THE POTENTIAL FOR LIDAR TO TEST AND DRAMATICALLY IMPROVE PUBLISHED MAPPING OF GLACIER EXTENTS IN THE PACIFIC NORTHWEST

Lidar data represents arguably one of the most dramatic technological advances in the past half-century for geomorphic mapping, particularly in regions with dense forest canopies. In the Pacific Northwest, Lidar’s ability to provide high-resolution digital bare-earth topography is particularly valuable for testing long-held concepts of glaciation, as well as providing valuable new constraints on ice extents and context for numerical dating of those events.

In one example, a dramatic late-glacial advance of glaciers proposed for Mt. Baker, northwest WA, (Kovanen and Easterbrook, 2001) appeared to conflict with evidence from elsewhere in the region that glaciers at that time were much smaller. Lidar data of the “moraines” used as a dominant line of evidence in the study demonstrate that they are either subglacial till flutes or erosional remnants, not ice-marginal moraines. The same lidar data show that late-glacial advances on Mt. Baker were much more restricted, consistent with the regional pattern. In a second example, lidar imagery in the lowlands west of Mt. Baker shows that ice-extent during the late-glacial Sumas advance of the Cordilleran Ice Sheet was significantly greater than previously appreciated; 14C dates associated with these newly identified terminal moraines also indicate that the maximum advance occurred significantly earlier than previously published, coincident with rather than postdating a major local sea-level high stand.

In a final example, sharply divergent fluted subglacial terrain in the northeast part of the Olympic Peninsula near Sequim indicates a previously unrecognized late-glacial ice margin and change in dominant flow direction. This change is likely related to collapse of the outer edge of the Juan de Fuca lobe during Vashon deglaciation. Because some of the flutes are cut by landslides and active faults, the timing of this change has implications for local geohazards as well as glacial geologic records.

These examples represent a small fraction of the thousands of locations that glacial (and other geomorphic) mapping and established concepts could be dramatically improved or completely reinterpreted based on the availability of high-resolution digital lidar topography. Lidar represents a sea-shift in our ability to interpret the geology of the Pacific Northwest; let’s get busy!