Periglacial weathering and headwall erosion in cirque glacier bergschrunds

Sanders, J. W.; Cuffey, Kurt M.; Moore, Jeffrey R.; MacGregor, K. R.; Kavanaugh, Jeffrey L.

doi:10.1130/g33330.1

Cited by 82 publications

(79 citation statements)

References 25 publications

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“…Although the connection between glacier under mining of the headwall and resultant retreat was recognized long ago (e.g., Johnson, 1904;Gilbert, 1904), less attention has been directed toward the processes by which cirque headwall retreat actually occurs (Battle and Lewis, 1951;Rapp, 1960;Hallet et al, 1991;Matsuoka and Sakai, 1999;Sanders et al, 2012). It is widely assumed that the headwall simply maintains a strength equilibrium slope (e.g., Mitchell and Montgomery, 2006).…”

Section: Overview Of Headwallmentioning

confidence: 99%

“…Their unmistakable morphology-steep fl uted bedrock walls and overdeepened rock basins containing resplendent tarns-has motivated alpine geomorphologists for more than a century to investigate the mechanisms driving their formation (e.g., Tyndall, 1862;Gastaldi, 1873;Helland, 1877;Hooke, 1991;MacGregor et al, 2009;Sanders et al, 2012). From the Alps to the Sierra Nevada, from Scandinavia to Snowdon, the ques-tion of cirque evolution remains the same: What processes are responsible for the development of cirques and at what rates do they act?…”

Section: Introductionmentioning

confidence: 99%

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The sediment budget of an alpine cirque

Sanders

Cuffey

MacGregor

et al. 2012

Geological Society of America Bulletin

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Cirques form and evolve as glaciers attack the bed and subaerial processes dismantle the surrounding walls. Collectively, these processes-which can make a cirque longer, or deeper, or both-profoundly infl uence near-divide regions of glaciated mountains and yet are rarely studied in a systematic way. Toward this end, we developed a theoretical framework for the sediment budget of a cirque that includes sediment sources, transport pathways, and storage elements. We quantifi ed each component of the sediment budget using fi eld measurements and remote-sensing data of a glaciated alpine cirque in British Columbia, Canada. The cirque has a plan-view area of 1.64 km 2 and relief of ~780 m. Our budget values, which correspond to a period of substantial glacier retreat, are based on measurements refl ecting time intervals ranging from 1 yr to 80 yr. We report errors as a range (enclosed in parentheses), analogous to 95% confi dence bounds.On average, 1640 (250-7950) metric tons of rock are released by the headwall each year; nearly 90% of this debris leaves the wall as small rockfalls or in snow avalanches. Our fi eld observations indicated that snow avalanches originating as cornice failures are currently the most important transport process on the headwall. We estimated the mass of debris transported annually by the glacier to the foreland using (1) the volume and age of the foreland ground moraine and (2) the product of rock mass per unit volume of ice and glacier velocity. Over the past several decades, the glacier delivered 6440 (1180-14930) tons/yr to the foreland via forward ice motion and margin retreat (mostly in subglacial till or sediment-rich basal layers). Less than 3% of the glacier-borne sediment fl ux traveled as supra glacial debris (170 [50-320] tons/yr). At present, sediment evacuation from the cirque occurs in a single meltwater stream. We monitored water discharge and suspended sediment concentration in this stream between 29 June and 28 August 2007. By season's end, 650 (80-1860) tons of sediment had passed our gauging station (equivalent to an erosion rate of 0.2 [0.03-0.70] mm/yr, when averaged over the glacier bed). Approximately one third of the total annual streamborne sediment transport occurred over a 2 d period during the fi rst major melt event of the year.Using our budget relations and fl ux magnitudes, we estimate the glacier is removing between 1240 and 2470 tons of rock from its bed per year, a rate equivalent to 0.5-0.9 mm/yr of erosion glacierwide. The headwall, by comparison, is being worn away horizontally at ~1.2 (0.2-5.9) mm/yr. Thus, our results suggest that the headwall is retreating at rates roughly equivalent to vertical incision by the glacier. Our sediment budget results demonstrate that the wide variety of sediment sources and transport processes active in cirques necessitates a holistic view of cirque formation, one that most morphometric, range-scale, and glacial erosion analyses ignore.

