Geology Reference
In-Depth Information
Ice
Proglacial
drainage
Figure 5.19
Proglacial drainage systems in northern Eurasia during the last glaciation.
Source:
Adapted from Grosswald (1998)
Antecedent rivers
took place during the last glaciation across northern
Eurasia (Figure 5.19; cf. p. 272).
The Murray River was forced to go around the Cadell
Fault Block, which was uplifted in the Late Pleistocene
near Echuca, Victoria, Australia (Figure 5.20a). The
Diamantina River, north-west Queensland, Australia,
was diverted by Pleistocene uplift along the Selwyn
Upwarp (Figure 5.20b). Faults may also divert drainage
(see p. 144).
An
antecedent stream
develops on a land surface before
uplift by folding or faulting occurs. When uplift does
occur, the stream is able to cut down fast enough to hold
its existing course and carves out a gorge in a raised block
of land. The River Brahmaputra in the Himalaya is prob-
ably an antecedent river, but proving its antecedence is
difficult. The problem of proof applies to most suspected
cases of antecedent rivers.
Captured rivers
Superimposed rivers
Trellis drainage patterns, which are characteristic of
folded mountain belts, result from the
capture
of strike
streams by dip or anti-dip streams working headwards
and breaching ridges or ranges. Capture is often shown
by abrupt changes in stream course, or what are called
elbows of capture
.
Superimposed drainage
occurs when a drainage net-
work established on one geological formation cuts down
to, and is inherited by, a lower geological formation.
The superimposed pattern may be discordant with the
structure of the formation upon which it is impressed.
A prime example comes from the English Lake District
