Professor Chris Clark

School of Geography and Planning

Sorby Chair of Geoscience

Prof Chris Clark
Profile picture of Prof Chris Clark
C.Clark@sheffield.ac.uk
+44 114 222 7941
E6, Geography and Planning Building

Full contact details

Professor Chris Clark
School of Geography and Planning
E6
Geography and Planning Building
Winter Street
Sheffield
S3 7ND
Profile

Chris Clark obtained his BSc in physical geography from University of Wales, Aberystwyth in 1985. After this he worked as a milkman in order to earn money for a climbing expedition to the Himalayas. He returned to academia at Department of Geology and Geophysics, University of Edinburgh to work on a PhD on "Reconstruction of the behaviour of the Laurentide Ice Sheet using satellite imagery", which was completed in 1990, and the results published in Nature.

Chris became a lecturer at Sheffield in 1990 and was awarded a personal chair in 2004, and holds the Sorby Chair of Geoscience since 2009. He currently lectures on Glacial Geomorphology and Glaciology, and on GIS.

Chris has supervised 19 PhD students, most (72%) of whom have continued in academia or industry research posts. He has acted as external examiner on PhDs in Britain, Sweden and France, as an associate editor for the Annals of Glaciology, and guest editor for Boreas. He has been external examiner for the Aberystwyth MSc in Glaciology, served on the Editorial Advisory Board of Earth Surface Processes and Landforms and as associate editor of the Journal of Maps.

Chris was a member of the Geography panel in the Research Excellence Framework (REF2014) and is a member for the current panel (REF2021) which aims to assess the quality of research in UK universities. He is a Fellow of Royal Geographical Society and a member of the International Glaciological Society, British Society of Geomorphology, Quaternary Research Association, and sometimes a member of the European Geophysical Union.

Research interests

My primary research interest is in glacial geomorphology, in particular the understanding of processes that lead to the formation of subglacial bedforms (drumlins, flutes etc), and the inverse solution that uses the pattern and distribution of such landforms to reconstruct the behaviour of ice sheets that existed during the last glaciation. I choose to use satellite imagery and elevation models for these purposes because they frequently permit new evidence to be detected and because they allow mapping at a scale compatible with the former ice sheet.

The ultimate aim of this work is to build up a detailed picture of the evolution of former ice sheets through the last glacial cycle and to use this information to improve both ice sheet and climate models.

BRITICE CHRONO

BRITICE-CHRONO is NERC consortium project that I led along with some 40+ researchers from eight universities, plus the British Geological Survey, British Antarctic Survey, NERC's radiocarbon facility and Scottish Universities Environmental Research Centre. The focus was on dating the retreat of the former British-Irish Ice Sheet to learn how rapidly ice retreated across the continental shelf and across the marine-to-terrestrial transition and then to use this knowledge to improve numerical ice sheet models used to predict changes in our existing ice sheets. Our team collected samples for dating from the Shetland to the Scilly Isles and from the seafloor surrounding Ireland and Britain, totalling 914 sites and yielding over 600 new ages on ice retreat. The British-Irish Ice Sheet is now the world’s most well constrained retreating ice sheet and is being used to develop ice sheet modelling. More on the BRITICE CHRONO project.

PALGLACEuropean Research Council

I am leading PALGLAC which is a European Research Council Advanced Grant. By focussing on the most numerous and spatially-extensive records of palaeo ice sheet activity - glacial landforms - this project aims to revolutionise understanding of past and future ice sheets. Our team will vastly increase the available record for tuning or validating ice sheet models, develop new tools for gathering landform and geochronological information, and establish procedures for integrating these into ice sheet modelling experiments.

Highlights of my research are:

  • Mega-scale glacial lineations
  • Ice sheet reconstructions
  • Palaeo ice streams
  • The British-Irish Ice Sheet – BRITICE-CHRONO
  • Drumlins
Publications

Journal articles

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Chapters

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Conference proceedings papers

  • Woodley SZ, Butcher FEG, Clark CD, Ng F, Davis JM & Gallagher C (2021) Multiple Sites of Amazonian Wet-Based Glaciation Identified in West Tempe Terra, Mars. Lunar and Planetary Science Conference. online, 15 March 2021 - 19 March 2021. RIS download Bibtex download
  • Livingstone S, Lewington ELM, Clark CD, Storrar RD, Sole AJ, McMartin I, Dewald N, Ng F, Vérité J & Ravier E (2021) MELTWATER LANDFORM PERSPECTIVES ON SUBGLACIAL HYDROLOGICAL PROCESSES: INSIGHTS FROM HIGH-RESOLUTION MAPPING IN NORTHERN CANADA. Geological Society of America Abstracts with Programs RIS download Bibtex download
  • Evatt GW, Abrahams ID, Heil M, Mayer C, Kingslake J, Mitchell SL, Fowler AC & Clark CD (2015) Glacial melt under a porous debris layer. Journal of Glaciology, Vol. 61(229) (pp 825-836) RIS download Bibtex download
  • Barr ID & Clark CD (2009) Distribution and pattern of moraines in Far NE Russia reveal former glacial extent. JOURNAL OF MAPS (pp 186-193) RIS download Bibtex download
  • Greenwood SL & Clark CD (2008) Subglacial bedforms of the Irish Ice Sheet. JOURNAL OF MAPS (pp 332-357) RIS download Bibtex download
  • Evatt GW, Fowler AC, Clark CD & Hulton NRJ (2006) Subglacial floods beneath ice sheets. PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol. 364(1844) (pp 1769-1794) RIS download Bibtex download
  • Stokes CR & Clark CD (2003) The Dubawnt Lake palaeo-ice stream: evidence for dynamic ics sheet behaviour on the Canadian Shield and insights regarding the controls on ice-stream location and vigour. BOREAS, Vol. 32(1) (pp 263-279) View this article in WRRO RIS download Bibtex download
  • Tulaczyk SM, Scherer RP & Clark CD (2001) A ploughing model for the origin of weak tills beneath ice streams: a qualitative treatment. QUATERNARY INTERNATIONAL, Vol. 86 (pp 59-70) RIS download Bibtex download
  • Clark CD & Stokes CR (2001) Extent and basal characteristics of the M'Clintock Channel Ice Stream. QUATERNARY INTERNATIONAL, Vol. 86 (pp 81-101) RIS download Bibtex download
  • Caves RG, Turpin OC, Clark CD, Ferguson RI, Quegan S & Johansson B (2000) The use of Earth Observation for monitoring snowmelt runoff from non-alpine basins. REMOTE SENSING IN THE 21ST CENTURY: ECONOMIC AND ENVIRONMENTAL APPLICATIONS (pp 183-190) RIS download Bibtex download
  • Clark CD (1999) Glaciodynamic context of subglacial bedform generation and preservation. ANNALS OF GLACIOLOGY, Vol. 28 (pp 23-32) RIS download Bibtex download
  • Stokes CR & Clark CD (1999) Geomorphological criteria for identifying Pleistocene ice streams. ANNALS OF GLACIOLOGY, Vol. 28 (pp 67-74) RIS download Bibtex download
  • Caves R, Hodson A, Turpin O, Clark C, Ferguson R, Quegan S, ESA & ESA (1998) Field verification of SAR wet snow mapping in a non-Alpine environment. SECOND INTERNATIONAL WORKSHOP ON RETRIEVAL OF BIO- & GEO-PHYSICAL PARAMETERS FROM SAR DATA FOR LAND APPLICATIONS, Vol. 441 (pp 519-526) RIS download Bibtex download
  • Clark C (1997) Automatic spectral classification of imaging spectrometer data. 6th International Conference on Image Processing and its Applications RIS download Bibtex download
  • Clark C, Robertson YC & Barnett ME (1988) Artefacts in AIS-I imagery. Digest - International Geoscience and Remote Sensing Symposium (IGARSS), Vol. 3 (pp 1813) RIS download Bibtex download
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Software / Code

