Field trip to Mount St. Helens

May 21, 2016

What this field trip is about:
During this field trip we will see a remarkable amount of geology including evidence of past volcanism from both Mount St. Helens and from volcanoes that have erupted over the past 30+ million years. We will evidence that glaciers have modified the landscape over the past ~2.6 million years, see geologic structures such as folded and faulted rocks, dikes, and sills; rocks cooked by intrusions of magma or sheared along a fault zone, deposits of lahars (volcanic debris flows), and observe several types of landslides as well as modern stream processes, landslide-dammed lakes, and primary and secondary successional landscapes.

What to do during this field trip (observe, ask questions, take notes, sketch): FIELD TRIP WRITE UP DUE JUNE 2ND.

Overview of trip: We will leave the Centralia College campus and proceed SOUTH on I-5 Exit 49 where we will head east on SR 504 into the Cascade Range toward Mount St. Helens. This trip will features discussions about geologic processes, history, and hazards revealed in the pre- and post- Mount St. Helens rocks and deposits, specifically in the scenic Toutle River valley. Although we will have several major stops with field activities (listed below), we will also stop at various scenic viewpoints to observe geologic features, landforms, natural process, and of course scenery!

Itinerary overview:

Leave Centralia College South on I-5.
EXIT 49: Go east on SR 504. See Pringle (2002), particularly “Leg A”
STOP 1: SILVER LAKE VISITOR CENTER (~5 mi east of I-5; Restrooms & water; free admission, exhibits, bookstore) We will stay here about 50 minutes.
STOP 2. HARRY GARDNER PARK—Mount St. Helens lahars (near Toutle WA). See detailed write up in Doukas (1990) for info en route and Mullineaux (1996) for ages of tephra. Vault privy.

OPTIONAL STOP. Oligocene lahars outcrop near MP 25. Sketch any geologic features you see here.

OPTIONAL STOPS. HOFFSTADT BLUFFS VISITOR CENTER OR FOREST LEARNING CENTER (
FLC)
. Restrooms and water.  At FLC views of spectacular dikes cutting Oligocene volcanics.

STOP 3. ELK ROCK VIEWPOINT.
STOP 4 (Depending On The Weather) JRO –JOHNSTON RIDGE OBSERVATORY  Restrooms and water.
STOP 5: HUMMOCKS TRAIL: We will see blocks and pieces of the mountain as we walk through the deposit of the great debris avalanche of 1980.
STOP 6: CASTLE LAKE VIEWPOINT: Castle Lake is dammed by the 1980 debris avalanche.

 


FIELD TRIP ACTIVITIES (detailed itinerary)

Exit 49: SR 504 to Mount St. Helens. The flat terrace on which the overpass is built is composed of lahars from Mount St. Helens that have been dated at ~20 ka.


STOP 1: SILVER LAKE VISITOR CENTER (~5 mi east of I-5; Restrooms & water; free admission, exhibits, bookstore) We will stay here about 50 minutes.
>>What to look for: Go through all the exhibits and do a brief but thoughtful write up about what you learned in the exhibits. See the short film and comment in your report on this as well. How was Silver Lake formed, and when?


STOP 2. HARRY GARDNER PARK—Mount St. Helens lahars (near Toutle WA). See detailed write up in Doukas (1990; p. 44) for info en route and Mullineaux (1996) for ages of tephra. (To get to this site, take a soft right on South Fork Toutle River Road after you pass the Toutle Lake Post Office and go about 1 mile; about ¼ mi after you cross the South Fork Toutle River make a hard left into Harry Gardner Park).

>>What to look for: Before we cross the river you can see some homes in the woods to the left of the van—They were half buried by the 1980 lahar. Draw a diagram a of the May 18th lahar deposits at the park visible along road and also of the ancient lahar deposits to the north. Use scale in your diagrams and in your photos. Describe the deposits as best you can. What grain sizes do you see? Poorly sorted or well sorted? What types of rocks do you see? Examine at least five. How are they similar or different. What is the percentage of angular vs. rounded rocks in the deposits. How many layers do you see?


