Field and Laboratory Project - Volcanology and Petrology of Interbedded Andesitic Lava Flows and Volcaniclastic Rocks from Washburn Volcano, Yellowstone National Park

Todd Feeley
Montana State University
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Initial Publication Date: July 29, 2008 | Reviewed: September 9, 2012


What follows is an example of a three part exercise for undergraduate petrology students involving volcanic and shallow intrusive rocks in the Washburn Range, Yellowstone National Park. We will loosely follow Part 1, although Parts 2 (petrology) and 3 (geochemistry) are also included. The exercise is largely based on a recent study by Feeley et al. (2002), although on this trip we will only examine stratigrahpically high rocks on Mount Washburn proper; stratigraphically lower rocks to the southwest beneath Dunraven and Hedges Peaks are off-road and off-trail.

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This field trip was part of the 2003 Teaching Petrology in the 21st Century workshop. It is designed for use by undergraduate or graduate courses in petrology.

Skills and concepts that students must have mastered

Students should have a basic understanding of petrology, geochemistry, and should have skills in observing and analyzing data.

How the activity is situated in the course

This is a field exercise that is meant to reinforce concepts learned in the classroom and to provide real-world examples of such concepts.


Content/concepts goals for this activity

Goals of this exercise include:
  1. To study intraflow characteristics of andesite lava flows and flow breccias;
  2. to study sedimentological characteristics of volcanic debris flows and related sedimentary deposits;
  3. to distinguish lava flows from dikes and sills;
  4. to interpret the volcanic feature represented by Mount Washburn; and
  5. to interpret the petrology and geochemistry of calc-alkaline volcanic rocks in order to discover their origins.

Higher order thinking skills goals for this activity

This activity involves analysis of data, formulation of hypotheses, and synthesis of ideas.

Other skills goals for this activity

This activity involves writing skills and potentially involves operating analytical equipment and group work.

Description of the activity/assignment

We anticipate that hikers will start from Dunraven Pass at 8:00 AM. Hikers should return to the vans at 12:00 PM, from there we will go to a picnic area for lunch. All hikers must therefore turn around and head for the vans no later than 10:45. Because of these strict time limitations, there will probably not be sufficient time to examine the rocks in as much detail as one would hope. The trip is thus largely a self guided tour. It will, nevertheless, give you an opportunity to examine several rock types associated with calc-alkaline composite cones and provide a spectacular view of the Yellowstone Caldera, weather permitting.

Determining whether students have met the goals

The goals of this exercise have been met upon satisfactory completion of the following final products:
  1. Sketches, descriptions, and interpretations (e.g., lava flow, dike, sill, debris flow, stream flow, flow breccia) of features of rock units at stations listed below and illustrated on the accompanying map (Fig. 1). The descriptions should include thickness of individual units. In addition, for dense, nonfragmental units (e.g., lava flows and tabular intrusions), include features such as chilled zones, distributions of vesicles, and a hand specimen petrographic description. For volcaniclastic units include clast sizes and composition, matrix texture, depositional structures. Answers to specific questions for stations.
  2. Petrographic descriptions of rock units (note: we will complete this back in laboratory on thin sections cut from previously collected Washburn samples).
  3. Interpretation of geochemical data for lava flows from Washburn volcano (note: we will complete this as a class project back at the university).

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