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Datasets

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Other

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Preprints

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Teaching interests

Aligning with my main research interests and skills, my teaching is used to impart knowledge, technological expertise and curiosity about glacial environments. I am particularly interested in teaching about how we can use landforms from past glaciations to better understand how ice sheets and glaciers work, and from this, to inform us about the operation of the existing ice sheets in Antarctica and Greenland and the mountain glaciers of the world.

I teach students how to use geographic information systems (GIS) and satellite images to analyse and advance knowledge, and in the second year I teach some of the basics of glaciology and glaciation. By the third year, once our students have become proficient at reading published academic papers on the latest advances, we get stuck in on some interesting topics about the production of glacial landforms and how we can use these to decipher the extent and dynamics of ice sheets, such as the one that once covered Britain.

My main teaching activity is via lectures but also includes practical classes, reading groups where we interrogate scientific publications, and some class debates and discussions. For me some of the most satisfying 'teaching' is in supervising the undergraduate research projects (dissertations) and especially so when we discover something new.

Additional research projects
Mega-scale glacial lineations

groovepatch (small)

Discovery of a new type of large-scale (10 –100 km) landform signature (mega-scale glacial lineations) in Canada, led me to predict that these were the specific record of high velocity ice flow (surges or ice streams). They have since been found elsewhere, and in the last few years, remarkable submarine finds have been made on the continental shelf surrounding Antarctica. These are significant in that their context in relation to fast flow features in the existing ice sheet validate my predictions. It is thus now well established that mega-scale glacial lineations are a reliable record of ice stream flow. Current research explores the formation of these landforms and their wide-reaching implications on the controls of ice stream flow.

Discovered and named the phenomena and argued they were an indicator of ice streams in:

Clark, C.D. (1993). Mega-scale glacial lineations and cross-cutting ice-flow landforms. Earth Surface Processes and Landforms, 18(1), 1-29.
doi:10.1002/esp.3290180102
  • Stokes, C.R., Spagnolo, M., Clark, C.D., O’Cofaigh, C., Lian, O.B. and Dunstone, R.B. (2013). Formation of Mega-Scale Glacial Lineations on the Dubawnt Lake Ice Stream Bed: 1. Size, Shape and Spacing from a Large Remote Sensing Dataset. Quaternary Science Reviews. 77, 190 – 209.
  • Ó Cofaigh, C., Dowdeswell, J.A., King, E.C., Anderson, J.B., Clark, C.D., Evans, D.J.A., Evans, J., Hindmarsh, R.C.A., Larter, R.D., and Stokes, C.R. (2010). Comment on Shaw J., Pugin, A. and Young, R. (2008): "A meltwater origin for Antarctic shelf bedforms with special attention to megalineations". Geomorphology, 117(1-2), 195-198.
    doi:10.1016/j.geomorph.2009.09.036
  • Clark, C.D., Tulaczyk, S. M., Stokes, C.R., and Canals, M. (2003). A groove-ploughing theory for the production of mega scale glacial lineations, and implications for ice-stream mechanics. Journal of Glaciology, 49(165), 240-256.
    doi:10.3189/172756503781830719
  • Tulaczyk, S.M., Scherer, R.P. and Clark, C.D. (2001). A ploughing model for the origin of weak tills beneath ice streams: a qualitative treatment. Quaternary International, 86(1), 59 –70.
    doi:10.1016/S1040-6182(01)00050-7
  • Clark, C.D. (1994). Large scale ice-moulded landforms and their glaciological significance. Sedimentary Geology, 91(1-4), 253-268.
    doi:10.1016/0037-0738(94)90133-3
  • Clark, C.D. (1990). Remote sensing scales related to the frequency of natural variation; an example from palaeo-ice flow in Canada. IEEE Transactions on Geoscience and Remote Sensing, 28(4), 503-508.
    doi:10.1109/TGRS.1990.572932

Their characteristics and possible formation mechanism:

Hillier, J.K., Smith, M.J., Clark, C.D., Stokes, C.R., Spagnolo, M. (2013). Subglacial bedforms reveal an exponential size-frequency distribution. Geomorphology, 190, 82-91. Ó Cofaigh, C., Stokes, C.R., Lian, O.B., Clark, C.D. and Tulacyzk, S. (2013). Formation of mega-scale glacial lineations on the Dubawnt Lake Ice Stream bed: 2. Sedimentology and stratigraphy. Quaternary Science Reviews. 77, 210 – 227. 99.
Ice sheet reconstructions

Ice sheet (small)Ice sheet UK (small)

Discovery that the beds of former ice sheets (ie whole of Canada) contain a complex and palimpsest record of former ice flow that be used to reconstruct the flow geometry and centres of mass of the ice sheets and how they evolved through time. This overturned the existing paradigm that viewed landforms as simply recording a single timeslice of activity or just retreat patterns.

