Lake-Level Fluctuations in the Western Great Basin during the Medieval Climate Anomaly: Episodes of Both Drier and Wetter Periods Than Modern

The Medieval Climate Anomaly (MCA) is characterized as a period during which several severe and sustained droughts occurred in the Great Basin from about 900-1350 AD, an interpretation primarily based on tree rings, pollen, and various lake-level proxies from cores and shoreline studies. Although not as temporally precise as tree ring studies, lake-level histories help discern the severity of droughts as well as the magnitude of wet periods.

This presentation focuses on the lake-level histories of Walker Lake, the Carson Sink, and Pyramid Lake through the MCA. Despite differences in hydrology, hypsometry, and the effects of thresholds, there are commonalities in the records. Walker Lake was low at 950 AD (<1205m), 1150 AD (<1224m), and at 1650 AD (<1215m). The first and last of these low periods, however, are associated with evidence for diversion of the Walker River into the Carson Sink. Walker Lake also reached relative highstands at about 1030 AD (~1245m) and 1290 AD (~1255m). A large lake in the normally dry Carson Sink formed around 1100 AD, reaching a surface area of about 3000 km² and volume of about 47 km³. The timing of this lake was coincident with falling or low lake levels at Walker, possibly because of river diversion.

At Pyramid Lake, levels were below 1174m around 950 AD and again at 1300 AD, but reached near the historic highstand level (~1181m) in the intervening time around 1100 AD. The relatively low amplitude of lake-level fluctuations at Pyramid through the MCA may be explained by a low threshold (~1177m) that exports water to Winnemucca Lake.

These interpreted lake-level fluctuations are correlative with hydrologic records interpreted from tree rings and pollen and show regional and dramatic responses to short-lived climate changes during the MCA, both drier and wetter than present.