The cross-valley moraines of north-central Baffin Island: a quantitative analysis

Abstract
Statistical evaluation of data collected during 1961 allows five working hypotheses on the genesis of the cross-valley moraines to be reexamined. The paper presents three complementary studies on the following: (1) the sediments of cross-valley moraines and central kames; (2) the orientation and dip of included particles within the cross-valley moraines; and (3) the spacing of the moraines in relation to distance from the Isortoq watershed and to the effective stress operating at the hase of the glacier when the moraines were being formed. For each section the sampling methods and statistical treatments are outlined. ln the first section this involves conversion of grain sizes in millimetres to a logarithmetic unit, phi, which enables the phi mean, standard deviation and skewness to be determined by graphical procedures. The t test enables comparisons to be made on tills from different sections of the moraines. The till-fabric diagrams are subject to the Chi-square and t tests to determine the degree of isotropicity of both orientation and dip of the 'a' axes and to evaluate the relation between the mean fabric orientation and the ice movement, the dip of the fabric and the slope angle. Finally, the spacing of the moraines is analyzed by regression analysis, and correlation coefficients for the number of moraines per unit distance to other factors are calculated. The cross-valley moraines are formed of a coarse, unsorted, sandy till. The change that certain parameters, notably skewness of grain size frequency distribution, roundness and sphericity show with elevation probably reflects the pre-last glacial distribution of river gravels and weathered materials. Two sections in which sand and grave! are separated by till deposits indicate at least a major fluctuation of the ice cap. The central kames are formed of bedded and sorted sand and grave! and in one locality overlie till of a cross valley moraine and are thus younger. Till fabrics were taken from proximal. distal and lateral slopes. Fabrics from proximal slopes show strong orientation at right angles to ridge crests and a predominant upglacier dip component. Distal fabrics, on the contrary, have no preferred dip direction, but the mean orientation is still at right angles to the crest. The fabrics from lateral ridges , on the other hand, have a mean orientation that is also at right angles to the crest and therefore bears no relation to the direction of ice movement. An analysis of the spacing of the cross-valley moraines indicates strong positive correlations between distance from the watershed and effective stress at the base of a glacier ending in a glacial lake ; correlation coefficients are as high as r = 0.90. On the basis of these results the various possible origins of the cross valley moraines are examined. A basic premise for each thesis is the association of former glacial-lake basins with the cross-valley moraines. It is concluded that three of the five hypotheses are not applicable, whereas the fourth , that they are formed by shear moraines in a shallow-water locality, cannot apply to the Rimrock and Isortoq valleys, where proglacial lakes attained depths of 400 to 700 feet . I t is further concluded that the moraines are formed by the flow of saturated till into a system of basal crevasses when a critical hydraulic condition is reached. This conclusion is supported by the till fabrics, the relation of the effective stress at the glacier base to the spacing of the moraines and the location and structure of the central kames. The similarity between the De Geer moraines, certain washboard moraines and the cross-valley moraines is pointed out.

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