This is the Lahar Viewpoint with an extraordinary view of Mt St Helens and the truncated valley cut by the Shoestring Glacier of which 75% of the glacier's volume was removed through the volcanic activity of Mt St Helens in 1980, creating deadly lahars down the mountainside. One of those lahars is displayed quite prominently here at the listed coordinates. This area was swept by a lahar within 15 minutes after the onset of the May 18, 1980, eruption. At this point, the speed of the lahar was estimated at about 44 miles per hour.
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of Indonesia. A lahar of sufficient size and intensity can raze virtually any structure in its path, and is capable of carving its own pathway, making the prediction of its course difficult. Conversely, a Lahar quickly loses force when it leaves the channel of its flow: even frail huts may remain standing, while at the same time being buried to the roof line in mud. A lahar's viscosity decreases with time, and can be further thinned by rain, but it nevertheless solidifies quickly when coming to a stop.
Lahar flows can be deadly because of their energy and speed. With the potential to flow at speeds up to 100 kilometres per hour (60 mph), and distances of more than 300 kilometres (190 mi), a lahar can cause catastrophic destruction in its path. Snow and glaciers can be melted by lava or pyroclastic flows during an eruption and a flood caused by a glacier, lake breakout, or heavy rainfall can release a lahar, also called glacier run or jökulhlaup.
♦ As evidence of completion of this Earthcache, please send me the answers to the following questions:
1) Estimate the width of the flow as it approaches the bridge.
2) What is the length of the bridge you are standing on that crosses this flow.
3) What fills the area of the flow before you.
4) As you approach the bridge from either direction, there are 'signs' that are 2 different colors on the sides of the roadway. What colors are they?
*Although not required, pictures are welcomed.
This is a beautiful area. Please take the time to enjoy the various trails and views.