Glacially-transported boulders, or erratics serve as key indicators of subglacial and glacier marginal positions. These depositional features have been identified and mapped for centuries along the margins of both modern and ancient glaciers. Despite this, significant misunderstandings persist in the origins, interpretation and significance of erratics and similar glacially-transported boulders in the context of glacier dynamics and the reconstruction of glacial history. This study examines the meaning and significance of subglacially and supraglacially transported boulders, using specific field examples from the late Pleistocene glacial record in Ireland, as well as examples described in the global literature. This study provides a critical analysis of how glacially-transported boulders and their characterisitcs can be interpreted within the context of glacial systems and dynamics. The outcome of this analysis, informed by primary field evidence and the wider literature, shows that glacially-transported boulders have the potential to be misinterpreted in terms of (1) their detachment and transport processes, (2) their relationships to the interpretation of ice flow dynamics and direction, and (3) the timing of boulder deposition and their subsequent evolution in the landscape. These limitations must be carefully considered when utilizing glacially-transported boulders as evidence in both subglacial and supraglacial contexts. • Erratic boulders are commonly used evidence for sediment source and ice flow direction • Subglacially and supraglacially transported erratics are examined in this study, using examples from the late Pleistocene glacial record in Ireland • Subglacial erratics can be transported by multiple ice flows from different directions over a long time period • Supraglacial erratics can be confused with paraglacial rockfall that is independent of glacial transport
Jasper Knight (Sun,) studied this question.