I have made reconstructions for the ice sheets that covered whole of Canada, for Quebec, and for Britain and Ireland, and in Arctic and Far Eastern Russia .

It is now widely known that the centres of mass (ice divides) may migrate considerable (~1000 km) distances during growth and decay.

Some methodology papers on how to use RS/GIS to help

Greenwood, S.L, Clark, C.D. and Hughes, A.L.C. (2007). Formalising an inversion methodology for reconstructing ice-sheet retreat patterns from meltwater channels: application to the British Ice Sheet. Journal of Quaternary Science, 22(6), 637-645.
doi:10.1002/jqs.1083 Clark, C.D., Greenwood, S.L. and Evans, D.J.A. (2006). Palaeo-glaciology of the last British-Irish Ice Sheet: challenges and some recent developments. In: Knight, P.G. (ed.) Glacier Science and Environmental Change, Blackwell, Oxford. 248-264.

And then application of such methods for a variety of ice sheets

Bigg, G. R., Clark, C. D., Levine R. C., Greenwood, S. L., Haflidason, H., Hughes, A. L. C., Nygård, A. and Sejrup H. P. (2012). Sensitivity of the North Atlantic circulation to break-up of the marine sectors of the NW European ice sheets during the last Glacial: a synthesis of modelling and palaeoceanography. Global and Planetary Change. 98-99, 153-165. Chiverrell, R.C., Thrasher, I.M., Thomas, G.S.P., Lang, A., Scourse, J.D., Van Landeghem, K.J.J., McCarroll, D., Clark, C.D., Ó Cofaigh, C., Evans, D.J.A. and Ballantyne, C.K. (2013). Bayesian modelling the retreat of the Irish Sea Ice Stream. Journal of Quaternary Science, 28(2), 200-209. Livingstone, S.J., Clark, C.D. and Tarasov, L. (2013) Modelling North American palaeo-subglacial lakes and their meltwater drainage pathways. Earth and Planetary Science Letters, 375, 13 – 33. Boulton, G.S. and Clark, C.D. (1990). A highly mobile Laurentide Ice Sheet revealed by satellite images of glacial lineations, Nature, 346, 813-817.
doi:10.1038/346813a0 Boulton, G.S. and Clark, C.D. (1990). The Laurentide Ice Sheet through the last glacial cycle: the topology of drift lineations as a key to the dynamic behaviour of former ice sheets. Transactions of the Royal Society of Edinburgh: Earth Sciences, 81, 327-347. Mitchell, W.A., and Clark, C.D., (1994). The last ice sheet in Cumbria. In: Boardman, J. and Walden, J. (eds.), The Quaternary of Cumbria: Field Guide. Quaternary Research Association, Oxford, England. 4-14. Clark, C.D., Knight, J.K. and Gray, J.T. (2000). Geomorphological reconstruction of the Labrador Sector of the Laurentide Ice Sheet. Quaternary Science Reviews, 19(13), 1343-1366.
doi:10.1016/S0277-3791(99)00098-0 Clark, C.D. and Meehan, R.I. (2001). Subglacial bedform geomorphphology of the Irish Ice Sheet reveals major configuration changes during growth and decay. Journal of Quatenary Science, 16(5), 483–496. Evans, D.J., Thomson, S.A. and Clark, C.D. (2001). The glacial history of East Yorkshire. In: Bateman, M.D. et al (eds), 2001. The Quaternary of East Yorkshire and North Lincolnshire. Field Guide, Quaternary Research Association, London. 1-12. Clark, C.D., Gibbard, P.L. and Rose, J. (2004). Pleistocene glacial limits in England, Scotland and Wales. In: Ehlers, J. and Gibbard, P.L. (eds.) Quaternary Glaciations: Extent and Chronology, Part I; Europe. Developments in Quaternary Science, Elsevier. 47 - 82. Clark, C.D., Sejrup, H.P., Bigg, G.R., Stoker, M., Lonergan, L., Raunholm, S. and Haflidison, H. (2004). Did the Punctuated demise of glacial ice in the North Sea affect the thermohaline circulation? Eos, Transactions, American Geophysical Union, 85(31), 293.
doi:10.1029/2004EO310006 Clark, C.D., Evans, D.J.A., Khatwa, A., Bradwell, T., Jordan, C.J., Marsh, S.H., Mitchell, W.A. and. Bateman, M.D. (2004). Map and GIS database of landforms and features related to the last British Ice Sheet. Boreas, 33(4), 359-375.
SHERPA Archive version (open access)
doi:10.1080/03009480410001983
BRITICE web site Evans, D.J.A., Clark, C.D. and Mitchell, W.A. (2005). The last British Ice Sheet: A review of the evidence utilised in the compilation of the Glacial Map of Britain. Earth Science Reviews, 70(3-4), 253-312.
SHERPA Archive version (open access)
doi:10.1016/j.earscirev.2005.01.001 Hättestrand, C. and Clark, C.D. (2006). Reconstructing the pattern and style of deglaciation of Kola Peninsula, northeastern Fennoscandian Ice Sheet. In: Knight, P.G. (ed.) Glacier Science and Environmental Change, Blackwell, Oxford. 199-201. Hättestrand, C. and Clark, C.D. (2006). The glacial geomorphology of Kola Peninsula and adjacent areas in the Murmansk Region, Russia. Journal of Maps, v2006, 30-42. Stokes, C.R., Clark, C.D. and Winsborrow, M.C.M. (2006). Subglacial bedform evidence for a major palaeo-ice stream and its retreat phases in Amundsen Gulf, Canadian Arctic Archipelago. Journal of Quaternary Science, 21(4), 399-412.
doi:10.1002/jqs.991 Bigg, G.R., Clark, C.D. and Hughes, A.L.C. (2008). A last glacial ice sheet on the Pacific Russian coast and catastrophic change arising from coupled ice–volcanic interaction. Earth and Planetary Science Letters, 265(3-4), 559-570.
doi:10.1016/j.epsl.2007.10.052 Greenwood, S.L. and Clark, C.D. (2008). Subglacial bedforms of the Irish Ice Sheet. Journal of Maps, v2008, 332-357. Stokes, C.R., Clark, C.D. and Storrar, R. (2009). Major changes in ice stream dynamics during deglaciation of the north-western margin of the Laurentide Ice Sheet. Quaternary Science Reviews, 28(7-8), 721-738.
doi:10.1016/j.quascirev.2008.07.019 Greenwood, S.L. and Clark, C.D. (2009). Reconstructing the last Irish Ice Sheet 1: changing flow geometries and ice flow dynamics deciphered from the glacial landform record. Quaternary Science Reviews, 28(27-28), 3085-3100.
doi:10.1016/j.quascirev.2009.09.008 Greenwood, S.L. and Clark, C.D. (2009). Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics. Quaternary Science Reviews, 28(27-28), 3101-3123.
doi:10.1016/j.quascirev.2009.09.014 Barr, I.D. and Clark, C.D. (2009). Distribution and pattern of moraines in Far NE Russia reveal former glacial extent. Journal of Maps, v2009, 186-193.
doi:10.4113/jom.2009.1108 Bigg, G.R., Levine, R.C., Clark, C.D., Greenwood, S.L., Haflidason, H., Hughes, A.L.C., Nygård, A., and Sejrup, H.P. (2010). Last Glacial ice-rafted debris off south-western Europe: the role of the British-Irish Ice Sheet. Journal of Quaternary Science, 25(5), 689-699.
doi:10.1002/jqs.1345 Hughes, A.L.C., Clark, C.D., and Jordan, C.J. (2010). Subglacial bedforms of the last British Ice Sheet. Journal of Maps, v2010, 543-563.
doi:10.4113/jom.2010.1111 Clark, C.D., Hughes, A.L.C., Greenwood, S.L., Jordan, C.J. and Sejrup, H.P. (2012). Pattern and timing of retreat of the last British-Irish Ice Sheet. Quaternary Science Reviews, 44, 112-146.
doi:10.1016/j.quascirev.2010.07.019 Barr, I.D. and Clark, C.D. (2012). Late Quaternary glaciations in Far NE Russia; combining moraines, topography and chronology to assess regional and global glaciation synchrony. Quaternary Science Reviews, 53, 72–87.
doi:10.1016/j.quascirev.2012.08.004
  • Clark, C.D. (1997). Reconstructing the evolutionary dynamics of former ice sheets using multi-temporal evidence, remote sensing and GIS. Quaternary Science Reviews, 16(9), 1067-1092.
    doi:10.1016/S0277-3791(97)00037-1
Palaeo ice streams

