Tag Archives: debris

3-D model of ice cliff backwasting published

Pascal and several team members have just had published their paper, A physically based 3-D model of ice cliff evolution over debris-covered glaciers, in the Journal of Geophysical Research: Earth Surface. They used a new data set of high-resolution observations of cliff evolution over one ablation season to identify patterns of changes over four cliffs on the debris-covered tongue of Lirung Glacier (Nepalese Himalaya). The four cliffs have different shape, dominant orientation and slopes, and different degree and history of coupling to a supraglacial pond. The observations show that cliffs on the same glacier and at short distance from each other can both flatten and recline, remain self-similar, or expand radially. Based on the observations a model accounting for the three main processes controlling cliff evolution was developed: atmospheric melt, pond contact ablation enhancement for the cliff base, and reburial by surrounding debris. This modeling approach is able to simulate the cliff evolution over one melt season in a satisfying way in terms of horizontal and vertical extent as well as mean slope and aspect. Modelled volume losses could be validated and were in agreement with TIN-based observations (Brun et al. 2016, Journal of Glaciology).

Simulated cliff evolution based on the monthly updated outlines.

Simulated cliff evolution based on the monthly updated outlines.

The model is able to capture the main cliff dynamics and geometric transformation. Importantly, the model application has clearly shown that for very high resolution studies, neglecting a dynamic update of the cliff geometry would lead to erroneous results in terms of backwasting patterns and volumes.

Updates from Cambridge: PhD, new OA paper, new project

Evan Miles passes PhD viva

Research team member Evan Miles, based at the University of Cambridge, has recently passed his PhD viva and will now be Dr Miles!  His thesis, titled ‘Spatio-temporal variability and energy-balance implications of surface ponds on Himalayan debris-covered glaciers’ has combined remote sensing, field surveys, and numerical modelling to understand the role of supraglacial ponds.

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Figure 1: Evan Miles and Anna Chesnokova installing thermistor strings and a pressure transducer in a supraglacial pond on Lirung Glacier, May 2014.

 

New OA paper studying spatio-temporal variability of supraglacial ponds

Evan and several other team members have just had an Open Access paper published in the Journal of Glaciology based on one aspect of Evan’s doctoral work, Spatial, seasonal and interannual variability of supraglacial ponds in the Langtang Valley of Nepal, 1999–2013.  The study uses 15 years of Landsat data (172 scenes) to analyse the variability of supraglacial ponds on a set of five debris-covered glaciers.  This is a major advance in several ways, as prior studies have used only a few scenes to assess ponded area for debris-covered glaciers.  The use of such an extensive dataset allowed the authors to also assess the spatial patterns of ponding and interannual changes in pond cover in a more robust way than has been done previously.

 

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Figure 2: Spatial distribution of supraglacial ponds as percent of May–October observations (n =68), also showing results for other lakes outside the debris-covered tongues (orange ellipses), 1999–2013.

 

One of the most important results is the seasonal variability of ponds, which controls the role they can play in a glacier’s mass balance.  Expect more news on that topic soon!

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Figure 3: Seasonal pattern of thawed pond cover as percent of observable debris-covered glacier area, with individual scenes coloured by year of observation (n =172) and dot tails highlighting the effect of a 34% overestimation of pond area. The solid black line is the monthly mean, with dashed lines showing the ± 1σ spread.

 

Evan Miles to start Post-Doc in Leeds

Finally, Evan has accepted a two-year research position at the University of Leeds to work with Dr Duncan Quincey, Dr Bryn Hubbard (Aberystwyth University), and Dr Ann Rowan (Sheffield University) as part of the NERC-funded EverDrill project. This is an exciting and ambitious effort to drill to the bed of Khumbu Glacier and install a sensor suite to understand englacial and subglacial processes, a first for the Himalaya, and a critical need identified by other MountainHydrology team members.  More project info can be found here.  Evan will continue to be peripherally involved in many MountainHydrology projects.