Understanding the nuances of the rockfall frequency-magnitude relationship: review and examples from two original case studies in Glenwood Canyon, CO, USA

The rockfall frequency-magnitude relationship is important for understanding rockfalls as a geomorphic agent and as a key mass-wasting hazard. The relationship is frequently modeled with a power law fit to frequency vs. volume, and the power law provides a basis for extrapolating recurrence intervals and quantifying cliff retreat and sediment transfer. While the frequency-magnitude relationship is a commonly-used tool for summarizing rockfall distributions, there are many unknowns about the variables that define the shape of the frequency-magnitude distribution. To address this, this dissertation presents a review of rockfall frequency topics along with a meta-analysis of 46 rockfall databases to test the influence of 11 physical and systematic factors on the power law exponent. The meta-analysis provides the strongest evidence for the influences of rockmass condition, geology, rockfall data collection method, and maximum inventory volume on the scaling exponent. Relationships between other variables and the scaling exponent are more nuanced and are affected by noise inherent in the meta-analysis database. The meta-analysis emphasizes the importance of sampling a representative rockfall distribution, along with carefully considering the characteristics of the site and inventory when extrapolating information from the distributions to larger volumes or to other sites. Following the review, we present two case studies using lichenometry and unpiloted aerial vehicle monitoring to shed light on the specifics of rockfall frequency-magnitude relationships in Glenwood Canyon, CO, USA, an area where rockfall from natural slopes presents a significant hazard to transportation infrastructure. The region was also affected by wildfire in 2020, raising the question of whether rockfall increased significantly in response. The case studies suggest that rockfall at the studied slopes is dominated by small, fragmental rockfalls over the last ∼ five centuries, where water availability in the slope may have a greater effect on rockfall frequency than joint conditions or lithology. No evidence was found either for large rockslides/rock avalanches during the evaluated period, nor any evidence for a significant increase in rockfall during months 6 – 18 after the beginning of the fire.

Name thesis:degree_name

Doctor of Philosophy (Ph.D.)

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Geology and Geological Engineering

Grantor dc:publisher

Colorado School of Mines. Arthur Lakes Library

Year dc:date.issued

2022

Author dc:creator

• Graber, Andrew Paul

Advisor dc:contributor.advisor

• Santi, Paul M. (Paul Michael), 1964-

Committee members dc:contributor.committeemember

• Walton, Gabriel
• Roth, Danica
• Kaunda, Rennie

• power laws
• rockfall frequency-magnitude
• rockfall monitoring
• scaling exponent
• UAV

Statement dc:rights

• Copyright of the original work is retained by the author.

Language dc:language.iso

eng, English

Identifier

T 9410

OAI identifier oai:identifier

oai:repository.mines.edu:11124/15515