Viscous beauties

Whenever I see pictures of the May 18, 1980 eruption of Mt. St. Helens, I can’t help myself. I wish I had been there. I wish I could have seen it, up close, in person. It’s gruesome, I know. The devastation was horrific. Fifty-seven people were killed. Twenty-one were never found. Seven thousand big game animals died. Twelve million Chinook and Coho salmon perished. Millions of birds and small mammals died. Carnage was everywhere, covered by ash.

As the stunningly beautiful plume of ash was exhaled 80,000 feet into the sky, nearly three times the altitude of the typical transatlantic flight, 1.4 billion cubic yards of ash was released. Those who witnessed the event tell stories about the ash, how it blanketed everything, got into their cars, and was nearly impossible to clean up. Volcanic ash is not the smooth velvety type of ash one gets from a campfire. Volcanic ash is abrasive, corrosive, and consists of tiny, sometimes microscopic pieces of rock and glass. It is damaging to the lungs when inhaled. It conducts electricity when wet and does not dissolve in water.

Within three days, the ash from Mt. St. Helens reached the East Coast. In addition to the ash that billowed into the sky and the atmosphere, an avalanche containing 23 square miles of debris rushed down the mountain at speeds of up to 150 miles an hour. What did that look like when much of the snow on the mountain instantly flashed to steam? The snow that turned to water combined with particulate material to form gooey mudflows. Twenty-seven bridges, 200 homes, 185 miles of roadway, and 15 miles of railway were consumed and destroyed. Temperatures soared to 660 degrees as the mountain released 24 megatons of thermal energy. Hours after the eruption, pyroclastic flows continued to be emitted from the crater. Temperatures reached 1,300 degrees. The heat from the flows killed the bacteria and micro-organisms in the soil, sterilizing it for six square miles. Signs of devastation were apparent as far out as 17 miles from the crater.

Before the 1980 eruption, Mt. St. Helens stood at 9,677 feet. After her expulsion of ash, rock and molten lava, Mt. St. Helens cut her size by over a thousand feet, to 8,363. Today, a lava dome inside the crater of Mt. St. Helens continues to grow. Forest visitors near the volcano are warned to prepare for potential ash fall.

How volcanoes erupt: from magma to lava

A volcanic eruption begins deep within the earth, temperatures reach such extremes that rocks melt. The resulting hot, fluid substance is called magma. Magma rises to the surface of the earth and collects in magma chambers. Pressure builds as more and more magma pushes into the limited space of the chambers. Eventually, the pressure is so intense that the magma breaks out onto the surface of the earth and becomes lava.

Volcanic eruptions can be either mild or explosive, depending on the viscosity of the magma. When the magma is thin and runny, gases can readily escape into the atmosphere. When the magma is thick and sticky, it is harder for gases to escape. Pressure builds in the magma until the gases explode out of the hot molten rock. The substance produced from explosive magma is called tephra and can range in size from tiny particles to “house-size boulders.”

Visiting volcanoes

The Pacific Northwest is a veritable volcanic paradise. The Cascade volcanoes are among the most notable and zigzag their way north to south from Washington through Oregon down into California. Although the volcanoes of the Cascades seem relatively quiet, many are merely resting. It is helpful to know which of them could awaken violently as Mt. St. Helens did in 1980. Before visiting a volcano it can be helpful to visit the U.S.G.S. website to see if any advisories or road closures are in effect. There may also be helpful advice for special preparations to make against such occurrences as minor ash fall.

If you feel compelled to get a wee bit closer, consider becoming a “volcano chaser.” In the volcano-chasing community, volcanoes are considered safer than earthquakes, floods and hurricanes. (Never mind that earthquakes often precede volcanic activity.) As a volcano chaser, you will know where the “death zone” of a volcano is, and you’ll know when to be there–never.

Besides the obvious, major dangers of volcano chasing come from falling rocks expelled from the volcano. It is advised to wear a helmet. Another not-so-obvious danger to volcano chasers is the mesmerizing effect of a volcano. When you approach the edge, don’t stay too long.

