Mount St. Helen is a volcano located along the Cascade range which is a
volcano chain stretching from Northern California to British Colombia. It now
stands at a height of 8,364 feet above sea level.
Mount St. Helen was on of the smaller eruptions of five major ones in
Washington State. Its elevation before the eruption was 9,677 feet high.
On March 29, 1980 after a period of one-hundred and twenty-three years
of inactivity a earthquake under the volcano quaked, and seven days later a
pheartic (steam) explosions began.
As magma pushed up from beneath the earths surface, the north side of
the mountain developed a bulge. Angle and slope-distance measurements
indicating that the bulge was growing at a rate of 1.5 feet per day (Lyn Topinka
Page 2). By May 17 the volcanos north-side had been pushed upward and
outward 450 feet (Lynn Topinka Page 2).
On May 18,1980 at 8:32 a.m. Pacific daylight time a magnitude 5.1
earthquake shook Mount St. Helen. The bulge on the North side of the mountain
gave way in a gigantic rock slide releasing pressure and triggering a major rock
and pumice eruption . At thirteen hundred feet the peak collapsed and as a result
24 square miles of the valley was filled with rock and debris. From that rock slide
250 square miles of timber, recreation and private lands were demolished from the
lateral blast. For more than nine hours the volcano spit vigorous ash in a large
plume. Eventually the plume reached 12-15 miles above sea level. The plume
went eastward at about sixty miles per hour. By noon the plume of ash had
reached as far as Idaho.
By the 19 the eruption was over. Now the volcanoes elevation is only 8,364 feet
above sea level before the eruption it was 9,677 feet above sea level knock off a
whopping 1,313 feet off of the top of the mountain. Now it has a mile wide
horseshoe shaped crater on the northern side of the mountain.
From the eruption noticeable ash fell in eleven states. The total amount of
ash that fell was .26 cubic miles or enough ash to cover a football field to a depth
of 150 miles(Lyn Topinka Page3). From the landslide 2/3 cubic miles of debris
was deposited in the valley that enough to cover Washington DC fourteen feet
thick.(Lynn Topinka, Page 4)
Mount St. Helen is said to have caused the most damage (Mattox Page 1) a
total of 1.6 billion dollars of damage was caused by the blast from the volcano.
That figure comes from losses due to home and road cleanup, damage to
agriculture, timber, roads, bridges, fisheries, houses, sewer treatment plants, and
the dredging of rivers.(MattoxPage1). 57 people were killed or still missing
(Topinka Page1) More than 100,000 acres of were demolished by the blast of that
100,000 acres include 41,000 acres of national forest,(Scooner Page1) also over
four billion feet of usable timber became unusable thats enough lumber to build
150,000 homes.(Topinka Page3) Nearly 135 miles of river channels were effected
by the volcano and more than 185 miles of roads and over 200 homes were
destroyed. (Topinka Page 5)
Now over 9.5 million tree seedlings have been planted to replace the ones
destroyed by the blast and of those 70 percent of those have survived(Scooner
Page 1)some already growing twenty feet high(ScoonerPage1). The fish and
wildlife have received considerable attention since the eruption. The heavily
hunted Elk have shown that the restrictions after the eruption have helped the
repopulating of them returning to the pre-eruption population within five years.
Also the Samon and trout have returned to there population since the eruption.
Stream temperatures have exceeded there legal threshold population in most years
since the eruption. (Sconner Page 1)
Now the United States Geological Survey has established both a continuos
twenty-four hour and periodic monitoring programs to study and predict future
eruptions Mount St. Helen. (Lyn Topinka). They also setup a seismic station near
the dome of the mountain. The University of Washington State in conjunction
with the US Geological Survey now monitor it.