LATE HOLOCENE GLACIAL STRATIGRAPHY OF COLUMBIA BAY ALASKA: EXTENDING THE RECORD

Columbia Glacier, one of the largest tidewater glaciers in the northern hemisphere, began a drastic retreat from its terminus in 1979 where it had remained for over a century. The glacier has thinned over 300 hundred meters and retreated 13 kilometers to its present calving margin. This drastic retreat has uncovered a previously buried mountain hemlock forest that was run over by advance of the glacier. Preliminary tree-ring dating of the outer ring of tree sections collected in the Summer 2003 from up-fjord sites within 1 km of the present calving margin reveal glacial advance dating to the early 11th Century A.D. with outer ring dates ranging from 1020 and 1025 A.D. Seventy subfossil samples from 8 sites in the fjord are currently being analyzed and should provide details to this advance history. Estimates of advance rates from these up-fjord sites are consistent with previous tree-ring estimated rates of about 40 meters per year. In addition to logs obtained from these sites, wood samples are being radiocarbon dated to understand the complex glacial stratigraphy composed of superimposed till layers discovered during the 2003 field season. This stratigraphy could reflect earlier advance/retreat cycles and extend the glacial history prior to the tree-ring dated advance and observed retreat of the past 1000 years.