Glacier erosion and response to climate, from Alaska to Patagonia

240 Pages·2012·9.26 MB·English

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: _
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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, with tracklines……………….162
5.4 Post-glacial sediment accumulation, with bathymetric contours…………………….163
5.5 Seismic profiles of moraines…………………………………………………………….164
5.6 Seismic profiles of laminated sediments……………………………………………….165
5.7 Seismic profiles of buried moraine……………………………………………………...166
5.8 Seismic profiles of ice proximal deposits………………………………………………167
5.9 Seismic profiles of fault scarp and slump deposits……………………………………168
5.10 Seismic profile of inner fjord channel………………………………………….....169
5.11 Submarine landforms in Laguna San Rafael……………………………………170
5.12 Erosion and retreat since the Little Ice Age, San Rafael glacier……………….171
6.1 Location of Tyndall Glacier………………………………………………………………178
6.2 Tracklines of the 2001 and 2005 bathymetric surveys of Lago Geike………………179
6.3 Cross section of Lago Geike at the ice front, 2001 and 2005………………………..180
6.4 The bathymetry of Lago Geike in March, 2001………………………………………..181
6.5 The bathymetry of Lago Geike in March, 2005 ……………………………………….182
6.6 Profiles across Lago Geike,. a) at 320 m b) at 1300 m …………………………...…183
6.7 DEM of Tyndall Glacier………………………………………………………………..…184
6.8 Cross-section of Tyndall glacier at 700 m.a.s.l. from radar traverse………………..185
7.1 Location of apatite FT sample, Laguna San Rafael…………………………………..194
7.2 Geology and extent of the LGM advance, Tierra del Fuego…………………………195
7.3 Location of apatite FT samples, Marinelli fjord……………………………………..…196
7.4 Photograph of detrital cobbles, San Rafael……………………………………………197
7.5 Photograph of detrital cobbles, Marinelli……………………………………………….198
7.6 Probability plot of apatite FT ages, San Rafael and Marinelli……………………..…199
7.7 AGE2EDOT age-exhumation curve…………………………………………………….200
7.8 Exhumation ages and timescales of chronometers, from Spotila et al. (2004)…....201
8.1 Erosion rates for basins worldwide, including Patagonian glaciers……………..….207
LIST OF TABLES

Table Number Page

1. Sediment volume in the Laguna San Rafael, 1959-2002…………………….……...129
2. Direct measurements of terminus ice speed, modeled ablation fluxes and
associated glacier dynamics for San Rafael glacier……………………………....130