Ice stream (small)Ice stream structure (small)

Ice streams are fast flowing corridors embedded within slower flowing ice sheets. For Antarctica they are responsible for around 90% of ice mass lost from the system, even though they occupy only a small part of the perimeter (12 %). Their activity largely determines the stability and response of ice sheets to climate perturbations, and accordingly their functioning receives intensive research activity, and constitutes the greatest challenge to knowledge within glaciology.

I have contributed to this field, by making theoretical advances with regard to the geomorphological and geological imprint that ice streams should leave behind, and using EO to search for them in former ice sheets.

We are currently searching and investigating the tracks of ice streams that drained ice sheets during the last glaciation. Once found and investigated their geomorphological signature provides information on ice stream basal characteristics that can be used for parameterising or testing numerical models. We can make inferences about the basal controls on ice stream functioning, which are relevant to both contemporary and palaeo glaciology. The first International sympoisum on palaeo-ice streams was held in Denmark in 2001. A special issue of Boreas (32(1), edited by myself and collegues) reported some of the key papers.


Contributions to palaeo ice streams

  •  
  • Chiverrell, R.C., Thrasher, I.M., Thomas, G.S.P., Lang, A., Scourse, J.D., Van Landeghem, K.J.J., McCarroll, D., Clark, C.D., Ó Cofaigh, C., Evans, D.J.A. and Ballantyne, C.K. (2013). Bayesian modelling the retreat of the Irish Sea Ice Stream. Journal of Quaternary Science, 28(2), 200-209
  • Ó Cofaigh, C., Stokes, C.R., Lian, O.B., Clark, C.D. and Tulacyzk, S. (2013). Formation of mega-scale glacial lineations on the Dubawnt Lake Ice Stream bed: 2. Sedimentology and stratigraphy. Quaternary Science Reviews. 77, 210 – 227.
  • Stokes, C.R., Spagnolo, M., Clark, C.D., O’Cofaigh, C., Lian, O.B. and Dunstone, R.B. (2013). Formation of Mega-Scale Glacial Lineations on the Dubawnt Lake Ice Stream Bed: 1. Size, Shape and Spacing from a Large Remote Sensing Dataset. Quaternary Science Reviews. 77, 190 – 209.
  • Bigg, G. R., Clark, C. D., Levine R. C., Greenwood, S. L., Haflidason, H., Hughes, A. L. C., Nygård, A. and Sejrup H. P. (2012). Sensitivity of the North Atlantic circulation to break-up of the marine sectors of the NW European ice sheets during the last Glacial: a synthesis of modelling and palaeoceanography. Global and Planetary Change. 98-99, 153-165.
  • Clark, C.D., Hughes, A.L.C., Greenwood, S.L., Jordan, C.J. and Sejrup, H.P. (2012). Pattern and timing of retreat of the last British-Irish Ice Sheet. Quaternary Science Reviews, 44, 112-146.
    doi:10.1016/j.quascirev.2010.07.019
  • Winsborrow, M.C.M., Clark, C.D. and Stokes, C.R. (2010). What controls the location of ice streams? Earth Science Reviews. 103(1-2), 45-49.
    doi:10.1016/j.earscirev.2010.07.003
  • Bigg, G.R., Levine, R.C., Clark, C.D., Greenwood, S.L., Haflidason, H., Hughes, A.L.C., Nygård, A., and Sejrup, H.P. (2010). Last Glacial ice-rafted debris off south-western Europe: the role of the British-Irish Ice Sheet. Journal of Quaternary Science, 25(5), 689-699.
    doi:10.1002/jqs.1345
  • Ó Cofaigh, C., Dowdeswell, J.A., King, E.C., Anderson, J.B., Clark, C.D., Evans, D.J.A., Evans, J., Hindmarsh, R.C.A., Larter, R.D., and Stokes, C.R. (2010). Comment on Shaw J., Pugin, A. and Young, R. (2008): "A meltwater origin for Antarctic shelf bedforms with special attention to megalineations". Geomorphology, 117(1-2), 195-198.
    doi:10.1016/j.geomorph.2009.09.036
  • Greenwood, S.L. and Clark, C.D. (2009). Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics. Quaternary Science Reviews, 28(27-28), 3101-3123.
    doi:10.1016/j.quascirev.2009.09.014
  • Stokes, C.R., Clark, C.D. and Storrar, R. (2009). Major changes in ice stream dynamics during deglaciation of the north-western margin of the Laurentide Ice Sheet. Quaternary Science Reviews, 28(7-8), 721-738.
    doi:10.1016/j.quascirev.2008.07.019
  • Stokes, C.R., Lian, O.B., Tulaczyck, S. and Clark, C.D. (2008). Superimposition of ribbed moraines on a palaeo-ice-stream bed: implications for ice stream dynamics and shutdown. Earth Surface Processes and Landforms, 33(4), 593-609.
    doi:10.1002/esp.1671
  • Evans, D.J.A., Clark, C.D. and Rea, B.R. (2008). Landform and sediment imprints of fast glacier flow in the southwest Laurentide Ice Sheet. Journal of Quaternary Science, 23(3), 249-272.
    doi:10.1002/jqs.1141
  • Nygård, A., Sejrup, H.P., Haflidason, H., Lekens, W.A.H., Clark, C.D. and Bigg, G.R. (2007). Extreme sediment and ice delivery from marine Ice streams; new evidence from the northern North Sea. Geology, 35(5), 395-398.
    doi:10.1130/G23364A.1
