Abstract

Recumbent folds exposed in an ice cliff at the southeast side of the Barnes Ice Cap occur in banded ice and have hinges subparallel to the glacier margin. The folds appear similar in shape and attitude to others expressed on the glacier surface as a series of irregular lenses of white ice that are elongate parallel to the margin and are surrounded by blue ice. Such lenses are all around the margin of the south dome of the ice cap. Both sets of folds are thought to have a common origin.

Fold geometry and fabric studies suggest that the ice is behaving homogeneously on the scale of the folds and that the banding is essentially passive. Flow considerations indicate that banding or foliation will tend to become parallel to the particle paths near the glacier base and toward the margin under steady-state conditions. However, departures from the steady state in the form of minor advances or retreats may change the flow pattern sufficiently for the particle paths to depart from parallelism with the banding, which may then become passively deformed and eventually folded. For this to occur, the bedrock surface must be appropriately irregular. A simple mathematical model describes this process and successfully accounts for the geometrical features of the folds observed. This theory is consistent with earlier observations of the Barnes Ice Cap, which suggest that there have been fluctuations in the position of the ice-cap margin in the last few centuries.

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