IDENTIFYING LATE LITTLE ICE AGE TERMINAL POSITIONS ON MOUNT BAKER, WASHINGTON

Lichenometric dating techniques applied to four terminal moraines and two rock walls in the Easton and Boulder glacier forelands on Mount Baker, Washington were used to provide numeric ages for past ice-margin positions. The ages determined currently provide the only chronological information of past ice-margin positions between the tree-ring dates for the Little Ice Age maximum at, or prior to, ca. 1850 and historical records starting in the early 20th century. Previous studies indicate that over the last six decades the terminal positions of glaciers on Mount Baker have advanced and retreated in phase with El Nino/ La Nina-like 20 to 30-year warm and cool climate periods in the Pacific Northwest known as the Pacific Decadal Oscillation (PDO). However, correlations with older ice-margin positions are complicated by a lack of available data. This study indicates that lichenometric dating techniques can be used to identify past ice-margin positions from the late 19th and early 20th centuries, thus filling a gap in the glacier position record that is necessary for correlation with older PDO phases.