  • Stokes, C.R., Clark, C.D., Lian, O.B., and Tulaczyk, S. (2007). Ice stream sticky spots: a review of their identification and influence beneath contemporary and palaeo-ice streams. Earth Science Reviews, 81(3-4), 217-249.
    doi:10.1016/j.earscirev.2007.01.002
  • Stokes, C.R., Clark, C.D. and Winsborrow, M.C.M. (2006). Subglacial bedform evidence for a major palaeo-ice stream and its retreat phases in Amundsen Gulf, Canadian Arctic Archipelago. Journal of Quaternary Science, 21(4), 399-412.
    doi:10.1002/jqs.991
  • Stokes, C.R. and Clark, C.D. (2006). Influence of ice streaming on the ocean-climate system: examining the impact of the M'Clintock Channel Ice Stream, Canadian Arctic Archipelago. In: Knight, P.G. (ed.) Glacier Science and Environmental Change, Blackwell, Oxford. 135-136.
  • Stokes, C.R. and Clark, C.D. (2006). What can the 'footprint' of a palaeo-ice stream tell us? Interpreting the bed of the Dubawnt Lake Ice Stream, Northern Keewatin, Canada. In: Knight, P.G. (ed.) Glacier Science and Environmental Change, Blackwell, Oxford. 208–209.
  • Clark, C.D., Greenwood, S.L. and Evans, D.J.A. (2006). Palaeo-glaciology of the last British-Irish Ice Sheet: challenges and some recent developments. In: Knight, P.G. (ed.) Glacier Science and Environmental Change, Blackwell, Oxford. 248-264.
  • Stokes, C.R., Clark, C.D., Darby, D.A. and Hodgson, D.A. (2005). Late Pleistocene ice export events into the Arctic Ocean from the M'Clure Strait Ice Stream, Canadian Arctic Archipelago. Global and Planetary Change, 49(3-4), 139-162.
    doi:10.1016/j.gloplacha.2005.06.001
  • Winsborrow, M.C.M., Clark, C.D. and Stokes, C.R. (2004). Ice streams of the Laurentide Ice Sheet. Géographie Physique et Quaternaire, 58(2-3), 269-280.
    pdf iconArchived PDF version (open access)
  • Stokes, C.R. and Clark, C.D. (2004). Evolution of Late Glacial ice-marginal lakes on the north-western Canadian Shield and their influence on the location of the Dubawnt Lake Palaeo-Ice Stream. Palaeogeography, Palaeoclimatology, Palaeoecology, 215(1-2), 155–171.
  • Clark, C.D., Tulaczyk, S. M., Stokes, C.R., and Canals, M. (2003). A groove-ploughing theory for the production of mega scale glacial lineations, and implications for ice-stream mechanics. Journal of Glaciology, 49(165), 240-256.
    doi:10.3189/172756503781830719
  • Stokes, C.R. and Clark, C.D. (2003). The Dubawnt Lake Palaeo-Ice Stream: evidence for dynamic ice sheet behaviour on the Canadian Shield and insights regarding the controls on ice-stream location and vigour. Boreas, 32(1), 263-279.
    doi:10.1080/03009480310001155
  • Clark, C.D. Evans, D.J.A, and Piotrowski, J.A. (2003). Palaeo-ice streams: an introduction. Boreas, 32(1), 1-3.
    pdf iconSHERPA Archive version (open access)
    doi:10.1080/03009480310001182
  • Clark, C.D. and Stokes, C.R. (2003). The palaeo-Ice Stream Landsystem. In: Evans, D.J.A. (ed.) Glacial Landsystems, Arnold, London. 204-227.
  • Stokes, C.R. and Clark, C.D. (2003). Laurentide ice streaming on the Canadian Shield: a conflict with the soft-bedded ice stream paradigm? Geology, 31(4), 347-350.
    doi:10.1130/0091-7613(2003)031<0347:LISOTC>2.0.CO;2
  • Stokes, C.R. and Clark, C.D. (2002). Are long bedforms indicative of fast ice flow? Boreas, 31(3), 239-249.
    doi:10.1080/030094802760260355
  • Stokes, C.R. and Clark, C.D. (2002) Ice stream shear margin moraines. Earth Surface Processes and Landforms, 27(5), 547-558.
    doi:10.1002/esp.326
  • Tulaczyk, S.M., Scherer, R.P. and Clark, C.D. (2001). A ploughing model for the origin of weak tills beneath ice streams: a qualitative treatment. Quaternary International, 86(1), 59 –70.
    doi:10.1016/S1040-6182(01)00050-7
  • Clark, C.D. and Stokes, C.R. (2001). Extent and basal characteristics of the M'Clintock Channel Ice Stream. Quaternary International, 86(1), 81-101.
    doi:10.1016/S1040-6182(01)00052-0
  • Stokes, C.R. and Clark, C.D. (2001). Palaeo-ice streams. Quaternary Science Reviews, 20(13), 1437-1457.
    doi:10.1016/S0277-3791(01)00003-8
  • Stokes, C.R., and Clark, C.D. (1999). Geomorphological criteria for identifying Pleistocene ice streams. Annals of Glaciology, 28(1), 67- 74.
    doi:10.3189/172756499781821625
  • Clark, C.D. (1993). Mega-scale glacial lineations and cross-cutting ice-flow landforms. Earth Surface Processes and Landforms, 18(1), 1-29.
    doi:10.1002/esp.3290180102
BRITICE

Map and GIS database of glacial landforms and features related to the last British Ice Sheet

Published map now available

See "Buying a printed map"

Most glaciated countries have for some time had some form of 'glacial map' recording landforms and evidence resulting from the activity of former ice sheets.
The Glacial Map of Canada is an exemplary example (Prest, V.K., Grant, D.R. and Rampton, V.N. 1968: Glacial map of Canada. Geological Survey of Canada. Map 1253A.)

