Holy Mount Helens

The mount Saint Helens is a active Stratovolcan located in the Comté of Skamania in the State of Washington in the peaceful area, in the North-West of the the United States. It is located at 154 kilometers in the south of the town of Seattle and at 85 kilometers in the North-East of the town of Portland. The mount Saint Helens draws its name from a diplomat English carrying the title of Lord St Helens. This diplomat was a friend of the explorer George Vancouver who made an exploration of the zone at the end of the 18th century. The volcano, well-known for its explosions slackening of the volcanic ash and the volcanic clouds, belonged to the Chain of the Cascades and the volcanic arc of the Cascades which is a section of the Ceinture of fire of the Pacific comprising approximately 160 Volcan S credits.

The mount Saint Helens is famous since its catastrophic eruption of May 18th, 1980 which caused the death of 57 people while destroying 250 houses, 47 bridges, 24 kilometers of railways and 300 kilometers of roads. Enormous a Landslide made pass the altitude of the volcano of: 2950 to 2549 meters while moving a volume of 2.3 km 3 of matters. The top was replaced by a crater in form of Horseshoe of a width of 1.5 kilometers.

As for the majority of the other volcanos of the mountainous chain of the Cascades, the Helens Saint is an eruptive cone made up of hardened lava mixed with volcanic ash and stone Ponce. The mountain comprises layers of Basalte and Andésite with through which pass several domes of lava made up of Dacite. Largest of these domes of the name of Goat Rocks dome the top of before 1980 formed before being partly destroyed and replaced by smaller.

Geography and description

General information

The mount Saint Helens is located at the the United States, in the South-west of the State of Washington, between Seattle (in north) and Portland (in the south). Surrounded by the national forest Gifford Pinchot, it is distant of 55 kilometers in the west of the Mont Adams, of 80 kilometers of the mount Rainier (the most volcano of the mountainous chain of the Cascades) and of 95 kilometers of the Mont Hood.

Of relatively conical form before the eruption of 1980, the volcano presents from now on the open horseshoe shape towards north in a broad valley which opens in direction of the lake Spirit. The summit crater shelters several domes of lava as well as a Glacier: the Crater Glacier. The edges of this crater are relatively regular and culminate with: 2549 meters of altitude. The eruption of 1980 having blown the Vegetation and having submerged the area under the volcanic ash, the sides of the volcano is completely deprived of vegetation while the neighborhoods, still strewn with the tree trunks uprooted by the breath of the eruption, start to be recolonized by the vegetation.

The mount Saint Helens is “young” from a geological point of view compared to the others Volcan S of the area. It started to be formed there is less than 40000 years whereas its top of before 1980 started to rise only 2200 years ago. It is about the most active volcano of the chain of the Cascades since the time Holocène (: 10000 last years).

Before its eruption of 1980, the mount Saint Helens was the fifth higher peak of the State of Washington and it largely exceeded cuts the surrounding hills of them. Its top was covered with snow and ice what was worth to him also by its conical form the name of “Fuji-san off America” (“Mont Fuji of America”). The top of the peak sat at a little more than 1500 meters above its base located between 1220 meters and 1340 meters altitude whereas the diameter of its base measured approximately nine kilometers.

The Ruisseau X which are born on the volcano throw in three different rivers. It is about the Toutle in north and the North-West, of the Kalama river in the west and the Lewis river in the south and the east. The oceanic currents coming from the Pacific Ocean and high altitude lead to abundant rainy or snow-covered precipitations. It falls thus on average 3600 millimetres from water per square meters and the thickness of snow can reach 4.9 meters. The mount probably caused dramatic effects on the life of the occupants of the area. Archeologists thus showed that an eruption covered a camping with Amerindian with stone Ponce approximately 3500 years ago. That involved the abandonment of the zone during approximately 2000 years.

They arrived at a place currently called The Dalles and were filled with wonder by the beauty at the landscape. The two wire disputed in connection with the place and to solve the quarrel, the father drew two arrows, one in direction of north and one in direction of the south.

