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Vallot, Dorothée
Publications (8 of 8) Show all publications
How, P., Schild, K. M., Benn, D. I., Noormets, R., Kirchner, N., Luckman, A., . . . Borstad, C. (2019). Calving controlled by melt-under-cutting: detailed calving styles revealed through time-lapse observations. Paper presented at International-Glaciological-Society Symposium on Timescales, Processes and Ice Sheet Changes, JUN 03-08, 2018, Buffalo, NY. Annals of Glaciology, 60(78), 20-31
Open this publication in new window or tab >>Calving controlled by melt-under-cutting: detailed calving styles revealed through time-lapse observations
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2019 (English)In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 60, no 78, p. 20-31Article in journal (Refereed) Published
Abstract [en]

We present a highly detailed study of calving dynamics at Tunabreen, a tidewater glacier in Svalbard. A time-lapse camera was trained on the terminus and programmed to capture images every 3 seconds over a 28-hour period in August 2015, producing a highly detailed record of 34 117 images from which 358 individual calving events were distinguished. Calving activity is characterised by frequent events (12.8 events h(-1)) that are small relative to the spectrum of calving events observed, demonstrating the prevalence of small-scale calving mechanisms. Five calving styles were observed, with a high proportion of calving events (82%) originating at, or above, the waterline. The tidal cycle plays a key role in the timing of calving events, with 68% occurring on the falling limb of the tide. Calving activity is concentrated where meltwater plumes surface at the glacier front, and a similar to 5 m undercut at the base of the glacier suggests that meltwater plumes encourage melt-under-cutting. We conclude that frontal ablation at Tunabreen may be paced by submarine melt rates, as suggested from similar observations at glaciers in Svalbard and Alaska. Using submarine melt rate to calculate frontal ablation would greatly simplify estimations of tidewater glacier losses in prognostic models.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2019
Keywords
Arctic glaciology, glacier calving, ice dynamics, ice/ocean interactions
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:uu:diva-387976 (URN)10.1017/aog.2018.28 (DOI)000469785700004 ()
Conference
International-Glaciological-Society Symposium on Timescales, Processes and Ice Sheet Changes, JUN 03-08, 2018, Buffalo, NY
Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-06-27Bibliographically approved
Memon, S., Vallot, D., Zwinger, T., Åstrom, J., Neukirchen, H., Riedel, M. & Book, M. (2019). Scientific workflows applied to the coupling of a continuum (Elmer v8.3) and a discrete element (HiDEM v1.0) ice dynamic model. Geoscientific Model Development, 12(7), 3001-3015
Open this publication in new window or tab >>Scientific workflows applied to the coupling of a continuum (Elmer v8.3) and a discrete element (HiDEM v1.0) ice dynamic model
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2019 (English)In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 12, no 7, p. 3001-3015Article in journal (Refereed) Published
Abstract [en]

Scientific computing applications involving complex simulations and data-intensive processing are often composed of multiple tasks forming a workflow of computing jobs. Scientific communities running such applications on computing resources often find it cumbersome to manage and monitor the execution of these tasks and their associated data. These workflow implementations usually add overhead by introducing unnecessary input/output (I/O) for coupling the models and can lead to sub-optimal CPU utilization. Furthermore, running these workflow implementations in different environments requires significant adaptation efforts, which can hinder the reproducibility of the underlying science. High-level scientific workflow management systems (WMS) can be used to automate and simplify complex task structures by providing tooling for the composition and execution of workflows - even across distributed and heterogeneous computing environments. The WMS approach allows users to focus on the underlying high-level workflow and avoid low-level pitfalls that would lead to non-optimal resource usage while still allowing the workflow to remain portable between different computing environments. As a case study, we apply the UNICORE workflow management system to enable the coupling of a glacier flow model and calving model which contain many tasks and dependencies, ranging from pre-processing and data management to repetitive executions in heterogeneous high-performance computing (HPC) resource environments. Using the UNICORE workflow management system, the composition, management, and execution of the glacier modelling workflow becomes easier with respect to usage, monitoring, maintenance, reusability, portability, and reproducibility in different environments and by different user groups. Last but not least, the workflow helps to speed the runs up by reducing model coupling I/O overhead and it optimizes CPU utilization by avoiding idle CPU cores and running the models in a distributed way on the HPC cluster that best fits the characteristics of each model.

