University of Nevada, Reno Quantifying environmental controls on the magnitude of glacial lake outburst floods and the resulting impacts to hydrology and geomorphology: Lago Cachet Dos, Patagonia, Chile A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Hydrology by Jonathan D. Jacquet Dr. Scott McCoy/Thesis Advisor December, 2016 THE GRADUATE SCHOOL We recommend that the thesis prepared under our supervision by JONATHAN DANIEL JACQUET Entitled Quantifying Environmental Controls On The Magnitude Of Glacial Lake Outburst Floods And The Resulting Impacts To Hydrology And Geomorphology: Lago Cachet Dos, Patagonia, Chile be accepted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Scott Mccoy, Ph.D., Advisor Daniel Mcgrath, Ph.D., Committee Member Adrian Harpold, Ph.D., Graduate School Representative David W. Zeh, Ph.D., Dean, Graduate School December, 2016 i Abstract The sudden release of water from an ice-dammed lake poses substantial hazard to the downstream environment, but the degree to which peak discharge depends on environmental variables that change with climate remains unclear. We combine in situ measurements of environmental variables with high-resolution discharge measurements from a glacier- dammed lake, Lago Cachet Dos (LC2), to evaluate environmental conditions that influence the peak discharge of observed glacial lake outburst floods (GLOFs). Since April 2008, 20 GLOFs have initiated out of LC2, located on the eastern edge of the Northern Patagonia Icefield, Chile and flooded areas along the Rio Colonia- Rio Baker system. GLOF frequency has averaged 1-3 events annually and calculated peak discharges exiting LC2 have ranged widely from 2,000 to >15,000 m3/s. We show that, consistent with physics-based theory, increasing water volume released, lake temperature, and the rate of meltwater input into the glacially dammed lake all increase the peak discharge of observed GLOFs. Additionally, we quantify the hydrologic and geomorphic response to episodic GLOFs using multi-temporal satellite imagery and field observations. Peak discharge exiting the source lake exceeded 15,000 m3/s, but became progressively muted downstream. At ~40 km downstream, peak discharges were generally < 2000 m3/s, but still > 15 times the median discharge. The GLOFs resulted in > 40 m of downcutting and erosion of ~25 x106 m3 of sediment from the source lake basin and a non-steady channel configuration downstream. Our results suggest that more accurate predictions of GLOF magnitude from ice dammed lakes can be made by incorporating additional measurements of environmental conditions and that quantifying GLOF water and sediment fluxes in the Colonia system may provide insight into potential changes that similar fluvial systems could experience after the onset of large floods. ii Table of Contents Chapter 1: Introduction ................................................................................................................... 1 What is a glacial lake outburst flood? .......................................................................................... 1 Examples of Paleo-GLOFs .......................................................................................................... 3 Where do GLOFs occur and why should we care? ...................................................................... 3 Chapter Summaries ...................................................................................................................... 5 Chapter 2: Environmental controls on the variability of peak discharge of glacial lake outburst floods: Lago Cachet Dos, Chile ...................................................................................................... 6 Abstract ........................................................................................................................................ 7 1 Introduction ............................................................................................................................... 8 2 Study Area: Lago Cachet Dos, Patagonia, Chile ...................................................................... 9 3 Theoretical Background for Drainage of Ice-Dammed Lakes ................................................ 12 4 Data and Methods ................................................................................................................... 14 4.1 Calculating GLOF Discharge from Glacially Dammed LC2 .......................................... 14 4.2 Estimating Total Volume of Water Drained from LC2 during GLOFs ........................... 16 4.3 Measurements of Water and Air Temperature ................................................................. 17 4.4 Rate of inflow .................................................................................................................. 17 5 Results ..................................................................................................................................... 18 5.1 Peak Discharge and Volume of LC2 GLOFs ................................................................... 18 5.2 Correlation of Environmental Variables to Peak Discharge ............................................ 20 6 Discussion ............................................................................................................................... 22 6.1 Accuracy of Empirical Equations Used to Predict Peak Discharge ................................. 22 6.2 Importance of Lake Temperature in Predicting Peak Discharge ..................................... 24 6.3 Significance of Inflow Rate and Implications under a Changing Climate ....................... 24 7 Conclusions ............................................................................................................................. 25 Supporting Information .............................................................................................................. 27 Chapter 3: Hydrologic and geomorphic changes resulting from episodic glacial lake outburst floods: Rio Colonia, Patagonia, Chile ............................................................................................ 32 Abstract ...................................................................................................................................... 33 1 Introduction ............................................................................................................................. 33 2 Study Area: Cachet-Colonia-Baker Valley, Patagonia, Chile ................................................ 35 2.1 Thinning and Retreat of the Colonia Glacier ................................................................... 35 2.2 History of GLOFs in Cachet and Colonia Valleys........................................................... 35 iii 3 Methods .................................................................................................................................. 38 3.1 Measuring Changes in Hydrologic Regime: Rio Colonia and Rio Baker........................ 38 3.2 Measuring Sediment Transport from Glacially Dammed LC2 Lake Basin ..................... 38 3.3 Estimating GLOF Discharge from Glacially Dammed LC2 ............................................ 40 3.4 Quantifying Changing Planform Channel Morphology: Rio Colonia ............................. 41 4 Results and Discussion ........................................................................................................... 42 4.1 GLOF Characteristics and Changes in Hydrologic Regime ............................................ 42 4.2 Sediment Transport in the Glacially Dammed LC2 Lake Basin ...................................... 44 4.3 Quantifying Changing Channel Morphology on the Rio Colonia ................................... 47 5 Conclusions ............................................................................................................................. 50 Supporting Information .............................................................................................................. 52 Chapter 4: Conclusions .................................................................................................................. 65 Environmental Controls on Peak Discharge from GLOFs ........................................................ 65 Effects on Hydrology and Geomorphology from Episodic GLOFs .......................................... 66 Future Research ......................................................................................................................... 67 References ...................................................................................................................................... 68 iv List of Tables Chapter 2 Table S1. GLOF peak discharges and volumes. ............................................................................ 31 Chapter 3 Table S1. GLOF peak discharges and volumes. ............................................................................ 64 Table S2. Areal, volumetric, and vertical metrics calculated for each DEM of difference ........... 64 v List of Figures Chapter 2 Figure 1. Map of the region surrounding the Colonia Valle .......................................................... 11 Figure 2. GLOF discharge hydrographs for the outlet of the source lake, LC2 ............................. 19 Figure 3. Correlation plot of peak discharge versus volume drained, lake and air temperature, and inflow rate .....................................................................................................................................