Permafrost

located less than 500m a.s.l. in limestone areas with glacial morphology. Many springs have
survived at least through the last glaciation. However, the size of these icing deposits was
similar to those found recently by identifying ASTER (Advanced Spaceborne Thermal
Emission and Reflection Radiometer) shortwave infrared (SWIR) data.
Key words: Historical variability, icing, china
148
Permafrost Condition After Tundra Fire in Seward Peninsula, Alaska
Koichiro HARADA 1 , Yuki SAWADA 2 , Larry D. HINTZMAN 3 and Masami FUKUDA 2
(1. Miyagi University, Sendai JAPAN; 2. Institute of Low Temperature Science, Hokkaido University, Sapporo
JAPAN; 3. University of Alaska Fairbanks, Alaska USA)
Abstract: Thermal, water and electrical conditions of permafrost after the tundra fire were
observed in Seward Peninsula, southwest Alaska, in order to evaluate the effect of fire on
permafrost conditions. Field observations were made in 2005 and four sites were established
where the slope direction and surface disturbance condition are different; south- or north-facing,
and burned or unburned. At each site ground temperature and water content were measured by
pit survey, and the seasonal thawed depth measurements were also conducted by using the steel
rod from the ground surface. Transient electromagnetic surveys were carried out along profiles
with the length of 140-180m to compare the permafrost condition using a transmitter loop of 60
x 60m.
The temperatures of 20-40cm deep at the burned sites were 4-5 ºC higher than that at the
unburned sites. The soil water contents at the burned sites showed the high condition. The
measured thawed depths are significantly different between the burned and unburned sites,
which were more than 20cm deeper in the burned sites than that in the unburned sites.
The obtained apparent resistivity curves and estimated resistivity models showed that a
significant difference was observed between south- and north-facing slopes. At the north-facing
sites, high resistivity layers were estimated near the ground surface with the thickness of
20-26m, which represents permafrost. The permafrost base could not be detected at the
south-facing sites by the transient electromagnetic surveys because the permafrost base may be
located in bedrock. There is no significant difference of the curves and models between burned
and unburned sites. However, only at the burned south-facing site, stable data could be obtained
by using the standard central induction configuration, which means that this site has a relative
low resistivity condition near the ground surface. Thus, the burned south-facing site may have a
different permafrost condition near the surface.
Key words: Tundra fire, resistivity, Alaska