Mono Lake Paleoshoreline Mapping

Sarah R. Hall, College of the Atlantic
Calla Schmidt, University of San Francisco
Becca Walker, Mt. San Antonio College

Summary

Students complete a series of geology, geomorphology, hydrology, and botany field exercises at a field site near the north shore of Mono Lake to generate interpretations of the lake through time. The Mono Lake paleoshoreline activity is an illustration of lake level changes and other geologic events by interpreting the depositional environments of a preserved sequence of paleoshoreline sediments.

This activity is part of the Mono North Synthesis Project in conjunction with the following activities.

Mono Lake North Geomorphic Mapping Transect Mapping

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Learning Goals

Content/Concept Goals:

Students will...

  • Characterize grain size, grain shape, sorting, color, composition, induration/resistance, and sedimentary structures of layers of sediment in a road/stream cut deposit.
  • Illustrate changes in sediment characteristics and the thickness of each distinct layer in a stratigraphic column.

Higher Order Thinking Skills Goals:

Students Will...

  • Interpret the depositional environment of a preserved sequence of sediments by making detailed field observations.
  • Use field data to compare paleoshoreline and modern shoreline stratigraphy.

Context for Use

Audience:

This activity was completed during the 2-week summer E-STEM Field Course with ~20 undergraduate students interested in environmental science.

Prerequisite Skills and Concepts:

Prior to beginning their work, students should be given an overview of the field site (i.e., they will be looking at paleoshoreline and lake deposits) and asked to think about the types of sediments that one would expect in this type of environment. They should also have an understanding of how to observe and measure layers (in this case, layers of sediment) the characteristics of each layer that need to be recorded, and how to record them systematically in their field notebook so that they have adequate data to construct their office stratigraphic column. This activity works best if this is not the first stratigraphic section that a student is making. Students in this course had already visited this field site once and had made a soil profile at the SSCZO and at Little Poleta. In the context of the E-STEM course, we implemented this activity after the Walker Lake moraine mapping and Panum Crater geomorphic mapping projects and as part of the final field project.

How the Activity is Situated in the Course:

This activity follows an overview of Mono Basin and viewing shoreline features from a distance and is run simultaneously with the Mono Lake Geomorphic Mapping and Botanical Transects. Each ~2-3 hour activity was run as a station that students rotated through throughout the day. The order does not matter. The field notes from this activity will be used to compare paleoshoreline stratigraphy with modern shoreline stratigraphy. View the E-STEM field course timeline for more information about how this activity is situated in the course.

Description and Teaching Materials

Student Handout

Mono Lake Shoreline Stratigraphy Handout (Microsoft Word 2007 (.docx) 13kB Apr24 20)
Mono Lake North Stratigraphic Column Instructions (Microsoft Word 2007 (.docx) 14kB Jun25 20)

The necessary materials:

  • printed image of road cut
  • tracing paper or vellum paper
  • pencil/eraser
  • colored pencils
  • rock hammer
  • hand lens
  • mapboard
  • Brunton compass
  • rulers (a sedimentary grain size card works well)
  • aerial image of the region MonoNorthMaps.pdf (Acrobat (PDF) 8.9MB Jun15 20)

Teaching Notes and Tips

There is no shade at this outcrop. We used Easy-ups adjacent to the outcrop to provide students with periodic respite from the sun. This outcrop is poorly indurated at best. Physical contact with the outcrop will be disastrous to its preservation, so it is important to supervise students and ensure that they are not touching the outcrop. This can be especially challenging for students who are used to working with soils and value tactile observations, but it isn't possible at this field site.

Some students recognized several layers whose color was anomalous compared to most of the other layers in the section. These are volcanic ash layers and an important part of the geologic history of the Mono Basin. It may be useful in the introduction to the field area to remind students that volcanic ash can be deposited in lakes as well!

This stratigraphic section is extremely tedious because there are dozens of layers, and many are only a few millimeters thick. It was helpful to have students visit this field site twice and refine their initial measurements during the second visit. We also instructed students to look for patterns/cyclicity in the layers and note when layers repeated for simplicity in their field notes. (For example, if a student meticulously described a particular layer and then saw a layer with the same characteristics 15 cm up-section, perhaps they designated that layer "layer A" and noted layer A every time they saw it, rather than describing it in detail each time.

Assessment

  • Assess the field notes and write-up with the rubric for the Field Notes Badge.
  • Assess the stratigraphic column and map-view interpretation of shorelines with the rubric for the Mapping Badge.