MODIFICATION OF CLAST SHAPE IN HIGH-ARCTIC GLACIAL ENVIRONMENTS

Clast Shape data from a range of different glacial environments at sev eral high-arctic valley glaciers in Svalbard are presented. These data add to the growing body of reference information about clast shape in modern glacial environments and is used to explore the role of lithol ogy in clast morphogenesis and to evaluate the different methodologica l approaches to the analysis of clast shape data. The following conclu sions are drawn: (1) it is possible to distinguish clasts transported subglacially from those moved supraglacially; (2) It is not possible t o differentiate among different types of subglacial sediment or to dis tinguish them collectively from glaciofluvial samples; (3) lithology h as some influence on clast shape, although not as much as previously s uggested; and (4) covariant plots of the RA (percentage of angular and very angular clasts) versus C-40 (percentage of clasts with c to a ax ial ratio less than or equal to 0.4) index give superior data visualiz ation and discriminate more effectively among different glacial sedime nts than sphericity and roundness plots.