A 1:100,000-SCALE MAP OF SURFICIAL DEPOSITS IN GLACIER BAY NATIONAL PARK AND PRESERVE, SOUTHEAST ALASKA

In 1794, when Captain George Vancouver arrived off the shores of what is now Glacier Bay National Park and Preserve, he described much of it as being filled with “compact and solid mountains of ice, rising perpendicularly from the water’s edge.” At that time, all of what is now “the bay” of Glacier Bay was occupied by a >3000 km³ ice field. Over the following 100-170 years, this ice mass thinned into numerous valley glaciers. Water-based ice in the main bay and Muir Inlet retreated 100 km northward, creating a world-class “natural laboratory” for the study of deglaciation and plant and animal succession. This rapid and well-documented retreat, combined with Glacier Bay’s relative accessibility, attracted many scientists and landmark studies were conducted on glacial processes and the return of terrestrial and marine life to deglaciated environments.

Despite this legacy of research, previously published surficial geology maps only covered approximately 3% of Glacier Bay’s area. We have rectified this problem by compiling a 1:100,000-scale surficial geology map of Glacier Bay National Park and Preserve, and some adjacent areas, from the previously published maps, aerial photography, and personal observations. The map covers 15,932 km² with 3624 different “polygons” belonging to 21 map units. This area is larger than the state of Connecticut. The map units were classified in terms of age (Pleistocene, Holocene, or currently active) and how they were deposited (i.e., by streams, glaciers, wind, etc.). Where there was some knowledge of underlying sediments, this information was captured as well. We required mappable deposits to be >2 m thick and >30,000 m² in area; they were drawn primarily by using the 1948 set of aerial photographs as a guide, but other photo sets were also consulted. We used all previous mapping available to us. Our mapping efforts were concentrated on the lowlands, as these deposits are most abundant, complex, and relevant to visitors and management. By our mapping definitions, 16% of the total map area (2475 km²) is sediment covered. Of this percentage, 27% is Holocene till, 26% is Holocene outwash, and 13% is currently active fluvial sediment; these are the three most common map units.