Page updated on May 19, 2016
Field trip to Mount St. Helens
May 21, 2016
What this field trip is about:
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
comments and descriptions and ask questions as you go—preferably in field notebooks.
- Draw and
label sketches or take photos at every field location of any geologic features or
location we stop is a potential field site, and you will be expected to
discuss each one in your field report. Remember to use a scale.
- Ask your instructor if you don’t
understand what to do. Be sure to include details where you can.
- Consult web references
and any of the references listed at the end of this guide (many on hold
or on reserve in the library).
Leave Centralia College South on I-5.
EXIT 49: Go east
on SR 504. See Pringle (2002), particularly “Leg A”
1: SILVER LAKE VISITOR CENTER (~5 mi east of I-5; Restrooms &
water; free admission, exhibits, bookstore) We will stay here about 50
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.
STOPS. HOFFSTADT BLUFFS VISITOR
CENTER OR FOREST LEARNING
FLC). Restrooms and water. At FLC views of spectacular dikes cutting
STOP 3. ELK
(Depending On The Weather) JRO –JOHNSTON
RIDGE OBSERVATORY Restrooms and water.
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).
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.
HOFFSTADT BLUFFS VISITOR CENTER, OR FOREST LEARNING CENTER.
Restrooms. At FLC views of spectacular dikes cutting Oligocene
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
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
>>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 6: Castle Lake Viewpoint: Castle Lake is dammed by the 1980 debris avalanche.
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
>>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?
on hold or in the collection in Kirk Library=* …or available online)
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]
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.
Michael P., 1990, Road guide to volcanic deposits of Mount St. Helens and
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)
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
*Pringle, Patrick T., 2002, Roadside geology of Mount St. Helens National
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]
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.
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.
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/]
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]
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/]
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]
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
http://www.agiweb.org/geotimes/may00/featurestory.html MSH 20 years later by Bob Tilling
Division of Geology and Earth Resources
Search the online bibliography
of the geology of Washington
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