ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

The movement of rock glaciers is influenced by a number
of natural factors. One of them is fluctuation of plastic
properties of frozen body caused by seasonal and longterm
fluctuations of air temperature. According to the results
of seasonal observations of the Gorodetsky rock glacier,
2/3 of annual displacement of the frontal scarp occur
in the period from July to October.
Most of investigated rock glaciers of the Northern Tien
Shan demonstrate average rate of surface movement about
0,5-2,5 m/yr. But sometimes under certain conditions, rapid
or ctastrophic movement may occur. Thus, the velocity
of the Burkutty rock glacier increased from 4,9 m/yr in
1969-1979 to 13-14 m/yr in 1979-1984 due to increasing of
angle of slope of the rock glacier bed from 13-15 to 35-38
so that the danger of a catastrophic landslide appeared.
As a result of study of distribution of rock glaciers, the
Map of rock glaciers of Central part of the Northern Tien
Shan at scale of 1:200 000 was compiled. The general regularities
of lower limits of rock glaciers and sporadic permafrost
belts as well as distribution of different types of rock
glaciers upon the river basins are shown on this map.
MANATSU TODA
Experimental study for the effects of particles on
bedrock channel erosion
Department of Geography, Rissho University, Osaki,
Shinagawa, 141 Tokyo, Japan
Though the particles such as sand, gravel or boulder seem
to be important roll for bedrock channel erosion in a
mountain stream, it is difficult to research the effects of
those in the field. To understand the influence of sediments
on bedrock erosion by running water quantitatively,
a experimental approach is useful. A series of experiment
was conducted in a 250 ern long, 16 em wide and 16 em
deep steel flume located in the Institute of Geoscience at
University of Tsukuba. The flume fixed at a slope of 0.2
during all runs. It had the artificial rock floor section which
could be eroded by running water. This artificial rock
was the mixture of sand, cement and water. The strength
of this material could be controlled. During the experiment
the flow discharge was kept constant in 3.7 l/sec,
then the flow velocity and depth were 180 ern/sec and 1.3
em respectively. In other hand the strength of the artificial
rock, the concentration of the sediment discharge and particle
size were varied.
To know the influence of particle containing qualitatively,
the result of erosion by clear water compared with that by
water containing 0.2 mm sand. Following results were obtained.
Erosion by clear water excavated a lot of sallow pits
or grooves on the surface of the artificial rock and they developed
as the erosion continuing. On the other hand, water
containing sand made the surface of the artificial rock
smooth. In addition to this erosion feature, it affect the
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erosion rate. The erosion rate by water containing 0.2 mm
sand was higher one order than that by clear water. Water
with 1.3 mm sand showed similar result. The roll of the sediment
in the streams was to smooth the surface of the
rock and increase the erosion rate.
Under the constant condition of stream the erosion rate
depends on the strength of the artificial rock, which changed
from 0.3 kgf/cm to 20 kgf/cm', The low strength material
was eroded faster than high strength one, and the relationship
between the erosion rate and the strength of the
material was evident. No erosion was occurred by clear
water and by water containing 0.2 mm sand when the
strengths of artificial rock were greater than critical values.
The sediment supply was varied from 100 g/sec to 800
g/sec to know its effect to the erosion rate. At the small
concentration of transported load the erosion rate rose as
the concentration increased rapidly. However its rate of increase
got lower as the concentration increased and it reached
critical value the erosion rate did not increase.
In order to know the effect of particle size, the diameter of
sediments were varied from 0.2 mm to 6.3 mm of uniform
size. At the small particle size the erosion rate rose as the
particle size get larger. However it reaches critical value
the erosion rate does not increase. This trend looked like
that of sediment supply.
The above results cannot apply to the field phenomena directly,
though it seems to be the cue of dissolving the
problems how and what influence of the sediment on the
erosion.
EIJl TOKUNAGA
Fractal properties and measure of drainage networks
Faculty of Economics, Chuo University, 742-1 Higashinakano,
Hachioji, Tokyo 192-03, Japan
Institute of Earth Sciences, Physical Geography, Uppsala University,
Norbyvagen 18B, S-752 36 Uppsala, Sweden
Mathematical analyses of some self-similar trees with branching
numbers 2 and 3 reveal fractal properties of individual
streams, stream networks, and drainage basins which
relate with each other. The fractal dimension Dn of a whole
stream network coincides with that Db of the drainage
basin for any value of fractal dimension Ds of an individual
stream which is equal with 1 or larger than 1 and smaller
than 2. Then Dn=Db