ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

YURII D. SHUISKY
Geomorphology and dynamics of the abrasive coastal
zone of the World Ocean
Geography Department, State Mechnikov University, Dvoryanskaya St.
2, 270000 Odessa, Ukraine
At present the World Ocean shores have stabilized in their
development after the end of Holocenic transgression. As
a result rather stable correlation between abrasive and accumulative
shores of both separate seas and the World
Ocean as a whole has been formed. Abrasive and accumulative
processes have formed in general and the greatest
short-term changes are connected with climatic factors influencing
biogenetic, termafrost-abrasive, corralline, shelly,
mangrove shores.
Abrasive shores whose regime of development has global
importance are of particular interest. These shores are considered
in the sphere of coastal zone structure, correspondingly
their above-water (cliffs) and under-water (submarine)
parts are genetically inseparable. They develop under
the impact of one and the same energy source, closely interact
with each other, are connected with other elements of
coastal zone by substance flows of the same type.
On the maps of middle scale the length of measured
World Ocean shores constitutes about 780,000 km, or
47.5 0/0. Within separate seas the part of abrasive destroyed
cliffs turned out to be equal from 20.9 % up to 67.2 % of
the general one, and the bench length was 10-40% greater
than these values. Approximately the same correlation is
within separate states adjoining seas and oceans as well.
Active benches are spread along 445,000 km of the coastal
line. Taking into account that 80 % of accumulative forms
length are subjected to retreat (..... 200,000 km), about
73.2 % (..... 570,700 km) are retreating and destructive at the
modern stage of the World Ocean development.
Guessing that spreading of destructive shores prevails some
authors explain this global phenomenon by equally
global general rise of the water level. However, the level
relative rise is not global, and in natural conditions no dependence
of cliff rate retreat on the Ocean level rise rates
has been found.
In connection with wide spreading of abrasive shores
lithodynamical significance of their development is of particular
interest. All variety of active cliffs can be represented
as three main groups: abrasive-collapsive, abrasivelandsliding
and abrasive-danudative. The rates of their
abrasion are different. In the average during a long-term
period about 5.7x10 9 t/year of sedimentary materials of various
composition are shedding off from them to seas. All
variety of abrasive nearshore bottom is devided into 5
groups, about 9.0x10 9 t/year of sedimentary materials are
shedding off from them. It is approximatelly 15% less than
river sediment flow into the boundaries of mouth areas.
Under the impact of processes of physic-mechanical desintegration
and wave differentiation 4.3x10 9
t/year of beachforming
fractions, or 11.7 t/year per 1 m of shoreline
354
length remain in the coastal zone. To extinguish wave
energy and protect cliffs against abrasion the amount of
beach-forming fractions coming to the coastal zone must
be an order greater. Besides they are not retained near
abrasive shores but move to the accretion sites in the conveyor
of alongshore drift flows. This phenomenon constantly
supports active wave influence on cliffs and their destruction.
As a result the following conclusions can be represent:
- modern spreading of abrasive forms of relief and processes
is not zonal in the Ocean coastal zone in total;
- abrasion of cliffs and benches is the main source of beach-forming
fractions (most often coarser than 0.1 mm) for
the coastal zone and bottom sediments of the World
Ocean in general; and this must made one reconsider theoretical
diagrams of marine sedimentation and exogenous
relief-formation;
- wide spreading of abrasive and retreating shores testifies
to such stage of the World Ocean evolution during which
summary drifting of sedimentary material decreased from
the land to the sea;
- rates of cliff and bench abrasion depend in general on
three global reasons: a) strength of rocks and deposits, b)
wave energy potential of the coastal zone, c) sediment volume
(content) in the coastal zone; their correlation determines
the numerical value of rates;
- abrasive destruction of shores takes place because at the
current stage of the World Ocean development the coastal
zone is subjected to acute deficit of beach-forming sediments
and irregular impulsive impact of stormy waves
against the background of higher energetic potential of the
coastal zone;
- direction and intensity of development of abrasive relief
forms mainly do not depend on the rate and signs of longterm
relative change of the World Ocean level.
ALEKSEY SIDORCHUK
The hierarchical system of river bed relief
Geographical Faculty, Moscow State University, 199899 Moscou, Russia
The interaction between the flow and movable bed in the
self-organizing dynamic system «stream flow-channel bed»
leads to quasi-periodic flow structure formation and fluvial
relief development. The hierarchical system of the macroturbulent
structures in the river flow can have a wide range
of size from depth order to meander length order. The river
channel relief is also hierarchical system of dunelike
features with the same range of size.
The quantitative basement for description of stream flow ­
channel bed interaction is the analysis of the initial instability
of the wave-like structures of the flow and channel bottom
relief. Stability analysis of 3-D equations of momentum
and conservation in curvilinear coordinates leads to