ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

2. The reasons for such difference are in various geological
structure: the depth at which the massive ice is found.
At site 1 the massive ground ice is not participating in the
detachment mechanism, shearing surface is at the active
layer base along the interface frozen ice-bonded
clay/thawed sand or frozen ice-bonded clay/thawed clay.
At site 2 mass waist is due to thawing of the ground ice
and flow of the liquefied clayey material down-slope.
3. Slope development is climate-dependent especially in
permafrost regions. All the slope processes are known to
result from the high water content (high pore pressure) of
deposits, but only in permafrost regions there is such a
source of water as melting ground ice. Slumps are more or
less active depending mainly on the air temperature. The
warmer is the summer, the deeper the thaw and the more
possible is massive ground ice melting on slopes. Melting
of ice gives enough water to provide mass waist. Active
layer detachments move due to the immense rise of the active-layer
pore pressure that depends on the summarized
effect of the high summer temperature (and thus - rate of
thaw and water liberation), summer atmospheric precipitation,
and high ice content at the active layer base (the last
is formed due to the specific conditions of freezing the
year before possible activation).
4. Modern slopes of the Central Yamal Peninsular are
sculptured by several stages ofactive layer detachment activation
that are seen in concave slopes, specifically branched
ravines, small thermokarst lakes on slopes, highly
meandering streams with series of dammed lakes «threaded»
on the narrow channel.
EVGENY P. LELIKOV, & YURY 1. MELNICHENKO
Deep structure and Japan sea floor morphology
Pacific Oceanological Institute, Feb Ras, Baltiyskaya St.,
690041 Vladivostok, Russia
A clear reflection of a deep-earth structure is an the Japan
sea floor landforms. Large morphostructures with a different
types of crust limited by deep-earth faults are defined
in the Japan sea. It is a shelf with a continental crust 25-30
km thick, large submarine upland (Jamato rise, Korean
plateau) with subcontinental crust 20-24 km thick, deep
sea basins with suboceanic crust 11-14 km thick.
Deep-sea basins have a flat bottom surface at a depth
(3000-3500 m) and are complicated by volcanic ridges.
They are built by cenozoic basaltoides discharged in submarine
conditions. The crust structure of large submarine
uplands consists of basaltic, intermediate (or second layer)
and sedimentary layers. Precambrian metamorfic, paleozoic-mesozoic
sedimentary, volkanic-sedimentary and
igneous rocks similar in age and composition to surrounding
land formations form the intermediate layer. These
rocks were generated in the crust structure thickness 30 -
246
35 km. Marine neogene-quaternary deposits have sedimentary
thickness 0-2500 m.
The submarine uplands were broken into separate blocks
by the north-easternward (Korean plateau) and sublatitudeward
(Yamato rise) faults. The rift valleys also of northeastern
and sublatitude directions take place at the centre
of uplands. Gradually they come to deep-sea basins. A
step-block structure is typical for the surface of the submarine
uplands. At the same time, upland blocks drop down
toward deep-sea basins limited by sizable faults. The rocks
of an intermediate layer are exposed on the sharp fault slopes.
The basaltic volcanoes often are located in region of
sizable faults. A gradual decrease of the crust thickness
(from 24 to 18 km) the to ward deep-sea basins and rift
valleys coincident with upland blocks along deep fault.
The difference between thicknesses of the modern crust
and crust formed during formation of precambrian complexes
and phanerozoic abbyssal and mesoabbyssal granitoids
is a sign of a sial destruction.A magmatic erosion associated
with a rise of mantle diapir in the. Meso-Cenozoic
time might work as the principal mechanism of the destructional
phenomena which caused the formation of Japan
sea basin. The destruction of the Japan sea area crust
leads to the appearance of the special destructional
morphostructures. The mentioned above submarine large
uplands belong to such kind of morphostructures.
BERTRAND LEMARTINEL
Essai d'evaluation de la denudation neogene
des Monts Iberiques Occidentaux
Departement de Geographie, Universite de Perpignan,
52 avo de Villeneuve 66860 Perpignan, France
et Ura 1562 Cnrs, 29 bd Gergovia,
63037 Clermont-Ferrand Cedex 1, France
L' analyse correcte des taux de denudation sur Ie long terme
suppose que les produits erodes soient en totalite conserves
en un lieu facilement accessible, ce qui est rarement
Ie cas. La chaine iberique occidentale presente a cet egard
un interet majeur: l' accumulation correlative de son orogenese
neogene s'est faite dans les bassins autrefois endoreiques
de 1'Ebre et du Duero. Nous pouvons done evaluer
les vitesses de sedimentation, mais aussi, par Ie biais
du calcul de la rapide deformation de la surface d'aplanissement
fini-oligocenc, la denudation de cette moyenne
montagne qui combine les traits d'une chaine alpine et
d'un massif en roches anciennes. Notre domaine s'avere en
cela fort original.
Cette appreciation de la duree est rendue possible par la
presence de microfossiles mammaliens dans Ie materiel qui
remblaye les bassins. Loin d'etre inscrit dans un continuum
propre a satisfaire Ie mobilisme ambiant, Ie decapage de la
montagne obeit au contraire a des rythmes saccades