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Mt. St. Helens 1980 Eruption Before, During and After.

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Presentation on theme: "Mt. St. Helens 1980 Eruption Before, During and After."— Presentation transcript:

1 Mt. St. Helens 1980 Eruption Before, During and After

2 Where is Mt. St. Helens The Cascade Range is a volcanic chain stretching from Northern California to British Columbia Mt. St. Helens is part of this range

3 Mt. St. Helens, the smallest of five major volcanic peaks in Washington state had an elevation of 9677 feet before the eruption of May Mt. Adams (12,286) in the distance

4 First Evidence of Activity Initial ice fractures on March 27, /28- First phreatic (steam) eruption The vent: 250 ft in diameter

5 March 29, 1980 Second Crater Crater appeared on the NE side of the first crater The new vent was 75ft. Wide and 30-60ft deep 3/31 the two craters joined together

6 March 30, 1980 Ash Darkens Slopes Ash came from rock pulverized by the explosively- expanding, high- temperature steam and other gases- No new rock produced Mt. Rainier in the background

7 Steam Explosion -4/10/80

8 Bulge Forms on N-NE Flank Bulge first detected on 4-23 End of April the bulging area was one mile long and 0.6 mile wide Maximum uplift 320 feet Some areas of uplift - 5 feet a day!

9 Another View of the Bulge April 27,1980

10 Steam Eruption Prior to Typical phreatic (steam) eruption in early May Eruptions reached 13,000 feet in elevation This activity was followed a two week quiet period

11 On may 18th 1980 at 8:32… Geologist David Johnston was taking measurements on a ridge just 5 miles NW of the summit when he radioed Vancouver! Vancouver! This is it! Moments later he was vaporized by the cloud of hot gas, ash, rock, ice and trees that hit him

12 For more than nine hours, the eruption continued. People that escaped had to drive 80+mph on old logging roads to escape

13 May 18th :32 AM PDT a magnitude 5.1 shook Mt. St. Helens The bulge and surrounding material slid away in a gigantic landslide and debris avalanche

14 Computer Version of Landslide The initial earthquake and eruption triggered one of the largest landslides in recorded history. The slide traveled mph Hit a 1150ft high ridge about 6 miles north. Some of the slide spilled over the ridge Most of the slide moved 13 miles down the North Fork of the Toutle River filling its valley up to 600 ft deep


16 The initial May 18th Eruption View From Less Than Three Miles The cloud rose to more than 12 miles in 10 minutes The cloud generated its own lightning Ash rained down initially in an area that extended miles to the north and east Later, ash covered parts of eleven states From an airplane that barely made it back!

17 For over nine hours, a vigorous plume of ash erupted reaching miles above sea level The plume moved eastward at an average speed of 60 mph with ash reaching Idaho by noon Many cities had to use snowplows to remove the several inches of ash accumulation


19 Eleven States Had Ash Fallout

20 View from the NE on June 19, 1980 This area was completely forested prior to the May 18, 1980 eruption

21 Helicopters were deployed to try and save survivors. Few were found Some people were found with their arms calmly folded or a camera held to their eye. The hot gasses killed them as they stood. It is believed that some people and vehicles were instantly incinerated The total volume of ash as approximately.26 cubic mile or enough ash to cover a football field to a depth of 150 miles

22 The initial blast flattened over four billion board feet - Enough to build over 150,000 homes.

23 Nearly 135 miles of river channels surrounding the volcano were affected by the lahars. Note the mud line on the trees and the person in the picture

24 The remains of Spirit Lake, once surrounded by lush forest Mt. Rainier, 14,410ft in the distance

25 After the May 18,1980 eruption, Mt.St. Helens elevation was only 8364 feet and the volcano had a one-mile wide horseshoe-shaped crater Craters were formed when water and hot ash came together making large steam explosions

26 Reid Blackburn, a National Geographic Photographers car Ried Blackburn along with Volcanologist David A. Johnston were never found

27 The U shaped basin formed by the landslide and 5/18/80 eruption June 4th Mudflows are visible in the picture

28 Mt. St. Helens erupted often between 1980 and 1986 An explosive eruption on 3/19/82 sent pumice and ash 9 miles into the air and resulted in a lahar

29 Pyroclastic flow from August 7,1980 eruption During the 5/18/80 eruption, at least 17 separate pyroclastic flows descended the flanks of the mountain Pyroclastic flows typically move at speeds of over 60 mph and reach temperatures of over 800 degrees

30 October 24, 1980 a new dome started growing. This October dome was 112ft high and 985 feet wide making it taller than a nine-story building and wider than the length of three football fields

31 Mt. St. Helens soon after the 5/18/80 eruption from Johnstons Ridge Taken September 10, 1980

32 USGS Scientist Explore Pumice Blocks from a Pyroclastc flow October 17, 1980

33 Geologists install a seismic station near the dome. An increase in seismicity is often the first precursor to an approaching eruption

34 5/19/82- Plume from Harry's Ridge Plumes of steam, gas, and ash often occurred at Mt. St. Helens in the early 1980s. On clear days, they could be seen from Portland Oregon, 50 miles to the south

35 Harry's Ridge Was Named After Harry Truman of Spirit Lake

36 Measuring magnetic field in crater 6/18/84 Geologist measured the strength of the magnetic field surrounding the dome. The strength of the field increased as the dome cooled and magnetic minerals formed. During the eruptions, the strength usually changed rapidly as magma heated and deformed the dome

37 USGS scientists survey the dome 5/26-84

38 April 18, 1988 USGS Deformation Monitoring on the Dome

39 Mt. St. Helens, Sept. 1994

40 Aerial View of Mt. St. Helens 2002

41 Mt.St Helens night shot of Dome

42 Mt.St Helens Spirit Lake before The May1980 Eruption

43 Mt.St. Helens Lake Reflection- After the Eruption Picture taken May 19, 1982

44 2005 Saw An Increase In Activity Picture Taken May 7, 2005

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