Study region: The Cordoriri watershed and vicinity in the Cordillera Real, Bolivia, South America Study focus: Recent warming has contributed to substantial reductions in glaciers in many regions around the globe. Melting of these glaciers alters the timing and magnitude of streamflows and diminishes water resources accumulated in past climates. These changes are especially acute in regions with small glaciers and problematic for populations relying on surface water. In Bolivia, most glaciers are less than 0.5 km(2) and about 2 million people draw water in part from glacier-fed watersheds. Sparse monitoring, however, has limited estimates of glacial meltwater contributions. The use of environmental tracers is one approach that can quantify the contributions of glaciers. We present isotopic and anion data for streams, reservoirs, arroyos, precipitation, and glaciers for the wet and dry seasons in 2010, 2011, and 2012. New hydrological insights for the region: Glacier meltwater data shows distinct seasonal isotopic values, presenting opportunities for end-member mixing analyses. From isotopes, we estimate 31-65% of the water measured in high altitude streams and reservoirs during the 2011 wet season originated from melting of ice and recent snow, while glacier ice contributed 39-71% of the water in reservoirs in the 2012 dry season. This study demonstrates that more comprehensive sampling in the region could quantify the contributions of glacial meltwater and nonglacial sources to surface water supplies. (C) 2016 The Author(s). Published by Elsevier B.V.

Postglacial rivers are part of the relatively young low-relief landscape system left behind by glaciers. Over time, postglacial rivers are susceptible to both minor and major channel planform changes as the Earth and its newly exposed rivers adjust to new isostatic and geomorphic equilibriums. Those planform changes result in topographic features that are well preserved among the largely unaltered landscape and offer opportunities to learn about the processes that create them. This work focuses on those minor and major planform changes and the resulting landforms, with a focus on processes effecting the glaciolacustrine Red River Valley. Here, three studies were conducted, two regarding minor planform changes and one focusing on major planform changes. Studies included in this work regard 1) the spatial distribution of meander cutoffs and meander cutoff relief on the Red River, 2), avulsion timing and length resulting from isostatic tilting and 3) mobile river ice and bank interaction frequency, locations, and erosion in meandering rivers. Results show that rivers develop meander cutoffs that faster in areas where geologic materials are more easily eroded and their relief shows a positive relationship with the rate of river incision. Major channel path changes (avulsions) in the presence of isostatic tilting were found to be most frequent soon after river establishment while rates of isostatic rebound are high enough to outpace channel incision. River ice was found to most frequently interact with the outer banks of channels with long, tight bends and high sinuosity, potentially contributing to the meandering process. From these results it can be interpreted that postglacial rivers were highly dynamic early in their history and have stabilized over time, with most of the changes occurring in areas with more erodible alluvium. Presently, rivers undergo most of their changes during the spring thaw when mobile river ice is impacting the banks, with sinuous river reaches impacted most frequently by mobile river ice. / North Dakota Water Recourses Research Institute (ND WRRI) Fellowship Program

