The Geology of Seattle

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  • Topic: Seattle, Washington, Earthquake
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  • Published : March 25, 2013
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The Geology of Seattle

Seattle is located in the state of Washington in the Pacific Northwest. Seattle is metropolitan and has a population of nearly 3.5 million. Seattle’s climate changes from wet and cold during the winter months to dry and hot during the summer months. The coast of Seattle is responsible for the growth of its economy, due to the large number of commercial ports. Seattle is in the destructive range of several volcanos within Washington, most prominently, Mt. Rainier.

Topography

Seattle is surrounded by large bodies of water and mountainous terrain. The city itself lies on top of several hills, which include; Capitol Hill, Second Hill, Denny Hill, Beacon Hill, and Queen Anne Hill. From the center of Seattle you can find shoreline to the north, Bainbridge Island to the north-west, The Puget Sound to the west, Vashon Island to the south-west, Tukwila to the south, Renton to the south-east, Lake Mercer to the East, and Lake Forest Park to the north-east. Past the Puget Sound lie the Olympic Mountains. Seattle owes its specific structure due to glacial scouring and deposition and tectonic activity, subsequently modified by landsliding, stream erosion and deposition, and human activity.

Geological hazards

Seattle is threatened by several geological hazards, such as earthquakes, flooding, volcanos and landslides and shore erosion. Perhaps one of the most prominent hazards to Seattle is the Massive volcano, MT. Rainier, which lies 54 miles southeast of Seattle. MT. Rainier stands at an elevation of 14,411 feet and is very topographically prominent. Rainier is considered one of the world’s most dangerous volcanos. The composition of Rainier is very andesitic and upon it eruption could cause a violent explosion. The glacial ice that sits atop the mountain can also cause massive lahars that could cause major damage to Seattle’s infrastructure as well as its economy.

Although MT. Rainier displays no signs of imminent eruption, it has gone through several major eruptions in the past 3000 years. These eruptions include the Twin Creek eruptive episode 1,500 years ago, the Fryingpan Creek eruptive period 1000 year ago, the Electron Mudflow 500 years ago, and several small eruption plumes in the 1800’s which caused black smoke to be seen to the early pioneers of the area.

It is projected that the potential damage to Seattle and the surrounding area would be catastrophic if MT. Rainer were to erupt.  Geoff Clayton, a geologist working for a company called RH2 Engineering, was asked by Seattle Weekly to estimate the damages to the Settle area. By using a computer program, he reached a conclusion that the result of Mt. Rainer spawning lahars would be a devastating natural disaster. Clayton then quoted that," Before approaching Seattle, a lahar, he says, would have "wiped out Enumclaw, Kent, Auburn, and most of Renton, if not all of it." Clayton went on to say that if such a massive lahar could potentially cause tsunamis in Lake Washington and the Puget Sound, effectively flooding the port of Seattle. It is needless to say that if Seattle were to lose its commercial ports, the economic consequences would be dire.

Another geological hazard that presents itself in Seattle is the risk of Earthquakes. Seattle lies within the ring of fire and is at risk of experiencing a crippling earthquake. The Seattle area has experienced several significant earthquakes in the past. The most recent notable quake was in February 28, 2001 when a magnitude 6.8 earthquake ravaged Pioneer Square. The quake caused significant property damage but no fatalities. More powerful earthquakes have occurred farther in the past. On January 26, 1700 the area was struck with a staggering 9.0 magnitude quake, and on December 14, 1872 Seattle was struck again with a 7.3 magnitude quake. A few more semi-powerful quakes occurred between 1940 to the present day, however, fatalities were minimal.

To predict the potential loss cause by...
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