ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

XIXI Lu & DAVID L. HIGGITT
Recent changes of sediment yield in the
Upper Yangtze, China
Department of Geography, University of Durham, Durham,
DR1 3LE, U.K.
Reservoir sedimentation is one of the many environmental
problems associated with the Three Gorges Project in China.
The rate and characteristics of sedimentation which directly
affect the operating life of the reservoir is closely related
to soil erosion and sediment transport dynamics in
the upstream catchment and to the ability to manage the
throughput of sediment-laden waters.Controls on recent
temporal changes in sediment yield is one issue of concern
to policy-makers engaged in the management of the sedimentation
problem.Temporal changes in sediment yield
have been examined using gauging data from stations in
the Upper Yangtze basin between 1956 and 1987.Whereas
many previous studies have concentrated on the trends in
the main channel of the Yangtze the distributed pattern of
temporal change across the whole catchment is complex.
Time series analysis indicates ten stations with increasing
trajectories of sediment yield and six with decreasing
trajectories. The relationship between observed changes
and patterns of runoff, land-use change and the construction
of water conservancy projects is analysed and the implications
of the changes discussed. It is suggested that human
activities of deforestation and the expansion of agricultural
land have had the most significant impact on sediment
yield but that the importance of fluctuating rainfall
and hence runoff cannot be excluded.
Y ANCHOU Lu, AI GUO LIU, GONGMIN YIN & JIE CHEN
Infrared stimulated luminescence (IRSL)
dating on river terraces
Institute of Geology, State Seismological Bureau, Beijing 100029, China
In this paper we describe our effort to determine the age
of some river terraces with infrared stimulated luminescence
(Irsl) method. Our Irsl measurements on the zero-age
samples collected from the surface of river terraces and alluvial
flats reveal that the majority of equivalent doses of
them are less than 1 Gy. This indicates river terraces can
be dated by Irsl dating of certain sediments on them. As an
example, three terraces in Gansu province were dated. Irsl
measurement on three samples collected from these terraces
has been. conducted. The age of them is 27±2 ka, 53±1
ka, and 10,5±0.9 ka respectively, which represent the age
of these river terraces. These data can be used to determine
rates and patterns of local neotectonic movement.
JOSE LUGo, M. TERESA GARCIA & OSCAR SALAS
Anthropic modifications in the south part
of Mexico's Basin
Instituto de Geografia, Unam. Ciudad Universitaria;
04510 Coyoacan, D.P., Mexico
The topography of the endorheic basin of Mexico was shaped
during the Pleistocene by intense volanic and exogenous
processes which still continue nowadys. Human activities
started a new transformation stage of such a topo­
graphy in the 14 th
Century with the foundation of Tenoch­
titlan on islets of a lake, which later became Mexico City,
actually one of the most populated zones in the world. The
constant transformation of the topography was increased
in the second half of the 20 th Century. This has led to the
presence of dangerous processes such as cracks now extending
some tens of kilometers on the lacustrine plain of
Mexico's basin, as well as landslides induced by human activities
which result in increasing damages.
In the middle of this Century, the sinking phenomenon of
Mexico City by water extraction from the subsoil was established.
From the 70's, a cracking phenomenon was recognized
on the borders of the City. At present, such cracks
represent, as a whole, some tens of kilometers, and damage
familiy housings and communication routes, mainly on the
lacustrine plain. A transformation is occuring on the topography
which changes the horizontal surface into an inclined,
corrugated or unevenly surface to the center of the
lake, with scarps even 60-80 em high.
The cause of this phenomenon can be explained by natural
factors such as the clayish and volcanic constitution of
the subsoil, and the arrangement of strata with horizontal
and vertical directions. Human influence is related to the
drying of lakes, plains urbanization and water extraction
from the subsoil. At the end of the zo" Century, we find
ourselves in a situation of uncontrolled growth of the City,
which means that we daily contribute to the transformation
of the environment and to the increase of risks.
S.A. LUKYANOVA & GALINA D. SOLOVIEVA
Coastal erosion of Russia
Department of Geography, Moscow State University,
119899 Moscou, Russia
Erosion of sea coasts is a very actual problem under conditions
of present-day sea level-rise and will be more important
in future if a prognosis of the sea-level rise acceleration
can become a real fact. The danger of coastal erosion
is now known all over the world. In our days more than
45 % the world shoreline experience wave erosion. This
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