Mountain glaciers have influenced the surface of our planet throughout geologic time. These large reservoirs of water ice sculpt alpine landscapes, regulate downstream river flows, perturb climate-tectonic feedbacks, contribute to sea level change, and guide human migration and settlement patterns. Glaciers are especially relevant in modern times, acting as buffers which supply seasonal meltwater to densely populated downstream communities and support economies via hydropower generation. Anthropogenic warming is accelerating ice loss in most glacierized regions of the world. This has sparked concerns regarding water resources and natural hazards, and placed glaciers at the forefront of climate research. Here we provide new observations of glacier change in key mountain regions to quantify rates of ice loss, better understand climate drivers, and help establish a more unified framework for studying glacier change across timescales. In Chapter 1 we use seismic observations, numerical modeling, and geomorphic analysis to investigate a destructive glacial lake outburst flood (GLOF) which occurred in Bhutan. GLOFs are a substantial hazard for downstream communities in many vulnerable regions. Yet key aspects of GLOF dynamics remain difficult to quantify, as in situ measurements are scarce due to the unpredictability and remote source locations of these events. Here we apply cross-correlation based seismic analyses to track the evolution of the GLOF remotely (~100 km from the source region), use the seismic observations along with eyewitness reports and a downstream gauge station to constrain a numerical flood model, then assess geomorphic change and current state of the unstable lakes via satellite imagery. Coherent seismic energy is evident from 1 to 5 Hz beginning approximately 5 hours before the flood impacted Punakha village, which originated at the source lake and advanced down the valley during the GLOF duration. Our analysis highlights potential benefits of using real-time seismic monitoring to improve early warning systems. The next two chapters in this work focus on quantifying multi-decadal glacier ice loss in the Himalayas. Himalayan glaciers supply meltwater to densely populated catchments in South Asia, and regional observations of glacier change are needed to understand climate drivers and assess impacts on glacier-fed rivers. Here we utilize a set of digital elevation models derived from cold war–era spy satellite film and modern stereo satellite imagery to evaluate glacier responses to changing climate over the last four decades. In Chapter 2 we focus on the eastern Himalayas, centered on the Bhutan–China border. The wide range of glacier types allows for the first mass balance comparison between clean, debris, and lake-terminating (calving) glaciers in the area. Measured glaciers show significant ice loss, with statistically similar mass balance values for both clean-ice and debris-covered glacier groups. Chapter 3 extends the same methodology to quantify glacier change across the entire Himalayan range during 1975–2000 and 2000–2016. We observe consistent ice loss along the entire 2000-km transect for both intervals and find a doubling of the average loss rate during 2000–2016 compared to 1975–2000. The similar magnitude and acceleration of ice loss across the Himalayas suggests a regionally coherent climate forcing, consistent with atmospheric warming and associated energy fluxes as the dominant drivers of glacier change. Chapter 4 investigates millennial-scale glacier changes during the Late Glacial period (15-11 ka). Here we present a high-precision beryllium-10 chronology and geomorphic map from a sequence of well-preserved moraines in the Nendaz valley of the western European Alps, with the goal to shed light on the timing and magnitude of glacier responses during an interval of dramatic natural climate variability. Our chronology brackets a coherent glacier recession through the Younger Dryas stadial into the early Holocene, similar to glacier records from the southern hemisphere and a new chronology from Arctic Norway. These results highlight a general agreement between mountain glacier changes and atmospheric greenhouse gas records during the Late Glacial. In Chapter 5 we use a numerical glacier model to simulate glacier change across a typical alpine region in the European Alps. Model results suggest that shorter observational timespans focused on modern periods (when glaciers are far from equilibrium and undergoing rapid change) exhibit greater spatial variability of mean annual ice thickness changes, compared to intervals which extend further back in time (to include decades when climate was more stable). The model agrees with multi-decadal satellite observations of glacier change, and clarifies the positive correlation between glacier disequilibrium and spatial variability of glacier mass balance. This relationship should be taken into account in regional glacier studies, particularly when analyzing recent spatial patterns of ice loss. Advances made in this work are of practical value for societies vulnerable to glacier change. This includes potential improvements to GLOF early warning systems via seismic monitoring, better constraints on glacier-sourced water scenarios in South Asia, strengthened understanding of long-term glacier responses to baseline natural climate variability, and a clarified relationship between glacier disequilibrium and spatial variability of ice loss. When placed within a global context, our observations highlight the correlation between regional mountain glacier change and greenhouse gas forcing through time.

This research developed a novel workflow for combining different types and scales of data to understand the development of small, steep, and sheltered glacial forefields across space and time using the Avalanche glacier of the Selkirk Range, BC as a case study. As glaciers recede, symbiotic geomorphological and ecological feedback loops determine the ecological succession in recently deglaciated terrain, which can in turn effect landform stability and water quality downstream. In order to describe emergent land cover patterns in the forefield, this research uses Corenbilt’s (2007) fluvial biogeomorphic succession (FBS) framework to interpret a century of land cover changes. To do so, an experimental protocol was developed that combined remotely sensed data – repeat photographs, historic air photographs, satellite imagery, and digital elevation models – and data collected in-situ using a photo transect method. Analysis of more than a century of photographs determined that the Avalanche glacier is receding at a slower rate than has been observed in the region’s larger glaciers, subsequently leading to a slower rate of forefield habitat expansion. Still, all four stages of fluvial biogeomorphological succession were found across the Avalanche glacier’s forefield. It was found that in the Avalanche forefield, terrain age seems to place a limit on which successional stage is possible at any given location within the forefield, but topographic features like slope angle seemed to influence succession patterns within areas that had the same terrain age. Further research is needed to see whether these findings are consistent for similar steep, small, and sheltered glaciers in the region. / Graduate

