Inactive and relict rock glaciers of the Deboullie Lakes Ecological Reserve, northern Maine, USA

Lobate talus slopes in the Deboullie Lakes Ecological Reserve (DLER) of northern Maine exhibit parabolic profiles characteristic of inactive and relict talus-derived rock glaciers. Vegetated rock glacier surfaces suggest that the landforms are no longer active, and lobes comprising two DLER rock glaciers document periods of past growth. Observations of perennial subsurface ice are supported by datalogger temperature measurements, indicating that sporadic permafrost exists throughout the DLER. We compare the DLER rock glaciers, along with similar features elsewhere in New England and adjacent Quebec, to the modern alpine permafrost distribution. Results indicate that a mean annual temperature cooling of ! 68C is required to promote active rock glacier growth. Ages of plant remains recovered from the basal sediments of a local pond constrain deglaciation to before 11 320 14 C a BP, and core stratigraphy and organic content reveal that a periglacial environment persisted during the early postglacial era. Thus, we hypothesise that the DLER rock glaciers were active during Lateglacial time despite the lack of glacier activity in the region. We take this to suggest that north-eastern US rock glaciers formed in response to mean annual temperatures skewed towards the frigid winters of the Younger Dryas chronozone. Copyright # 2009 John Wiley & Sons, Ltd.