The Burtness Comb rock avalanche, English Lake District: a rare case of rock slope failure–glacier interaction

The alignment of the upper part of the Burtness Comb rock avalanche debris tongue, in the Lake District of northwest England, indicates that glacier ice played a role in its emplacement. The debris initially moved directly downslope but was deflected from this course on contact with the glacier and was channelled along its margin. Debris deposition on an oblique alignment across a 25–30° slope was ice-supported. With glacier wastage the debris settled, opening a sinuous longitudinal tension furrow. The lower, older part of the debris tongue, aligned along the comb floor, may also have an association with glacier ice and was likely sourced from a different area of the comb. Parts of both areas of the debris tongue are underlain by fine-grained materials attributed to glacial deposition. This is one of very few rock avalanche deposits in Great Britain for which a direct association with glacier ice can be demonstrated, a sparsity at odds with what might be expected.