Possible late Quaternary pingo remnants in central London

Abstract

Active pingos are ice-cored mounds formed within permafrost¹. Actual and suspected remnants of such features have been reported widely^1–7 from former periglacial and glacial areas of the British Isles (Fig. 1)^8–10. They are characteristically located in slope-foot situations with associated present-day springs or poor drainage^4–6. Most of the observed features lie between the latitudes of The Wash and River Thames and are generally thought to have originated as open-system pingos¹¹ in the late Devensian. No pre-Devensian pingos have hitherto been recognised. Here I suggest that many of the anomalous, drift-filled, closed depressions in the surface of the rockhead (usually the London Clay) beneath some of the central London terraces, recently reviewed by Berry¹², are the partly eroded remains of former open-system pingos, dating both from the Devensian and from earlier cold stages of the Pleistocene.