Monday, August 17, 2015

Mt St Helens

Visited Mt St Helens for the first time in at least 20 years last week during a week-long vacation with my family. While the focus was checking out a volcano with a trio of young boys, I couldn't help but marvel at how important the mountain, and its eruption in May 1980, has been to how we view perceive, study, and prepare for natural hazards.

We spent the entirety of our two days on the north side of the volcano, in the areas directly affected by the massive landslide that preceded the blast, the pyroclastic flow that characterized the eruption itself, and the lahar that swept down the Toutle River in the hours after the eruption, and visited both the Johnston Ridge Observatory and Weyerhauser's Forest Learning Center. The Forest Learning Center, in particular, was a surprise hit for both its diverse and innovative interpretive materials, and its awesome playground (which Theodore found particularly appealing):

Our first stop, though, was the buried A-frame alongside the Toutle River, some 25 miles downstream from the volcano. While this place is, at its heart, a classic American road-side also really helps to transport you back to mid-day during the eruption, when mud enveloped the entire floodplain:

McHenry and my nephew Silas staring into the second floor window of a house buried by the lahar that followed the eruption

Part and parcel of the story of the Toutle Valley lahar was getting to view and grapple with the management implications of the massive quantity of sediment injected into lowland watersheds during the eruption. The management of that sediment is an on-going issue, and includes a dam purpose built to retain sediment in the upper Toutle River valley. Here is a view looking downstream along the Toutle Valley:

The Toutle was transformed by the massive dump of sediment from the eruption, and its floodplain, 35 years later, still gives every appearance of trying to work through the massive sediment supply. It is generally poorly vegetated, highly braided, and very broad.

Up at the volcano itself, the geology is absorbing. We walked the Hummocks Trail through the landslide area just down valley from the mountain, through giant piles of debris, most of it composed of angular chunks of the mountain itself.

An angular rock carried down valley by the massive landslide that preceded the eruption, as the whole north flank of the mountain collapsed.

One of the hummocks, huge piles of dust, angular boulders, and ash, associated with the massive landslide that came off of Mt St Helens on the morning of May 18

However, I found myself focusing on the stories that provided insight into how people at that time viewed and responded to the risk of an eruption. Some of the interpretive materials at the Johnston Ridge Observatory and the Forest Science Center really helped me to understand how difficult the days leading up to the eruption were for scientists, local and state decision-makers, and emergency managers. The scale of the devastation, even 35 years later, makes it hard to believe that many doubted the advice provided by scientists working on the project...but some died as a result of that doubt.

Indicators of destruction: The remnants of trees at Johnston Ridge, ripped from their stumps

Those that died. Front and center is the name of David Johnston, a USGS scientist that died in the line of duty during the eruption, manning a volcano observation post, on what is now called Johnston Ridge. The landslide that preceded the eruption swept over this ridge within seconds of it breaking loose from the flank of Mt St Helens.