Schmidt-hammer exposure-age dating (SHD) of coarse rockfall debris, Mountains of Mourne, Northern Ireland: Inferences regarding deglaciation and the paraglacial response of the rock walls

Schmidt-hammer exposure-age dating was conducted on granite boulders from 23 accumulations of coarse rockfall debris, situated between 270 m and 560 m above sea level, in the Mountains of Mourne, Northern Ireland. Each site was close to the distal margin of the debris where large boulders were abundant. The results indicate that at 15 sites the debris accumulated between ~20–17 ka, at seven sites between ~17–14.3 ka, and around ~13–12 ka for one site. It is inferred that these data reflect the operation of paraglacial processes on rock slopes that were deglaciated by ~20–19 ka. These processes likely involved some combination of glacial debuttressing, oversteepening and structural-weakening of the slopes, along with glacio-isostatic rebound and seismic activity. The majority of the sites had started to fail within ~3 ka following deglaciation, other sites lagged deglaciation by ~4–7 ka. The results also indicate that the Mournes lost their glacier ice earlier than other mountain areas in Ireland and Britain adjacent to the Irish Sea. Because the sampled boulders represent small components of their respective accumulations, which are themselves likely to represent diachronous surfaces, future work could determine exposure-ages from mid-slope and proximal locations and provide whole-slope age profiles.