Abstract Glaciers are a significant natural resource in Alaska and the Western United States, covering respective areas of ~74,600 and 688 km 2 ( Dyurgerov, 2002 ; Fountain et al., 2007 ). A large percentage of these glaciers exist within the boundaries of lands managed by the U.S. federal government. For example, glaciers in Wrangell-St. Elias National Park and Preserve and Denali National Park and Preserve in Alaska cover a total area of ~20,000 km 2 ( Adema, 2004 ). In contrast to geologic processes that operate on time scales on the order of thousands or even millions of years, significant glacier change can occur within a human lifetime. The dynamic nature of glaciers strongly influences the hydrologic, geologic, and ecological systems in the environments in which they exist. Additionally, the sensitive and dynamic response to changes in temperature and precipitation make glaciers excellent indicators of regional and global climate change ( Riedel and Burrows, 2005 ). Long-term monitoring of glacier change is important because it provides basic data for understanding and assessing past, current, and possible future conditions of the local, regional, and global environment. A basic understanding of local and regional environmental systems is critical for responsible land management and decision-making.

G. K. Gilbert, as a member of the Harriman Alaska Expedition of 1899, studied and described nearly 40 glaciers, many of which reached the sea and produced icebergs. Gilbert’s maps and photographs from marked locations are still being used to record glacier fluctuations, as at Columbia Glacier. Noting that some termini were stable or advancing but that others were retreating rapidly, he suggested that a general change in climate, perhaps related to a change in ocean temperature, might cause such local differences in behavior. This conclusion was remarkably prescient, but it is now known that terminus stability is also involved. Gilbert’s discussions of the processes of glacier flow adjustment to an uneven bed, glacial erosion (including erosion below sea level), and variations in the rate of iceberg calving are remarkably modern and relate to one of the most important problems in glaciology today—the role of a water layer in coupling a glacier to its bed.