Roy-Leveillee_2017_Incipient ponds_NWTgeoscience forum.pdf (2.09 MB)
Evolution of incipient lowland thermokarst features in the Blackstone River Valley, Yukon
Roy-Leveillee, P (2017) Evolution of incipient lowland thermokarst features in the Blackstone River Valley, Yukon. In 45th Annual Yellowknife Geoscience Forum Abstracts; Northwest Territories Geological Survey, Yellowknife, NT., Compiled by Irwin, D., Gervais, S.D., and Terlaky, V. YKGSF Abstracts Volume 2017.
Abstract:
Widespread thermokarst initiation and the
acceleration of thermokarst development in
permafrost peatlands can result in ecological
change, threaten the cultural integrity of
northern indigenous people, change rates of
carbon storage and release at high latitudes,
and affect the geomorphology of Arctic and
subarctic landscapes. Despite the
multilayered significance of intensified
thermokarst activity the processes
controlling the early stages of thermokarst
development and the factors differentiating
features that will stabilize from those that
will continue to expand are still poorly
understood. Here we present preliminary
observations of conditions associated with
the stabilization or expansion of incipient
thermokarst ponds in the Blackstone River
valley, central Yukon. In this large valley
located near the limit between continuous
and discontinuous permafrost, the alluvial
deposits of the river bed are surrounded with
extensive moraines and outwash deposits.
The vegetation cover is dominated by
tundra, and ice wedge polygon networks are
extensive. Signs of ice wedge degradation
are widespread in several parts of the valley.
However, comparison of recent remotely
sensed imagery with historical aerial
photographs indicates that several
degradation features have been stable for at
least 20 years, while others have expanded
rapidly. This stabilization is associated with
vegetation growth in the thaw features,
causing partial terrestrialization of incipient
ponds and cooling of the ground beneath.
Mean annual temperatures near the ground
surface beneath small ponds with dense
Carex spp. or aquatic mosses ranged from -
1.5 to -2.7°C, whereas such temperatures
ranged from 0.3 to 2.9°C beneath similarly
shallow but unvegetated or sparsely
vegetated water in expanding ponds.
Expanding ponds exhibiting signs of
aggressive shore erosion were often
connected to thermo-erosion gullies, which
visibly contributed to destabilising the shore
bank. Such association with thermo-erosion
gullies also enabled rapid degradation along
some banks of seasonal ponds, preventing
the stabilization that could result from
prolonged loss of contact between the bank
foot and water every summer.