8 Climatic Hypotheses of Alluvial-fan
Evolution in Death Valley Are Not
Testable
Ronald I. Dorn
Department of Geography, Arizona State University
ABSTRACT
For the last two decades, climatically based interpretations have been the major focus in
evolutionary studies of dryland alluvial fans. Climatic hypotheses to explain the
development of alluvial fans in southern Death Valley, however, do not fare well when
they are assessed with criteria used by philosophers of science. First and foremost, dating
techniques do not have the chronometric precision or accuracy to correlate Pleistocene fan
aggradation (or hiatuses in deposition) to Pleistocene climatic changes. Second, there is
only one clear correlation of fan aggradation and a climatic interval: in the hyperarid
Holocene in Death Valley. A single temporal correlation, no matter how many data points
go into it, does not comprise abundant support for a climatic hypothesis. Third, climatic
hypotheses are difficult to separate from nonclimatic explanations of Death Valley fan
evolution. Fourth, it, is very difficult to successfully predict or model Death Valley fan
behavior from climatic hypotheses. Lastly, it is not possible to falsify the competing
hypothesis that aggradation on Death Valley alluvial fans is entirely from high-magnitude
meteorological storms that are not necessarily tied to any climatic regime. This analysis
indicates that climatic hypotheses are not testable for Pleistocene-age fans in Death
Valley, and perhaps for alluvial fans in other drylands.
INTRODUCTION
Dryland alluvial fans have been viewed through the spectacles of a variety of geomorphic
paradigms (Table 8.1). In the last two decades, however, the dominant perspective has
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The Scientific Nature of Geomorphology: Proceedings of the 27th Binghamton Symposium in Geomorphology held 27-29
September 1996. Edited by Bruce L. Rhoads and Colin E. Thorn. 1996 John Wiley & Sons Ltd.