ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

per streams. In DEM-based networks, more than two
streams confluent simultaneously. Therefore, the streams
which have maximum stream order are joining on same time,
stream order of after joining is increased.
Rs = 4.27 and RI= 1.89 is obtained for average bifurcation
ratio (Rb) and average stream length ratio (RI) of manualextracted
drainage 1, respectively. These results agree with
results of other studies treating Japanese rivers (for example,
Tokunaga, 1966). On the contrary, Rb is bigger and Rl
is smaller than that of manual-extracted networks, respectively,
for All Order Type, (Rb =5.93 and RI= 1.69), VI =
10 Type (Rb= 5.35 and RI= 1.76) (figs. 1 and 3). This is
caused by All Order Type and VI = 10 Type simulate too
many 1st. order streams than manual-extracted networks.
This means All Order Type and the threshold value VI =
10 cannot eliminate the valleys or gullies which are not represent
on the topographical maps. About stream numbers,
the number of VI =27 show the best agreement with
manual-extracted networks (fig. 2). However, the stream
length of VI = 27 agree only that of 2nd. and 3rd. order
streams (fig. 3). These differences may be caused by locations
where stream starts. The uppermost points of these
are regarded as stream heads in this study, but not always
the case in real. The length of 1st. order streams, therefore,
are estimated irregularly. The further study will take this
problem into account.
VLADIMIR N. NEVSKY
Do isostasy and rotational regime control relief evolution
of continental margins? "
Pacific Institute of Geography, Radio st. 7, Vladivostok, 690041, Russia
Can Earth's surface processes influence geotectonics? The
common answer has been done in hypothesis of denudation-accumulative
and glacio isostasy. Its main principles
have to be corrected according to recent geophysics and
paleogeography data.
As is known surface mass movement both and water-ice
transformation causes asthenosphere compensation in sublateral
directions. All these inner and outer processes are
connected dynamically by means of Earth's rotational regime
such as polar wandering and Earth's flattering. There is
the interesting fact: R-polarity geomagnetic excursions during
Brunhes epoch correlate chronologically with fluctuations
of north continental ice volume much better, than
with some another processes. In other words north ice coves
and rotational parameters change due to glacioisostasy
are very probable causes of short-term geomagnetic events.
Secondly, locality of some island arcs is assumed to correspond
to ancient sedimentary basins of the most large rivers.
For instance the L. Antilles arc corresponds to Paleogene
accumulation basin of South America rivers of north
direction. Pacific arc Ryukyu has been formed near abyssal
fans of Paleogene -Neogene Great China streams. These
processes are supposed to be caused by extremely high
gradients of mass balance on continent-ocean boundary
near abyssal sedimentary basins of large rivers. As is postulated
lithosphere is of mainly compression and fracturing
conditions, so the most probable result of denudation-accumulative
isostasy at the boundaries is a subduction. Rifting
has a passive role. Subduction of west Pacific type develops
under superposition of compensative and global east
(according to Nelson and Temple) asthenosphere flows
together with opposite vertical movement of interacted
blocks. Subsequently the relief of continental margins is
reformed. Island arc and margin seas must be regarded as
obligatory effect, whereas continental relief has different
variants of evolution. In the first case ancient river network
is quite reoriented as it was in North-East Asia. In another
case network can save its structure, but accumulation basins
remove upwards as in Central East China.
ANDREI A. NIKONOV & A.P. SERGEEV
Identification and quantification of seismogravitational
relief disturbances: the caucasian mountain
area as an exsample
Joint Institute of Physics of the Earth, Acad. Sci. Russia.
Bol. Gruzinskaya 10, 123810 Moscou, Russia
In contrast to seismotectonic ruptures, seismogravitational
relief disturbances (slope movements due to earthquakes)
have so far received quite insufficient attention. There are
some unresolved problems. The following ones are considered
in this paper:
Discrimination seismogravitational disturbances proper as
distingnished from pure gravitational ones. Six features of
seismogravitational slope disturbances are identified.
7.i I.i '.i
...----f-----+---+---.....----+.
FIG. 1 - Quantitative correlations between recent big bedrock seismodeformations
on slopes (V - volume in m) and parametres of related
earthquakes (I - intensity) of the Caucasus have been derived (see Fig.).
This was used to make an attempt to resolve the inverse problem, namely,
to assess the intensity and magnitudes of past strong earthquakes
from dimensions of relevant deformations.
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