ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

different.decades show that hydrologic recovery lags significantly
behind erosion during landscape restoration. Whereas
soil detachment rates approached those of the forest
(control) area outside the basin within the first decade after
replanting, runoff generation decreased very gradually
over time. Thus, contemporary land-use alone provides insufficient
information for extrapolating runoff rates in this
historically disturbed basin.
The Ecuadorian case demonstrates that abandonment of
formerly cultivated lands significantly accelerates both
rainfall runoff generation and soil detachment. Revegetation
of abandoned lands in Andean Ecuador is hindered
by degraded soil, drought, and/or informal grazing.
Although the condition of abandoned lands (and lands in
unmanaged fallow) varies considerably, the tendency is for
abandoned lands to have high runoff coefficients and high
soil erosion rates. Analysis of soil carbon also indicates significant
organic matter depletion on these lands. Because
abandoned lands can play such an important role in surface
runoff generation, runoff conveyance and soil erosion,
efforts to extrapolate hydrologic properties and erosion rates
need to differentiate between active and inactive croplands
and to investigate the actual hydrologic conditions
of abandoned lands. Identification of abandoned lands as
erosional «hot spots» challenges watershed managers to
develop new management options for otherwise unmanaged
lands. The Ecuadorian case also demonstrates that
roads and footpaths in the Ecuadorian Andes play a hydrologic
and erosional role far out of proportion to the
area they occupy in the landscape.
CHARLES HARRIS 1 & ANTONI G.oLEWKOWICZ 2
Active-layer detachment slides on Ellesmere Island,
NWT Canada: movement mechanisms,
stability thresholds and environmental controls
1Department of Earth Sciences, University of Cardiff, p.o. box 914,
Cardiff CFl 3YE, UK
2 Department of Geography, University of Ottawa, p.o. box 450 Stn A,
Ottawa, Ontario, KIN 6N5, Canada
Active-layer detachment slides are shallow translational
slope failures triggered by late-summer melting of ice-rich
soil near the base of the active layer, immediately above the
permafrost table. Such slides, developed in low to medium
plasticity clays and silts, are widespread in the Fosheim Peninsula,
Ellesmere Island, where permafrost is continuous,
the active layer ranges up to approximately 0.75 m in
thickness, and summer temperatures are unusually high in
comparison with much of the Canadian high arctic.
Lewkowicz (1992) has shown that slope failures are triggered
by rapid late-summer thawing of the ice-rich basal zone,
and the last such event in the Fosheim Peninsula was in
August 1988 when many new failures were initiated. Two-
sided freezing of the active layer leads to the concentration
of segregation ice at its base, and cryodesiccation of its
middle and upper parts (Harris & Lewkowicz, 1993). Slope
failures involve translational sliding of the rigid active
layer over a thin basal shear zone in which thaw consolidation
leads to elevated porewater pressures. Surface seepage
was reported on flat plateau surfaces immediately prior to
the initiation of widespread slope failures in 1988, suggesting
high basal porewatare pressures.
Porewater pressures at the base of the active layer were recorded
in late July and early August 1995 on a detachment
slide at Hot Weather Creek and on a smooth slope at Big
Slide Creek. There was no morphological evidence for past
instability at the Big Slide Creek measurement site, but there
were a number of slides immediately to the south. It was
considered, therefore, that this location may allow assessment
of pre-failure conditions. Geotechnical testing provided
data on soil classification, and on shear strength and
consolidation parameters allowing slope stability analysis to
be undertaken in terms of effective stress conditions. Applying
the thaw consolidation theory to an infinite slope
model (McRoberts & Morgenstern, 1974), the thaw consolidation
ratio R and the thaw rate necessary to initiate failure
of these slopes were estimated. The significance of environmental
and site factors to the triggering of active-layer
landsliding is investigated by means of a sensitivity analysis,
and results are discussed in the context of meteorological
and ground thermal conditions during previous years.
STUART A. HARRIS 1, ZHIJIU CUI 2 & GUODONG CHENG 3
Nature and origin of a major congelifluction landform,
Kunlun Pass, Qinghai-Zizang Plateau,
People's Republic of China
1 Department of Geography, University of Calgary, Calgary,
Alberta, T2N IN4 Canada
2 Department of Geography, Peking University,
Beijing, China
3 Lanzhou Institute of Glaciology & Geocryology, Academia Sinica,
Lanzhou 73000, Gansu Province, China
The military road to Tibet follows the Jing-Xian valley as it
crosses the Kunlun Shan. On its west side, a major congelifluction
deposit is slowly moving away from the ridge crest
at 4800 m in a northerly and easterly direction. The material
consists of middle Pleistocene till deposits and the underlying
Pliocene alluvial gravels lying on the north slope
of the ridge crest. Lithologies of the clasts include granite,
granodiorite and pyroxenite of local origin. More than
10% of the material is composed of boulders longer than
2 m, with 45 % of the material having long axes between
0.5 and 2 m. The matrix is sandy loam and the diamicton is
poorly sorted.
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