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Comprehensive Observations of Episodic Basal, Englacial and Lateral Influences on Ice Stream Dynamics

Applicant Lüthi Martin Peter
Number 197015
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 01.03.2021 - 28.02.2025
Approved amount 1'639'910.00
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All Disciplines (3)

Discipline
Hydrology, Limnology, Glaciology
Other disciplines of Engineering Sciences
Geophysics

Keywords (9)

glacier dynamics; geophysics; glaciology; ice stream; ice sheet; seismology; Greenland; discontinuous processes; drone

Lay Summary (German)

Lead
Detaillierte Untersuchung von sehr schnellem Gletscherfliessen
Lay summary
Schnell fliessende Gletscher sind die Arterien des Grönländischen
Eisschildes, durch welche grosse Mengen von Eis ins Meer transportiert
werden. Der schnellste davon, Jakobshavn Isbrae, fliesst mit 30-40 m
pro Tag in einen tief eingeschnittenen Fjord, und verschiebt pro Jahr
35 Milliarden Tonnen Eis vom Landesinneren an die Küste. Dort brechen
riesige Eisberge ab, die weit in den Atlantik hinaustreiben. Einer
davon wurde der Titanic zum Verhängnis.

Die Bedingungen für schnelles Fliessen von Gletschern sind nur
teilweise erforscht. Bei Eisdicken bis zu 1500 Metern ist es sehr
schwierig, genaue Beobachtungen der Prozesse im und unter dem Eis
anzustellen. Sicherlich ist Schmelzwasser, das durch die Reibung bei
der schnellen Eisbewegung entsteht, wesentlich für das Gleiten über
den Felsuntergrund. Gleichzeitig steht das Wasser unter hohem Druck
und verflüssigt so das feinkörnige Sediment unter dem Eis. Im Sommer
dringt zusätzlich viel Schmelzwasser von der Oberfläche durch Spalten
und Kanäle unter das Eis, hebt es teilweise an, und beschleunigt so
das Gletscherfliessen.

In diesem Projekt untersuchen wir, inwiefern episodische Prozesse das
schnelle Fliessen verstärken. So wird durch die extreme Deformation
das Eis zerrissen und geschwächt, was wiederum zu grösseren
Geschwindigkeiten führt. Solche Bruchprozesse sind nicht
kontinuierlich, sondern weisen eine chaotische Dynamik auf, das
sogenannte Stick-Slip Verhalten.

Diese Dynamik erfassen wir mit einer Vielzahl von Instrumenten wie
präzisem GPS, seismologischen Messungen, speziellen Drohnen und
interferometrischen Radarsystemen. Diese Messdaten werden mit neu
entwickelten Computermodellen analysiert und interpretiert. Mit diesen
Erkenntnissen erlauben es, die zukünftige Entwicklung der grossen
Eisschilde von Grönland und der Antarktis genauer zu berechnen.

Direct link to Lay Summary Last update: 04.02.2021

Responsible applicant and co-applicants

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Associated projects

Number Title Start Funding scheme
156098 Understanding long-term outlet glacier calving dynamics with a combined high-resolution field,- remote-sensing- and modeling approach. 01.03.2015 Project funding (Div. I-III)
113503 Understanding the causes and future direction of the present rapid thinning of Jakobshavn Isbrae, Greenland 01.04.2007 Project funding (Div. I-III)
113503 Understanding the causes and future direction of the present rapid thinning of Jakobshavn Isbrae, Greenland 01.04.2007 Project funding (Div. I-III)
127197 Subglacial Controls on the Short Term Dynamics at the Margin of the Greenland Ice Sheet 01.02.2010 Project funding (Div. I-III)

Abstract

Outlet glaciers and ice streams are the main arteries of ice sheets which rapidly transport ice from the interior towards the ocean. They are typically delineated by highly crevassed margins separating the fast flowing trunk from slower moving inland ice. Figure 1 shows the lateral shear margins of Jakobshavn Isbrae (JI), a major outlet glacier of the Greenland Ice Sheet (GrIS) which has flowed at 20 m/day over the past century, and at double this speed over the last two decades.Fast glacier flow is often associated with anisotropic and discontinuous processes such that the commonly made assumptions about continuum fluid flow break down. In ice sheet outlet glaciers and ice stream margins, deeply cracked crevasse zones are ubiquitous, crystal orientation fabrics control the rheology, and non-continuous processes such as thrusting and folding, and stick-slip motion are likely active. All of these processes result in a bulk flow dynamics that is different from the conventionally assumed smooth fluid flow approximation. Despite considerable observational evidence, numerical models continue to ignore the actual complexities of glacier flow, which introduces additional uncertainty into projections on the future evolution of the ice sheets.In this project we will use concentrated field and modeling studies to better understand the consequences of stick-slip motion, thrusting, etc., on outlet glacier dynamics and evolution. We will investigate the susceptibility of ice deformation and seismicity within and across ice stream margins to continuous and episodic external forcings like surface melt, lake drainage events, and iceberg calving. At the example of JI, and taking full advantage of novel and proven field methods, we will monitor ice deformation and fracture processes at high spatial and temporal resolution. Combining continuous in-situ monitoring of ice motion, seismicity, vertical stretching, detailed long-range UAV (drone) surveys of surface motion and topography, and ground-based radar interferometry, we will produce a unique data set of ice deformation, fracturing rate and the external forcings. This data set will be interpreted with state-of-the-art numerical models: seismic source inversion, seismic noise tomography, a particle model for crevassing and faulting, and a multi-physics finite element model for ice stream flow.We are a team of researchers with complementary skill sets and ample experience with geophysical and seismological field setups, long-range UAV operations, and ground-based remote sensing. We have successfully performed field projects on the GrIS and specifically JI, and are used to dealing environmental and logistical challenges. Each team member has advanced glaciology by employing numerical modeling methods to interpret these hard-won field data.The proposed process study at JI is the next step in understanding the dynamics of fast ice sheet outlet glaciers and ice streams. The future evolution of the Greenland and Antarctic ice sheet is largely controlled by these fast flowing arteries. Understanding their physics is therefore mandatory for quantification and predictions of the ongoing rapid changes of the polar ice sheets.
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