Geology Reference
In-Depth Information
Convex upper
slope unit
Free
face
Angular
changes of slope
Straight middle
slope unit
Concave lower
slope unit
Smooth
changes of slope
Gradient increases
downslope
Gradient
constant
Gradient decreases
downslope
Distance,
x
Figure 7.1
Three form elements of slopes.
Figure 7.2
Abrupt and smooth transitions between slope
elements.
Anthony Young (1971) defined them as follows: a
slope
unit
is either a segment or an element, whereas a
segment
is a portion of a slope profile on which the angle remains
roughly the same, and an
element
is a portion of a slope
profile on which the curvature remains roughly the same.
Convex, straight, and concave hillslope units form
a
geomorphic catena
, which is a sequence of linked
slope units (cf. Speight 1974; Scheidegger 1986). Several
schemes devised to describe hillslope profiles recognize
these three basic units, although subunits are also distin-
guished (Figure 7.3). One scheme recognizes four slope
units: the waxing slope, also called the convex slope or
upper wash slope; the free face, also called the gravity or
derivation slope; the constant slope, also called the talus
or debris slope where scree is present; and the waning
slope, also called the pediment, valley-floor basement,
Plate 7.1
Concavo-convex slope on the chalk ridge, Isle of Purbeck, Dorset, England. The ruins of Corfe Castle lie in the
middle ground.
(
Photograph by Tony Waltham Geophotos
)
