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Alethea M. Shaules - Honors Thesis

"Rockfall Hazard Assessment for the Eagle Formation in Billings, Montana: Analyzing the Major Weathering and Erosional Processes to Explain Rockfall Events"

B.A. in Sociology
First Reader: Emily Geraghty-Ward, Associate Professor of Geology
Second Reader: Derek Sjostrom, Associate Professor of Geology

Abstract

As erosional processes shape the land around us, the result of these processes pose a large threat. Analysis of such occurrences is crucial to properly mitigate the hazards that result from weathering and erosional processes. Understanding how and what drives erosional processes is essential in assessing hazards. In Billings, Montana rockfall events are a regular occurrence on the Rimrocks; a bedrock hillslope composed of sandstone (the Eagle Formation). These events are not only threat to the communities who live on top and below the Rimrocks, but also to motorists and hikers who pass along the cliff face on a daily basis. Proper monitoring of these hazardous zones is crucial for the continued safety and protection of the public. The purpose of this study is to determine how changes to temperature and precipitation influence rockfall on the Rimrocks. Previous work monitoring rock movement along the cliff face has been done since the late 1970s. This monitoring has been inconsistent and limits our ability to draw conclusions about how temperature and precipitation influence rockfall events in Billings. This research consistently monitors slab movement at 14 sites on a monthly basis. Using data from past years (2009-2010) along with current (2016-2017) data, changes in temperature and precipitation are compared to horizontal slab movement. The data reveal that the slabs move during months when seasonal variation in temperature and precipitation. However, the magnitude of movement cannot be directly tied to monthly changes in temperature and precipitation because slab movement occurs regardless of large changes in temperature and precipitation. By looking at the type of movement for the rock slabs (i.e. fracture opening or closing) the measurements reveal that the rocks are moving each month but may show no, or minimal total displacement for the year. These data highlight the importance of continued consistent monitoring (i.e. daily) through the use of crackmeters or strain gages and using more accurate geodetic instruments such as GPS and LiDAR.

Citation

Shaules, Alethea M. "Rockfall Hazard Assessment for the Eagle Formation in Billings, Montana: Analyzing the Major Weathering and Erosional Processes to Explain Rockfall Events" 
Honors Senior Thesis, Rocky Mountain College, 2017.

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