Place, publisher, year, edition, pages
COPERNICUS GESELLSCHAFT MBH, 2019
National Category
Computer Sciences
Identifiers
urn:nbn:se:uu:diva-390781 (URN)10.5194/gmd-12-3001-2019 (DOI)000475466700004 ()
Funder
NordForsk, 57001
Available from: 2019-08-16 Created: 2019-08-16 Last updated: 2019-08-16Bibliographically approved
Lindbäck, K., Kohler, J., Pettersson, R., Nuth, C., Langley, K., Messerli, A., . . . Brandt, O. (2018). Subglacial topography, ice thickness, and bathymetry of Kongsfjorden, northwestern Svalbard. Earth System Science Data, 10(4), 1769-1781
Open this publication in new window or tab >>Subglacial topography, ice thickness, and bathymetry of Kongsfjorden, northwestern Svalbard
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2018 (English)In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 10, no 4, p. 1769-1781Article in journal (Refereed) Published
Abstract [en]

Svalbard tidewater glaciers are retreating, which will affect fjord circulation and ecosystems when glacier fronts become land-terminating. Knowledge of the subglacial topography and bathymetry under retreating glaciers is important to modelling future scenarios of fjord circulation and glacier dynamics. We present high-resolution (150m gridded) digital elevation models of subglacial topography, ice thickness, and ice surface elevation of five tidewater glaciers in Kongsfjorden (1100 km(2)), northwestern Spitsbergen, based on similar to 1700 km airborne and ground-based ice-penetrating radar profiles. The digital elevation models (DEMs) cover the tidewater glaciers Blomstrandbreen, Conwaybreen, Kongsbreen, Kronebreen, and Kongsvegen and are merged with bathymetric and land DEMs for the non-glaciated areas. The large-scale subglacial topography of the study area is characterized by a series of troughs and highs. The minimum subglacial elevation is 180m above sea level (a.s.l.), the maximum subglacial elevation is 1400m a.s.l., and the maximum ice thickness is 740m. Three of the glaciers, Kongsbreen, Kronebreen, and Kongsvegen, have the potential to retreat by similar to 10 km before they become land-terminating. The compiled data set covers one of the most studied regions in Svalbard and is valuable for future studies of glacier dynamics, geology, hydrology, and fjord circulation.

Place, publisher, year, edition, pages
COPERNICUS GESELLSCHAFT MBH, 2018
National Category
Physical Geography
Identifiers
urn:nbn:se:uu:diva-367386 (URN)10.5194/essd-10-1769-2018 (DOI)000446324600001 ()
Funder
The Research Council of Norway, 243808EU, European Research Council, 320816The European Space Agency (ESA), 4000109873/14/I-NB
Available from: 2018-12-04 Created: 2018-12-04 Last updated: 2018-12-04Bibliographically approved
Vallot, D., Pettersson, R., Luckman, A., Benn, D. I., Zwinger, T., van Pelt, W. J. J., . . . Hulton, N. R. J. (2017). Basal dynamics of Kronebreen, a fast-flowing tidewater glacier in Svalbard: non-local spatio-temporal response to water input. Journal of Glaciology, 63(242), 1012-1024
Open this publication in new window or tab >>Basal dynamics of Kronebreen, a fast-flowing tidewater glacier in Svalbard: non-local spatio-temporal response to water input
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2017 (English)In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 63, no 242, p. 1012-1024Article in journal (Refereed) Published
Abstract [en]

We evaluate the variability in basal friction for Kronebreen, Svalbard, a fast-flowing tidewater glacier. We invert 3 years (2013–15) of surface velocities at high temporal resolution (generally 11 days), to estimate the changing basal properties of the glacier. Our results suggest that sliding behaviour of Kronebreen within a year is primarily influenced by changes in water input patterns during the meltwater season and basal friction is highly variable from a year to another. At present, models usually employ parameterisations to encompass the complex physics of glacier sliding by mathematically simulate their net effect. For such ice masses with strong seasonal variations of surface melt, the spatio-temporal patterns of basal friction imply that it is neither possible nor appropriate to use a parameterisation for bed friction that is fixed in space and/or time, at least in a timescale of a few years. Basal sliding may not only be governed by local processes such as basal topography or summer melt, but also be mediated by factors that vary over a larger distance and over a longer time period such as subglacial hydrology organisation, ice-thickness changes or calving front geometry.

