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Glacier Erosion and Response to Climate, from Alaska to Patagonia

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Glacier Erosion and Response to Climate, from Alaska to Patagonia Glacier erosion and response to climate, from Alaska to Patagonia Michèle N. Koppes A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2007 Program Authorized to Offer Degree: Department of Earth & Space Sciences University of Washington Graduate School This is to certify that I have examined this copy of a doctoral dissertation by Michèle N. Koppes and have found that it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made. Chair of the Supervisory Committee: Bernard Hallet Reading Committee: Bernard Hallet Alan Gillespie David Montgomery Date: _ In presenting this dissertation in partial fulfillment of the requirements for the doctoral degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of the dissertation is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Requests for copying or reproduction of this dissertation may be referred to ProQuest Information and Learning, 300 North Zeeb Road, Ann Arbor, MI 48106-1346, 1-800-521-0600, or to the author. Signature ______________________________ Date ______________________________ University of Washington Abstract Glacier erosion and response to climate, from Alaska to Patagonia Michèle N. Koppes Chair of the Supervisory Committee: Professor Bernard Hallet Department of Earth and Space Sciences Contemporary glacial erosion rates based on sediment yields from tidewater glaciers in coastal Alaska and Patagonia are unsurpassed worldwide, and significantly exceed regional exhumation rates. These erosion rates are exceptionally high because the tidewater glaciers have been anomalously dynamic during a century of rapid retreat. To investigate the influence of climate and retreat on erosion, this dissertation presents seismic data defining the volume of sediments recently produced by one tidewater glacier in southeast Alaska and two glaciers in Chilean Patagonia. These glaciers have all been in steady retreat during the 20th century, and all calve into a fjord, providing an efficient trap for the sediment delivered to the calving front. Using a model of proglacial sedimentation, the annual sediment yield from, and erosion rate of, each glacier are calculated. A strong correlation emerges between glacial retreat and sediment yields, implying that most contemporary sediment yield data from retreating tidewater glaciers may correspond to recent erosion rates that are a factor of 3.5 ± 1.5 higher than over the entire advance-retreat cycle. To examine the influence of ice dynamics on glacier erosion, the flux of ice into the Patagonian glaciers is compared to the retreat rate and to the sediment flux. Reanalysis climate data, adjusted to local conditions by correlation with weather gauges installed at the glacier termini, and coupled to ablation stakes and a linear model of orographic enhancement of precipitation over the glacier basins, were used to reconstruct the daily ice flux into and out of the glaciers over 50 years. Results indicate that basin-wide erosion rates increase as a function of ice flux through the equilibrium line. As ice accumulation has decreased, the glaciers have responded by thinning and retreating rapidly, drawing down hundreds of meters of ice and delivering more sediment to the fjords. Interestingly, erosion rates from these glaciers, even after taking into account short-term acceleration during retreat, remain over an order of magnitude higher than long-term exhumation rates derived from detrital apatite thermochronometry in the basins, indicating that current glacier erosion rates far exceed orogenic rates, and reflect short periods of warming climate. TABLE OF CONTENTS Page List of Figures...................................................................................................................ii List of Tables....................................................................................................................v Introduction.......................................................................................................................1 Chapter 1: Methods…………...