Exploring pyroclastic density current deposits from the 18 May 1980 eruption of Mount St Helens, Washington

Mt St. Helens PDC

Pre-meeting field trip, August 10-13; max/min participants, 30/10

During this four-day excursion we will examine pyroclastic density current deposits (PDCs) from the 18 May 1980 eruption of Mount St. Helens (MSH), explore field relations that can be used to constrain PDC conditions at the time of emplacement, and use PDC deposit characteristics to interpret and discuss transport and depositional mechanisms within the depositional (basal) region of the currents that produced them. We will compare well-exposed deposits along the steep flanks (10-30° slopes) and across the pumice plain (5 - 12° slopes) up to 8 km north of the volcano. Excellent exposures at MSH allow us to explore the influence of surface roughness, substrate erosion and self-channelization as they are recorded in the PDC deposits, and to assess the influence of these factors on current mobility and runout distance. Field discussions will result in new ideas and hypotheses to test using experiments and numerical modeling in the future. 

Participants must arrive to Portland no later than August 9th, 2016 to be ready for an early departure on August 10th, 2016. We will stay at a common hotel on the 9th and leave from there early on the 10th. After making a few stops along the southern flank (Ape Caves, and Stratigraphy View), we will arrive at the Windy Ridge Mt St Helens Institute tent camp where we will stay for 3 nights. We will return to Portland around 6:30 p.m. on August 13th.

Access to the sites on this field trip requires excellent physical fitness and the ability to hike long distances (between 12 and 20 km round trip each day for three days). The terrain is rough (boulder-strewn drainages and steep talus slopes) and there is often no shade. The steepest part of our hiking efforts is the ~350 vertical meters we will climb over 1.75 km to enter the eastern part of the crater. 

Estimated cost:
$365, includes all transportation, lodging, water and food, except dinner on August 9 and lunch on August 10.  Cost is based on a shared, double room in a hotel on August 9, private rooms available for additional $72 charge. The Mount St. Helens Institute will provide tents, cots or sleeping pads, and all meals. Participants must bring their own sleeping bags and field gear.

Trip Leaders:
Brittany Brand,Boise State University
Nicholas Pollock, Boise State University
Damiano Sarocchi, Instituto de Geología, Universidad Autónoma de San Luis Potosí
Josef Dufek, Georgia Institute of Technology
Mike Clynne, U.S Geological Survey