ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

more diffusional erosional processes, such as creep.
Furthermore, river channels demonstrate transitions from
bedrock to loose-bed conditions in areas of linear and
rounded topography respectively. It is therefore important
to gather morphometric data on the mountain belt, and to
incorporate these quantitative Dem data with qualitative
field observations in order to assess the spatial distribution
of erosional processes within the orogen.
Quantitative analyses of Dems may be operated through
the various algorithms existing within the Arc/Info Grid
package in which data are recorded in a series of rectangular
grids. Grid allows for the rapid, relatively easy computation
of numerous quantitative topographic variables
from Dem data. Such variables include slope angle (topographic
gradient), convexity (rate of change of slope), slope
reversal, aspect and the elevation-relief ratio. The latter
may be used as a quantitative measure of the degree of dissection
of a landscape, as in this case, to compare the
morphology of rounded and linear ridge topography. These
morphometric variables in turn allow for the definition
of drainage courses and divides, which may then be utilised
in modeling hydrological and geomorphic processes.
Examination of the Italian Dem therefore provides a macro-scale
representation of an active orogen from which
the spatial distribution of different erosional processes may
be modeled. Analysis at a finer resolution than previous
work I allows for the incorporation of field data, and the
assessment of the relative roles played by lithology and tectonics
in determining orogenic surface morphology. A similar
methodology may also be applied to Dem data for
other active orogenic belts, such as the Southern Alps. By
examining mountain belts other than the Apennines, the
apparent coupling of tectonic and erosional processes demonstrated
for the Italian orogen may be tested under different
structural, lithological and climatic conditions.
TOMAS SPENCER\ ].R. FRENCH 2, A.W. TUDHOPE 3
& T.P. SCOFFIN 3
Ocean dynamics and sealevel change from coral
micro-atolls, Tongareva Atoll, Northern Cook Islands
I Department of Geography, Cambridge University,
Downing Place, Cambridge CB2 3EN, U.K.
2 Department of Geography, University College London,
26 Bedford Way, London WCIH OAP,U.K.
3 Department of Geology, Edinburgh University, West Mains Road,
Edinburgh EH9 3]W, U.K.
Sealevel change on low-lying, often heavily-populated,
oceanic islands is a major environmental concern for the
late twentieth and early twenty first centuries. However,
estimates of the magnitude and rates of future sea-level rise'
and thus the evaluation of their significance, need to be
set in the context of the natural variability of ocean water
360
levels. In some areas, inter-annual changes, associated with
large scale oceanographic processes, can be considerable
and can mask longer-term trends.
In the absence of long mid-ocean tidegauge records, it is
necessary to find a sensitive indicator of palaeo sea-level to
extend the instrumented record back in time. Intertidal corals
have potential as recorders of historical sealevel change.
Flat-topped coral colonies up to several meters in diameter,
or «microatolls», growing to an upper limit related
to low spring tide level can be used to reconstruct sea-level
histories over 1-100 year timescales. At Tongareva Atoll,
South Central Pacific Ocean, a micro-atoll based sea level
record for the last 60 years has been constructed from i)
detailed (2 em spacing) transects of micro-atoll surface micro-topography
and ii) X-ray photographs of annual skeletal
density bands in coral slabs recovered from coherent
coral wedges sawn from selected micro-atolls.
The concentric ring structure of the micro-atoll surfaces
shows i) a general rise in sea level (1.51mm a-I 1949-1979
(comparable to the 1.81mm a-I recorded by the tidegauge
at Pago Pago, American Samoa, 1500km to the southwest))
and ii) substantial sea level variations on inter-annual
times cales related to Enso (EI Nino Southern Oscillation)
driven sea level fluctuations. Warm-phase Enso events in
the West-Central Pacific Ocean are characterised by sealevel
fall; this results in die-back of the micro-atoll growth
surface on subaerial exposure followed by recovery growth
back to sealevel. Thus low sealevels interrupt the usual relationship
between microatoll surface height and sealevel,
with the magnitude of this interruption being related to
the strength of the warm phase event. Enso chronology
suggests that the Tongarevan microatolls have experienced
nine warm phases of varying severity over the period of
their growth history; internal microatoll growth structures
indicate that «moderate» Enso events interrupt the record
by 3-14 years but that reef recovery from the «severe»
1982-83 Enso event is unlikely to be completed before
2003. Whilst microatolls have potential for filling in the gaps
of the sealevel record, both over space and time, such
records need to be treated with caution at some localities.
BARBARA SPONHOLZ
The South-German Muschelkalk-Karst and its impact
on the landscape system
Geographisches Institut, Universitat Wiirzburg, Am Hubland,
D-97074 Wiirzburg, Germany
In the South-German Muschelkalk region (Triassic marine
limestones with some clayey and marly strata and salt/gypsum
in the middle part) different karst areas have developed.
Aside from a number of caves in the lower and upper
Muschelkalk most of the karst phenomena are sinkholes,
uvalas and dry valleys. Their formation has often been ini-