ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

ced a longer, more gentle gradient to base level for Atlantic
streams. The relatively gentle fluvial gradients, coupled
with a wide outcrop belt of resistant Piedmont and Blue
Ridge rock-types, has slowed the westward extension of
east-flowing streams. Here the drainage divide is stalled on
the Blue Ridge, forming a steep, east-facing escarpment
with locally over 800 m of relief. The location of maximum
late Cenozoic flexural uplift, coincident with the Blue Ridge
crest, has worked to maintain the position of the modern
drainage divide, slowing its westward migration.
The characteristics of the Blue Ridge and Allegheny
escarpments in eastern North America broadly match those
described as Type-1 and Type-2 escarpments respectively;
however, important discrepancies remain. Our results
are in agreement with other studies which conclude that
eastern North America does not have a strictly Type-I
Great Escarpment, that is, an escarpment inherited from
an initial high-relief margin whose long-term expression is
favored by minimal post-rift offshore sediment loading.
Clearly, the U.S. Atlantic margin, especially the middle and
northern portions, is dominated by subsidence driven by
post-rift offshore sediment loading. Similarly, our analysis
does not support the Blue Ridge and Allegheny front as
strictly Type-2 escarpments, that is, escarpments well adjusted
to rock-type and structure and etched into the landscape
on the seaward side of a flexural peripheral bulge.
For the Blue Ridge and Allegheny escarpments, the modern
drainage divide is not everywhere coincident with the
location of maximum landward flexural uplift, the escarpments
are not everywhere well adjusted to rock-type and
structure, and the preservation of Paleogene marine sediments
in the southern Piedmont argues for rapid westward
retreat of the initial rift-flank escarpment. The only true
Type-2 escarpment on the Atlantic margin is the Fall Zone,
which exploits the difference in rock erodibility between
resistant Piedmont rocks and non-resistant Coastal Plain
sediments and is best expressed along the steepest,
seaward-facing portion of the flexural peripheral bulge.
We conclude that the larger Allegheny and Blue Ridge
escarpments are a hybrid between the Type-1 and Type-2
escarpments and share at least some characteristics in common
with the Great Escarpments of the southern continents.
MANUELA PELFINI 1, MARCO NERI 2 & ALVISE CASANOVA 1
Dendrogeomorphology as a method of dating seismic
events along active faults: the case of the Pernicana Fault
(Mt, Etna, Sicily, Italy)
1 Dipartimento di Scienze dell' Ambiente e del Territorio,
Universita di Milano, via Emanueli 15,20129 Milano, Italy
2 Istituto Internazionale di Vulcanologia,
p.zza Roma 2,95123, Catania, Italy
Dendrochronology today represents a proven method for
dating geomorphological events of various types. Among
such events, seismic and volcanic events should be included.
Soil movements created by the activity of a volcano
can cause damage to tree vegetation such as breakage of
tree tops, root damage, tilting of trunks. Such conditions
can lead to failure to produce rings, the formation of narrow
rings or the formation of reaction wood (compression
wood in conifers). The latter is formed when a tree starts
to produce eccentric rings in order to return to its original
vertical stance. Identification of these signs, with annual
definition allows for indirect dating of events.
The objective of this study was to apply the dendrochronological
method in order to date the activity of Mt, Etna occurring
prior to instrumental records, in the area NE of
the volcano characterized by the NE rift - Pernicana fault,
an association of particularly active volcanic and tectonic
units, associated with the activity of the NE crater.
A dendrochronological study was thus conducted on specimens
of Pinus laricio in an area of about 15.000 m', along
the Pernicana fault plane at about 1700 m above sea level.
Over 300 trees were sampled, including several cores in
areas several kilometers away from the fault, and their
growth over time was analyzed in detail.. The tree specimens
cover a time span of about 200 years. During this chronological
time interval, at least 15 major periods of bad
conditions affecting the vegetation were identified, plus
another ten of smaller scale, at fairly regular intervals. The
more distant trees, used as reference samples, had not recorded
the stress periods observed in the samples collected
along the fault and also excluded the climatic influence
(records of climatic conditions) as no significant correlations
emerged from the comparison with the meteorological
data pertaining to the last 50 years.
Comparisons were then carried out with the volcanic activity
of Mt. Etna and the macroseismic data pertaining to
both the Pernicana Fault and the regional context. The
quality of the volcanic activity data and the seismic data is
particularly reliable only for the last 25 years and. the comparison
was thus concentrated, at the beginning on that
period of time. The initial results obtained revealed that
the volcanic activity had not significantly influenced the
growth of the vegetation, with the exception of when it occurred
together with telluric events associated with the
eruptions themselves. To the contrary, the macroseismic
activity of the Pernicana fault appears to have had a definite
influence on tree growth, creating periods of stress repeated
over time and of varying intensity.
This analysis led to the conclusion that even the periods of
stress for the vegetation occurring between 1807 and
1970, can be correlated mainly with the macroseismic activity
of the fault, revealing probable seismic activity that involved
the study area. Moreover, the comparison showed
that local earthquakes are those most felt by the vegetation'
probably due to the strong macroseismic intensity related
to the surface hypocenters, typical of the structure
analyzed.
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