davidgraham.org.uk

New publication: Origin and significance of ‘dispersed facies’ basal ice: Svinafellsjokull, Iceland

admin — Sun, 01 Jan 2012 13:10:04 +0000

Abstract: Dispersed facies basal ice – massive (i.e. structureless) ice with dispersed debris aggregates – is present at the margins of many glaciers and, as a product of internal glacial processes, has the potential to provide important information about the mechanisms of glacier flow and the nature of the subglacial environment. The origin of dispersed facies is poorly understood, with several hypotheses having been advanced for its formation, and there is disagreement as to whether it is largely a sedimentary or a tectonic feature. We test these established hypotheses at the temperate glacier Svínafellsjökull, Iceland, and find that none fully account for dispersed facies characteristics at this location. Instead, dispersed facies physical, sedimentological and stable-isotope (δ¹⁸O, δD) characteristics favour a predominantly tectonic origin that we suggest comprises the regelation and strain-induced metamorphism of debris-rich basal ice that has been entrained into an englacial position by tectonic processes operating at the base of an icefall. Further thickening of the resultant dispersed facies may also occur tectonically as a result of ice flow against the reverse bed slope of a terminal overdeepening. Lack of efficient subglacial drainage in the region of the overdeepening may limit basal melting and thus favour basal ice preservation, including the preservation of dispersed facies. Despite the relatively low sediment content of dispersed facies (∼1.6% by volume), its thickness (up to 25 m) and ubiquity at Svínafellsjökull results in a significant contribution to annual sediment discharge (1635-3270 m³ a⁻¹) that is ∼6.5 times that contributed by debris-rich stratified facies basal ice.

Cook, S.J., Swift, D.A., Graham, D.J. and Midgley, N.G., (2011). Origin and significance of ‘dispersed facies’ basal ice: Svinafellsjokull, Iceland. Journal of Glaciology, 57 (204), pp. 710-720.

Publisher link: http://dx.doi.org/10.3189/002214311797409703 (subscription required)

New publication: Sedimentary signatures of basal ice formation and their preservation in ice-marginal sediments

admin — Mon, 31 Jan 2011 14:13:15 +0000

Abstract: Reconstruction of subglacial processes from sedimentological evidence is central to our understanding of glaciological conditions beneath former ice masses. At Svínafellsjökull, southeast Iceland, we assess the extent to which two different processes of basal ice formation (regelation and glaciohydraulic supercooling) can be identified from ice-marginal sediments. Our results indicate that the sedimentary characteristics of deposits produced by these two processes can be distinguished from one another and that it may be possible to recognise evidence of these processes in Quaternary sediments and to reconstruct their spatial pervasiveness. Sediments derived from the melting of regelation basal ice have (i) a massive structure; (ii) a sediment matrix (0 to 10Ф) dominated by coarse sand; and (iii) a higher proportion of angular clasts than supercool basal ice and associated sediments. Sediments derived from “supercool” basal ice (i) can be either massive or layered; (ii) tend to have a silt-dominated matrix; and (iii) contain a slightly higher proportion of rounded and well-rounded clasts than regelation basal ice and sediments. Previous studies indicate that the dominance of silt within supercool basal ice may be unique to this process, and hence, supercooling should leave a readily recognisable signature in the sedimentary record. Our results from Svínafellsjökull lend support to that idea, although we suggest that further work is required to assess whether silt dominance is a process signature diagnostic of supercooling, and in particular, the extent to which subglacial sediment supply determines the sedimentary character of basal ice facies and associated sediments.

Cook, S.J., Graham, D.J., Swift, D.A., Midgley, N.G. and Adam, W.G., 2011. Sedimentary signatures of basal ice formation and their preservation in ice-marginal sediments. Geomorphology, 25 (1), pp.122-131.

Publisher link: http://dx.doi.org/10.1016/j.geomorph.2010.08.018 (subscription required)

Preprint: http://hdl.handle.net/2134/7884 (no subscription required)

Sedimetrics is an award winner!

admin — Thu, 14 Oct 2010 10:48:37 +0000

David Graham and Ian Reid (centre) receiving their award from Sir Nigel Rudd, Chancellor of Loughborough University, and Anne Davies, presenter of BBC East Midlands Today.

David Graham, Steve Rice and Ian Reid have been highly commended in the ‘Consultancy’ category of the Loughborough University Enterprise Awards. They were nominated for the development of software that helps engineers, ecologists and geomorphologists better understand and manage the river environment by providing information about river-bed sediments in a cost-effective way. The software – marketed under the brand name ‘Sedimetrics®’ – was developed in the Department of Geography at Loughborough University

The Enterprise Awards are a celebration of the enterprising culture that is such an integral part of the University. Sir Nigel Rudd, Chancellor of the University and BAA Chairman, presented the awards on 6 October 2010.

Read the press release here: http://www.lboro.ac.uk/service/publicity/news-releases/2010/152_Enterprise_Awards.html

Further information about Sedimentrics® is available at http://sedimetrics.com.

ResearcherID profile

admin — Wed, 06 Oct 2010 11:37:52 +0000

David now has a ResearcherID profile: