KING 5's Jeff Renner looks back at Mount St. Helens eruption

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by JEFF RENNER / KING 5 Meteorologist

NWCN.com

Posted on May 18, 2010 at 7:30 PM

Updated Tuesday, May 18 at 11:28 AM

Back in 1980, I served as KING 5's science reporter and filed reports beginning with the first earthquakes at Mount St. Helens in mid-March. Our crew literally camped at the volcano for days at a time.

On March 16th, 1980, the volcano shuddered awake from its 123-year slumber. Just nine days after the first earthquakes, steam flashed upward, exploding through the summit ice cap and opening a quarter-mile-wide crater.

The Cascade Range is home to the some of the biggest and most dangerous volcanoes in the continental U.S. Hiking along a ridge in the Cascades reveals the most active cones in the Northwest, but the best way to appreciate their number, size and majesty is to take to the air.

The volcano that first commands your attention is Mount Rainier. Mount Rainier first erupted during the Ice Age. It's a monument of both fire and ice. Rainiers' glaciers equal those of all other Northwest volcanoes, which stretch from northern California to British Columbia. 

From space, we would see our Cascade volcanoes are part of the larger Ring of Fire, circling the Pacific coastline like the seam on a baseball extending 24,000 miles.

Scientists discovered what makes the "ring" so explosive by descending beneath the Pacific to the ocean floor. Sophisticated tools revealed a collection of rigid "plates," pieces of the earth's crust and upper mantle, that "float" on the superheated, bendable mantle beneath. Those plates move, some grinding past each other, some separating and others colliding.

In 2005, a University of Washington research team voyaged 200 miles offshore. A robotic submarine descended to the crushing depth of almost 7,000 feet to a dark place where the Juan de Fuca and Pacific plates are spreading apart.  Images revealed underwater "black smokers" - hot, chemical-rich plumes that support an astonishing variety of life.

The eastern edge of that same plate is plunging beneath our feet into the extreme heat of the mantle. That converts the plates' minerals into magma, or molten rock, which in turn melts other rocks from the earth's crust. This new mix is less dense than surrounding rock and rises, forming the magma chambers that feed our Cascade volcanoes.

One morning in early April, we climbed out of our sleeping bags and noticed the north side of Mount St. Helens seemed to be bulging outward. USGS scientists confirmed magma was rising and the volcano was inflating.

"As I was reading, I heard some people yelling," said Keith Ronnholm, who was a young graduate student at the time.

On the morning of May 18th, 1980, Ronnholm camped just 10 miles away from the volcano.

 "I glanced out and I saw the entire north face of Mount St. Helens sliding down," he said.

Shaken by an earthquake at 8:32 a.m., the bulge simply collapsed

"Here I was watching this massive landslide. It must have been half a mile wide," said Ronnholm.

The hot gas bottled up inside blasted northward, accelerating to 300 mph. It obliterated everything in its path.

"I watched as the gray ash cloud, churning and turbulent, hit the first ridge," said Ronnholm.  "I was driving as fast as I could down this road…Behind me was a wall of cloud."

Ronnholm outdistanced the wall of ash - barely.

A vertical blast followed, punching 80,000 feet straight up in just minutes. Its force dwarfed the atom bombs dropped in World War II.

The mudflow just beneath a KING 5 helicopter near the volcano was actually a stew of trees, mud, melted glaciers and snow that destroyed 200 homes and cabins, flash- melted by avalanches of hot ash, pumice and gas surging from the crater. That debris avalanche of rock and ash was vast enough to bury the entire city of Seattle under 18 feet of rubble.

Multiple eruptions continued throughout the day, blowing 520 million tons of ash across the U.S. The cloud circled the earth in 15 days.

The initial blast uprooted 10 million trees. At 660 degrees, it was hot enough to melt lead. The result was a vast dead zone that included both of our broadcast bases. We discovered one victim just feet from where we'd pitched our tent hours before. There would be 56 others.
 

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