Mount St. Helens and the Hoodlum!

Crater with lava dome in center

On Sunday, faced with an unusually bright and clear day, we set out for Mount St. Helens. We drove north into Washington state and then headed to two of the Mount St. Helens visitor centers. We watched a short film on the eruption of the volcano on May 18, 1980. The visitor center also offered a museum exhibit that explained Mount St. Helens' long eruption history and that the mountain is one of the newest and most active in the Cascade Mountain range. The exhibit went on to explain the scientific studies geologists began conducting after the initial earthquake on March 16 when they realized the volcano was 'waking up'.

Ken on Johnston Ridge

As we stepped outside, a park ranger offered a talk on the eruption with the volcano in the distant background. She explained that before it erupted a huge bulge had formed over the previous 2 months on the north face of the mountain. The bulge grew so alarmingly quickly that geologists suspected their equipment was faulty. The bulge reached out from the mountain almost 850 feet before it collapsed under the gravity of its own weight at 8:32am on May 18th, 1980. The landslide caused by the collapse formed a crater where the summit once stood 1.2 miles wide, 1.8 miles long and over 2,000 feet deep. Wow.

Trees shattered by the blast

Geologists had predicted an eruption and recommended an evacuation 5 miles out from the north side and 3 miles out from east and west. Unfortunately, the blast cloud, traveling 17 miles north (and 11 miles east and west) at up to 500 miles an hour, and the ensuing landslide (the largest in Earth's recorded history) together caused a wide swath of destruction that obliterated almost everything in a 230 square mile area. The volume of material in the landslide would be enough to pave a 7 lane highway three feet thick from Seattle to New York...impressive.

Lahar deposits on valley floor
of the North Fork Toutle River

When the collapse released the magma and steam building in the bulge, the heavy volume of snow and ice at the summit melted instanteously. This sudden gush of water added to the rocks and ash of the landslide resulted in a thick wet cement-like mudslide (or lahar) that overtook everything in its way. The lahar deposited huge rocks, earth and mud up to 640 feet thick at the base of the Johnston Ridge, about 5 miles northwest of the summit, and on down the North Fork Toutle River for 14 miles to an average depth of 150 feet, while it swept away every tree, building and animal in its path. Many other lahars flowed down all sides from the summit choking streams and creating two new lakes in the process. The surface area of existing Spirit Lake doubled when the lahar filled the lake basin. Some 25 to 30 miles away, the Columbia River depth decreased from 40 to 14 feet. Even today, 32 years later, the valley floor where the North Fork Toutle River runs remains choked with large rocks and old trees ripped from their roots all lodged in a thick clay.

View from the Johnston Ridge
Observatory theater

The eruption, when it finally occurred, extended 17 miles to the north and 11 miles to the east and west. And sadly, 57 people were killed, but only 6 were inside the evacuation area, with the remainder in the "safe zone". Since the blast, geologists have learned from their misunderstanding of the data recorded during the observation of Mount St. Helens prior to the eruption. The key miscalculation occurred when (they later discovered) a crust had developed over the bulge, eliminating the steam vents thus allowing even more pressure to build underneath. At the same time, the earthquake activity slowed to a "harmonic tremor", which they now understand is the prelude to a release of magma. Most devastating was the expectation that all volcanoes erupt vertically, where this one erupted laterally (and in a really big way). Initially, the bulge collapsed which triggered the lateral blast, closely followed by a vertical blast. Yikes.

Tree pointing away from the blast

We drove to Hoffstadt Bluffs visitor center (about 25 miles from the volcano) because we were told there would be buffaloes and elk herds roaming around. Not so...at least not while we were there, of course. We dined on tasty sandwiches at the cafe there waiting for the big animals to show up, but no dice. In any case, from our table on the patio we could see the river bed of the North Fork Toutle River, where the landslide had filled the basin and still the plants haven't grown back in many places.

We continued on up to the Johnston Ridge Observatory a mere 5 1/2 miles from the volcano (after an aggravating 18 mile detour back to Toutle for gasoline). The observatory overlooks the valley between the mountain and the Johnston Ridge on which it is perched without so much as a single tree to obscure the view.

View of valley of the jolly (ho,ho,ho) green giant

We listened in on a ranger talking about some of the features of the crater...the lava dome inside of it is over 1300 feet tall, formed in just 32 years. The landslide shortened the height of Mount St. Helens from 9600 to 8300 feet, and the ash cloud from the eruption reached 80,000 feet in the air within 15 minutes. The staggering number of old growth trees lost from the immense speed of the blast cloud is immeasurable, though scientists estimate it at enough wood to build 300,000 two-story homes. Within 5 miles of the mountain, trees were either shattered by the blast cloud or ripped from the ground by the fast-moving lahars. Beyond the 5 mile zone, the trees were stripped of their leaves and bark and knocked down like millions of compass needles pointing in the direction the blast was moving.

Mount Hood...gotcha!

We watched a film on the geology of the eruption and then listened to a ranger talk about the same subject, again, with the mountain in the background. The entire day was absolutely fascinating. We walked up the highest peak on Johnston Ridge and then down a hiking trail along the ridge. What a spectacular event in history.

On our way back to the RV, we f.i.n.a.l.l.y. caught sight of Mount Hood peeking at us through the trees and over the buildings on our journey south along the highway. We raced to find an open view to snap a picture and finally found one at the airport, near the RV park. Yay!

What an awesome day!