For the first time we now have a compilation map for the last British Ice Sheet.

The methods of production, scope and caveats, and the printed 'Glacial Map' at a scale of 1:625 000 are reported in:

Clark, C.D., Evans, D.J.A., Khatwa, A., Bradwell, T., Jordan, C.J., Marsh, S.H., Mitchell, W.A. and Bateman, M.D. (2004). Map and GIS database of landforms and features related to the last British Ice Sheet. Boreas, 33(4), 359-375.
SHERPA Archive version (open access)
doi:10.1080/03009480410001983

Please note that it is important to consult this source as it fully describes the nature of the data, and caveats which are essential for appropriate interpretation of the features.

BRITICE map

The purpose of this web page is to support the above publication, and to permit academic users to have free access to the data used in compiling the 'Glacial Map'.

Example visualisations

BRITICE GIS

On-screen view of some of the GIS layers: trimlines (nunataks) in red, moraine ridges in brown and limit of glacigenic deposits in dashed black, overlaid on a DEM of topography for part of Wester Ross, Scotland. This illustrates how it is possible to interrogate any individual feature and receive information on the published source from where it derives and a brief explanatory comment.

BRITICE DEM

Oblique view of the York-Escrick moraines (in brown) from the GIS overlaid on a DEM rendition of topography.

BRITICE GIS2

Example of a small extract of the BRITICE GIS around the Solway Firth. Drumlins as black lines, meltwater channels in blue, moraines in brown, eskers in red, and erratic information in green.

What is included?

Emphasis is on information that constrains the last ice sheet. The following are included:

moraines eskers drumlins meltwater channels tunnel valleys trimlines limit of key glacigenic deposits glaciolacustrine deposits ice-dammed lakes erratic dispersal patterns shelf-edge fans and the Loch Lomond Readvance limit of the main ice cap.

PDF files of the map are available from this page - see "Downloads" top-right. Feel free to print this out yourself (although rather large) or print extracts of it.

Bibliography of all academic publications and BGS maps from which data were extracted is also available as a Microsoft Word document - see "Downloads" top-right.

An extensive review paper, organised thematically and regionally, describing the nature and range of evidence utilised to compile the map is published:

Evans, D.J.A., Clark, C.D. and Mitchell, W.A. (2005). The last British Ice Sheet: A review of the evidence utilised in the compilation of the Glacial Map of Britain. Earth Science Reviews, 70, 253-312.
SHERPA Archive version (open access)
doi:10.1016/j.earscirev.2005.01.001

Buying a printed map

If you want your own copy of the printed maps, these are available as North and South Sheets (each 116 x 80 cm in size) either folded or as flat maps. There is a charge for this to offset our initial printing costs and post & package. Send your request to Chris Clark stating whether you want north or south, or both sheets, and whether flat or folded versions. Cheques to be made payable to "University of Sheffield"; £10 per map or £16 for north and south sheets, inclusive of post & packing.

Chris Clark, Department of Geography, University of Sheffield, SHEFFIELD, S10 2TN, United Kingdom

GIS data download

All data are stored as shapefiles, as fully-attributed polygons or arcs. These can be easily loaded into ArcGIS®, Arc View® and Erdas Imagine® and are importable into other GIS or CAD software packages. For ease of download all files are provided in one zipped folder  - see "Downloads" top-right.

Details about the data layers and file naming and geographic projection are stored in a accompanying 'readme.txt' file Consult the paper in Boreas for extra details.

To download all data layers and use an Arcview project file (*.apr) that allows a 'ready-made' and easy viewing of the database:
Download the zip file into a suitable folder name, say /britice. Unzip it in this folder such that all files remain in it. Start Arcview and 'open project' selecting the filename 'britice.apr'. The full database should appear with all categories labelled in the legend.

[Note that the data layer COAST is the property of Bartholomew's and cannot be used in publication or in commercial applications without their permission].

Important Links

The British Geological Survey can provide further information, maps for purchase and digital data for elements within the GIS that came from their mapping programmes.
The BGS has web pages devoted to digital data for purchase and sample datasets.

How was it compiled?

The compilation was produced by reviewing over 1,000 publications of the academic literature and British Geological Survey mapping. Relevant data were extracted from these and digitised and entered into a GIS. Note that the printed Glacial Map in Boreas is a generalisation (necessary for the reduced scale) of the data. For full-resolution data the GIS should be used.

Who has done the work?

Chris Clark (University of Sheffield) and Dave Evans (University of Glasgow) led the work assisted by Wishart Mitchell (University of Durham) and Mark Bateman (University of Sheffield). Important collaborators at the British Geological Survey (BGS) were Colm Jordan and Stuart Marsh, without whom the work would not have been possible. Anjana Khatwa and Tom Bradwell were employed to perform much of the data assessment and input. Neal Salomon and Lisa Collings are thanked for their work digitising some of the features, and Graham Allsopp is acknowledged for cartographic production of the map. Steve Wise is thanked for help regarding GIS implementation.

The BRITICE project was conceived and started in 1995, and rapidly grew in ambition from a simple A3 map to a fully-fledged GIS, bibliography and large map. Essential to the success of the project was the recognition of its value by Stuart Marsh and Colm Jordan and consequent timely support of funds from the BGS under their University Collaboration Scheme. The universities of Sheffield and Glasgow are also acknowledged for their financial support, as is the Carnegie Trust for the Universities of Scotland, who greatly assisted in funding the production of the map.

Hey, you have missed an important feature. What about future editions?

