Lucas, S.G., Morgan, G.S. and Zeigler, K.E., eds., 2005, New Mexico’s Ice Ages, New Mexico Museum of Natural History and Science Bulletin No. 28. 115 RIVER RESPONSES TO ICE AGE (QUATERNARY) CLIMATES IN NEW MEXICO FRANK J. PAZZAGLIA Department of Earth and Environmental Science, Lehigh University, 31 Williams, Bethlehem, PA 18015,
[email protected] Abstract–Rivers shape landscapes by responding to a range of external forces including climate and climate change. This paper examines the general role that Quaternary climates play in river channel form and process and how rivers in New Mexico have responded specifically to Pleistocene and Holocene climatic changes. The impact of Quaternary climates on New Mexican streams is cast in the context of how channel form and process has evolved through the Phanerozoic and in light of a large and growing data set for measurable changes in channel form and watershed hydrology over human time scales. Changes in channel form and process are commonly equivocal; there is no single unique response that follows from a given change in climate. Neverthe- less, geomorphologists have developed process-response models that limit the range of expected responses and help guide an interpretation of how Quaternary climates ultimately have shaped the New Mexican landscape. Long-term landscape evolution trends like the rate of valley incision and human-scale trends like the arroyo incision-aggradation cycle are discussed in the context of Quaternary climates. The general conclusion is that climate change through the Quaternary has had a major impact on pacing the rate of valley incision and defining the geomorphic thresholds that control arroyo incision, but that other factors, including tectonics and humans, also contribute.