……….............................................................................14 Chapter 2: Erosion rates during rapid deglaciation, Icy Bay, Alaska...............................49 Chapter 3: Late 20th century retreat and erosion from Marinelli Glacier, Tierra del Fuego……………………………………………………………….............................71 Chapter 4: Relating glacier erosion to ice dynamics, San Rafael Glacier.....................102 Chapter 5: Centennial sediment yields and submarine landforms during retreat of a tidewater glacier, Laguna San Rafael, Chilean Patagonia.................................146 Chapter 6: Recent erosion rates at Tyndall Glacier, Southern Patagonian Icefield.......172 Chapter 7: Exhumation rates from glaciated basins in the Patagonian Andes..............186 Chapter 8: Summary and Future Work..........................................................................202 List of References..........................................................................................................208 LIST OF FIGURES Figure Number Page 1. Diagram of the influence of erosion on rock uplift, from Zeitler et al. (2001)…….…..11 2. Elevation of ranges and snowline in the Americas, from Porter (1981)……………...12 3. Erosion rates for glaciated and non-glaciated basins, from Hallet et al. (1996)…….13 1.1 Photograph of acoustic reflection profiler deployment………………………………...34 1.2 Photograph of CTD deployment…………………………………………………………35 1.3 Leave one out error analysis……………………………………………………………..36 1.4 Photograph of sediment traps used……………………………………………………..37 1.5 Diagram of glacier mass flux model……………………………………………………..38 1.6 Photograph of meteorological station, Marinelli fjord…………………………………39 1.7 Comparison of gauge and NCEP precipitation rates, 1983, Laguna San Rafael…..40 1.8 Comparison of gauge and NCEP temperature, Laguna San Rafael………………..41 1.9 Daily wind direction and wind strength for 2005, Marinelli fjord……………………..42 1.10 Comparison of gauge and NCEP precipitation rates, Marinelli fjord………………..43 1.11 Ablation vs. local mean daily temperature, San Rafael glacier……………………..44 1.12 Ablation vs. local mean temperature, Glaciar Lengua……………………………….45 1.13 Orographic model parameters………………………………………………………….46 1.14 Orographic enhancement factor, San Rafael glacier………………………………...47 1.15 Flow chart of glacier mass flux model………………………………………………...48 2.1 Tyndall Glacier and Mount St. Elias, 1938……………………………………………....63 2.2 DEM of Taan Fjord showing ice retreat history and 1999 tracklines ……………….64 2.3 Sample acoustic profiles from Taan Fjord……………………………………………..65 2.4 Contours of sediment thickness in Taan Fjord………………………………….……..66 2.5 DEM of Taan Fjord and Tyndall Glacier………………………………………….…….67 2.6 Erosion rate and retreat rate for Tyndall Glacier, 1962-1999………………………..68 2.7 Erosion rate and retreat rate for Tyndall Glacier, 1962-1999………………………..69 2.8 Erosion rates for glacial and non-glacial basins……………………………………….70 3.1 Location map and DEM of Marinelli Glacier…………………………………………....90 3.2 Photograph of trimline in upper Marinelli Fjord………………………………………...91 3.3 Sedimentation rate with distance from Marinelli ice front……………………………..92 3.4 Profile of glacimarine sediment thickness and bathymetry along Marinelli fjord…..93 3.5 Samples acoustic reflection profiles from Marinelli fjord …………………………… 94 3.6 Contour map of 2005 bathymetry and sediment thickness in Marinelli fjord………95 3.7 Erosion rate and retreat rate for Marinelli Glacier since 1962…………… ………96 3.8 Precipitation rates from NCEP and gauges installed at Marinelli fjord....................97 3.9 Temperature and precipitation variability and retreat, Marinelli fjord….…… ……98 3.10 Ice fluxes into and out of Marinelli glacier and retreat rate, 1950-2006………… 99 3.11 Ice fluxes into and out of Marinelli glacier and erosion rate, 1950-2006…...…… 100 3.12 Volume of entrained debris and total sediment flux, Marinelli glacier ……………101 4.1 Location map of San Rafael glacier…………………………………………………...131 4.2 Sample acoustic profiles from the inner fjord of Laguna San Rafael…………….....132 4.3 Bathymetric map of inner fjord, including tracklines and seismic samples……….133 4.4 Map of sediment accumulation in inner fjord…………………………………………134 4.5 DEM of San Rafael glacier……………………………………………………………..135 4.6 Annual erosion vs. retreat rates, San Rafael glacier………………………………..136 4.7 Volume of entrained debris and total sediment flux, San Rafael glacier ………..137 4.8 Calving speeds required for englacial entrainment, San Rafael glacier …………138 4.9 Calving speeds required for englacial entrainment, Marinelli glacier……………...139 4.10 Orographic enhancement of precipitation over San Rafael glacier……………....140 4.11 Temperature and precipitation anomalies at Laguna San Rafael…………………141 4.12 Annual accumulation and ablation fluxes and retreat…………………………….142 4.13 Modeled ice fluxes and erosion rate, 1960-2006………………………………...143 4.14 Retreat rates and ice front melt area, 1950-2006………………………………...144 4.15 Erosion rates and ice flux at ELA, San Rafael glacier……………………………145 5.1 Landsat image of Laguna San Rafael...………………………………………………..160 5.2 Bathymetry of Laguna San Rafael, with location of seismic images………………..161 5.3 Total sediment accumulation in Laguna San Rafael,
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