ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

ALI HAMZA
Crue et erosion des terres en Tunisie Centrale
Departement de Genie Rural, Institut National Agronomique de Tunisie
En Tunisie centrale a climat aride et Subaride, lirregularite
inter amnuelle et intersaisonniere des preecipitations
font que les crues et inondations constituent urn phenomene
tres frequent. Outre les implications sur le plan hydrologique
et hydrogeologique, leurs consequences sur le plan
morphologique sont notables: extension des sebkhas, deplacement
de lits d' oueds, apparition des cones de dejections
et de secteurs d' epandage en plus du declenchement
du ravinement. L' auteur developpe en particulier le phenomene
erosion des terres qui enregistre al'occasion de
ces crues une activation impressionnante aux dcpens de
milieux sensibles de nature et largement fragilises par ume
occupation humaine Ie plus souvent non conservatrice,
Dans tous les cas des crues etudiees, l'erosion hydrique effectue
le travail de plusieurs amnees en quelques jours.
Quelques recommandations sur le plan de l' amenagement
sont formulees afin d' eclairer les decideurs charges de la
mise en valeur de la region.
MARIAN HARASIMIUK, J6ZEF SUPERSON
& WOICIECH ZGLOBICKI
Structural relief of the northern part of the
Murmansk Upland (Kola Peninsula)
Department of Geology, Maria Curie-Sklodowska University,
20-033 Lublin, Poland
Relief and geological structure interdependence manifests
itself in a particularly distinctive way in fold mountains and
in the vicinity of crystal rock uplands having a long history
of development. The Murmansk Upland, being a part of
the Precambrian Baltic Shield, belongs to the latter areas.
The relief of the northern part of the upland, shaped by a
long-lasting continental period includes elements of different
genesis and age. Therefore it is occasionally described
as structural - denudative or block - tectonic.
Murmansk Upland is built out of Archaic, microcline granite
containing numerous veins of quartz. The granite belongs
to the extensive tectonic structure called the Murmansk
Block. The examined part of plutonium is divided
on macro and mesoblocks by the net of dislocations of different
ranks. SE-NW and SW-NE directions related to
main tectonic zones of the Kola Peninsula are predominant.
The separated tectonic blocks are broken by a dense
net of splits, dislocations, and crevices of tensive character.
The authors on the basis of the morphostructural analysis
distinguish between two types of structural relief in the
northern part of the Murmansk Upland: denudative relief
conditioned by different plutonium rock resistance and a
complicated system of joint cracks, and disjunctive relief
connected with dislocational activity of supraregional rank
and regional glaciisostatic movements of tensive character.
The oldest denudative element of the examined area is the
highest part of the Murmansk Upland (240-260 ill a.s.l.)
which is a remnant of Mesozoic peneplane. Below the peneplane,
the Murmansk Upland falls down with distinctive
steps towards the Barents Sea within the precincts of which
there are numerous inselberg forms. These steps are interpreted
by the authors as pediments which originated in
conditions of semi arid climate as a result of isostatic periodical
movements. The denudative relief developed also in
conditions of periglacial climate. In this climate the old edges
of tectonic and denudative origin were remodelled by
the weathering processes and mass movements. The destruction
of edges was most effective in the places of a dense
net of joint cracks. Also nowadays the edges are destroyed
by frost weathering and mass movements. Sea cliffs
retreat intensively as a result of undermining and falling off
of weathered and cracked granite. Lithology of rocks and
diversified density and direction of the net of cracks brings
about uneven run of coast line.
There are the following elements of disjunctive tectonics in
the, relief of the analysed area: tectonic troughs, tectonic
edges. and open tensive crevices.
Troughs create long and narrow depressions in the relief.
The length of forms of this type reaches from twenty to ninety
kilometres maximally, the width being a few hundred
meters and depth up to 100-200 m. These forms are characterised
by rectilinearity with the dominant depressions
running NW-SE and SW-NE. They divide the area of the
northern part of the Murmansk Upland into a row of meso
and microblocks.
Tectonic edges create trough-sides, semi-troughs and splits
and are present within tectonic blocks, on the lines of ordinary
faults. These edges are mostly of rectilinear run related
to the characteristic directions of a given tectonic
block. The height of the edges depends on the rank of the
tectonic form. Open tensive crevices are characterised by
the width of up to 15-20 m and depth reaching from eleven
to nineteen meters. Sporadically they have the shape of
canyons with vertical walls and narrow bottom. These are
the youngest of the forms under discussion. The appearance
of crevices is related to current tectonic activity resulting
from the postglacial uprising of the Kola Peninsula.
Within the analysed area one can also meet other forms
connected with disjunctive tectonics: rectilinear «valleys»
and depressions created in the axes of dislocated zones
and depressions with no outlet connected with tectonic
loops located on the intersections of structural directions.
Dense net of tectonic cracks advance the processes of mechanical
weathering. During the Pleistocene zones of tectonic
dislocations were the object of intensive directed
exaration and fluvioglacial erosion. Valleys and depressions
are of diversified morphometry and morphology.
Their length reaches several kilometres and depth does not
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