difficult to determine even though official figures estimate the cost to be US$1.1 billion.
Mount St. Helens on May 17, 1980, one day before the devastating eruption.
Source: http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH80_st_helens_from_johnston_ridge_05-17-80_med.jpg
Before 1980, Mount St. Helens, known for its serenity and symmetry, was known as the “Fujiyama of America”. The majority of 20th century residents and visitors did not think of Mount St. Helens as a volcanic hazard but as a peaceful mountain for leisure activities.
However, as early as 16 March 1980, the first signs of volcanic activity in the form of earthquakes were observed. It was only on March 27 when the volcano began to emit ash and steam. There was visible deformation and swelling of the volcano due to the movement of magma from the magma chamber into the volcano. The north face of Mount St. Helens was especially affected by the deformation and the area became known as the “bulge”.
A "bulge" developed on the north side of Mount St. Helens as magma pushed up within the peak.
Source: http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH80_bulge_on_north_side_04-27-80_med.jpg
As seen from the above photograph, the visible “bulge” developed on the north side of the volcano. From angle and slope-distance measurements, it was observed that th
e “bulge” was growing at a rate of nearly 1.5 metres per day.
On May 18, the deformed and unstable north flank of the volcano suddenly collapsed, apparently due to an earthquake of magnitude 5.1 beneath the volcano. This collapse of the north flank gave rise to a landslide-debris avalanche, which moved northwards at speeds of 175 to nearly 250 km per hour, recorded.
The sudden removal of the “bulge” on the north face of the volcano abruptly released the pent-up pressure of the volcanic system of Mount St. Helens and triggered an almost immediate and explosive lateral blast. The blast’s quickly increased from its initial velocity of about 354 kilometres per hour to about 1078 kilometres per hour. The lateral blast, loaded with volcanic debris, caused widespread destruction as far as 30 kilometres from the volcano.
Ash fall and its effects
A strong, vertically directed explosion of ash and steam began v
ery shortly after the lateral blast. The resulting column of ash rose very quickly into the atmosphere, attaining a height of almost 20 kilometres.
Near the volcano, the ash particles in the atmosphere gave rise to
lightning which started many forest fires in return. More ash was emitted into the atmosphere as the eruption continued for 9 hours, adding to the growth of the ash cloud. By the time the eruption subsided and stopped on May 19, the ash cloud had spread to the central United States.
Some of the ash also drifted around the globe, only reaching t
he Earth’s surface after several weeks. However, the smallest fragments and aerosols remained suspended in the atmosphere for years which eventually had an impact on modifying the global climate. The aerosols participate in complex chemical reactions in the stratosphere, altering chlorine and nitrogen chemical compounds. This effect led to the formation of radicals and, accompanied by chlorofluorocarbon (CFC) pollution, contributed to the depletion of the ozone layers as the radicals break down ozone molecules that protect us from ultraviolet rays from the sun.
Pyroclastic flows and its effects
Pyroclastic flows were observed a few hours after the start of the lateral blast and continued to occur intermittently during the next 5 hours of strong eruptive activity. At least 17 separate pyroclastic flows occurred during the May 18 eruption, and thei
r aggregate volume was about 0.21 cubic kilometres.
When the hot pyroclastic flows encountered water bodies such as Spiri
t Lake, it led to steam-blast explosions as water flashed explosively into steam. Plumes of ash and steam were sent as high as 1.9 kilometres above the ground. These steam-blast eruptions formed many explosion pits on the sides of the pyroclastic flow deposits, at the south shore of Spirit Lake, and along the upper part of the North Fork of the Toutle River.
Pyroclastic flows were very dangerous as they were directed
sideways by the lateral eruption of Mount St. Helens. The force and full volume of the pyroclastic materials are forced down the volcano and the resulting high velocities and temperatures of the flow can destroy everything in their paths.
Lahars and their effects
The largest and most destructive lahar developed several hours later in the North Fork of the Toutle River, when the water-saturated parts of the massive debris avalanche deposits began to collect and eventually overflow. The resulting lahar in the Toutle River
drainage area dumped more than 0.05 cubic kilometres of sediment along the lower Cowlitz and Columbia Rivers.
Lahars occurred along the southeast flank of the volcano-along the Swift Creek, Pine Creek, and Muddy River drainages and emptied nearly 0.01 cubic kilometres o
f water, mud, and debris into the Swift Reservoir. Fortunately, the volume of the additional load was insufficient to cause overtopping even if the reservoir had been full, thus preventing further damage to property and loss of lives.