In the McMurdo Dry Valleys, Victoria Land, East Antarctica, melting of glacial ice is the primary source of water to streams, lakes, and associated ecosystems. To better understand meltwater production, three hypotheses are tested: 1) that small changes in the surface energy balance on these glaciers will result in large changes in melt, 2) that subsurface melt does not contribute significantly to runoff, and 3) that melt from 25-m high terminal cliffs is the dominant source of baseflow during cold periods. These hypotheses were investigated using a surface energy balance model applied to the glaciers of Taylor Valley using 14 years of meteorological data and calibrated to ablation measurements. Inclusion of transmission of solar radiation into the ice through a source term in a one-dimensional heat transfer equation was necessary to accurately model summer ablation and ice temperatures. Results showed good correspondence between calculated and measured ablation and ice temperatures over the 14 years using both daily and hourly time steps, but an hourly time step allowed resolution of short duration melt events and melt within the upper 15 cm of the ice. Resolution of short duration melt events was not important for properly resolving seasonal ablation totals. Across the smooth surfaces of the glaciers, ablation was dominated by sublimation and melting was rare. Above freezing air temperatures did not necessarily result in melt, and low wind speed was important for melt initiation. According to the model, subsurface melt between 5 and 15 cm depth was extensive and lasted for up to six weeks in some summers. The model was better able to predict ablation if some subsurface melt was assumed to drain, lowering ice density, consistent with observations of a low density weathering crust that forms over the course of the summer on Dry Valley glaciers. In extreme summers, drainage of subsurface melt may have contributed up to half of the observed surface lowering through reduction of ice density and possibly through collapse of highly weathered ice. When applied spatially, the model successfully predicted proglacial streamflow at seasonal and daily time scales. This was despite omitting a routing scheme, and instead assuming that all melt generated exits the glacier on the same day, suggesting refreezing is not substantial. Including subsurface melt as runoff improved predictions of runoff volume and timing, particularly for the recession of large flood peaks. Because overland flow was rarely observed over much of these glaciers, these model results suggest that runoff may be predominantly transported beneath the surface in a partially melted permeable layer of weathered ice. According to the model, topographic basins, particularly the low albedo basin floors, played a prominent role in runoff production. Smooth glacier surfaces exhibited low melt rates, but were important during high melt conditions due to their large surface area. Estimated runoff contributions from cliffs and cryoconite holes was somewhat smaller than suggested in previous studies. Spatial and temporal variability in albedo due to snow and debris played a dominant role in flow variations between streams and seasons. In general, the model supported the existing assumption that snowmelt is insignificant, but in extreme melt years snowmelt in the accumulation area may contribute significantly to runoff in some locations.

Glacial till from the Mt. Achernar moraine (MAM) records pre- and post- last glacial maximum (LGM) compositional variability of an East Antarctic moraine sequence through time and space. Pebble lithology, detrital zircon geochronology, and till geochemistry were analyzed on samples from a 6.5 km transect. Hummocky topography occurs with the most recently exposed material along the active ice margin (Zone 1), followed by a relatively flat and low region (Zone 2), and then a series of ~2 m high parallel/sub-parallel ridges and troughs accompanied by distinct color changes that are directly related to the dominant lithology of the region (Zones 3–5). Zone 3 is dominated by ~38% more sedimentary rocks than adjacent zones and has an overall shape of a broad arch superimposed with smaller ridges. Zone 4 is composed of distinct colored bands that alternate between dominant sedimentary and mafic igneous lithologies. These dominant sedimentary and intermediate/mafic igneous rocks for all Zones are interpreted to be primarily the Beacon and Ferrar Supergroup rocks respectively. The U/Pb data from the till is consistent with a Beacon Supergroup source as samples consistently show significant populations from the Permian ~250-260 Ma, the Proterozoic ~565–600 Ma, ~950–1270 Ma, and ~2300-2320 Ma, as well as (and) the late Archean ~2700-2770 Ma. The Pagoda, Mackellar, Buckley, and Fremouw Formations are potential sources of the detrital zircons. When paired with surface exposure ages, the U/Pb data indicates that the debris source has been consistent over the past ~555 ka, implying relatively stable ice sheet behavior. However, ice sheet change is indicated by a trim line present on Mt. Achernar that can be traced back to the boundary between Zones 3 and 4, as well as a change in pebble lithology, geochemistry, and morphology of Zone 3. Zone 3 records a time of ice sheet thickening and a change in provenance during the LGM. Zone 4 is pre-LGM, Zone 2 records deglaciation, and Zone 1 is still actively connected to the Law Glacier. This study reveals the broader importance of using multiple provenance techniques when interpreting provenance changes in till over time.

Thesis (Ph.D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2000. / Vita. / Includes bibliographical references. / by Robert P. Ackert, Jr. / Ph.D.

No description available.

No description available.

No description available.