Geology Reference
In-Depth Information
( ) Initial palaeoplain sloping down from the Tasman Divide
a
( ) Downwarp of palaeoplain to coast, forming the initial divide
b
( ) Formation and retreat of the Great Escarpment facing the coast
c
( ) Retreat of slopes from the coast and inland reduces the palaeoplain to isolated High Plains
d
(
e
Continued retreat of the escarpment of the inland slopes consumes the High Plains
and produces a sharp divide
Figure 15.14
Evolution of the south-east Australian drainage divides.
Source:
Adapted from Ollier (1995)
continental margin, the eruption of the huge Monaro
volcano, and the faulting of huge blocks in Miocene
times. The geomorphology is evolving, and there are no
signs of erosional cycles or steady states.
a suitable system descriptor (elevation or regolith thick-
ness for instance) is an immensely significant indicator of
stability behaviour in a geomorphic system. In landscape
evolution, convergence associates with downwasting and
a reduction of relief, whilst divergence relates to dis-
section and an increase of relief. More fundamentally,
convergence and divergence underpin developmental
'equilibrium' conceptual frameworks, with a monotonic
move to a unique endpoint (peneplain or other steady-
state landform), as well as evolutionary 'non-equilibrium'
frameworks that engender historical happenstance, mul-
tiple potential pathways and end-states, and unstable
states. The distinction between instability and new equi-
libria is critical to understanding the dynamics of actual
geomorphic systems, and for a given scale of observation
or investigation it separates two conditions. On the one
hand sits a new steady-state equilibrium governed by sta-
ble equilibrium dynamics that develops after a change in
Reconciling history and process
Jonathan D. Phillips (1999), after many years of research
into the behaviour of Earth surface systems, has offered
eleven principles that have immense relevance to geomor-
phology and may help to reconcile the split between the
process and historical aspects of the subject (Box 15.4).
His later work shows even more clearly the role of nonlin-
ear dynamics in unifying the two grand geomorphologi-
cal traditions. A starting point is his discussion of meth-
ods for detecting chaos in geomorphic systems (Phillips
2006). He argues that convergence versus divergence of
