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Friday 10 June 2022

Glacial clast morphology


Long ago I lectured in Durham University about this sort of thing, and was somewhat immersed in the topic during my research in the Arctic and Antarctic.    Basic question:  is it possible to look as a clast (a stone or a boulder) and identify it as having been transported by glacier ice?  There is a vast literature, and hundreds of geomorphologists have attempted to find criteria that can be numerically or statistically quantified.  There has been considerable success in this enterprise -- but it is nonetheless true that every clast has a unique history and is therefore unique in its shape and surface characteristics.  So just as skilled doctors will make diagnoses on the basis of "instinct" or "experience", glacial geomorphologists will assess clast origins on the basis of "look" and "feel".  Sound and taste do not often come into it.........

When I say that the bulk of the bluestones at Stonehenge (including Newall's boulder) "look like glacial erratics" what do I actually mean?  Well, this is a good start:

Glacial clasts are typically subangular to subrounded, exhibit asymmetrical wear patterns, and often have characteristic polished and faceted faces with abundant striae oriented parallel to the long axis of the clast (Benn and Evans 2010).

Clasts can range from pebble (4–8 mm) to boulder (>256 mm) size and can be of varying lithologies. They can exhibit a variety of shapes but are characteristically subangular to subrounded, and clasts exhibiting bullet, pentagonal, and/or stoss and lee forms are considered especially diagnostic (Boulton 1978; Sharp 1982; Krüger 1984; Eyles 1993; Benn and Evans 2010). Clast shape and roundness can be visualized using RA-C40 plots developed by Benn and Ballantyne (1994), systematized using TRI-PLOT by Graham and Midgley (2000) and used by Atkins.


If you go to the SpringerLink web page you will find hyperlinks to many of these articles.

Adam WG, Knight PG (2003) Identification of basal layer debris in ice-marginal moraines, Russell Glacier, West Greenland. Quat Sci Rev 22:1407–1414

Agassiz L (1840) Études sur les glaciers, Neuchâtel. Available via Accessed 07 Oct 2012

Atkins C (2003) Characteristics of Striae and Clast shape in glacial and non-glacial environments. Dissertation, Victoria University of WellingtonGoogle Scholar

Atkins CB (2004) Photographic atlas of striae in glacial and non-glacial environments (Antarctic Data Series Report 28). Victoria University of Wellington, New Zealand. Accessed 07 Oct 2012

Benn DI, Ballantyne CK (1994) Reconstructing the transport history of glacigenic sediments: a new approach based on the co-variance of clast shape indices. Sediment Geol 91:215–227

Benn DI, Evans DJA (1996) The interpretation and classification of subglacially deformed materials. Quat Sci Rev 15:23–52

Benn DI, Evans DJA (2010) Glaciers and glaciation, 2nd edn. Arnold, London

Bennett MR, Hambrey MJ, Huddart D (1997) Modification of clast shape in high-Arctic glacial environments. J Sediment Res 67:550–559

Boulton GS (1978) Boulder shapes and grain-size distributions of debris as indicators transport paths through a glacier and till genesis. Sedimentology 25:773–799

Crowell JC, Frakes LA (1972) Late paleozoic glaciation: part V, Karroo Basin, South Africa. GSA Bull 83:2887–2919

Dreimanis A (1989) Tills: their genetic terminology and classification. In: Goldthwait RP, Matsch CL (eds) Genetic classification of glacigenic deposits. Balkema, Rotterdam, pp 85–88

Eyles N (1993) Earth’s glacial record and its tectonic setting. Earth Sci Rev 35:1–248

Graham DJ, Midgley NG (2000) Graphical representation of particle shape using triangular diagram: an excel spreadsheet method. Earth Surf Process Landf 25:1473–1477.

Hambrey MJ (1982) Late Precambrian diamictites of northeastern Svalbard. Geol Mag 119:527–551

Harland WB (1964) Evidence of Late Precambrian glaciation and its significance. In: Nairn AEM (ed) Problems in palaeoclimatology. Interscience/Wiley, London, pp 119–149

Hart JK (1995) Subglacial erosion, deposition and deformation associated with deformable beds. Prog Phys Geogr 19:173–191

Hart JK (2006) An investigation of subglacial processes at the microscale from Briksdalsbreen, Norway. Sedimentology 53:125–146

Head JW, Mustard JF, Kreslavsky MA, Milliken RE, Marchant DR (2003) Recent ice ages on Mars. Nature 426:797–802

Head JW, Marchant DR, Dickson JL, Kress AM, Baker DM (2010) Northern mid-latitude glaciation in the Late Amazonian period of Mars: criteria for the recognition of debris-covered glacier and valley glacier landsystem deposits. Earth Planet Sci Lett 294:306–320

Hoffman PF, Kaufman AJ, Halverson GP (1998) Comings and goings of global glaciations on a neoproterozoic tropical platform in Namibia. GSA Today 8:1–9

Holmes CD (1960) Evolution of till-stone shapes, central New York. Geol Soc Am Bull 71:1645–1660

Humlum O (1985) Changes in texture and fabric of particles in glacial traction with distance from source, Mýrdalsjökull, Iceland. J Glaciol 31:150–156

Krüger J (1984) Clasts with stoss-lee forms in lodgement tills: a discussion. J Glaciol 30:241–243

Lucchitta BK (1981) Mars and Earth: comparison of cold climate features. Icarus 45:264–303

Neukum G, Jaumann R, Hoffmann H, Hauber E, Head JW, Basilevsky AT, Ivanov BA, Werner SC, van Gasselt S, Murray JB, McCord T (2004) Recent and episodic volcanic and glacial activity on Mars revealed by the high resolution stereo camera. Nature 432:971–979

Nobles LH, Weertman J (1971) Influence of irregularities of the bed of an ice sheet on deposition rate of till. In: Goldthwait RP (ed) Till: a symposium. Ohio State University Press, Columbus, pp 117–126

Oberbeck VR, Marshall JR, Aggarwal H (1993) Impacts, tillites, and the breakup of Gondwanaland. NASA Publications. Paper 74. Available via Digital Commons. 

Rampino ML (1994) Tillites, diamictites, and ballistic ejects of large impacts. J Geol 102:439–456

Sharp MJ (1982) Modification of clasts in lodgement tills by glacial erosion. J Glaciol 28:475–481

Van Hoesen JG, Orndorff RL (2004) A comparative SEM study assessing the micromorphology of glaciated clasts of varying lithologies. Can J Earth Sci 41:1123–1139

Wentworth CK (1936) An analysis of the shapes of glacial cobbles. J Sediment Petrol 6:85–96

How to cite
Cite this entry as:Van Hoesen J.G. (2015) Glacial Clast. In: Hargitai H., Kereszturi Á. (eds) Encyclopedia of Planetary Landforms. Springer, New York, NY. 

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