The census date was 2002, and so anything published after this time is not included. It is inevitable that some of the information may be incorrect and require rejecting or revising. Additionally, we have likely missed some important aspects. If material is not included it might be because the information was not presented in map form, the mapping was of insufficient quality (with regard to geographic referencing), it did not fit our target layers, it conflicted with other, perhaps better mapped data on the same feature, or we simply did not find the relevant publication.

Our intention is that the GIS will be periodically updated to include newly published information, and for revisions where found necessary. We therefore appeal for extra information, criticisms or suggested amendments. Please direct these to Chris Clark (c.clark@sheffield.ac.uk) who will ensure that they are considered for the next update of the GIS. Please send a copy of the relevant publication, highlighting the features for consideration. It should be noted that data is restricted to published information (but including PhD theses) which provides a crude quality-control and more importantly ensures that all data can be traced back to more detailed descriptions and observations.

When future updates are made (BRITICE 2nd edition), the results will be posted on this web page for downloading.

How can I get hold of the BRITICE data?

All data is available at no cost, providing that the BRITICE project is acknowledged and cited in any publications or presentations. Commercial use is not permitted.

Clark, C.D., Evans, D.J.A., Khatwa, A., Bradwell, T., Jordan, C.J., Marsh, S.H., Mitchell, W.A. and. Bateman, M.D. (2004). Map and GIS database of landforms and features related to the last British Ice Sheet. Boreas, 33(4), 359-375.
SHERPA Archive version (open access)
doi:10.1080/03009480410001983

The printed map is available in the Boreas publication listed above, at a scale of 1:625,000 (ca. 2m x 1 m in size). The paper also contains important details regarding the scope and accuracy of the data layers and caveats required to make appropriate interpretations.

The GIS contains over 20,000 features split into thematic layers (as above). Individual features are attributed such that they can be traced back to their published sources. Given that the published sources of information that underpin this work were derived by a piecemeal effort over 150 years then our main caveat is of data consistency and reliability.

Why have we done this?

It is hoped that this compilation will:

Stimulate greater scrutiny of published data Assist in palaeo-glaciological reconstructions of the ice sheet Facilitate use of field-evidence in numerical ice sheet modelling Help direct field-workers in their future investigations.
General contributions in Remote Sensing/Geographic Information Systems/Digital Elevation Models

Essentially other geospatial projects I have dabbled in (mostly in tropical coasts - coral reefs and mangroves), but also some archaeology, ecology, lineaments and other things), but I haven't relisted all my glacial ones here, see the other sections for these.

