Seminar announcement at AWI
Building A43 - lecture room at AWI

Clifford Voss
(US Geological Survey,  Menlo Park, CA, USA)

"Geophysical permafrost mapping and permafrost-hydrology interaction - US Geological Survey studies in Yukon Flats, Alaska"

All are welcome

Geophysical permafrost mapping and permafrost-hydrology interaction - US Geological Survey studies in Yukon Flats, Alaska

 Clifford I. Voss1, Jared D. Abraham1, Frederick D. Day-Lewis1, Steven M. Jepsen1, Jeffrey M. McKenzie2, Burke J. Minsley1, Jay Nolan3, Jennifer Rover1, Bruce D. Smith1, Michelle A. Walvoord1, Tristan P. Wellman1, and Bruce K. Wiley1

 1 US Geological Survey

2 McGill University

3 Rutgers University

US Geological Survey (USGS) and collaborators have, in recent years, undertaken a program in the Yukon Flats, Alaska, to characterize the current permafrost distribution and to evolve understanding of permafrost interactions with hydrology. This effort was motivated by the fact that changes in climate can cause permafrost to thaw in the region, resulting in major hydrologic and ecological changes. Several studies in this program are highlighted in this presentation.

(1) Both ground-based and aerial geophysical mapping provide a first-ever shallow to deep three-dimensional picture of discontinuous permafrost over large areas. The complex patterns observed and their interpretation may serve as a touchstone for cold-regions studies for some years to come.

(2) Electrical resistivities of the shallow subsurface in areas in the Yukon Flats not directly mapped by the aerial geophysics were estimated by a regression-tree analysis that correlated measured resistivity with Landsat indices, reflectance, and ancillary data. This allows proxy maps of shallow conditions (e.g. permafrost table depth) to be created where only remotely-sensed data, not geophysics, are available.

(3) A time-lapse remote-sensing study resulting in a map of shrinking and growing lakes indicates the widespread hydrologic changes that have occurred over the past 30 years.

(4) Hydrologic analysis of one shrinking lake's water budget shows how changes in permafrost depth and several other factors, such as a sub-lake talik, might have caused the observed changes in lake volume.

(5) Classical groundwater-flow modeling analysis, for the entire Yukon Flats basin, indicates how groundwater flow and groundwater discharge to surface-water bodies would change, should permafrost coverage decrease.

(6) Recently-developed software for groundwater-flow modeling with heat transport that includes the dynamic process of groundwater flow and ground ice interaction demonstrates the importance of groundwater flow in creating and changing the large-scale permafrost distribution, and illustrates how groundwater flow affects formation of taliks below lakes.

(7) Reverse geophysical modeling of the simulated permafrost-talik evolution, provided by the groundwater-ice models, shows how electrical resistivity would appear given different lithologies and permafrost configurations. This allows more confident inversion and interpretation of geophysical data.
Work at USGS is underway to combine the results of these field characterization and hydrologic analyses in order to understand the changing landscape of permafrost and hydrology. Hopes are that improved understanding can lead to more-effective management of water resources and ecosystems in permafrost areas, especially with regard to mitigation of possible climate-change impacts.