Keywords
Arctic glaciology, glacier modelling, ice dynamics, ice velocity, subglacial processes
National Category
Physical Geography
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-334293 (URN)10.1017/jog.2017.69 (DOI)000418852500007 ()
Available from: 2017-11-22 Created: 2017-11-22 Last updated: 2018-02-05Bibliographically approved
Vallot, D. (2017). Modelling calving and sliding of Svalbard outlet glaciers: Spatio-temporal changes and interactions. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Modelling calving and sliding of Svalbard outlet glaciers: Spatio-temporal changes and interactions
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Future sea level rise associated to global warming is one of the greatest societal and environmental challenges of tomorrow. A large part of the contribution comes from glaciers and ice sheets discharging ice and meltwater into the ocean and the recent worldwide increase is worrying. Future predictions of sea level rise try to encompass the complex processes of ice dynamics through glacier modelling but there are still large uncertainties due to the lack of observations or too coarse parameterisation, particularly for processes occurring at the glacier interfaces with the bed (sliding) and with the ocean (calving). This thesis focuses on modelling these processes from two marine-terminating glaciers in Svalbard, Kronebreen and Tunabreen. By inverting three years of high temporal resolution time-series of surface velocities on Kronebreen, basal properties are retrieved with the ice flow model Elmer/Ice in Paper I. Results suggest that surface melt during the summer greatly influences the dynamics of the following season and that sliding laws for such glaciers should be adapted to local and global processes changing in space and time. The subglacial drainage system, fed by the surface melt, is modelled in Paper II during two melting seasons. Results show different configurations of efficient and inefficient drainage systems between years and the importance of using a sliding law dependent on spatio-temporal changes in effective pressure. The interaction with the ocean is incorporated in Paper III by combining a series of models, including an ice flow model, a plume model and a particle model for discrete calving and compares the output with observations. Results show the importance of glacier geometry, sliding and undercutting on calving rate and location. However, more observations and analytic methods are needed. Time-lapse imagery placed in front of Tunabreen have been deployed and a method of automatic detection for iceberg calving is presented in Paper IV. Results show the influence of the rising plume in calving and the front destabilisation of the local neighbourhood.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 82
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1606
Keywords
cryospheric science, glacier modelling, time-lapse imagery, undercutting, sliding inversion, discrete particle model, calving model, subglacial hydrology, sliding law, automatic detection method, calving events size and frequency, ocean interaction, melt water runoff, ice dynamics, ice flow model
National Category
Geosciences, Multidisciplinary
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-334787 (URN)978-91-513-0170-9 (ISBN)
Public defence
2018-01-24, Hambergsalen, Villavägen 16, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-12-22 Created: 2017-11-27 Last updated: 2018-03-08
Adinugroho, S., Vallot, D., Westrin, P. & Strand, R. (2015). Calving events detection and quantification from time-lapse images in Tunabreen glacier. In: Proc. 9th International Conference on Information & Communication Technology and Systems: . Paper presented at ICTS 2015, September 16, Surabaya, Indonesia (pp. 61-65). Piscataway, NJ: IEEE
Open this publication in new window or tab >>Calving events detection and quantification from time-lapse images in Tunabreen glacier
2015 (English)In: Proc. 9th International Conference on Information & Communication Technology and Systems, Piscataway, NJ: IEEE , 2015, p. 61-65Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Piscataway, NJ: IEEE, 2015
National Category
Computer Vision and Robotics (Autonomous Systems) Geosciences, Multidisciplinary
Research subject
Computerized Image Processing
Identifiers
urn:nbn:se:uu:diva-267413 (URN)10.1109/ICTS.2015.7379872 (DOI)000380531800011 ()978-1-5090-0095-1 (ISBN)
Conference
ICTS 2015, September 16, Surabaya, Indonesia
Available from: 2015-09-16 Created: 2015-11-23 Last updated: 2018-01-10Bibliographically approved
Vallot, D. (2014). First-principles Simulations and the Criticality of Calving Glaciers: Termini of calving glaciers as self-organized critical systems. In: : . Paper presented at AGU (American Geophysical Union) Fall Meeting, San Francisco, 15-19 December 2014.
Open this publication in new window or tab >>First-principles Simulations and the Criticality of Calving Glaciers: Termini of calving glaciers as self-organized critical systems
2014 (English)Conference paper, Oral presentation only (Other academic)
Abstract [en]

