| dc.description.abstract | The study examines the nature and distribution of periglacial
lobes, terraces, gliding boulders, rockfalls and avalanches in
granite and metaroorphic terrains in 8, part of the South-East
Grampian Mountains of Scotland. Areal variations in the
weathering of granite boulders were also investigated.
Massive granite boulder lobes are extensively developed
upon slopes in the Lochnagar and Mount Keen granite areas.
The values of 14 parameters, established to describe the main
elements of a lobe, were measured on 300 granite lobes. Various
techniques were used to analyse the resultant dato,. Granite
lobes are rare upon north-facing slopes, and absent from
ground believed to have been covered by Loch Lomond age
glaciers. It is concluded that these lobes are fossil features
formed during the severe conditions of the Loch Lomond Stadial.
Detailed sampling of 50 metamorphic lobes revealed that they
are smaller features, largely restricted to the upper slopes
of quartzite hills. Terraces are rare in both types of terrain.
Gliding boulders are common in the granite and metamorphic
areas. The values of 15 parameters were measured on 200
metamorphic and 150 granite gliding boulders. The resultant
data were analysed and compared. Individual boulder movements
of up to 2cm/year were recorded between 1971 and 1975.
Dendrochronological investigations of calluna and vaccinium
plants growing in four furrows suggested that gliding boulder
movements have decreased in the last 7 or 8 years.
Rockfalls are frequently released from the backwalls of
the three Lochnagar corries, contributing to the extensive
postglacial screes. Nine rockfalls were observed between
13 June and 1 August 1972. The largest fall involved almost
4 tonnes of granite boulders. Avalanches are common on snow
accumulation slopes. Their erosional activity is restricted,
but they are efficient transporting agents.
Four techniques were used to investigate possible differences
in the extent of weathering of granite boulders in sites 'inside'
and 'outside' the mapped limits of four presumed Loch Lomond age
corrie glaciers. The tests assessed the amount of edge and corner
rounding of the blocks, and also the degree of surface and
subsurface granular disintegration. All tests indicated that
boulders 'inside' the presumed limits are marginally but
consistently less 'weathered' than those in 'outside' sites,
independently supporting the view that corrie glaciers
occupied these sites. | en |
