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T5
The Moffatdale RSF cluster, Southern Uplands: a paraglacial signal of concentrated
erosion of bedrock
D. Jarman 1 and D. Pearce 2
1 Mountain Landform Research
2 University of Worcester
Awareness of RSF in the Southern Uplands has been negligible. A dense RSF cluster is
identified around Moffatdale, on the south side of the 800 m-high Tweedsmuir Hills. With a
total area of 3.11 km 2 , this group of 14 RSFs affects 7-8% of the catchment. This is one of
the highest densities discovered in the British mountains. All RSF modes are represented,
in steeply-dipping, generally weak metasediments. Three extensive, rather diffuse, slope
deformations exceed 0.5 km 2 . The sites are generally beyond Younger Dryas limits and
are thus a paraglacial response to the LGM (including associated glaciofluvial meltwater
channel incisions). Sparse RSF across the rest of the Tweedsmuir Hills suggests that this
cluster is associated with the unusual profundity of Moffatdale, a glaciated valley which
has 650 m available relief, but is not a main fault trough. It implies that concentrated
erosion of bedrock (CEB) may have occurred during recent glacial cycles, thus raising
slope stresses above prevailing thresholds of stability, and provoking rebound breakouts.
Most glaciated troughs are thought to have adapted to ice discharge earlier in the
Pleistocene, with only low erosion rates latterly. Recent CEB by glacier ice might here be
due to late-onset cirque and side-trough development in an easterly location, or to
breaching of the regional divide, perhaps as icesheds and dispersal routes fluctuate,
including by icestream piracy. However, incision of Moffatdale is also part of the very longterm
re-equilibration of an asymmetry created by the opening of the Solway Basin,
reflected in higher RSF incidence on the south side of the Southern Uplands divide.
Keywords: Rock Slope Failure; Scotland,