During this time, many glaciers in Alaska, including those which flow from the Juneau Icefield, fluctuated with the climate, advanced, and again retreated after reaching their glacial maximum in the mid 1700s. In Southeast Alaska, maritime climate and coastal mountains work together to create favorable conditions for glaciation. Moist air rushes toward the mountains, rises, cools, and releases snow and rain. Annual snowfall on the Juneau Icefield exceeds 100 feet, and mild Southeast summers assure that snow accumulation exceeds snow melt at higher elevations. As the snow continues to accumulate, its own weight compacts snow layers from previous years into solid ice, causing changes in volume, density and crystal structure.
Glacial ice absorbs all colors of the visible light spectrum except blue, which it transmits.
Scientists estimate the icefield's snow and ice depth to be from 800 to over 4,500 feet deep. As snow and ice continue to accumulate, gravity eventually pulls the ice mass into motion. Terrain determines the flow and boundaries of an icefield . Icefields form when numerous tongues of ice known as valley glaciers interconnect around peaks called nunataks which push through the ice. Devil's Paw, the icefield's highest peak, stands at 8,584 feet.