Complex relationships between younger dryas glacial, periglacial and paraglacial landforms, Brecon Beacons, South Wales

The Brecon Beacons represent the most southerly area subject to marginal glaciation during the Younger Dryas/Loch Lomond Stadial in the British Isles and the interpretation of upland landforms in this area therefore has particular palaeo-environmental significance. This study reports geomorphological evidence within two trough-heads in the central Brecon Beacons previously thought to reflect Younger Dryas glaciation. A complex suite of landforms is identified at both sites, reflecting a range of environmental processes dating from throughout the Lateglacial period. Possible Younger Dryas terminal and recessional moraines are identified at each site, consisting of passively and actively transported debris, which have subsequently undergone considerable paraglacial modification. A number of other non-glacial landforms and sediments are identified, including a protalus/pronival rampart. The initial interpretations are tested using a glaciological approach of reconstructing former glacier dynamics, and suggests that some of the terminal moraines observed reflect mountain glaciation prior to the Younger Dryas, and may demonstrate final stages of retreat from the Last Glacial Maximum (LGM). A morphostratigraphic sequence for both sites is reconstructed, reflecting landscape evolution in a range of environments from final LGM deglaciation through to Holocene landscape stability. It is concluded that associations of such landforms may be common in marginal areas of former glaciation, and that interpretations of former niche/cirque glaciation should be supported by the reconstruction of probable mass-balance, glacier dynamics and palaeoclimatic implications to improve on geomorphological speculation.