ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

T AREK M. SADEK, CHRIS J. GIPPEL, RODGER B. GRAYSON,
THOMAS A. Mc MAHON & Q.J. WANG
Landslides hazard modelling using Gis
and logistic multiple regression
Department of Civil and Environmental Engineering,
University of Melbourne, Parkville 3052, Victoria, Australia
Preliminary field investigations have revealed the existence
of many shallow landslides on steep forested areas in the
upper headwaters of Traralgon Creek catchment (176 km")
in Gippsland, Victoria. Multivariate statistical techniques
were applied to determine the probability of occurrence
(i.e. risk map) of landslides as a function of statistically significant
environmental variables. The Geographic Resources
Analysis Support System (Gis/Grass) was used to
derive 9 digital inputs for the logistic multiple regression
model. The independent topographic variables used in this
analysis were elevation, aspect (north-south and east-west
components) and slope maps, which were derived from a
digital elevation model of basin topography at high resolution
(25 x 25 m grid cells). Vegetation index and land use
maps were classified from multi-thematic Landsat satellite
imagery. The Landsat bands (bands 2, 3, 4 and 5) were initially
normalised to minimise the shading effects on vegetation
classification due to rugged steep terrain in the upper
areas of the catchment. A non-Lambertian based backwards
radiance correction transformation using Minnaert
constant was conducted for topographic normalisation of
the four Landsat TM spectral bands. Other independent
variables were geology (mainly dominated by sedimentary
and volcanic rocks) and proximity to roads and stream lines
maps.
Landslides in the catchment were identified from stereoscopic
coloured aerial photographs (scale 1:15,000) and
site visits for ground truthing. Locations of the landslides
(total number of active cells = 131) were determined,
mapped and imported to Grass digital database. The resulting
landslides map was used as the dependent variable
in the regression analysis. The developed logistic regression
model determined the probability of occurrence
of individual cells based on the values of input variables
at both active sites and a set of randomly selected inactive
cells. The result is a map of continuous probability values
that was discretized into five categories and overlaid
with active sites for comparison between observed landslides
and model predicted hazard sites. Reasonable
agreement between observations and predictions was observed.
The model revealed higher risk of landslides at
steep forested sites that were located close to road
networks and that had a low vegetation index. Most of
active shallow landslides were located on brown loams
and clays with dark and friable loamy shallow or moderately
deep topsoils.
RUDOLF SAILER & HANNS KERSCHNER
Three-dimensional reconstruction of Younger Dryas glacier
surfaces with a raster-based Gis
Institut fur Geographie, Universitat Innsbruck, .
Innrain 52, A-6020 Innsbruck, Austria
The Ferwall group is situated at the western margin of the
crystalline central Tyrolean Alps. In the central part of the
group, there are V-shaped, almost straight valleys (Schoenferwall
valley, Fasul valley) with simple topography. During
the Egesen Stadial (Younger Dryas), both valleys were
occupied by large valley glaciers, which deposited beautifully
developed end moraines at their confluence. The extent
of the largest Younger Dryas glaciers is well documented
by the end moraines and lateral moraines in both valleys.
In the Schoenferwall, at least two more morainic systems
of later phases of the Egesen Stadial are preserved.
Recent glaciers, the well documented 1850 (Little Ice Age)
glacier extent and the well developed Egesen moraines allow
the reconstruction of the maximum depression of the
Younger Dryas equilibrium line altitude (Ela) in that area
(ca. -350 m relative to 1850). The Ela depression correlates
well with other areas of the western part of the central
Alps. The morphology of the moraines (well preserved,
steep slopes, large amount of boulders) is also typical for
the Egesen Stadial. Therefore a correlation with the well
dated Egesen moraines at Julier pass in Switzerland (Ivy­
Ochs & alii 1996) is easily possible. From that point of
view, the moraines at the confluence of Schoenferwall and
Fasul valleys were deposited during the earlier part of the
Younger Dryas (ca. 12.000 cal. years B.P.), indicating the
glacier's response to the climatic collapse at the beginning
of the Younger Dryas.
The simple topography of the valley and the well defined
boundaries of the Schoenferwall glacier during the Younger
Dryas allow a detailed numeric calculation of its long
profile (Nye 1952). Considering the wide range of Geographic
Information System Tools available, we will try to
marry the complexity of the numerical reconstruction of
glacier surfaces with the possibilities of the raster-based
Gis module of Arc/Info.
The well defined spatial information on the former glacier
margins (lateral and end moraines) as well as the Digital
Elevation Model (Dem) are the basis of our Gis-based three-dimensional
reconstruction of the Egesen-Maximum of
Schoenferwall glacier. With Nye's mathematical model
and a Dem with a resolution of 25 meters a sufficient accuracy
can be obtained. According to our model the long
profile of a glacier can also be calculated if only a lateral
moraine were found in an V-shaped valley. Vice versa, if
there is an end moraine complex, it should be possible to
reconstruct a glacier's surface and its thickness with a high
degree of reliability.
Within the context of applied geomorphology, the final
aim of the Gis-based modelling of a glacier tongue is to
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