OPTIONAL STOP. Oligocene lahars outcrop near MP 25. Sketch any geologic features you see here.


OPTIONAL STOPs: HOFFSTADT BLUFFS VISITOR CENTER, OR FOREST LEARNING CENTER. Restrooms.  At FLC views of spectacular dikes cutting Oligocene volcanics.

FOREST LEARNING CENTER (optional): Greenish color of rocks visible in roadcuts is low grade metamorphism caused by burial and creation of clay minerals. Note dikes! Sketch these. 

STOP 3: ELK ROCK VIEW POINT:

>>As we approach Elk Rock Viewpoint look at the rocks to the left of the highway. Why do some have bolts through them? What different things can you see at the viewpoint. You might try to draw a landscape sketch. Sketch and label landscape—note blown down trees.  Take notes on metamorphism of the bedrock—blackish rock is hornfels, a recrystallized volcanic rock.


STOP 4 (Depending On The Weather) JRO –JOHNSTON RIDGE OBSERVATORY: Mount St. Helens is the main attraction, but also note the layering and dip of the exposed bedrock.

>>Note when the next video is going to be shown. If you have time, examine some of the exhibits before or after the video. Read at least two of the eye witness panels that are just to the east of the theater exit.  Describe the landscape and in particular the different deposits and features that are evidence of the eruption. Can you distinguish which features are related to the blast pyroclastic flow and which are related to the debris avalanche (landslide)?


STOP 5: HUMMOCKS TRAIL: We will see blocks and pieces of the mountain as we walk through the deposit of the great debris avalanche of 1980. The pre-1980 highway is buried about 200 ft under this deposit! Weather permitting, we will hike the two mile loop.
>>What to look for. Compare the forest growing along the valley walls as we approach the volcano with the vegetation atop the debris avalanche deposit. What evidence do you see that shows this landform is new? Note any evidence that the landform has changed since it was deposited here. What evidence do you see that shows how the landform was formed?
We will stop at Coldwater Lake to use restrooms before heading back. Coldwater Lake is also dammed by the 1980 debris avalanche.


STOP 6: Castle Lake Viewpoint: Castle Lake is dammed by the 1980 debris avalanche.
>>What are your thoughts about the stability of the lake given what you learned about how the great lahars were formed whose deposits you saw at Harry Gardner Park?

Assignment: Pick an aspect of the eruption or its effects or the deposits of previous eruptions and write a one or two page short paper (extended abstract) using some of the references below and/or others. Perhaps make some interpretations on the significance of the 1980 eruption to geology in general and to how we perceive stratovolcanoes. Be sure to cite all you references properly! In addition to the sketches, descriptions, and notes you are taking, you must do this assignment to get credit for this field trip. At the end of your assignment, add a section in which you share any feelings, observations, and new perceptions about the eruption and the landscape that you may have derived from this trip and/or from your encounters with this disturbed landscape. Does knowing more about this landscape and about the scale, nature, and history of volcanic processes make you think differently about some of the other Cascade volcanoes or about volcanism and humans in general? Please explain this. Is this important to Pacific Northwesterners? NOTE: Check the online rubric mentioned on the class syllabus for guidelines on writing papers.
References (some on hold or in the collection in Kirk Library=*    …or available online)

