St Helens 1980 Eruption example essay topic

Mount St. Helens is an active in Skamania County, Washington, in the Pacific Northwest region of the United States. It is located 96 miles south of Seattle and 53 miles northeast of Portland, Oregon. The mountain is part of the Cascade Range. It is most famous for a catastrophic eruption on May 18, 1980. That eruption was the most deadly and economically destructive volcanic eruption in the history of the United States. 57 people were killed, and 200 homes, 47 bridges, 15 miles (24 km) of railways and 185 miles (300 km) of highway were destroyed.

The eruption blew the top of the mountain off, reducing its summit from 9,677 feet to 8,364 feet in elevation and replacing it with a mile-wide crater. Like most of the other volcanoes in the Cascade Range, St. Helens is a great cone of rubble, consisting of lava rock inter layered with ash, pumice and other deposits. Volcanic cones of this internal structure are called composite cones or. Mount St. Helens includes layers of basalt and andesite through which several domes of da cite lava have erupted. The largest of the da cite domes formed the previous summit; another formed Goat Rocks dome on the northern flank. These were destroyed in St. Helens' 1980 eruption.

The first recorded sighting of Mount St. Helens by Europeans was by Royal Navy Commander George Vancouver and the officers of HMS Discovery on May 19, 1792, while they were surveying the northern Pacific Ocean coast from 1792 to 1794. Vancouver named the mountain for British diplomat Alley ne Fitz herbert, Baron St. Helens on October 20, 1792. According to geological evidence, St. Helens started growth 37,600 years ago with da cite and andesite eruptions of pumice and ash. Mudflows were very significant forces in all of St. Helens' eruptive cycles.

Starting around 2500 BC eruptions of large amounts of ash and yellowish-brown pumice covered thousands of square miles. This eruptive cycle lasted until about 1600 BC. After 400 years of inactivity, St. Helens came alive again around 1200 BC. This cycle, which lasted until about 800 BC, is characterized by smaller volume eruptions.

Mt. Saint Helens woke up on March 20, 1980, with a Richter magnitude 4 earthquake. Steam venting started on March 27. By the end of April, the north side of the mountain started to bulge. With little warning, a Richter magnitude 5.1 earthquake triggered a massive collapse of the north face of the mountain on May 18. The magma inside of St. Helens burst forth.

For more than nine hours, a vigorous plume of ash erupted, eventually reaching 12 to 15 miles above sea level. The plume moved eastward at an average speed of 60 miles per hour, with ash reaching Idaho by noon. By around 5: 30 PM on May 18 the vertical ash column declined in stature but less severe outbursts continued through the night and the following several days. In all, St. Helens released an amount of energy equivalent to 27,000 Hiroshima-sized atomic bombs.

Fifty-seven people were killed along with 1500 elk, 5000 deer, and an estimated 11 million fish. In addition, 200 homes, 47 bridges, and 185 miles of highway were destroyed. Between 1980 and 1986, activity continued on St. Helens, with a new lava dome forming in the crater. Numerous small explosions and dome-building eruptions occurred during this time. Beginning with the winter snows of 1980/1981, a still unnamed horse shoe-shaped glacier began to evolve in the shadow of the crater.

Between 1989 and 1991, a series of seismic events occurred, sometimes accompanied by small explosions from the dome. Later, in 1995, 1998, and 2001, earthquake swarms were recorded beneath the crater, though without explosive activity. On October 1, 2004, Mount St. Helens sent an enormous amount of steam and ash into the air for approximately 25 minutes, yielding evacuation orders from nearby areas. Mount St. Helens vented steam, ash and rock once more into the air.

On October 6, 2004, the U.S. Geological Survey announced that the alert level was being lowered, saying 'We no longer think that an eruption is imminent in the sense of minutes or hours'.