Pahto followed the arrow of north and its brother that of the south. Saghalie built the Tanmahawis then (bridge of the gods) so that its family can gather periodically. The geologists think that it acted in fact of a landslide which blocked the river.

To punish them, Saghalie transformed them into two large Montagne S. Wy' east became the Mont Hood and Pahto the Mont Adams. Loowit was transformed into mount Saint Helens, known under the name of Louwala-Clough at Klickitats, which means “Mountain smoking” in their language (the Amerindians Sahaptin S named this one “Loowit mountain”).

European exploration

A commander of the Royal Navy of the name of George Vancouver and his crew of HMS '' Discovery '' saw the mount the May 19th 1792 at the time of a Northern voyage of exploration from the coasts of the Pacific which led them in the mouth of the river Colombia. It was the first time that European explorers mentioned the presence of the volcano. Alarmed by the fall of volcanic ash, the Amerindian of the tribe of the Nespelem in the North-West of the State of Washington danced and requested for food necessary to the passage of the winter. They discovered nevertheless moving sands blocking the access of the mouth of the river Sandy close to Portland, suggesting an eruption of the Mont Hood in the previous decades.

European colonists in the area

The first nonAmerindian local inhabitants were the Trappeur S Europeans. Those worked for the Hudson' S Bay Company. With the beginning of the year 1890, a hermit of the name of Ole' Peterson settled in a hut with Cougar Flats , along the high Lewis river. He sent his testimony to the Edinburgh New Philosophical Journal which published its letter in January 1836. The geologist James Dwight Dana of the university of Yale saw the volcano during an exploration carried out by the the United States. Another member of forwarding described formations of basaltic lava at the base of the mount.

At the beginning of the winter 1842, inhabitants were the witnesses of what one called at the time the “Great eruption”. During 15 years, the mount spit of the clouds of ashes. The eruptions of this period were of phreatic type (explosions of Vapeur S). The reverend Josiah Parrish saw the phenomenon in the locality of Champoeg in the Oregon the November 22nd 1842. Ashes reached the locality of The Dalles in Oregon located at 80 kilometers in the south-west of the volcano.

Whereas the volcano had not made any more speak about him since 1854 but the weakness thickness of the layers of ashes associated with this event indicates an eruption of low intensity.

Before the eruption of 1980, the lake Spirit proposed entertaining activities all the year like Bateau in summer or Ski in winter.

Impact of the eruption of 1980

The Helens Saint entered in eruption the May 18th 1980. After intense months of activity which raised part of the Northern side of the volcano, a Earthquake caused the total rupture of the Northern side of the volcano at the time of gigantic a Landslide. The evacuated rock released the matters under Pression inside the volcano what gave place to the greatest volcanic eruption ever recorded inside the continental part of the the United States.

Among the victims is a Géologue 30 years of the name David A. Johnston, positioned near the volcano. Just before its position is not invaded by a pyroclastic casting, Johnston shouted in its last words: “Vancouver! Vancouver! Ca is there! ”. Its body was never found.

The US president Jimmy Carter seeing the damage declared: “Somebody said that the landscape was lunar but the Moon is a golf course in comparison to this place”. A team of turning was héliportée on the mount on May 23rd to film the range of the damage. They were lost at the time of the catches of sight but fortunately they were found healthy and safe on May 27th by a helicopter of the national guard whereas an eruption still had took place on May 25th. Their documentary film The Eruption off Mount St Helens became later popular.

Recent protections and stories

In 1982, the president Ronald Reagan and the American congress made volcano a national monument (Mount St Helens National Volcanic Monument). It is about a zone of a surface of 445 km2 around the mountain including/understanding the national forest Gifford Pinchot.

In 1987, the national service of the forests (National Forest Service) reopened the access to the mountain for the climbing. In 2004, the volcanic activity increased again what stopped the activities on and around the mount.

The July 21st, 2006, the mountain was again opened to the mountaineers.

