Video Guide The Eruption of Mount Saint Helens
By Otto Sieber
Video Study Guide By M. Mustoe ©1996

Abstract
This is an an incredible, almost cult like film. Everything in the film is real and the setting for the film is actually on Mt. St. Helens. The music is by a Seattle garage type band and it includes both regional folk music and some jazz. The songs are great, listen to the words as they liken what happened at St. Helens to the dust bowl period of the 1930s.
The film begins with a climb up St. Helens prior to the main eruption of 1980. St. Helens came back to life entering into an eruptive phase on 30 March 1980 after 123 years of sleep. A series of small eruptions followed. Then a main eruption and some dome building activity since then.
St. Helens was a very climbable mountain. The smooth sides and even ice flows made it a fun day climb to its 9,677 foot summit. 11 glaciers were at home on St. Helens' slopes. The climbing team that you see in the beginning of the film are doing the mountain just after the March episodes began. They use crampons and ice axes to traverse the ash covered snow near the summit. Notice how wide the climbing path is. This mountain had a very smooth newness to it. It has not been exposed long enough to show the effects of erosion like Rainier, Shasta, or Hood. St. Helens went through an active stage from 1800 to 1857 and has been building slowly upward, layer by layer for the last 37,000 years. Yes, thousands of years....this is not an old volcano.
The Native Americans in this region called the mountain "Lawelatala" The person from whom smoke comes, "tah-one-lat-claw" Fire Mountain and also Keeper of the fire. St. Helens' eruptive attitudes have been witnessed by these people as well as other settlers in the area. In 1792 British Navigator, George Vancouver named the mountain after a famous diplomat and friend of King George III. During the European period of exploration there has actually been paintings made of the mountain erupting.
On 18 May, 1980 St. Helens exploded with a bang that could be heard as far away as Canada. Your teacher was there and heard it clearly that Sunday morning in E. Wenatchee nearly 180 miles northeast. The mountain's eruption affected the region two ways. Prevailing winds from the NW blew Ash to the east of the Cascade Crest, shutting down Interstate 90 all the way to Montana. Yakima a town to the east, reported 600,000 tons of ash fell there with an average weight of 95 pounds per cubic foot. Ash fell as far east as Oklahoma on May 18th. Second a pyroclastic cloud flowed down from the mountain filling up the Toutle River drainage valleys with mud and debris.
The Cascade volcanoes, part of the ring of fire began their development during the late Eocene (22 mya) and Oligocene (11 mya) during the Cenozoic Era.....some say as far back as about 36 million years ago. Looking through the layers of volcanic rock at St. Helens and elsewhere through the Cascades, there is evidence that the type of material erupted from these volcanoes has changed considerably. At St. Helens, early on the volcano erupted mostly dacite and andesite lavas until about 2500 years ago. In its more contemporary activity the composition of the lava has changed to basalt with olivine to dacite and andesite. This is important to note when considering how the mountain was formed.
During the Oligocene the lavas from these mountains, mostly rhyolite and andesite, became more silicic, that is lava that has higher concentrations of silica. This kind of lava is very sticky and does not flow well. It forms domes that can plug (plug domes) which ultimately may erupt in explosive ash eruptions from the plug dome being blasted off the top of the mountain. This is basically what happened during the 18 May event. Many Cascade volcanoes are plug domes. They are also known as composite cones or Stratovolcanos. If you cut through the mountain you will see layers of alternating pyroclastic materials and viscous lava. The plug of lava that is slowly filling up the gigantic crater and breech left by the explosion at St Helens is now over 800 feet high and at its present rate should take about 250 years to fill the crater to form a dome or top to the mountain again.
In 1980 St. Helens did not erupt massive amounts of lava, what did occur was normal for a mountain of this type in the Cascades....an eruption of ash....incandescent rock fragments, moving at about 220 to 670 miles per hour and heated to nearly 700 degrees Fahrenheit 57 people died, mostly by suffocation from the hot gases. The glowing cloud of ash contained parts of the old dome and bombs of new lava. The pyroclastic surge carried about .045 cubic mile of material which, in composition was about a third, new lava. But this was not a flowing lava like that found in the shield volcanoes of Hawaii. The surge almost instantly melted hundreds of years of snow and ice and created massive mud slides in the Toutle valley of Western Washington. This activity dammed up the Toutle and eventually the Columbia River. One main hazzard from this mountain was from the mud it generated.
Prior to the main event a huge bulge formed on the north side of the mountain just below the summit. It was defined by a crack nearly a mile and a half long. The whole side of the mountain seemed to be moving. The USGS measured this block of the mountain to be offsetting nearly 270 feet up and out from the mountain. It was this mass and the plug dome that erupted into chaos that Sunday in May; burying Spirit Lake, and Harry Truman, his cats and the lodge, and blowing down 230 square miles of Douglas Fir, some 200 feet high and six feet in diameter. After it was finished tens of thousands of trees lay down like match sticks. The blast came in three parts. A horizontal blast, landslide, and a vertical blast, made up the sequence.
Directly after the main event of 18, May Otto Sieber and his film crew went up into the region around the mountain. This area was totally devastated by the blast. Watch what happens when the Skamania County Sheriff comes to take them out of the area.
In this film you will be travelling to the following regions:
Your teacher knows this mountain very well. Some of my relatives mined silver on its flanks in the late 40s and fifties and named some of the landform features around it. This was an absolutely beautiful place and as a little child I remember enjoyment I got exploring along the shores of Spirit Lake. It was crystal clear, full of trout, and reflected the mountain, like a mirror. I also remember gazing up at St. Helens in the distance and taking special notice of some of the features on its slopes. The Goat Rocks and especially the Sugar loaf dome. Now when I have been back to the mountain to do research it takes me awhile to get used to it. The devastation was so complete and so permanent (at least for our lifetime), it is like remembering about loosing a part of myself when I see it again. But changes are taking place on the mountain continually. The vegetation is coming back, the elk and deer have shown back up, and humans are planting trees that are growing well in the ash covered soil. The fireweed paints the hillsides pink in the area of the blow down and the honey bees take full advantage of the nectar it provides.

