Variations in annual growth rings can be utilized to assign precise calendar dates to the study of Quaternary geologic or geomorphic events such as earthquakes, mass movements, glaciations and flooding. Living trees may provide the necessary absolute dates of events or minimum ages for surfaces. Crossdating among living trees and with subfossil wood can identify missing rings and extend tree-ring chronologies further back in time. These methods can lead to the accurate dating of tree rings in both living and dead trees that may have been affected by a geomorphic process. The dating of partial to complete ring growth, compression and release, as well as dating externally apparent responses, such as tree scarring or root sprouting, can often lead to the identification of the season and the year an event occurred. Ring-width patterns when compared with control chronologies can reveal the growth anomalies in witness trees that may be related to geomorphic events.Examples of the application of tree rings to Quaternary geology and geomorphology are varied and numerous. Root shearing, topping of trees, and missing rings tie a rupture along the San Andreas fault to the year 1812 A.D. Narrow tree rings linked to defoliation and tephra fallout differentiated distinct eruptions of Mt. St. Helens in 1480 and in 1482 A.D. Ring analysis has helped unravel glacial chronologies, and tree-ring linkages with climate have also verified that late Holocene ice advances in Argentina correlated with intervals of cool, wet summers. In another application, an 1818 A.D. Quebec landslide has been tied to the growing season, whereas slides dated to 1834 and 1846 A.D. occurred during the spring.
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