ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

Variability in bed elevations was evaluated using the standard
deviations of detrended thalweg elevations for each
study reach. Logarithms of the thalweg elevations were
used to obtain a normal distribution. The length of each
survey transect was about 3000 m. Standard deviations increased
steadily after 1977, and then, in the degrading reach,
leveled off after 1986. Pool depths were significantly
deeper and pool spacing was significantly closer in the degrading
reach than in the aggrading reach of river. Average
pool spacing was three times the channel width. Not only
did pools become.more frequent and deepen, and riffles
become more prominent, but finer scale undulations in the
bed also developed. Such heterogeneity is important for
providing habitat complexity for aquatic organisms.
Pattern development was analyzed by the use of semi-variograms
and correlograms to test for spatial autocorrelation.
Such an analysis of channel pattern needs to be designed
at a scale capable of discerning critical phenomena.
In this case, pools and riffles form critical aquatic habitats,
and so a minimal discernible length of 10 m was chosen, as
it is less than the length of pools and riffles in this particular
system.
Bed surface elevations were first linearly interpolated to
obtain similar spacings of about 10m. The spatial autocorrelation
function was. calculated for distance classes (lags)
of 10 m to a maximum lag of 1000 m. Initial results based
on semi-variograms and the spatial autocorrelation coefficient
Moran's I showed the development of both fine scale
and broader scale spatial autocorrelation in the channel
bed through time. Fine scale « 50 m) correlation appeared
first, probably due to localized processes such as scour
around woody debris and bedrock outcrops forming
pools. Later larger features at the scale of alternate bars became
better defined. Still later, in the degrading reach, spatial
correlations at an intermediate scale (200 to 350 m)
emerged.
In conclusion, both variation in bed elevations and their
spatial characteristics can be used to characterize the development
of channel bed pattern on a reach scale after large
inputs of sediment. The scale and degree of pattern development
differed in aggrading and degrading reaches of
the river channel.
ABDEL-MoNEIM A. MAHMOUD
Paleodrainage and prehistory settlement,
Farafra Depression, Western Desert, Egypt
Department of Biology and Geology, Faculty of Education
Ain Shams University, p.o. 11341 Roxy, Cairo, Egypt
The Farafra Depression is located between Lat. 26° 40' to
27° 30' North and Long. 27° 30' to 28° 40' East at the western
Desert, Egypt. It is chosen to illustrate the dependen-
ce and response of prehistoric human settlement to the occurrence
of surface water durng the humid episods. The
first phase in the eaerly Holocene, ended at about 8000 bp,
while the two others correspond to mid-Holocene moist
intervals (5900-5000 and 4800-4600/4500 BP). The onset
of an arid trend in the central Sahara not later than 4500
BP, may have led people to move from the inner Sahara
towards the Nile Valley. .
The major trends of the paleodrainages in the Farafra depression
are directed mainly towards NE, NW and SW directions.
These drainages played an important role not
only for making a permanent playa lakes but also for sculpturing
the depression itself promoting the Karstic activities.
Also the geomorphology played a role for protecting
some of these playa in the depression. Most Neolitic settlements
found out around these playas.
GIVI M. MAISURADZE
The role of young volcanism in the formation
of the relief in Georgia
Geological Institute, Georgian Academy of Sciences, M. Aleksidze Str. 1,
380093 Tbilisi, Georgia
In the formation of the present morphologic features of
the territory of Georgia considerable role had tectonic
movements and volcanism which revealed at the lete-orogenic
stage of the Alpine geotectonic cycle. Volcanism
took place in subaerial conditions, had specific areal type
of eruption, and manifested itself, with some interruptions,
in all geotectonic zones in Georgia during the Neogene
and Quaternary. Sublatidudinal interzonal and submeridional
tranversal deep faults controlled magmatic cycles
of the Mio-Pliocene and Late Pliocene-Pleistocene.
Especially distinctly the role of volcanism in morphogenesis
revealed within the Transcaucasian tanversal uplift,
particularly in the central segment of the Greater Caucasus
and in the South-Georgian upland (the Lesser Caucasus).
Accumulation of pyroclastic and effusive material of
great thickness led to the relative leveling and inversion of
relief. At the places of the intensely dissected erosionaldenudational
relief on the Paleogene-Neogene substratum
were formed volcanic uplands (Keli, Erusheti, Javakheti),
lava plateaus (Akhalkalaki, Gomareti etc.) and
flows infilling paleo-valleys of the rivers Khrami, Mashaveri
etc.
Some Alpine morphostructeres of the Greater and Lesser
Caucasus controlling the pattern of ancient hydrographic
network were buried under lava and pyroclastic formations.
The inversion of relief resulted in rebuilding of hydrographic
network of such large rivers as the Mtkvari
(Kura), Khrami, Aragvi etc. There appeared new volcanoaccumulative
watershed astructural ridges of meridional
259