ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

DAN BALTEANU
Slope instability in the Vrancea seismogenic
region (Romania)
Institute of Geography of the Romanian Academy,
12, Dimitrie Racovita, 70307 Bucaresti 20, Romania
The most active subcrustal earthquake province in Europe
(the Vrancea seismogenic region), lies in the South-eastern
part of the Carpathian Mountains; it is characterised by an
average of three seismic events in every century, including
strong earthquakes of magnitude 7,2 ..7,4. The region is formed
predominantly of folded and faulted Cretaceous and
Palaeocene flysch and Neogene molasse and is characterised
by an eccessive human pressure on the environment.
Mass movements playa most significant role in the evolution
of the relief and show a great diversity. The main controlling
factor influencing the range of mass movements
and their spatial and temporal distribution are the geological
structure, seismic activity, climate and human activity.
The papezr presents the distribution and variety of mass
movements (landslides, mudflows and rockfalls) in connection
with land use changes and different extreme
events during the last century. The closely studied earthquake
of Maich 4, 1977, magnitude 7,2 had marked effects
on the relief of the epicentral area.
The following phenomena were triggered by the March 4,
1977 quake (magnitude M .,;- 7,2 on the Richter scale): 1.
distinct movement of fault-line divided compartments; 2.
emergence or reactivation of some mudvolcanoes; 3. deep
slidings; 4. regression of steep slopes through fall and topple
of rock fragments; 5. intensification of creep processes;
6. formation of cracks in channel-beds and on slopes;
7. suppression of clays and marls at the bottom of channelbeds;
8. formation of sinking dolines on salt breccias; 9.
collapse of gallery roof in some deserted mines; 10. liquefaction
of loess deposits and sands; 11. underground water
level changes; 12. emergence of highly mineralized
springs.
Our study will focus only those phenomena which brought
changes in the morphology of slopes.
SUNANDO BANDYOPADHYAY
Coastal erosion in Sagar Island, Hugli Estuary, India:
causes, consequences and human adjustments
Department of Geography & Environment Management,
Vidyasagar University, Medinipur 721102, WB, India
The reclamation of Sagar island (21°37'-58'N; 88°02'­
11'E) from the Sundarban mangrove wetlands of the cyclone
prone western Ganga-Brahmaputra delta was initiated
in 1811. Mainly due to different government policies that
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viewed the wetlands as waste lands and ignored the eroding
nature of the coastal delta, the island has now become
almost wholly settled with an agrarian population of
184,942 (1997 estimate), growing by 40 per cent per decade.
Coastal erosion, that steadily reduced the supratidal
area of Sagar by a quarter within the last 143 years (from
285 km 2 in 1851-55 to 213 km 2 in 1996) and at places triggered
dune encroachment over farmland, forms the most
important natural environmental hazard affecting this resident
population. The conditions at Sagar are closely comparable
with rest of the sea-board sections of the 5,360 km 2
reclaimed Sundarban (Indian part) and the island can be
used as a model for the region.
Among other factors, the erosion of the island can primarily
be linked to the reclamation process itself. It disturbed
the morphological steady state of the resonant macrotidal
Hugli estuary by reducing the intertidal area and increasing
the mean depth of the channel. The abandoned and
subsiding nature of the western delta as well as sediment
sink in the Swatch of No Ground submarine canyon and
in. the post-independence (1947) river valley projects also
contributed to the problem. The erosional trend of Sagar
is likely to continue in the future.
Generally, most of the erosion takes place during the rainy
monsoons (June-September). During this season, a destructive
wave climate, increased occurrence.of tropical cyclones
and a raised local sea level owing to increased fresh
water input-all coincide. The severe cyclonic storms of
Beaufort force 10 and above have a recurrence interval of
3.28 years within 100 km of Sagar. The most destructive of
these struck the island in 1833, 1864 and 1942, causing damages
of the highest magnitude.
The human adjustments to the erosion hazard include elementary
technological control, acceptance, relocation, regulation
and emergency measures-in that order. The erosion
management schemes of Sagar are managed by seven
government/semi-government agencies often with little
coordination. These include 61 km of low ..tech marginal
earthen embankments, built at US$ 7.2 per metre of length
and requiring extensive unskilled maintenance; 14.5 km of
comparatively more permanent brick-paved marginal embankments,
built at US$ 62.9 per metre of length and re ..
quiring skilled maintenance not always available locally;
580 ha of mangrove plantations in 11 localities, three relocation
projects involving about 250 families and 13 degraded
storm refuges dating from the late 19th century. In a
typical year, the calm late post-monsoon period (December-January)
is the best time for repair or construction of
the erosion prevention structures.
For the present, achieving rational and coordinated use of
the available resources with proper understanding of the
natural feedback mechanisms would significantly ameliorate
the efficiency of the existing management schemes. For
the future, in view of the possible effects of the global
greenhouse warming that might further increase the mean
depth of the estuary and rate of coastal erosion, possibilities
of gradual abandonment of the island for wetland
restoration and relocating its population need to be considered.