HEAT FLOW AND GEOTHERMAL RESOURCES OF THE ALASKAN INTERIOR
WILLIAMS, Colin F.1, GALANIS, S. Peter1, GRUBB, Frederick V.2, and SASS, John H.3, (1) US Geological Survey, Mail Stop 977, 345 Middlefield Road, Menlo Park, CA 94025, [email protected], (2) US Geol Survey, Sacramento, CA 95819, (3) US Geological Survey, Flagstaff, AZ 86001
As part of a project to compile a new national geothermal resource
assessment, we have collected and analyzed new and previously unpublished
temperature and thermal conductivity measurements to determine conductive heat
flow at 11 sites in the Alaskan interior from the Brooks Range in the north to
Cook Inlet in the south. The heat flow values range from 42 to 130 mW m-2
with a mean of 88 mW m-2. Heat
flow at four of the sites exceeds 100 mW m-2.
The high heat flow values at two of these four sites most likely reflect the
effects of magmatic heating from the nearby Wrangell Mountains and Prindle
volcanic areas. Thermal conditions at the other two sites may be due to the
combined effects of erosion and rapid near-surface ground-water flow. Although
the limited spatial coverage of measurements leaves significant uncertainties in
some areas, such as southwestern Alaska, we can draw some preliminary
conclusions about the thermal regime
of central Alaska and the degree to which
crustal heat flow influences the formation of hydrothermal systems.
Geothermal manifestations in central Alaska are dominated by the belt of
thermal springs that extends along an east-west trend from the Canadian border
to the Seward peninsula. Heat flow measurements at five sites cover the portion
of this trend from Fort Yukon in the east to the base of the Seward peninsula in
the west and average 77±7 mW m-2.
Limited temperature gradient data from the Seward peninsula itself are
consistent with a higher background heat flow. The 77 mW m-2
average is elevated relative to average continental heat flow, and simple
thermal models indicate that it is favorable for the formation of low to
moderate temperature (up to 150 oC)
hydrothermal systems from the deep circulation of water along fault
zones or
within permeable strata. Geothermometer estimates of temperatures for geothermal
reservoirs located in the same area are consistent with this result, and such
systems are capable of supporting local geothermal direct use and electric power
generation from binary power plants. Large, high temperature hydrothermal
systems are unlikely to be found outside of areas of Quaternary magmatic
activity, but comparisons with other thermally active regions indicate that the
identified thermal springs and manifestations in central Alaska are only a
fraction of the number likely to be found with more extensive exploration.