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Studies of the processes of fracturing, deformation and iceberg calving in Antarctica: A history of the Mertz Glacier. Etude des processus de fracturation, deformation et velage d'iceberg en Antarctique: Une histoire du glacier Mertz.

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Lescarmontier, L (2012) Studies of the processes of fracturing, deformation and iceberg calving in Antarctica: A history of the Mertz Glacier. Etude des processus de fracturation, deformation et velage d'iceberg en Antarctique: Une histoire du glacier Mertz. PhD thesis, University of Tasmania.

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Abstract

This thesis presents a study of the processes of fracturing of an outlet glacier leading to its
calving. During the CRAC-ICE program, we studied the evolution of the Mertz outlet
glacier, which is located on the George V coast in East Antarctica. Before the calving event
of the Mertz glacier, which took place in February 2010 releasing an iceberg of 80 km
long by 35 km wide, this glacier was characterized by a floating ice tongue. This ice
tongue, separated by a fault which was initiated at the beginning of the 1990s, was 150
km long by 35 km wide. Using a set of in-situ GPS data, satellite images of both high and
low resolution and the development of a numerical ocean model (TUGO-Mertz), we have
followed the evolution of this glacier and the fate of its iceberg. The first part of this study
was to develop a strategy for processing of the GPS data, thereby allowing us to obtain the
best possible accuracy for our in-situ data. These data were processed using the GINS
software and a processing technique based on absolute positioning (IPPP), allowing full
integer ambiguity resolution of the GPS carrier phase data. The accuracy of these
positioning results has allowed us to observe oscillations of the ice tongue at centimetric
amplitudes and vibrational periods of a few minutes, which, when compared to an EulerBernoulli
beam model, correspond to ice tongue vibration modes in three different
configurations. These oscillation periods range from 5 minutes to a few hours. In this
range of periods, the major oceanic forcings are swell and infra-gravity waves. In
addition, we were able to demonstrate that the movements associated with the vibration
of the glacier lead to bending effects on the ice tongue promoting its fracturing. On a
larger scale, tidal currents and the height of the ocean surface (tidal amplitude) impact on
the evolution of the ice tongue. The effects of ocean currents impact mainly on the
opening of the main crevasse, whilst the tidal amplitudes tend to modulate the flow rate
of the glacier. This modulation is approximately 5 cm per day or 14 per cent of the
average speed of the ice tongue. In addition, we have followed the evolution of the main
crevasse of the glacier; originally opening on the eastern side of the ice tongue, then
opening on the western side. The ice tongue then continued its development until the
glacier calving event.
Finally, we were interested in the different mechanisms involved during the breakdown
of the ice tongue leading to the calving event. The impact of the B09B iceberg with the ice
tongue and the change in local ocean currents played a role during this calving event,
despite the fact that the crevasse was already well developed. All of these results have
allowed us to identify a broad spectrum of processes operating before and during a
calving event. These processes are the major contributors in the evolution of the Mertz
glacier, but such processes are not yet taken into account in the universal models of
calving.

Ces travaux de these presentent les processus de fracturation des glaciers
emissairesmenant au velage. Dans Ie cadre du programme CRAC-ICE, nous no us sommes
interessesna l' evolution du glacier emissaire Mertz, situe sur la cote George V en
Antarctique de rest. Avant son vel age qui a eu lieu en Fevrier 2010, liberant un iceberg
de 80 km de longpar 35 km de large, ce glacier etait caracterise par une langue de glace
se developpant sur l'eau. Cette langue de glace, separee par une faille depuis Ie debut des
annees 1990, etait longue de 150 km par 35 km de large. Grace a un ensemble de
donnees in-situ et d'images satellite basse et haute resolution et Ie developpement d'un
modele oceanique (TUGO-Mertz), nous avons suivi l'evolution de ce glacier ainsi que Ie
devenir de son iceberg. La premiere partie de ce travail a consiste a developper une
strategie de traitement de donnees GPS nous permettant ainsi d'obtenir la meilleure
precision possible sur nos donnees in-situ. Ces donnees ont ete traitees via Ie logiciel
GINS et une technique de traitement appelee IPPP basee sur Ie positionnement absolu et
la resolution des ambiguitiesen valeurs entiere. La precision des resultats de
positionnement no us a permis d'observer des oscillations d'amplitude centimetrique et
de periode de quelques minutes, qui, comparees a un modele de poutre d'EulerBernoulli
correspondent a des modes de vibration de la langue de glace dans trois
configurations differentes. Les periodes de ces oscillations s'echelonnent de 5 minutes a
quelques heures. Dans ces gammes de valeurs, les principaux for~ages oceaniques sont
la houle et les ondes d'Infra-Gravite. De plus, nous avons pu demontrer que les
mouvements associes a la vibration du glacier entrainent une torsion favorisant sa
fracturation. A plus grande echelle, les courants de maree ainsi que la hauteur de surface
impactent sur l'evolution de la langue de glace. Les effets des courants se concentrent
principalement sur l'ouverture de la crevasse principale tandis que la hauteur de surface
tend a moduler la vitesse d'ecoulement du glacier. Cette modulation represente environ
5 cm/jour soit 14 % de la vitesse moyenne. Par ailleurs, nous avons suivi l'evolution de
la crevasse principale du glacier; une originellement ouverte sur la partie est de la
langue de glace puis ouverte sur la partie ouest. Elle a ensuite continue son
developpement jusqu'au vel age du glacier.
Pour finir, nous nous sommes interesses aux differents acteurs en jeu lors de la rupture
de la langue de glace menant au velage. L'action de l'iceberg B09B et la modification des
courants a joue un role lors de cet eVEmement meme si la crevasse eta it en cours de
developpement. L'ensemble de ces resultats nous a permis d'identifier un large spectre
de processus operant avant et pendant un episode de velage. Ces processus sont
majoritaires dans l'evolution du glacier Mertz, mais ne sont pas encore pris en compte
dans les modeles universels de velage.

Item Type: Thesis (PhD)
Keywords: Outlet Glacier, Antarctica, Iceberg, calving, fracturing, ocean-ice interaction, GPS processing. Glacier emissaire, Antarctique, Iceberg, Velage, Fracturation, Interaction ocean-glace, Traitement GPS.
Additional Information:

Copyright 2012 the Author

Date Deposited: 17 Aug 2012 04:47
Last Modified: 11 Mar 2016 05:53
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