ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

iver channels, (6) change of incision depth and river gradient
along river course, (7) high (steep) river gradients associated
to the flexural scarp, implying that the ground
surface is being tilted, (8) dammed channels and rivers,
implying erosion by river flow is smaller than tectonic
uplift, (9) abandoned gullies or gorges (no river pouring
through it) at the thrust front or across the flexural scarp
(it frequently accompanies dammed or diverted rivers),
(10) disproportion between present river flow and size of
creek and/or gorge -previous evolutive stage of (9) or it
comes with (5)-(11) abandoned alluvial wedges at the
front of the foothills; C) tectonic «gutters» (rivers running
parallel and close to the thrust front on the down-thrown
block) and broom-shaped river patterns on the basinward
side of these foothills, which suggest the occurrence of tectonic
loading due to foreland-vergent thrusting; D) increase
of tilt of ground surface or stratigraphic dip with age of
Quaternary (and even older) formations or alluvial ramps
(successive unconformities) and E) staircased alluvial terraces
exclusively present in the hangingwall block, meaning
that river flow is important enough to keep cutting
through the area under uplift; and F) in many cases, the
erosion has been so intense that anticline cores have been
washed away and these bridged anticlines present and erratic
river flow.
PAUL C. AUGUSTINUS 1 & DAMIAN GORE 2
Reconstruction of ice flow across Bunger Hills,
East Antarctica
1 Department of Geography; University of Auckland,
PB 92019 Auckland, New Zealand
2 School of Earth Sciences, Macquarie University,
North Ryde, NSW 2048, Australia
Mapping of glacial drift sheets and examination of striae
patterns throughout the Bunger Hills, suggests that the largely
ice-free region records the imprint of several phases of
ice sheet expansion during the late Pleistocene. In. particular,
ice moulded features and cross-cutting striae in the
southern Bunger Hills suggest at least two episodes of ice
sheet overriding. The older event relates to thin ice moulded
to and strongly constrained by the topography, whilst
the younger ice expansion event relates to regional expansion
of thick ice. In addition, where salt weathering and
freeze-thaw processes are least severe, the younger event is
recorded by nail-head striae and well preserved glacial polish.
Discriinination of the order of emplacement of the
cross-cutting striae patterns is possible at many sites,
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although whether they relate to separate ice expansion
events, or different phases of the same expansion of the ice
sheet is not clear at present. Paleo-ice flow indicators confirm
that ice sheet expansion over the southern Bunger
Hills was from the southern and eastern margins, although
minor advance of the Edisto Glacier onto coastal areas occurred
at least three times following retreat of the last extensive
phase of ice sheet expansion. Hence, the glacial history
of the Bunger Hills appears to be more complex than
had previously been recognised, emphasising the need for
detailed glacial geologic work in this and other ice-free
coastal areas of east Antarctica.
ANDRE DE SOUZA AVELAR 1 & WILLY ALVARENGA LACERDA 2
Mass movement caused by rock block impact at the
Soberbo slope, Rio de Janeiro, Brazil
1 Civil Engeneering Program, Coppe, Federal University of Rio de
Janeiro, caixa postal 68506, Cep 21945-970, Rio de Janeiro (RJ), Brazil
2 Civil Engeneering Program, Coppe, Federal University of Rio de
Janeiro, caixa postal 68506, Cep 21945-970, Rio de Janeiro (RJ), Brazil
This paper refers to the causes of the Soberbo mass movement
initiation in Rio de Janeiro, Brazil. The initial failure
occurred at the middle slope in January of 1966 and runned
out like a debris flow; dragging large volumes of soil
rich in rock blocks causing demage to Furnas road, a paper
factory and many others losses. In February of 1988
there was a new event reactivating erosion and causing
new damages.
According to the literature, the initial failure was caused
by the impact of a rock block against the saturated soil at a
point downslope Soberbo road. To confirm that.inlormation
it have been investigated the environmental conditions
on Soberbo slope, before and after the initial mass movement.
Undrained shock tests in a colluvium and saprolite
occurring in the Soberbo slope were also carried out.
The history of the Soberbo mass movement has beenreconstructed
with data found in the literature and from aerial
photographs interpretation taked in 1954 and 1967.
The 1954's photos show mainly the occurrence of rock
blocks in dropped position and the 1967's indicate the initial
point of slope failure.
The shock tests results show that the failure of the Soberbo's
soils happen with lower loads comparing to the static
failure loads applied in triaxial tests. These tests also provided
shock failure parameters.
A final analysis of a rock block ready to drop (identified at
1954's photos) and the shock failure parametersled to the
conclusion that it is geotechnically possible that the initiation
of the Soberbo mass movement was caused by the impact
of this rock block.