University of Denver Digital Commons @ DU Electronic Theses and Dissertations Graduate Studies 2020 Rock Glacier Development in the San Juan Mountains Brandon K. Bailey Follow this and additional works at: https://digitalcommons.du.edu/etd Part of the Glaciology Commons, and the Physical and Environmental Geography Commons Rock Glacier Development in the San Juan Mountains _______________ A Thesis Presented to the Faculty of the College of Natural Sciences and Mathematics University of Denver _______________ In Partial Fulfillment of the Requirements for the Degree Master of Arts _______________ by Brandon K. Bailey June 2020 Advisor: J. M. Daniels Author: Brandon K. Bailey Title: Rock Glacier Development in the San Juan Mountains Advisor: J. M. Daniels Degree Date: June 2020 ABSTRACT Rock glaciers are common landform features found in deglaciated alpine areas. They are commonly used in the study of climatic changes throughout the Holocene and the reconstruction of neoglacial chronologies. For this research, Schmidt hammer rebound values, weathering rind thicknesses, and the length of lichen thalli diameters found on rock glacier surfaces are used to investigate their effectiveness as field-based relative age determination techniques. Additionally, the ability to identify periods of neoglacial activity using these methods is assessed in two neighboring cirque basins in the San Juan Mountains of Colorado. 41 field sites across three rock glaciers are established with approximately 2,050 Schmidt hammer measurements and 300 weathering rind thicknesses collected in total. The Schmidt hammer proved to be the most effective of the three relative age indicators in distinguishing between surfaces of different relative age. The R-values collected indicate three periods of neoglacial activity, which aligns with the neoglacial history of the area. Values derived by the Schmidt hammer in combination with morphological analysis conducted using Google Earth Pro and ArcGIS are then used to model how each rock glacier may have developed over time. This research demonstrates that Schmidt hammer exposure dating is an efficient and robust field method for determining the relative ages of rock glaciers in the San Juan Mountains. ii TABLE OF CONTENTS Chapter 1: Introduction ....................................................................................................1 Chapter 2: Background ....................................................................................................3 2.1 Origin and Formation .............................................................................................4 2.2 Development ..........................................................................................................5 2.3 Movement ..............................................................................................................6 Chapter 3: Research Questions ........................................................................................9 Chapter 4: Study Area - The San Juan Mountains .......................................................... 11 4.1 Neoglacial Activity .............................................................................................. 11 Chapter 5: Methods ....................................................................................................... 13 5.1 Schmidt hammer method ...................................................................................... 13 5.2 Weathering Rind Thickness .................................................................................. 15 5.3 Lichenometry ....................................................................................................... 16 Chapter 6: Results.......................................................................................................... 19 6.1 Blaine Basin ......................................................................................................... 19 6.2 Cirque Basin ........................................................................................................ 21 Chapter 7: Discussion .................................................................................................... 23 7.1 Schmidt Hammer ................................................................................................. 23 7.2 Weathering Rind Measurements ........................................................................... 24 7.3 Lichens ................................................................................................................ 26 7.4 Summary of Methods ........................................................................................... 27 7.5 Rock Glacier Development................................................................................... 27 7.5.1 Blaine Basin East ........................................................................................... 27 7.5.2 Blaine Basin West.......................................................................................... 29 7.5.3 Cirque Basin .................................................................................................. 29 7.5 Neoglacial Activity .............................................................................................. 35 7.6 Water Resources and Climate Change .................................................................. 35 7.7 Schmidt Hammer Potential ................................................................................... 36 Chapter 8: Conclusion ................................................................................................... 38 Chapter 9: Bibliography................................................................................................. 40 Chapter 10: Appendix .................................................................................................... 43 10.1 Raw Schmidt Hammer Data ............................................................................... 43 10.2 Raw Weathering Rind Thickness Data ................................................................ 63 10.3 K-means Clustering (4 Groups) .......................................................................... 64 iii LIST OF TABLES 4.1: Glacial and Neoglacial Chronology of The San Juan Mountains ............................. 12 5.1: R-Value Angle of Inclination Correction Chart ....................................................... 14 6.1: Mean R-Values Collected From Blaine Basin. ........................................................ 20 6.2: Mean Weathering Rind Thickness of Field Sites in Blaine Basin. ........................... 21 6.3: Mean R-Values Collected From Each Field Site in Cirque Basin. ........................... 22 6.4: Mean Rind Thicknesses Collected From Field Sites in Cirque Basin. ...................... 22 10.1: Raw Schmidt Hammer Data .................................................................................. 43 10.2: Raw Weathering Rind Data................................................................................... 63 iv LIST OF FIGURES 2.1: Ridge and Furrow Structures on Cirque Basin ...........................................................3 2.2: Morphological Features Associated with Rock Glaciers ............................................8 7.1: Mean R-Values From All Field Sites ...................................................................... 23 7.2: Comparing Rind Thicknesses and R-Values ............................................................ 25 7.3: Mean R-Values and Field Site Locations in Blaine Basin ........................................ 28 7.4: Mean R-Values and Field Site Locations in Cirque Basin ....................................... 30 7.5: Movement Rates of Lobes in the Upper Section of Cirque Basin ............................ 33 7.6: Movement Rates of Lobes in the Lower Section of Cirque Basin ............................ 34 10.1: R-Values From All Field Sites Clustered Into Four Groups ................................... 64 v Chapter 1: Introduction Rock glaciers are alpine landforms made up of rock debris and ice. As mountain glaciers retreat due to the effects of climate change, these features are expected to become more common (Knight et al., 2019). Like glaciers, rock glaciers may serve as potential reservoirs of fresh water (Janke, 2007). The coarse rocky debris that covers them insulates the ice underneath, allowing rock glaciers to withstand warmer temperatures and extend to lower elevations. Rock glaciers have also been used to study changes in climate throughout the Holocene. Rock glacier activity has been correlated with neoglacial expansion and has been used to determine past equilibrium line altitudes (ELAs) and the lower limits of permafrost in alpine areas (Refsnider and Brugger, 2007). Continued study of rock glaciers will allow researchers to better understand their potential as a natural resource and tool for understanding the impacts on mountainous landscapes from a warming planet. Relative age determination techniques have been useful in paleoclimate studies involving rock glaciers. This research investigates rock glacier development in the San Juan Mountains of Colorado. Schmidt hammer exposure dating, and the thickness of weathering rinds are used to identify periods of advancement on large multi-lobed rock glaciers. By using relative age determination methods, this research also examines their effectiveness in differentiating between different neoglacial periods. The overall goal of 1 this research is to investigate how