The following places are discussed:
Mount St. Helens: once 9677 feet now....8,377 feet
Toutle River: Main drainages from the mountain flowing West in two forks, the North and South. The North was heavily hit by pyroclastic flows and the South by mudflows.
Columbia River: Main drainage to the Pacific, bordering Washington and Oregon.
Seattle: 100 miles to the North and West, on the west side of the Cascades. No ash.
Yakima: 90 miles to the North and East. Lots of Ash.
Ellensburg: 130 miles to the North and East. Lots of Ash. Home of Central Washington University.
Ritzville: 160 miles North and East. Light Ash covering.
The Ring of Fire: All the volcanoes in the area surrounding the coastal basin of the Pacific Ocean
Key Words:
Pyroclastic materials: Hot glowing rock fragments and gases; sometimes containing Pumice or dense rock. Travels like sirup hugging the ground.
Silica: Silicon and oxygen and a strong component of volcanic rocks.
Basalt, Rhyolite, Andesite: Lavas of various compositions.
Nuée Ardante: A glowing cloud of hot gases and ash.
Ash: Very fine particles of pulverized rock. These measure less than .1 inch in diameter.
Lapilli: Explosive materials .1 to 2.5 inches in diameter. Latin for Little Stones. These can be round or jagged and can either of been erupted in a molten or solid state.
Composite Cones or Stratovolcanos: Layered volcanoes, that are well above 8,000 feet.
Plug Dome: The lava rock mass which makes up the cap or top of the mountain. Typical in the Cascades.

Questions:
What were the hazards St. Helens imposed on people in the region? What impact did the eruption have on the natural environment? What if it had been raining in Eastern Washington on May 18th? What other kinds of geologic hazards do people face in the Northwest or the Ring of Fire area? What plans can people make to adjust for an event such as this?