The algorithm of a first principles calving-simulation computer-code is outlined and demonstrated. The code is particle-based and uses Newtonian dynamics to simulate ice-fracture, motion and calving. The code can simulate real-size glacier but is only able to simualte individual calving events within a few tens of minutes in duration. The code couples to the Elmer/Ice ice flow-simulation code: Elmer is employed to produce various glacier geomteries, which are then tested for stability using the particle code. In this way it is possible to pin-point the location of calving fronts. The particle simulation code and field observations are engaged to investigate the criticality of calving glaciers. The calving mass and inter-event waiting times both have power-law distributions with the same critical exponents as found for Abelian sand-pile models. This indicate that calving glaciers share characteristics with Self-Organized Critical systems (SOC). This would explain why many glacier found in nature may become unstable as a result of even minor changes in their environment. An SOC calving glacier at the critical point will display so large fluctuations in calving rate that it will render the concept 'average calving rate' more or less useless. I.e. 'average calving rate' will depend on measurement time and always have fluctuaions in the range of 100% more or less independent of the averaging time.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-242555 (URN)
Conference
AGU (American Geophysical Union) Fall Meeting, San Francisco, 15-19 December 2014
Available from: 2015-01-27 Created: 2015-01-27 Last updated: 2015-01-27
Åström, J. A., Vallot, D., Schäfer, M., Welty, E. Z., O'Neel, S., Bartholomaus, T., . . . Moore, J. (2014). Termini of calving glaciers as self-organized critical systems. Nature Geoscience, 7(12), 874-878
Open this publication in new window or tab >>Termini of calving glaciers as self-organized critical systems
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2014 (English)In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 7, no 12, p. 874-878Article in journal (Refereed) Published
Abstract [en]

Over the next century, one of the largest contributions to sea level rise will come from ice sheets and glaciers calving ice into the ocean1. Factors controlling the rapid and nonlinear variations in calving fluxes are poorly understood, and therefore difficult to include in prognostic climate-forced land-ice models. Here we analyse globally distributed calving data sets from Svalbard, Alaska (USA), Greenland and Antarctica in combination with simulations from a first-principles, particle-based numerical calving model to investigate the size and inter-event time of calving events. We find that calving events triggered by the brittle fracture of glacier ice are governed by the same power-law distributions as avalanches in the canonical Abelian sandpile model2. This similarity suggests that calving termini behave as self-organized critical systems that readily flip between states of sub-critical advance and super-critical retreat in response to changes in climate and geometric conditions. Observations of sudden ice-shelf collapse and tidewater glacier retreat in response to gradual warming of their environment3 are consistent with a system fluctuating around its critical point in response to changing external forcing. We propose that self-organized criticality provides a yet unexplored framework for investigations into calving and projections of sea level rise.

Keywords
Cryospheric science, Calving process, Calving events size and frequency, Earth science modelling, Self-organised critical systems, Calving model
National Category
Geosciences, Multidisciplinary Physical Sciences
Identifiers
urn:nbn:se:uu:diva-239421 (URN)10.1038/ngeo2290 (DOI)000345915300013 ()
Projects
Svali - NoCE
Available from: 2014-12-22 Created: 2014-12-22 Last updated: 2017-11-27
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