Glacial chronology of the Sierra Nevada, California, from the Last Glacial Maximum to the Holocene

During the Last Glacial Maximum the Sierra Nevada in California, USA, supported a mountain glacier/ice cap complex that covered over 20,000 km2. The history of this ice cover can be reconstructed using 14C and cosmogenic-nuclide surface-exposure dating. These show that the glaciers reached their maximum extent for the last glacial cycle between 21 and 18 ka, i.e., during the global Last Glacial Maximum. This is termed the Tioga 3 advance. A slow retreat began at 18 ka and accelerated rapidly at about 17 ka. After retreating an unknown distance, the glaciers began to readvance at about 16.7 ka, reaching the Tioga 4 limit at 16.2 ka. They then rapidly retreated to the crest of the range, probably within 500 to 1000 years. There is no indication of subsequent glacial expansion until the Recess Peak advance between 14.0 and 12.5 ka. Unfortunately, chronological control is not adequate to determine whether this advance was during the early Younger Dryas or slightly preceded it. The equilibrium-line-altitude reduction during the Tioga 3 was about 1200 m, that during the Tioga 4 about 800 m, and during the Recess Peak 100 to 200 m. The Tioga 4 advance coincided with the expansion of nearby pluvial Lake Lahontan to its maximum size. The Sierra Nevada advances correlate well with the glacial chronology of the Alps during the same period, and also with the episodes of melting and advance of the European and Laurentide Ice Sheets. Times of glacial advance in the Sierra Nevada may be connected to the melting history of the ice sheets, and to Heinrich events, by expansion and contraction of sea ice in the southern North Atlantic.