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Understanding and quantifying the transient dynamics and evolution of debris covered glaciers

Applicant Vieli Andreas
Number 169775
Funding scheme Project funding (Div. I-III)
Research institution Geographisches Institut Universität Zürich
Institution of higher education University of Zurich - ZH
Main discipline Hydrology, Limnology, Glaciology
Start/End 01.11.2016 - 30.04.2021
Approved amount 514'140.00
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Keywords (13)

debris-covered glaciers; glacier dynamics; climate change; glacier; Himalaya; glacier change; debris cover; remote sensing; numerical modelling; Alps; debris transport; glaciology; glacier flow

Lay Summary (German)

Lead
Dynamisches Verhalten schuttbedeckter GletscherGletscher mit schuttbedeckten Zungen sind in Hochgebirgen weit verbreitet. Bereits eine Schuttbedeckung von wenigen Zentimetern wirkt thermisch isolierend und reduziert dadurch die Eisschmelze und folglich den Massenverlust unter einer Erwärmung. Dies zeigt sich an typischerweise flachen und ausgedehnten schuttbedeckten Gletscherzungen welche im Rückzug stagnieren. Während der Einfluss der Schuttbedeckung auf die Oberflächenschmelze relativ gut untersucht ist, sind der indirekte Einfluss auf das dynamische Verhalten und Wechselwirkungen zwischen Eisfliessen, der Evolution der Oberfläche und der Schuttbedeckung wenig verstanden und in gegenwärtigen Vorhersagen nicht berücksichtigt
Lay summary

Das Projekt hat zum Ziel das dynamische Verhalten  schuttbedeckter Gletscher besser zu verstehen und quantifizieren. Dies wird Mittels einer Kombination von Fliessmodellierungen, Prozessstudien und der Erhebung von Langzeitdatensätzen am Beispiel  zweier ausgewählter Gletscher (Zmutt in den Schweizer Alpen  und Santopanth im Indischen Himalaya ) angegangen. Darauf aufbauend wird eine einfache Parametrisierung erarbeitet, die anhand weiterer Gletscher evaluiert wird. Neben der Entwicklung  quantitativer Instrumente wird dieses Projekt zu einem besseren Verständnis der Wechselwirkungen zwischen Schuttbedeckung und dem dynamischen Verhalten solcher Gletscher beitragen.

 

Die in diesem Projekt erarbeiteten Grundlagen und Modelle erlauben eine verbesserte Beurteilung der aktuellen und zukünftigen Entwicklung  schuttbedeckter Gletscher sowie deren Rolle als Wasserressource oder für die Entstehung von möglicherweise gefährlichen Gletscherseen. Dies ist im Zusammenhang mit dem jetzigen Klimawandel und der damit verbundenen  starken Zunahme der Schuttbedeckung auf Gletschern von besonderer Bedeutung.
Direct link to Lay Summary Last update: 28.10.2016

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Abstract

This project aims at understanding and quantifying the short and long-term dynamics and evolution of debris-covered glaciers with a specific focus on the transient process interactions between flow dynamics and debris cover. We will collect and combine historical, field and remote-sensing data on the evolution of geometry, flow and debris cover with transient numerical flow modelling, that includes a fully dynamic treatment of debris evolution and that is coupled to geometry and surface melt. Debris-covered glacier tongues are widespread and typical for avalanche-fed glaciers in high relief mountain ranges such as the Himalayas. Supra-glacial debris cover has long been known to reduce surface melt with increasing debris thickness. This results in debris accumulation and strongly subdued ablation rates on the tongues of such glaciers and supresses the influence from atmospheric forcing. Hence, such glaciers experience clearly less retreat and thinning with increasing temperatures than debris-free glaciers. This typically results in extended, low reaching, flat and slowly flowing heavily debris-covered ice tongues, that are often not far from their maximum historical extent. Dynamic adjustment of such glaciers to climatic forcing therefore differs fundamentally from debris-free glaciers, which is also reflected in seemingly much longer response-times and hysteresis-like behaviour. Mass loss of debris-covered glaciers in a warming climate is therefore not a simple function of elevation but additionally influenced by the extent and evolution of debris cover, their dynamic state and the related downwasting processes such as ice-cliff melt and lake formation. Whereas the relationship between debris thickness and surface melt is well studied and being integrated in existing mass balance models, the effects of surface debris on glacier dynamics and mass loss are poorly understood and current observations difficult to comprehend. Further, the related dynamical feedbacks, such as between debris evolution, ice flow and downwasting processes, are not included in existing predictive models and provide substantial uncertainties in projecting their long-term evolution. In order to address these issues, we are combining numerical flow modelling with long-term observational data from remote sensing, field investigations and historical records. This also requires to develop modelling tools for simulating debris evolution, debris entrainment and related downwasting processes and integrate them into a time-dependent 3-dim. glacier flow model.The project targets two heavily debris-covered glaciers of which the first, Zmuttgletscher in the Swiss Alps, provides a unique historic long-term (>120 years) data record of geometry, debris change and climate forcing and easy field-access for in-situ measurements for constraining model parameters. The second target is Satopanth Glacier in Garhwal Himalaya (India), which is a typical medium-sized debris-covered Himalayan glacier and aims to evaluate the modelling at a contrasting climatic and topographic setting. The findings of the 3-dim. modelling will further be used to develop and test simple parametrizations of debris evolution and geometry adjustment for a given climatic forcing. We apply this reduced model to a set of additional debris-covered glaciers such as Zinalgletscher and Miage Glacier in the Alps and Gangotri and Khumbu Glacier in the Himalaya for which the minimum required data sets are existing and provided by our project partners, if not available from own research. Ultimately this project will provide an improved understanding and quantification of the transient dynamics and evolution of debris-covered glaciers. Regarding the observed strong increase of debris cover under the current and future warming trend, this is crucial for predicting their mass loss, terminus dynamics and sediment budgets. Besides sea-level projections this is also relevant for water resource management and for assessing glacier-related hazards such as lake outburst floods that are typical of degrading debris-covered glacier tongues.
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