November 2010


I was delighted to receive an email today that read as follows:

Congratulations! Your article, “A hydrologically coupled higher-order flow-band model of ice dynamics with a Coulomb friction sliding law”, was published today in Journal of Geophysical Research.

The complete citation is

Pimentel, S., G. E. Flowers, and C. G. Schoof (2010), A hydrologically coupled higher-order flow-band model of ice dynamics with a Coulomb friction sliding law, J. Geophys. Res., 115, F04023, doi:10.1029/2009JF001621.

The link to the article can be found here, although you will need personal or institutional access to read it in full.  If you are interested, but do not have access I can email you a copy.  Here is the abstract:

The influence of hydrologic transience and heterogeneity on basal motion is an often-neglected aspect of numerical ice-flow models. We present a flow-band model of glacier dynamics with a Coulomb friction sliding law that is coupled to a model of the basal drainage system by means of subglacial water pressure. The ice-flow model contains “higher-order” stress gradients from the Stokes flow approximation originally conceived by Blatter (1995). The resulting system of nonlinear equations is solved using a modified Picard iteration that is shown to improve the rate of convergence. A parameterization of lateral shearing is included to account for the effects of three-dimensional geometry. We find that lateral drag has a discernible effect on glacier speed even when glacier width exceeds glacier length. Variations in flow-band width are shown to have a greater influence on flow line speed than either different valley cross-sectional shapes or the presence or absence of glacier sliding along valley walls. Modeled profiles of subglacial water pressure depart significantly from pressures prescribed as a uniform fraction of overburden, thus producing profiles of glacier sliding that are distinctly different from those that would be described by a sliding law controlled by overburden pressures. Simulations of hydraulically driven glacier acceleration highlight the value of including a representation of basal hydrology in models aiming for improved predictive capability of glacier dynamics.

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So I mentioned in an earlier post that I attended (and spoke at) a workshop organized by a nuclear waste consortium consisting of NWMO (Canada), SKB (Sweden), and Posiva (Finland). They’ve initiated a research study called the Greenland Analogue Project (GAP). I should just add here that although I am doing research related to this project (GAP) I am not funded by GAP (I receive no money from a nuclear waste company – not that I would necessarily have anything against that!).

I will now attempt to explain why nuclear waste companies are interested in Glaciology and more particularly modelling subglacial hydrology (which is what I do). So here goes …

High-level radioactive waste from spent nuclear fuel (as a result of nuclear power generation) has to be disposed of – safely of course! This is a difficult problem because every precaution has to be made to contain and isolate radioactive material and prevent any interaction with the biosphere for at least 100,000 years.  The radioactive waste will be buried deep (>0.5 km) in an underground repository in ancient bedrock and measures taken to ensure against every possible scenario.

Within its lifespan, this final repository site, will undergo glaciation (an ice age) – how will these conditions affect the stringent safety standards?  What are the conditions and processes that impact the recharge of glacial meltwater into the geosphere, in particular to repository depth in a fractured crystalline rock?  In order to help answer these questions investigations are focused on Greenland – the closest current analogue to these conditions (hence the title name GAP).

The overall aim of the Greenland Analogue Project is to improve the current understanding of how an ice sheet affects the groundwater flow and the water chemistry around a deep geological repository in crystalline bedrock during glacial periods.

My own research in modelling subglacial hydrology has principally been driven by a need to understand how hydrology influences ice dynamics, because water at the base of an ice sheet governs glacier sliding.  However, the interest related to the above project is how subglacial and ice dynamic interactions influence the geosphere, i.e. what is the interaction with the groundwater circulation around a deep geological repository.

Quantities of interest include knowledge of subglacial water volumes and pressures.  They will want to know how much meltwater seeps into the underlying bedrock, and whether seasonal subglacial network evolution and discrete flooding events are important in constraining leakage into the groundwater system on geological timescales.

This is my own personal understanding of the situation and does not represent any official take on the matter or the views of any nuclear waste management organization.

On Friday I had the chance to visit The Courtauld Gallery at Someset House, London.  The Courtauld Gallery has been branded as “… one of the finest small museums in the world” and has a number of exceptional art pieces in its permanent collection.  However, I was most interested in their special exhibition on Paul Cezanne’s famous paintings of peasant card players.  I’m quite a fan of the peasant theme – whether that be Tolstoy or van Gogh.  Cezanne has some really excellent painting on this theme, apparently in his day turning this tired theme on its head.  Where previously peasants were shown as dissolute characters Cezanne’s iconic works portray them with gravitas and stoicism carrying out a time honoured activity, playing cards; taking them out of their tradition outdoor setting (e.g. ploughing the field), but yet still conducting an age old tradition.  Here are few photos I took of these magnificent portraits.

Last week I was in Toronto at a modelling workshop for the GAP (Greenland Analogue Project).  This is a project funded by three nuclear waste companies (NWMO – Canada, SKB – Sweden, and Postiva – Finland).  Why they are interested in Glaciology and my work I shall explain in a future post, but for now here are the slides from the talk that I presented.

GAP_talk_2010

There wasn’t too much time for playing around, but I did get to go up the CN Tower and we were treated to a 3 course meal at the 360 restaurant at the top.