Clynne, Michael A.; Ramsey, David W.; Wolfe, Edward W., 2005, Pre-1980 eruptive history of Mount St. Helens, Washington: U.S. Geological Survey Fact Sheet 2005-3045, 4 p. [accessed Jul. 7, 2005 at http://pubs.usgs.gov/fs/2005/3045]
Crandell, D. R., 1987, Deposits of pre‑1980 pyroclastic flows and lahars from Mount St. Helens volcano, Washington: U.S. Geological Survey Professional Paper 1444, 91 p., 1 plate.
Doukas, Michael P., 1990, Road guide to volcanic deposits of Mount St. Helens and vicinity, Washington: U.S. Geological Survey Bulletin 1859, 53 p. [accessed Jan. 19, 2001 at  http://vulcan.wr.usgs.gov/Volcanoes/MSH/Publications/Bulletin1859/  (See the entire report, but you will have to download the DJVU  plugin to your web browser to read it.  See pp. 41–48 is SR 504 Spirit Lake Highway area; p. 44 is the description of the Harry Gardner Park exposure)
Mullineaux, Donal R., 1996, Pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington: U.S. Geological Survey Professional Paper 1563, 99 p. [accessed Feb. 12, 2002 at http://greenwood.cr.usgs.gov/pub/ppapers/p1563/]

*Pringle, Patrick T., 2002, Roadside geology of Mount St. Helens National Volcanic Monument and vicinity; rev. ed.: Washington Division of Geology and Earth Resources Information Circular 88, rev. ed., 122 p. [accessed on May 1, 2011 on p. 15 of http://www.dnr.wa.gov/Publications/ger_publications_list.pdf & at http://campus.albion.edu/geol210/files/2011/03/MSH1.pdf]

*Pringle, P.T.; Cameron, K. A., 1999, Eruption-triggered lahar of May 14, 1984, In Pierson, T. C. ed., Hydrologic consequences of hot-rock/snowpack interactions at Mount St. Helens Volcano, Washington, 1982-1984: U.S. Geological Survey Professional Paper 1586, p. 81-103.
*Scott, Kevin M., 1988, Origin, behavior, and sedimentology of prehistoric catastrophic lahars at Mount St. Helens, Washington. IN Clifton, H. E., editor, Sedimentologic consequences of convulsive geologic events: Geological Society of America Special Paper 229, p. 23-36.
Sherrod, David R.; Scott, William E.; Stauffer, Peter H., editors, 2008, A volcano rekindled--The renewed eruption of Mount St. Helens, 2004-2006: U.S. Geological Survey Professional Paper 1750, 856 p. and DVD. [accessed Aug. 27, 2009 at http://pubs.usgs.gov/pp/1750/
Tilling, Robert I., 1983, Monitoring active volcanoes: U.S. Geological Survey, 13 p. [accessed Feb. 12, 2002 at              http://pubs.usgs.gov/gip/monitor/contents.html]
Tilling, Robert I.; Topinka, Lyn J.; Swanson, Donald A., 1984, rev. 1990, Eruptions of Mount St. Helens--Past, present, and future: U.S. Geological Survey, 56 p. [accessed Feb. 12, 2002 at http://pubs.usgs.gov/publications/msh/]
Wolfe, Edward W.; Pierson, Thomas C., 1995, Volcanic-hazard zonation for Mount St. Helens, Washington, 1995: U.S. Geological Survey Open-File Report 95-497, 12 p., 1 plate. [accessed Feb. 12, 2002 at http://vulcan.wr.usgs.gov/Volcanoes/MSH/Hazards/OFR95-497/framework.html
]



Selected Web References

  CVO, Cascades Volcano Observatory 

  Pacific NW Seismic Network 

Mount St. Helens (MSH) USFS webcam    MSH webcam assortment   

http://www.dnr.wa.gov/Publications/ger_washington_geology_1980_v8_no3.pdf               Washington Geology Mount St. Helens issue, July 1980

http://www.fs.fed.us/gpnf/mshnvm/index.shtml                    MSH National Volcanic Monument

http://www.agiweb.org/geotimes/may00/featurestory.html   MSH 20 years later by Bob Tilling

http://mshinstitute.org/                                                           MSH Institute

    Division of Geology and Earth Resources  

    Search the online bibliography of the geology of Washington State 

   Washington Division of Geology and Earth Resources: Publications and Maps  

http://www.centralia.edu/academics/earthscience/resources/resources.htm           Student resources and tools at Centralia College Earth Sciences page

    Volcano World   Volcano World—Mount St. Helens  


Page updated on May 19, 2016