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Section: Overview Of Headwallmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The sediment budget of an alpine cirque

Sanders

Cuffey

MacGregor

et al. 2012

Geological Society of America Bulletin

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“…Studies of headwall recession have highlighted the importance of frost weathering along the bergschrund (Johnson, 1904;Gardner, 1987;Sanders et al, 2012), whereas studies of cirque floor features emphasize subglacial processes (Galibert, 1962;White, 1970). A composite model, arguing for a systemic link between frost-driven headwall retreat and subglacial scouring promoted by rotational slipping of glacier ice, contends that debris released from the headwall provide abrasive tools to the glacier base.…”

Section: Introductionmentioning

confidence: 97%

“…The key processes that drive bedrock denudation by glaciers and affect the growth pattern of alpine cirques continue to be a topic of debate in Quaternary geomorphology (Dühnforth et al, 2010;Sanders et al, 2010Sanders et al, , 2012Sanders et al, , 2013. By definition, all cirques contained glaciers intermittently during the Pleistocene; however, the connection between glacier-related processes and the morphology of the topographic basin remains ambiguous.…”

Section: Introductionmentioning

confidence: 98%

A critical appraisal of allometric growth among alpine cirques based on multivariate statistics and spatial analysis

2015

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“…However, very small glaciers (here defined as being smaller than 0.5 km 2 today) account for 80-90% of the number of glaciers in mid-to low-latitude mountain ranges (Paul et al, 2004;Pfeffer et al, 2014). Although the total area and volume of these glaciers is rather small (≈13% of overall glacier area, ≈ 5% of overall ice volume), they affect the hydrological regime in poorly glacierized drainage basins (Huss, 2011;Jost et al, 2012) and are highly relevant for landscape formation and bedrock erosion in cirques (Sanders et al, 2012;Seppi et al, 2015). Furthermore, several winter tourism resorts in the Alps rely on the presence of small remnants of glacier ice and increasingly try to protect them from further melting (Fischer et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of Very Small Glaciers in the Swiss Alps to Future Climate Change

2016

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Very small glaciers (<0.5 km 2 ) account for more than 80% of the total number of glaciers in mid-to low-latitude mountain ranges. Although their total area and volume is small compared to larger glaciers, they are a relevant component of the cryosphere, contributing to landscape formation, local hydrology, and sea-level rise. Worldwide glacier monitoring mostly focuses on medium-sized to large glaciers leaving us with a limited understanding of the response of dwarf glaciers to climate change. In this study, we present a comprehensive modeling framework to assess past and future changes of very small glaciers at the mountain-range scale. Among other processes our model accounts for snow redistribution, changes in glacier geometry, and the time-varying effect of supraglacial debris. It computes the mass balance distribution, the englacial temperature regime and proglacial runoff. The evolution of 1133 individual glaciers in the Swiss Alps is modeled in detail until 2060 based on new distributed data sets. Our results indicate that 52% of all very small glaciers in Switzerland will completely disappear within the next 25 years. However, a few avalanche-fed glaciers at low elevation might be able to survive even substantial atmospheric warming. We find highly variable sensitivities of very small glaciers to air temperature change, with gently-sloping, low-elevation, and debris-covered glaciers being most sensitive.

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Periglacial weathering and headwall erosion in cirque glacier bergschrunds

Cited by 82 publications

References 25 publications

The sediment budget of an alpine cirque

The sediment budget of an alpine cirque

A critical appraisal of allometric growth among alpine cirques based on multivariate statistics and spatial analysis

Sensitivity of Very Small Glaciers in the Swiss Alps to Future Climate Change

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