RS image (small) Chris on boat

Hodson, A.J., Anesio, A.M., Ng, F., Watson, R., Quirk, J., Irvine-Fynn, T., Dye, A., Clark, C.D., McCloy, P., Kohler, J. and Sattler, B. (2007). A glacier respires: quantifying the distribution and respiration CO2 flux of cryoconite across an entire Arctic glacial ecosystem. Journal of Geophysical Research (Biogeosciences), 112, G04S36.
doi:10.1029/2007JG000452 Smith, M.J., Dunlop, P. and Clark, C.D. (2006). An overview of subglacial bedforms in Ireland, mapped from digital elevation data. In: Knight, P.G. (ed.) Glacier Science and Environmental Change, Blackwell, Oxford. 384–387. Smith, M.J. and Clark, C.D. (2005). Methods for visualisation of high resolution digital elevation models for landform mapping. Earth Surface Processes and Landforms, 30(7), 885-900.
doi:10.1002/esp.1210 Mumby, P.J., Hedley, J.D., Chisholm, J.R.M., Clark, C.D., Ripley, H. and Jaubert, J. (2004). The cover of living and dead corals from airborne remote sensing. Coral Reefs, 23(2), 171-183.
doi:10.1007/s00338-004-0382-1 Stokes, C.R. and Clark, C.D. (2003). Giant glacial grooves detected on Landsat ETM+ satellite imagery. International Journal of Remote Sensing, 24(5), 905-910.
doi:10.1080/01431160110115069 Mumby, P.J., Chrisholm, J.R.M., Clark, C.D., Hedley, J.D. and Jaubert, J. (2001). Spectrographic imaging: a bird's-eye view of the health of coral reefs. Nature, 413, 36 (06 Sep 2001).
10.1038/35092617 Mumby, P.J., Chisholm, J.R.M., Edwards, A.J., Clark, C.D., Rourk, E.B., Andrefouet, S., and Jaubert, J. (2001). Unprecedented bleaching-induced mortality in Porites spp. at Rangiroa Atoll, French Polynesia. Marine Biology, 139(1), 183-189.
doi:10.1007/s002270100575 Clark, C.D., Mumby, P.J., Chisholm, J.R.M., Jaubert, J., and Andrefouet, S. (2000). Spectral discrimination of coral mortality states following a severe bleaching event. International Journal of Remote Sensing, 21(11), 2321-2327.
doi:10.1080/01431160050029602 Clark, C.D. (2000). Future prospects of remote sensing for tropical coastal management. In: Green, E.P., Mumby, P.J., Edwards, A.J. and Clark, C.D. Remote Sensing Handbook for Tropical Coastal Management. Coastal Management Sourcebooks 3, UNESCO, Paris, 287-291. Mumby, P.J., Green, E.P., Edwards, A.J. and Clark, C.D. (2000). Cost-effectiveness of remote sensing for coastal management. In: Green, E.P., Mumby, P.J., Edwards, A.J. and Clark, C.D. Remote Sensing Handbook for Tropical Coastal Management. Coastal Management Sourcebooks 3, UNESCO, Paris, 271-285. Green, E.P., and Clark, C.D. (2000). Assessing mangrove leaf area index and canopy closure. In: Green, E.P., Mumby, P.J., Edwards, A.J. and Clark, C.D. Remote Sensing Handbook for Tropical Coastal Management. Coastal Management Sourcebooks 3, UNESCO, Paris, 245-254. Edwards, A.J. and Clark, C.D. (2000). Monitoring coastal water quality. In: Green, E.P., Mumby, P.J., Edwards, A.J. and Clark, C.D. Remote Sensing Handbook for Tropical Coastal Management. Coastal Management Sourcebooks 3, UNESCO, Paris, 201-218. Green, E.P., Clark, C.D. and Edwards, A.J. (2000). Image classification and habitat mapping. In: Green, E.P., Mumby, P.J., Edwards, A.J. and Clark, C.D. Remote Sensing Handbook for Tropical Coastal Management. Coastal Management Sourcebooks 3, UNESCO, Paris, 141-154. Mumby, P.J and Clark, C.D. (2000). Radiometric correction of satellite and airborne images. In: Green, E.P., Mumby, P.J., Edwards, A.J. and Clark, C.D. Remote Sensing Handbook for Tropical Coastal Management. Coastal Management Sourcebooks 3, UNESCO, Paris, 109 –120. Green, E.P., Clark, C.D. and Edwards, A.J. (2000). Geometric correction of satellite and airborne imagery. In: Green, E.P., Mumby, P.J., Edwards, A.J. and Clark, C.D. Remote Sensing Handbook for Tropical Coastal Management. Coastal Management Sourcebooks 3, UNESCO, Paris, 93 –108. Green, E.P., Mumby, P.J., Edwards, A.J. (ed.) and Clark, C.D. (2000). Remote Sensing Handbook for Tropical Coastal Management, Coastal Management Sourcebooks 3, UNESCO, Paris. ISBN: 9789231037368.
Available online: http://www.unesco.org/csi/pub/source/rs.htm Mumby, P.J., Green, E.P, Edwards, A.L and Clark, C.D. (1999). The cost-effectiveness of remote sensing for tropical coastal resources assessment and management. Journal of Environmental Management, 55(3), 157-166.
doi:10.1006/jema.1998.0255 Green, E.P., Mumby, P.J., Edwards, A.J., Clark, C.D. and Ellis, A.C. (1998). The assessment of mangrove areas using high resolution multispectral airborne imagery (CASI). Journal of Coastal Research, 14, 433-443. Green, E.P., Mumby, P.J., Clark, C.D., Edwards, A.J. and Ellis, A.C. (1998). Remote sensing techniques for mangrove mapping. International Journal of Remote Sensing, 19(5), 935-956.
doi:10.1080/014311698215801 Mumby, P.J., Clark, C.D., Green, E.P. and Edwards, A.J. (1998). Benefits of water column correction and contextual editing for mapping coral reefs. International Journal of Remote Sensing, 19(1), 203-210.
doi:10.1080/014311698216521 Mumby, P.J., Green, E.P., Clark, C.D. and Edwards, A.J. (1998). Digital analysis of multispectral airborne imagery of coral reefs. Coral Reefs, 17(1), 59-69.
doi:10.1007/s003380050096 Clark, C.D., Garrod, S.M. and Parker Pearson, M. (1998). Landscape archaeology, deforestation and remote sensing of southern Madagascar. International Journal of Remote Sensing, 19(8), 1461-1477.
doi:10.1080/014311698215298 Turpin, O.C., Ferguson, R.I. and Clark, C.D. (1998). The transient snowline on glaciers: topographic controls and implications for melt predictions. In: Lane, S.N., Richards, K.S. and Chandler J.H. (eds.) Landform Monitoring, Modelling and Analysis, John Wiley and Sons. 363-383. Vencatasawmy, C.P., Clark, C.D. & Martin, R.J. (1998). Landform and lineament mapping using radar remote sensing. In: Lane, S.N., Richards, K.S. and Chandler J.H. (eds.) Landform Monitoring, Modelling and Analysis, John Wiley and Sons. 165-194. Mumby, P.J., Green, E.P., Edwards, A.J. and Clark, C.D. (1997). Coral reef habitat mapping: how much detail can remote sensing provide? Marine Biology, 130(2), 193-202.
doi:10.1007/s002270050238 Mumby, P.J., Green, E.P., Edwards, A.J. and Clark, C.D. (1997). Measurement of seagrass standing crop using satellite and digital airborne remote sensing. Marine Ecology Progress Series, 159, 51-61.
doi:10.3354/meps159051 Turpin, O.C., Ferguson, R.I., and Clark, C.D. (1997). Remote sensing of snowline rise as an aid to testing and calibrating a glacier runoff model. Physics and Chemistry of The Earth, 22(3-4), 279-283.
doi:10.1016/S0079-1946(97)00144-4 Mumby, P.J., Edwards, A.J., Green, E.P., Anderson, C.W., Ellis, A.C. and Clark, C.D. (1997). A visual assessment technique for estimating seagrass standing crop. Aquatic Conservation: Marine and Freshwater Ecosystems, 7(3), 239-251.
doi:10.1002/(SICI)1099-0755(199709)7:3<239::AID-AQC240>3.0.CO;2-V Green, E.P., Mumby, P.J., Edwards, A.J., Clark, C.D. and Ellis, A.C. (1997). Estimating leaf area index of mangroves from satellite data. Aquatic Botany, 58(1), 11-19.
doi:10.1016/S0304-3770(97)00013-2 Clark, C.D. (1997). Reconstructing the evolutionary dynamics of former ice sheets using multi-temporal evidence, remote sensing and GIS. Quaternary Science Reviews, 16(9), 1067-1092.
doi:10.1016/S0277-3791(97)00037-1 Clark, C.D., Ripley, H.T., Green, E.P., Edwards, A.J. and Mumby, P.J. (1997). Mapping and measurement of tropical coastal environments with hyperspectral and high spatial resolution data. International Journal of Remote Sensing, 18(2), 237-242.
doi:10.1080/014311697219033 Green, E.P., Mumby, P.J., Edwards, A.J. and Clark, C.D. (1996). A review of remote sensing for the assessment and management of tropical coastal resources. Coastal Management, 24(1), 1-40.
doi:10.1080/08920759609362279 Clark, C.D. and Wilson, C. (1994). Spatial analysis of lineaments. Computers & Geoscience, 20(7-8), 1237-1258.
doi:10.1016/0098-3004(94)90073-6 Clark, C.D. (1993). Satellite remote sensing of marine pollution. International Journal of Remote Sensing, 14(16), 2985-3004.
doi:10.1080/01431169308904414 Clark, C.D. (1993). Satellite remote sensing for marine pollution investigations. Marine Pollution Bulletin, 26(7), 357-368.
doi:10.1016/0025-326X(93)90182-J Clark, C.D. (1990). Remote sensing scales related to the frequency of natural variation; an example from palaeo-ice flow in Canada. IEEE Transactions on Geoscience and Remote Sensing, 28(4), 503-508.
doi:10.1109/TGRS.1990.572932