The majority of the landslides recorded appeared to have
been caused by the effects of higher wet season groundwater
and perched water levels in soils and weathered rock masses
exposed in steep roadside cuts. Slope failures were often
observed to originate from the upper portions of cut slopes
where colluvium or the weaker, more weathered material,
predominates in the weathering profile. Ground movements
affecting the carriageway or outside edge of road from below
appeared to be associated with localise shallow failures in fill
slopes and construction spoil or more extensive areas of deeper
failure of the natural hillside, in some instances associated with
river scour. It should be noted that ground movements taking
place on slopes below the road are often less easily identified
than those above, and some of these may therefore be missing
from the inventory.