Mount St. Helen’s By: Stephanie Graves

Mount St. Helen’s is located in the state of Washington

On May 18, 1980 at 8:32 am. Mount St. Helen’s Erupted

Summary of volcano, lava dome, and glacier dimensions Volcano Elevation of summit 9,677 feet before 1980; 8,363 after; 1,314 feet removed Volume removed by May 18, 1980, eruption 0.67 cubic miles (3.7 billion cubic yards) Crater dimensions 1.2 miles (east-west); 1.8 miles (north-south); 2, 084 feet deep Crater floor elevation6,279 feet Crater glacier area (September 2000) 0.4 square miles Crater glacier ice volume (September 2000) 105 million cubic yards Maximum glacier thickness (September 2000) 650 feet Lava Dome Elevation of top of dome7,155 feet Height876 feet above 1980 crater floor DiameterAbout 3,500 feet Volume97 million cubic yards

Lava Dome (as of February 1, 2005) Elevation of top of dome7,642 feet Height 1,363 feet above 1980 crater floor; 700 feet above 2000 glacier surface Dimensions of "whaleback" About 1,550 feet long, 500 feet wide Diameter of lava dome and welt deformed by magma intrusion, excluding deformed east glacier arm About 1,700 feet Volume of lava dome and welt defomred by magma intrusion, including deformed east glacier arm 50 million cubic yards

After 123 years of silence, St. Helens showed her first signs of life on Thursday, March 20th with a 4.1 magnitude earthquake centered beneath the volcano. Most northwest newspapers completely ignored this earthquake because President Carter's announcement of the Moscow Olympics boycott dominated the news.

One week later, on March 27th, the mountain smudged the usually pristine snow at her summit with its first puff of ash. No one on the groud knew what had happened at first because the top of the mountain was encased in clouds for her first show. The small explosion left a 250 foot wide crater in the otherwise perfect cone. On March 30th there were a record 79 earthquakes recorded on the mountain.

On April 3rd, the first harmonic tremors were recorded signaling the movement of magma somewhere deep within the dome. The crater was by now 1,500 feet wide. Explosions of ash, rock and ice chunks were almost a daily occurrence by this time. The mountain had taken on an eerie, sinister look with her ash covered slopes.

In late April a noticeable "bulge" began to form on the north face of the mountain. The bulge was created by the building pressure of hot gases and magma inside the mountain. All through early May the bulge grew at an astonishing 5 feet per day. The mountain soon lost its perfect cone shape that had characterized it as the "Mt. Fugi of the West".

Mount St. Helen’s is a typical subduction-zone volcano. That Means that eruptions are often explosively violent.

At 8:32 a.m. a 5.1 magnitude quake struck one mile below the mountain. While there had been literally hundreds of earthquakes at the mountain since March 20th, the unstable north face could not sustain another. Within moments the largest landslide in recorded history removed more than 1,300 feet from the summit and swept away almost the entire north side of the mountain. The elevation of the mountain dropped from 9,677 feet to its present day 8,363 feet. What was once the 9th highest peak in Washington state was suddenly reduced to the 30th highest peak. The intense high pressure/high temperature steam that escaped, instantly turned more than 70% of the snow and glacial ice on the mountain to water. This massive movement of rock, ash, water and downed trees swept into Spirit Lake and down the north fork of the Toutle River Valley at speeds in excess of 175 miles per hour.

Mount St. Helen’s from the air.

Mount St. Helen’s is recovering from the scars from the Explosive eruption and is on the road to beautiful once again.

Works Cited Page Kids Discover. Volcanoes pg. 6-7.

The End