CAUSES OF HIGH LAKES STANDS IN THE GREAT BASIN DURING THE “PLUVIAL ÉPOQUE” AT 18 KYR BP: PALEOCLIMATIC EVIDENCE

During the last glacial maximal stage in North America about 18 kyr BP, numerous large lakes existed in the Great Basin of the United States. Richard Foster Flint's classic explanation for the existence of these lakes is that the expansion of continental ice sheets in North America produced pluvial conditions in the Great Basin. By "pluvial conditions", Flint meant an increase in the ratio of precipitation to evaporation. His explanation has been adopted by many subsequent researchers, despite the fact that Flint provided alternative mechanisms for high stands of lakes in other regions during glacial stages.

Our analysis of existing studies from the Great Basin indicates that not all of the data are consistent with the idea that glacial stages in North America produced substantial increases in precipitation in the Great Basin. Furthermore, published modeling of climate patterns in the Great Basin during glacial times suggests that increases in precipitation occurred primarily in the winter, in association with snowfall, and not during the summer when they would have the greatest effect on lake levels. This suggests that hydrologic contributions to lake levels (groundwater discharge, river run-off, etc.) may have been more important than direct precipitation in raising the lake levels. The pollen data also provide a contradictory picture of paleohumidity.