Enormous glacier icefields have advanced and retreated from the Glacier Bay fjord many times in the last 20,000 years. These trees were alive and growing in the McBride Inlet area perhaps 2000 years ago. While still alive, they were covered by gravel and buried beneath advancing ice. In the last 100 years, the retreating glacier and erosion have exposed them to air and weathering which causes them to slowly decay. Scientists specially authorized to collect the wood of these ancient 'interglacial trees' use tree ring analysis and radio carbon dating to help reconstruct the sequences of glacier advance and retreat in Glacier Bay. Photographer: Elizabeth Flory