Lahars can case high economic and environmental damage and
in the case of the May 18 eruption of Mount St. Helens, it destroyed the forests around the volcano. The impact of a lahar’s flow front can remove and destroy anything in its path, in fact lahars can even crush or carry away buildings. Valuable land may be buried by layers of rock debris, lowering their value and rendering them unusable for agriculture, adding on to the economic cost of lahars. These flows can destroy bridges and roads, trapping people in areas that may be vulnerable to other volcanic hazards.
Aftermath of the May 18 Eruption
The May 18, 1980, eruption was the most destructive in the history of the United States. Landscape changes caused by the eruption was obvious especially from high-altitude photographs and the devastation on people and their property widespread, claiming 57 lives and injuring many others.
More than 200 homes and over 185 miles (300 kilometers) of roads were destroyed by the 1980 lahars.
Source: http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH81_damaged_home_south_fork_toutle_river_07-19-81_med.jpg
More than 200 homes and over 300 kilometres of roads were destroyed by the 1980 lahars. Pictured here is a damaged home along the South Fork Toutle River. The lateral blast, debris avalanche, mudflows, and flooding caused extensive damage to land and man-made structures, rendering many people homeless.
There was also a large impact on the fauna in the Mount St. Helens area. It is estimated that nearly 7,000 large animals like bears and deer perished in the area most affected by the eruption, as well as all birds and most small mammals. Many small animals, mainly burrowing rodents, frogs, salamanders, and crawfish, managed to survive because they were below ground level or water surface when the disaster struck.
In areas of thick ash accumulation, many agricultural crops, such as wheat, apples, potatoes, and alfalfa, were destroyed. As for areas blanketed only by a thin layer of ash, many crops survived. In fact, the apple and wheat production in 1980 was higher than normal due to greater-than-average summer precipitation as a result of the ash falls. Effects of the ash fall on the water quality of streams, lakes, and rivers were short lived and minor.
May 18, 1980- ash along the roadside, Connell, Washington.
Source: http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH80_may18_ash_road_connell_washington_06-80_med.jpg
The photograph shows ash along the roadside in Connell, Washington. Visibility was reduced during the ash falls, forcing roads to close to traffic for up to weeks. Air transportation was disrupted as several airports in eastern Washington shut down due to ash accumulation and poor visibility. Over a thousand commercial flights were also cancelled as a result.
The volcanic ash caused problems for internal-combustion engines and other mechanical and electrical equipment. The ash was able to infiltrate most openings and was highly abrasive, thus contaminating oil systems, clogging air filters, and scratching moving surfaces. In fact, there were cases where blackouts were caused by the coating of fine ash on electric transformers, causing short circuit. The sewage-disposal systems of several areas were plagued by ash clogging and damage to pumps, filters, and other equipment.
The removal and disposal of the ash was not easy. Ash removal cost $2.2 million and took 10 weeks in Yakima. To minimize the effect of wind on ash dumps, the surfaces of some disposal sites have been covered with topsoil and seeded with grass. About 191 138 square meters of ash have been stockpiled at five sites for constructional and other beneficial economic uses in the future.
The eruption had indirect costs in the form of its effects on residents in the affected areas. Unemployment in the immediate region of Mount St. Helens rose quickly in the weeks following the eruption before returned to normal once the operations to clean up the ash and to salvage timber began. Several months after May 18, a few residents reported suffering stress and emotional problems, even though they had coped successfully during the crisis. Funding for mental health programs were requested to help these people.
Immediately after the eruption, tourism, an important industry in Washington, was badly affected. Conventions, meetings, and social gatherings also were canceled or postponed at cities and resorts elsewhere in Washington. The negative impact on Washington’s tourism proved only to be temporary as the tourists began to return to Mount St. Helens, possibly attracted by its reawakening.
Mount St. Helens is considered to be one of the most beautiful and interesting of the Cascade volcanic peaks.
Source: http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/Images/MSH82_st_helens_spirit_lake_reflection_05-19-82_med.jpg
Mount St. Helens is no longer symmetrical and has an amphitheatre-shaped caldera instead. It is still considered to be one of the most beautiful and interesting of the Cascade volcanic peaks. Mount St. Helens and the devastated area is now within the 110,000-acre Mount St. Helens National Volcanic Monument, under jurisdiction of the United States Forest Service. Visitor centers, interpretive areas, and trails are being established as thousands of tourists, students, and scientists visit the monument daily.
