ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

MANUELA PELFINI 1 & CLAUDIO SMIRAGLIA 2
Geomorphological evidences of the recent advance of the
glaciers in the Central Italian Alps
1 Dipartimento di Scienze dell' Ambiente e del Territorio,
Universita di Milano, via Emanueli 1, Milano, Italy
2 Dipartimento di Scienze della Terra, Universita di Milano,
via Mangiagalli 34, 20133 Milano, Italy
For about twenty years (1965-1985) most of the glaciers in
the Italian Alps have been advancing. In the main mountain
groups of the central sector of this region (Bernina,
Disgrazia, Piazzi, Ortles-Cevedale), the snouts of the glaciers
have been moved downward some tenths meters on
average from 1965.
Then, from 1985, the glaciers fastly retreated leaving new
particular morphological features, mainly end and lateral
moraines ridges. These new moraines have been observed
in front of all main glaciers, either valley glaciers (Ventina
and Forni Glaciers, for instance; the last one advanced more
than 300 meters) or mountain glaciers (Castelli, Sforzellina,
Gran Zebru Glaciers, for example).
The morphology and the evolution of some new moraines,
especially in the Ortles-Cevedale Group: Forni, Sforzellina,
Gran Zebru Glaciers have been examined carefully.
The landforms of the Sforzellina aud Gran Zebru Glaciers
are real frontal and lateral moraine complex, mainly formed
by angular metamorphic debris. Near the snouts of
theStorzellina and Gran Zebru Glaciers, there is, 20-30
meters far from the today ice-edge, a group of ridges (two
and sometimes three); their thickness varies between 0,5
and 3 meters. These moraines have a steep distal side with
a gentle proximal slope. Field observations and grain size
analysis show that they are mainly formed by coarse debris;
their genesis probably derives mainly from dumping of supraglacial
debris along the growing snout slope.
The data of some meteorological stations in the Italian Central
Alps (Sondrio and S. Caterina Valfurva in Valtellina)
have been then considered for understanding the links
between the origin of the above mentioned glacial landforms
and the climatic variations. Between 1965 and 1985 a
small reduction of summer temperature (less than 0.5 °C)
as well as an increase of winter precipitation were observed.
MANUELA PELFINI 1 , GIORGIO STRUMIA 1
,
ANDREA CARMINATI 1, SEVERINO BELLONI 2
& GIANCARLO ROSSI 3
Response times of alpine glaciers, as defined
by tree vegetation signs: the example of the Lys Glacier
(Valle D'aosta)
308
1 Dipartimento di Scienze dell' Ambiente e del Territorio,
Universita di Milano, via Emanueli 15,20129 Milano, Italy
2 Dipartimento di Scienze della Terra, Universita di Milano,
via Mangiagalli 34, 20133 Milano, Italy
3 Enel Cris, corso del Popolo 245,30100 Venezia-Mestre, Italy
Glaciers represent an interesting source of information
about the climate of the past, as they are valid recorders of
climatic fluctuations. After a changes in temperature and
precipitation, glaciers first change their mass balances and
the equilibrium line altitudes, then the fronts either advance
or retreat. However, there is a certain delay between the
climatic forcing and a shifting of the glacier front. The response
time for Alpine glaciers is often estimated using
methods based on a linear correlation between front variations
and the patterns revealed by several climatic parameters
such as temperature and precipitation.
The purpose of this study was to calculate the response time
for a sample glacier, the Lys Glacier in Valle d'Aosta.
Front variation data is available for this glacier and the series
starts from 1914. The study methods included dendrogeomorphological
investigations, thus proposing a method
that can be used even when suitable meteorological data
series are not available. Four mean dendrochronological
curves were plotted from data collected from the analysis
of 216 larch trees. The curves correspond to areas from
which the glacier retreated in time intervals that gradually
reach more recent periods. The curves were then correlated
with the glacier front variation data. The linear correlations
were repeated by progressively breaking down the
data into time periods differing by one year. In other
words, first the immediate effect of climate on the trees
and thus on the glacier was analyzed, and then analyzed
again, based on time delays gradually increased by one
year at a time, based on the supposition that the impact of
climate on the glacier occurs in that year, or in the following
years. The correlation coefficient r tends to drop after
the year 0, corresponding to an initial immediate response
of the glacier, to then increase the time period until
the maximum point is reached, corresponding to a delay in
glacier response to the climatic variations (an absolute value).
This maximum is reached in the 5 th year, which represents
the delay between the two curves and thus the re­
sponse time for the Lys Glacier. The value obtained refers
only to the 19 th
century. Therefore, the result holds only
for the time interval considered. The results obtained by
correlating the mean dendrochronological data curves with
the front variation data curves for the Lys Glacier, were similar
to those obtained from the correlation between the
temperature data and front variation data. The use of running
means provided confirmation of these findings, adding
to their validity in that the correlation coefficient, r,
increased.
The reliability of the utilization of vegetation to evaluate
the response times of Alpine glaciers was also confirmed
by the fact that there was no delay between the climatic input
and tree response.
The trees that are most suited to this type of investigation
are those located outside the area of the maximum Holocene
expansion of the glacier. Such trees probably are effected
by the climate of the valley head without, however,
being disturbed by their extreme closeness to the glacier
mass. It should also be kept in mind that glaciers respond
to a number of climatic parameters, although temperature
has the greatest impact on Alpine glaciers. Thus the use of