Evolutionary Geomorphology of Australia: A Reply

Abstract

First I should stress that my paper was first presented in England at a symposium on longterm landscape evolution, and delivered to an audience that had a very short time-scale in mind, as seen by an Australian. I was not trying to preach to the converted. The typical British view is indicated by the recent book on Timescales in geomorphology (Cullingford et al., 1980) which deals with short time-scales (c. 101 to 102 years); medium time-scales (c. 103 to 104 years); and long time-scales (104 to 105 and above). Of the five papers in the last section only one related to a time-scale greater than 105 years. My paper is concerned with time-scales of 106 to 108 years, and I would think it surprising if some new ideas were not needed to cope with this extra-long time-scale. I quite agree that other Australian workers have been well aware of the long time-scale of Australian geomorphology, including Hills, Carey, Twidale and Young. Lester King used it on a world scale in his Morphology of the earth (1962). My contribution is just one more attempt to get these ideas considered in the northern hemisphere. I reviewed various paradigms of geomorphology not to assess them in some absolute way, but to see how they suited geomorphology on the very long time-scale appropriate to Australian geomorphology, and concluded that new ideas are involved for which evolutionary geomorphology might be an appropriate term. The chasmic faults that separate fragmented continents, and the sutures that mark collisions are not accounted for in other geomorphic models, but are relevant in Australia and Papua-New Guinea. The idea may be seen as an extension of the Schumm and Lichty (1965) notion of appropriate time-scales: on short timescales steady state ideas may be appropriate; a longer time-scale may be suitable for dynamic equilibrium or cyclic time; and the longest geomorphic time-scale may be considered as that of evolutionary geomorphology. I apologise for not having more references to Twidale (a fault he has thoroughly rectified) but it is easy to overlook references, as shown by the recent review of bornhardts in which Twidale (1980) forgot to refer to my paper on inselbergs of Uganda (Ollier, 1960).