Obsidian Dome Outcrop Tour

Jessica F Larsen, University of Alaska, Fairbanks

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Summary

Virtual outcrop tour of a part of Obsidian dome in California. This Google Earth based tour shows photos and outcrop/process descriptions of the different lithologies in the Obsidian dome in Eastern California. Obsidian Dome is a slicic lava dome that erupted ~450 years ago as part of a series of eruptions along a lineation that extends from inside the Long Valley Caldera, towards the north-northeast towards the Mono Craters, and Mono Lake.

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Context

Audience

This tour could be used as part of an activity in any level of college or University course in geology or volcanology. In courses where field trips are difficult or not possible due to geographic location, this tour could be used to help augment learning about lava flows, silicic volcanism, and the Inyo-Mono chain of craters, in the context of Long Valley Caldera and volcanism in the Western US.

Skills and concepts that students must have mastered

The tour would be best suited for students who have had a lecture or other introductory material about volcanoes, volcanic rocks, magmas, and plate tectonics. The instructor will also likely want to include background information or a lecture focused on the Inyo-Mono and Long Valley area, the age of Obsidian Dome, the origination of the different lithologies and structures described in the dome by previous workers.

Students should have basic understanding about how volcanoes work, including differences between effusive and explosive eruption styles. Students should have had a section describing the different basic types of magma (Basalt, Andesite, Dacite, Rhyolite), and knowledge about how composition is tied to viscosity. Students should have a basic understanding about how gas exsolves into bubbles in a magma during ascent, how vesiculation occurs, and how gas escapes from magma differently during explosive versus effusive eruptions. Students should also understand the concept of buyoancy and diapirism, as a result of differences in density in lava flow layers.

How the activity is situated in the course

This activity would work best in a volcanology module in a general Geology course for majors or non-majors. It would be best in a section focused on explosive to effusive silicic volcanism in a Volcanology course.

Goals

Content/concepts goals for this activity

Goal is to provide virtual outcrop and map-view examples of the different vesicle textures and lithologies in a silicic lava dome (ie Axisymmetric, coulee-type rhyolite lava flow). This is not a stand alone activity, but can be used to augment other lab activities or classroom activities, or lecture as part of material designed by the instructor.

Higher order thinking skills goals for this activity

While this is not a stand alone activity, the tour will require students to be able to match outcrop photos and descriptions with the concepts of vesicularity (gas content), vesicle collapse/obsidian formation, and diapirism in the formation of the crease structures (or "squeeze up" regions).

Other skills goals for this activity

Description and Teaching Materials

Students will need access to Google Earth, or instructor will need to show tour to students using computer and projector. Link to kmz file is included here: Obsidian_dome_tour.kmz (KMZ File 111.5MB Jul15 19)

Assessment

No assessment included with the tour. Assessment will be up to the instructor, depending on how they use this tool in their course.

References and Resources

https://www.usgs.gov/volcanoes/long-valley-caldera/long-valley-caldera-field-guide-obsidian-dome

https://www.usgs.gov/volcanoes/mono-inyo-craters/inyo-lava-flows-erupt-quietly-after-explosive-activity


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