Geological history

Oldest eruptive activities

The first eruptive period of the mount Saint Helens is known under the name of Ape Canyon Training course (approximately 35000 years ago), the “Cougar period” ( Cougar Stage ) date of approximately: 18000 years and the period of Swift Creek of approximately: 8000 years. These the first three periods are grouped under the denomination of “Old Period”. The modern period which began in 2500 years front J. - C. is called Spirit Lake Stage . The modern period and the old period differ in the composition from the lava. The old ones are made up of Dacite and Andésite whereas the composition of the modern period is diversified with in particular of the Olivine, of the Basalte in addition to the andesite and dacite.

The mount Saint Helens began its growth with the Pléistocène there is approximately: 37600 years. During the period Ape Canyon training course occurred eruptions made up of stones Ponce S and ashes. That lets think that a quantity of approximately 10 km 3 of matters was rejected during this cycle. The top of before 1980 then started to be formed. Important castings of lava characterized this period compared to the old ones which was made up in greater proportion of rejections of ashes. A lava flow was thrown in the rivers Lewis and Kalama hundred years front JC. In 1482, another eruption similar in volume to that of 1980 took place. At the end of April, the Northern side of the mountain started to bulge. A second tremor magnitude 5,1 began on May 18th with 8:32 without precursory sign. This one strongly damaged the Northern side of the volcano by creating a gigantic crumbling. The volcanic matters under pressure inside the Helens Saint were released in an enormous pyroclastic casting which covered the vegetation and the dwellings on 600 km2. The eruption was classified in force 5 in volcanic Indice of explosiveness.

The destruction of the side created Lahar S (mud flows) composed of ices, snows and of water. The lahars ran out on several kilometers along the rivers Toutle and Cowlitz by destroying bridges and camps of loggers. A total of approximately three km 3 of matters was thus transported up to 27 kilometers of the volcano.

During more than nine hours, an enormous plume of ashes obscures the sky while climbing with a height ranging between 20 and 27 kilometers of altitude. The plume moved towards the east at a mean velocity of 95 km/h by reaching the State of the Idaho at midday.

Around 17:30, the plume decreased in the face and the number of explosions decreased the following days. Released energy was equivalent to 350 megatons of TNT what is similar to: 27000 atomic bombs of Hiroshima. The volcano on the whole rejected 2.9 km 3 of matters without counting the matters moved at the time of the landslide and a crater 3.2 kilometers in diameter for 800 meters of depth was created. The eruption killed 57 people, approximately: 7000 large wild animals (stags, Wapiti S, and Bear) and an estimate of twelve million fish.

2004 with today

The magma reached the top of the crater the October 11th 2004 by creating a new dome in the south of the existing Cratère. It continued to grow in 2005 and 2006. The mount Saint Helens showed a reinforced activity the March 8th 2005 when a plume of dust went up to: 11000 meters of altitude what made it visible from the town of Seattle. This minor eruption was accompanied by a Earthquake magnitude 2,5.

The October 22nd 2006, an earthquake of magnitude 3,5 on the scale of Richter caused the fall of part of the magmatic dome which sent a projection of ashes to more than 600 meters height.

The December 19th 2006, a broad plume of ashes was observed making accept the population which a large eruption had had place. With contrario, the regional observatory of volcanos (USGS) did not mention anything of alarming in the face plume observed. The volcano is in fact in permanent eruption since October 2004 but the eruptions always were very limited.

Others

The French vulcanologist Haroun Tazieff had considered to be this volcano inoffensive and had qualified it “small Soufrière”. Finally, it entered in eruption at a few minutes only of the hour planned for the return of: 30000 people who had been moved. Strange fact, among the victims appears the American geologist David Johnston, leader of those which estimated that the risk was real.

The crater of the mount Saint Helens was used as place of turning for a scene of the film the Peak of Dante (1997) in which vulcanologists were supposed to take various measurements referring to this fictitious volcano.

This volcano is of explosive type because of the andesitic increase of magma very rich in Silice. This characterizes a volcanicity of Subduction running in California.

Appendices

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