Stratovolcanoes of the Northwest

Scientists classify volcanoes into six distinctive categories. From least to most violent, these volcanic types are: flood/plateau basalt, shield, cinder cone, composite/stratovolcano, volcanic dome, and caldera. Mt. St. Helens is a stratovolcano. Stratovolcanoes are middle-of-the-road volcanoes in terms of violence and viscosity. Stratovolcanoes have viscous lavas and produce explosive, pyroclastic debris emitted from a single vent.

Mt. Baker

Located in Northwestern Washington state due east of Bellingham by about 25 miles, Mt. Baker is the northernmost volcano in the U.S. Cascade Range. According to the U.S. Geological Survey, Mt. Baker is one of the youngest volcanoes of the range. Currently reaching a height of 10,775 feet, Mt. Baker’s last eruptive event was in 1976 with emissions of gas, steam and small lahars, or moving fluid masses composed of volcanic debris and water.

Glacier Peak

Also in Washington, Glacier Peak is about 50 miles southeast of Mt. Baker. Its height is 10,541 feet and it has been fairly active, with six eruptions in the past 4,000 years, and small eruptions between 200 and 300 years ago.

Mt. Rainier

About 50 miles southeast of Seattle, Mt. Rainer has the highest peak in the state of Washington at 14,411 feet. Mt. Rainer has had four significant eruptions over the past 4,000 years, showing volcanic activity within the last 200 years. Mt. Rainer is expected to erupt again within the next few hundred years.

Mt. Adams

Mt. Adams is about 40 miles south of Mt. Rainer and 30 miles east of Mt. St. Helens. Mt. Adams stands at a height of 12,276 feet. Although it has been relatively quiet over the last few thousand years, geologists expect Mt. Adams to erupt again. When it does, its eruptions are expected to occur from vents on the summit and upper flanks of the mountain. Mt. Adams’ last eruption occurred about 1,000 years ago.

Mt. St. Helens

The last and most active of the major Cascade volcanoes in Washington, having 15 major eruptions in the past 4,000 years, Mt. St. Helens is 30 miles west of Mt. Adams and stands at a height of 8,363 feet. Its last major eruption was on May 18, 1980, but it has had numerous smaller eruptions since that date. It is expected to erupt again.

Mt. Hood

Mt. Hood is the northernmost of the major Cascade volcanoes in Oregon and can be prominently seen from Portland on a clear day. It is located south of Mt. Adams by about 60 miles and is the highest peak in Oregon at 11,239 feet. Mt. Hood has erupted three times in the last 2,000 years and with two of those eruptions occurring within the last 200 years, Mt. Hood is expected to erupt again.

Major volcanoes in Oregon Mt. Bachelor (stratovolcano)Mt. Bailey (cinder cone)Belknap Shield Volcano (shield volcano)Broken Top (stratovolcano; potential exists for eruption)Crater Lake National Park (Mt. Mazama–caldera, potential exists for eruption)Diamond Peak (shield volcano) Mt. Jefferson (stratovolcano)Lava Butte (cinder cone) Mt. McLoughlin (shield volcano) Newberry National Volcanic Monument (shield volcano, potential exists for eruption)Pilot Butte (cinder cone)Three-Fingered Jack (shield volcano) South Sister (composite volcano, potential exists for eruptionMiddle Sister (composite volcano, potential exists for eruption)Mt. Theilsen (shield volcano, potential exists for eruption)Mt. Hood (stratovolcano, potential exists for eruption)Mt. Washington (shield volcano)

For More Information:

PSU Geology Department, www.geol.pdx.edu/

Safety for Volcano Chasers, www.volcanolive.com/safety.html

The Live Volcano Cam from Johnston Ridge, www.fs.fed.us/gpnf/volcanocams/msh/

Pacific Northwest Seismic Network, www.ess.washington.edu/SEIS/PNSN/INFO_GENERAL/volcanoes.html

Seismo-surfing, www.pnsn.org/seismosurfing.html

USGS, earthquake.usgs.gov/eqcenter/helicorders.php

Cascade Mountains, vulcan.wr.usgs.gov/Imgs/Gif/Cascades/EruptiveHistory/cascades_eruptions_4000yrs.gif

Mt. St. Helens National Volcanic Monument, www.fs.fed.us/gpnf/mshnvm/

Volcanic Ash, volcanoes.usgs.gov/ash/