Anna Wirbels first PhD paper is out, and downloadable from my publications page (Wirbel et al., 2018). What she has done is take an existing freely available 3D model of ice flow (icetools; Jarosch et al., 2008) that employs the full Stokes equations to describe the flow of ice. This type of numerical treatment of ice flow offers the most realistic representation of the flow of complex mountain glaciers, assuming adequate inputs, such as terrain properties and ice temperatures are well known.
Anna worked, with guidance from Alex, to introduce a numerically robust, mass conserving, treatment of advection of deformable inclusions within this ice flow field. This allows her to represent englacial debris transport – illustrated in the video below by artificially imposing layers of initially circular inclusions into a cross-section of a glacier with fixed geometry and flow field (Time is in years):
Isn’t that cool?! (The full resolution video is downloadable as supplementary material to the publication)
Imagine the initial circular feature as a lump of rock material from a rockfall that has been buried in the accumulation zone, or sediment trapped in a hollow in an englacial channel, imagine the initial surface layer as an ashfall, and the initially vertical bands part way down the glacier as rocks and detritus that has fallen into crevasses, then look how over time they all get deformed and elongated into bands, which is what we see in real glaciers!
Also, notice how over time, even in this fixed flow field case, the location of debris emergence and the angle of incidence of the debris band with the surface both change over time. In these cases the model does not keep track of the debris once it emerges to the glacier surface, but its clear that both of these aspects will affect the debris flux to the glacier surface, and, combined with the surface ablation will determine the manner in which a supraglacial debris cover forms.
The model code is available from Anna on github: https://github.com/awirbel/debadvect/releases/tag/v1.0.0
References:
Jarosch, A. H. (2008) Icetools: A full Stokes finite element model for glaciers, Computers & Geosciences, 34(8), 1005–1014, doi:10.1016/j.cageo.2007.06.012.
Wirbel, A., Jarosch, A. H. and Nicholson, L. (2018) Modelling debris transport within glaciers by advection in a full-Stokes ice flow model, The Cryosphere, 12, 189-204, https://doi.org/10.5194/tc-12-189-2018.
