ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

e mapped by photogrammetric methods based on terrestrial
or aerial stereo photographs, one gets a tool to quantify
long-term glacier surface changes. This has been done
in many years, mainly for analysis of the mass balance
(analysis of surface elevation change) or to measure surface
flow velocities. In the latest years geographical information
technology (Cit) has been applied for this purpose.
This presentation presents an integrated approach to longterm
glacier analysis, considering both the surface function
and its derivates. The main aim is:
- to demonstrate how mathematical surface descriptors
calculated from grid-based Dems can be applied to classify
and to quantify glacier surface changes over a period of
time
- to demostrate how changing surfaces can be quantified
depending on scale, accuracy and noise in the data material.
The concept was tested on five Svalbard valley glaciers.
The geomorphometric analysis reflects the different dynamics
of these glaciers. The method seems suitable to give a
first impression of changes in the glaciers surface morphology.
Such observations can further be related to changes
in the glacier dynamics. This is important, especially for
non-monitored glaciers.
SILVIO EVANGELISTA 1, WILLIAM E. FULL 2,
GIOVANNI BATTISTA LA MONICA 1 & DOUGLAS D. NELSON 3
Littoral dynamics of the Circeo-Terracina coastal system
(Lazio, ItaIia)
1Dipartimento di Scienze della Terra - Universita «La Sapienza»,
piazzale AIdo Moro 5,00185 Roma, Italia
2 Department of Geology, Wichita State University,
Wichita, Kansas 67260, U.S.A.
3 Marine Science Department, Coastal Carolina University,
Conway, South Carolina, 29526, U.S.A.
The littoral dynamics was modeled from wave climate data
across the bottom topography within the Circeo-Terracina
coastal area (100 km SE of Roma). Wave data were obtained
from a previous study conducted by Delft Hydraulics
in 1991. The wave height, period, direction and frequency
of occurrence were transformed into fully developed sea
wave spectra using classic methods of Pierson and Moskowitz.
The bottom topography was obtained from the
Istituto Idrografico della Marina as unpublished bathymetric
survey maps at scale of 1:25,000 and were hand digitized.
The depth data were interpolated to generate a 125 m
square grid using kriging techniques. The effects of wave
refraction, diffraction and height modification, upon waves
approaching the coast, were calculated using a program
that considers spectra of wave heights, spectra of wave periods
and spectra of wave directions. The program utilizes a
finite difference model of differential equations for velocity
potential assuming first order waves traversing slopes that
approximate the tangent of the slope. The potential sedi-
ment transport was calculated at 24 shore perpendicular
profiles distributed along 16 km of coastline. Breaking wave
dynamics, longshore current velocity and sediment transport
were modeled using formulations of Longuet-Higgins,
Guza, Inman, Thornton, Wright and Short. The values
of longshore transport, current velocity, maximum or-bital
velocity at the sea floor, shear stress, significant
breaker height and percent of breaking waves were calculated
along each profile from about 18 meters of depth to the
shore. The longshore sediment transport was calculated incrementally
along the profiles to allow observations of the
spatial variations in the sediment transport along each profile
and between profiles. Computations were done for a
combination of periods and directions of wave approach.
These were chosen from available wave frequency data by
multiplying the frequency of occurrence by the square of
the significant wave height. Wave conditions corresponding
to high values were used. This does not represent all the sediment
transport but yields a view of the major transport in
the area. The sea from 150 and 180 and the swell from 180
and 210 have been analyzed. The values of periods are
about 5 seconds and the wave height about 1 meter.
The results of the analysis shows modest values of longshore
currents. In particular the sea from 150 produces a current
from Terracina toward the west, whereas the current
produced by a sea from 180 is directed, toward the east
starting from Circeo. For both directions, the current decreases
proceeding alongshore. The shear stress on the
bottom is similar for the two directions for each profile,
but has higher values for the sea from 150. The swell with
periods of 5.5 sec and wave height of about 1 m either
from 180 or from 210 induces a current from Circeo
towards Terracina. With respect to swell coming from the
south, swell from 210 shows anincrease in values 1 km west
of the harbour of Terracina. From this point both decay
towards east. The shear stress on the sea floor is always higher
for the swell coming from 180 than for swell coming
from 210.
DAVID LA. EVANS 1 & BRICE R. REA 2
The geomorphology and sedimentology of
surging glaciers: a landsystems approach
1 Department of Geography & Topographic Science,
University of Glasgow, Glasgow, G 12 8QQ, Scotland, UK
2 School of Geosciences, Queen's University, Belfast,
BT7 INN, Northern Ireland
The surging glacier landsystem can be reconstructed by
utilizing observations on contemporary surging glacier
snouts in Iceland and Spitsbergen. This landsystem is critical
to the identification of ancient surging margins and
their differentiation from fast flowing palaeo-ice streams.
Examples of the geomorphology and sedimentary structures
of possible ancient surge margins in western Canada
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