Teach the Earth > Structural Geology > Structure, Geophysics, and Tectonics 2012 > Teaching Activities > Recognizing and mapping faults using lidar and field data

Recognizing and mapping faults using lidar and field data

Anne Egger, Central Washington University

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This activity was selected for the On the Cutting Edge Exemplary Teaching Collection

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This page first made public: Jun 1, 2012

Summary

In this activity, students create a geologic map and cross-section of the Fish Springs cinder cone and surrounding area in the Owens Valley, CA, using a high-resolution DEM developed from airborne lidar data as a base map. The primary features that students learn to recognize and map are normal faults, alluvial fans of different ages, and the cinder cone itself.

Context

Audience

I have used this activity in an introductory field methods course as the first exercise in order to introduce students to basic methods of field mapping. However, I believe it could also be used without going to the field using Google Earth and the lidar-based DEMs only.

Skills and concepts that students must have mastered

Students need to have a basic understanding of major rock types and be able to recognize volcanic rocks, describe grain sizes of sediments, and describe what a fault is. It is helpful (but not necessary) for students to have been introduced to the tectonic setting of the Owens Valley.

How the activity is situated in the course

This is the first exercise in an introductory field methods course. The students integrate this small map into a larger map along the Owens Valley fault zone and use their data in combination with the literature to describe a geologic history of the area.

Goals

Content/concepts goals for this activity

By the end of this activity, students will be able to:
  • Recognize and map a normal fault using offset features,
  • Recognize and map alluvial fans of different ages using geomorphological characteristics,
  • Draw a cross-section across a normal fault that indicates offset features.

Higher order thinking skills goals for this activity

By the end of this activity, students will be able to:
  • Synthesize information from the field, lidar data, and the literature to draw and interpret their map
  • Interpret the geology of the map area in the context of the larger tectonic setting

Other skills goals for this activity

By the end of this activity, students will be able to
  • Use Google Earth to explore the map area, including adding layers and navigating in three dimensions.
In addition, students receive feedback on their mapping right at the beginning of the course so that they have the opportunity to improve their future assignments.

Description and Teaching Materials

This activity occurs over a two-day period in the field; it could be easily modified for a classroom-based mapping exercise, however, using the same lidar data and Google Earth. This description covers the field-based approach.

Prior to going out into the field, students are given an introductory lecture to the geologic and tectonic setting of the Owens Valley (see Owens Valley slides file). This lecture is meant to introduce them to the area and remind them of some of the concepts they should already be familiar with (normal faults, plate boundaries, earthquakes). We pass out the field maps for the following day (see field map).

On the first day in the field, we drive to Fish Springs cinder cone and locate ourselves on the field map. We then climb the cinder cone to get a view, and from the top, we describe geomorphic features, devising a strategy for looking more closely at the units below. While still on top of the cinder cone, we:

  • Compare appearance of different alluvial fans and the active stream, describe both types of deposits.
  • Describe Fish Springs volcanic feature, both geomorphology and rock unit description.
  • Describe the relationship between units we've described so far: what are options for age relationships? What do we look for to determine the answer?
  • Describe the Fish Springs fault: How do we know it's there, estimate offset, how does it fit in with the other features?
Over the rest of the day, we go to each alluvial fan unit and make detailed descriptions (see unit description cheat sheet). We discuss where exactly to plot the fault trace on an eroded scarp, and get them to start drawing lines between units.

In the evening, we hand out copies of two papers and talk about how to go about reading them:

Martel, S. J., 1989, Structure and late quaternary activity of the northern Owens valley fault zone, Owens valley, California: Engineering Geology, v. 27, no. 1-4, p. 489-507.

Zehfuss, P. H., Bierman, P. R., Gillespie, A. R., Burke, R. M., and Caffee, M. W., 2001, Slip rates on the Fish Springs fault, Owens Valley, California, deduced from cosmogenic 10Be and 26Al and soil development on fan surfaces: Geological Society of America Bulletin, v. 113, no. 2, p. 241-255.

We focus the students on the description of units and their maps (which differ). We talk about how and why these maps differ and how it compares to their map, highlighting the fact that they have a new dataset that was not available to any of those authors: the airborne lidar. They spend time "revisiting" the field site using Google Earth (see kmz files), and strategize for what they are going to do the following day to complete the map on their own.

The second day in the field, we return to Fish Springs and ask students to complete their unit descriptions for the different fans and the cinder cone, decide how many different units they have, and draw contacts on their maps. In the afternoon, we return to the field station where students ink their maps and draw a cross-section across the cinder cone (and fault) along a line we have given them.

Field map of Fish Springs cinder cone (Acrobat (PDF) 1.4MB Apr29 12)
Unit descriptions cheat sheet (Microsoft Word 2007 (.docx) 81kB Apr29 12)
Slides to introduce tectonic setting of Owens Valley (PowerPoint 4.2MB Apr29 12)
Google Earth files for Fish Springs project (Zip Archive 12.6MB Apr29 12)

Teaching Notes and Tips

In the field, the primary safety concerns are heat exhaustion and dehydration. For many students, this is their first time in the desert, and they are not familiar with the necessary precautions. Students will have a hard time learning much if they are in physical discomfort, so it is important to make sure every student is well-prepared for a full day in the hot sun.

As noted earlier, however, I believe that this exercise can be modified for classroom use only with the use of the lidar imagery and Google Earth. Material from the two papers could be more fully integrated into the exercise as necessary.

Assessment

Students turn in a map, cross-section, and unit descriptions, which we grade and return to them the following day so that they have the opportunity to integrate this feedback into their subsequent assignments. Since mapping is an entirely new experience for them, I use this exercise primarily to provide them (and us) with formative assessment. These quick assignments also allow us to effectively create pairs that will work together for a larger project – we can pair students with complementary skills, for example.

References and Resources

The lidar data for this exercise is available through OpenTopography.
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