ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

that of West Gujarat coast. It is characterized by a very high
tidal range of approximately 12.5 m which in turn generates
very strong tidal currents, constantly churn up the sediments
from the shallow bottom, mix them up and depositing
them along the gentle coast as well as at the bottom.
The coastal areas of the Gulf are made up of geologically
diverse rocks and provide a wide variety of landforms. These
includes; recent mudflats, raised mudflats, salt-waste drylands,
beaches, wave-cut platforms, rocky cliffs, recent coastal
dunes, older dunal ridges, relict alluvial patches,
river mouth bars and offshore banks, islands and point
bars, alluvial cliffs and alluvial plains. The coastal areas on
the Saurashtra side consists of landforms related to the Tertiary
and Quaternary periods whereas the Mainland side the
landforms are exclusively within the Quaternary deposits.
It is observed that the evolution of the coastal landscape of
the Gulf of Cambay has been controlled by the factors of
geology (structure and lithology), sea level changes, climatic
variations (rainfall and wind) and strong tidal currents, which
have acted in a variety of combinations giving rise to a
wide variety of erosional and depositional landforms. The
different combination of fluctuating sea level and differential
tectonism along some major lineaments appear to be the
factors responsible for generating contrasting landscapes.
ANTONIN IVAN & KAREL KIRCHNER
Inselbergs in the eastern part of the Bohemian Massif,
Czech Republic
Institute of Geonics, Branch Brno, Academy of Sciences
of the Czech Republic, p.o. box 23, 613 00 Brno, Czech Republic
There are numerous isolated hills in the E marginal part of
the Bohemian Massif and adjacent part of the Carpathian
Foredeep, where they stand above unconsolidated molasse
sediments. The hills are mostly composed of rocks of the
crystalline basement, but the Paleozoic conglomerates,
sandstones and limestones are also present.The hills have
been explained as monadnocks, fault-block (horsts) or inselbergs.
The problem of their origin, however, is very
complex a no simple explanation seems to be admissible.
The reason is longterm post-Paleozoic subaerial denudation
and planation taking place in different climatic environments'
accompanied by several marine transgressions
resulting in burial and exhumation of landforms. The underthrusting
of the Bohemian Massif towards SE below
the Carpathian orogen (as result of plate collision in the
Tertiary) was probably still more important. Owing to it,
the whole eastern part of the massif subsided and was
deformed into huge marginal flexure. In its downwarped
part (today below the Carpathian Foredeep and flysch
nappes), the Jurassic sediments buried an ancient probably
Lower Mezozoic planation surface. On the other hand, in
other places the Tertiary sediments under the foredeep
and flysch nappes rest on weathered crystalline rocks of
the Bohemian Massif from which oil is mined! The margi-
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nal flexure is complicated by narrow ridges composed of
basement rocks. These ridges (upbulges, horsts ?) run parallel
with fronts of nappes and some of their top parts,
originally covered by the Miocene sediments, protrude
above adjacent hilly country owing to subaerial denudation.
Another complication on the marginal flexure are
deep cross grabens trending NW (e.g, Nesvacilka Graben)
filled by the Cretaceous, Paleogene and Neogene sediments.
The block-faulted topography of small horsts and
grabens is characteristic feature of these cross structures
used by major rivers draining the eastern part of massif.
Thus, we can distinguish three topographic situations or
relief types where the isolated hills occur:
1. low-lying marginal parts of the Bohemian Massif, as a
upper part of the marginal flexure, with extensive parts of
planation surface (stripped basal surface of weathering and
roots of deep saprolite, up to 100 m thick, possibly of Cretaceous
age). The isolated hills composed of granite or
schists are believed to be true inselbergs;
2.· top parts of longitudinal ridges in the Carpathian Foredeep.
Both tectonic and erosional processes were possible
mechanisms;
3. the Mezo-Cenozoic cross grabens penetrating as fault
embayments into the Bohemian Massif. Some isolated hills
seems to be true inselbergs (e.g, those composed of Devonian
limestone with traces of fossile tropical karstification),
other maintain their tectonic features.
MASARU KEN IWAMOTO
Geomorphological changes and hazard potential by
eruption and debris discharge, Unzen Volcano, Japan
Department of Civil Engineering, Nishi-Nippon Institute of Technology,
Kanda-machi, Fukuoka, 800-03, Japan
The volcanic disaster at Unzen is the worst eruption in the
modern history of Japan because it is located near the city
and still continues the activity. In this disaster, pyroclastic
flows were frequently generated by the fall of lava domes.
Further worse, in a rainy day, debris flows easily occurred
and damaged many facilities. However. these potential risk
could be gradually predicted by the researches regarding
to the characteristics of geomorphological changes. For instance,
pyroclastic flow was predicted by the relationships
among the earthquake, magma supply, lava dome growth
and shape changes. On the pyroclastic plateau, erosion
mechanism and river struggle were investigated by the decrement
of permeability due to the volcanic ashes. Successively,
the characteristics of debris flow was also simulated
under the heavy rainfall conditions in a short period of time,
and clarified the mechanical difference from pyroclasic
flow. Since then, the evacuation system and countermeasures
were alternatively conducted by using these geomorphological
changes and hydrological conditions, namely
the evacuation system for pyroclastic flow was strongly
arranged in the midstream and the warning system for
debris flow was arranged especially in a rainy day.