Sepe, Ciro

In the mountainous area of the «Parco Nazionale d' Abruzzo », characterized by several massifs with maximum altitudes frequently above the 2 000 m, a large number of glacial traces can be observed. The examination of new evidence discovered and the re -examination of those already known has permitted to reconstruct several distinct glacial events. In the studied area the cirques are the most frequent forms due to glacial modelling, even though other glacial remains like troughs and moraine deposits are found in association with them. In a number of places the existence of several episods of glaciation is provided by the occurence of a cirque stairway observed on the same slope. Starting from the more complete and best preserved local sequence an attempt was made to put into order all the other glacial traces. Correlations have been based on relative position and morphology of the cirques and the snow limits. As a result, it seemed likely to refer the observed evidence to four distinct events of glaciation. The first glacial event (pre -wiirmian glaciation, probably Riss) is characterized by a snow limit situated about 1 340 meters a.s.l, and evidenced by few glacial forms in the massifs of Toppe del Tesoro, S. Nicola and the Meta Mountains. They consist of large badly preserved cirque-like depressions situated about 1 300-1 400 meters a.s.l., and moraine deposits whose position and distribution largely contrasts with the actual orographic configuration. During a new glacial advance (maximum wiirrnian expansion) the snow limit rised to 1 560 m. Numerous are the traces relative to this ad vance, consisting in a large number of erosional forms , like cirques and glacial troughs, and morainic deposits which frequently preserve their ori ginal morphology forming lateral and frontal moraines. The third event (first late Wiirmian stage = first apenninic stage of FEDERICI, 1979) is characterized by a further rise of the snow limit now situated about 1 760 m. The evidences rel ative to this minor expansion consist only of erosional forms except one morainic deposit rico gnized on the eastern side of the Meta Mountains. Effects relative to the fourth event (second late Wiirmian stage = second apenninic sta ge of FEDERICI, 1979) can be observed only in the reliefs situated North of the Sangro Valley and in the Meta Mountains, while in the other reliefs the snow limit, situated about 1 970 m, had already reached or passed the altitude of their highest peaks. A summary examination of the distribution and the morphological features of the glacial traces studied shows that the area South of the Sangro valley seems to have developed greater glaciers that the part of the studied area situated at the North of the same valley.

In the present paper, the capillary barrier formation at the interface between soil layers, which is characterized by textural discontinuities, has been analyzed. This mechanism has been investigated by means of a finite element model of a two-layer soil stratification. The two considered formations, belonging to the pyroclastic succession of the “Pomici di Base” Plinian eruption (22 ka, Santacroce et al., 2008) of the Somma–Vesuvius volcano, are affected by shallow instability phenomena likely caused by progressive saturation during the rainfall events. This mechanism could be compatible with the formation of capillary barriers at the interface between layers of different grain size distributions during infiltration. One-dimensional infiltration into the stratified soil was parametrically simulated considering rainfall events of increasing intensity and duration. The variations in the suction and degree of saturation over time allowed for the evaluation of stability variations in the layers, which were assumed as part of stratified unsaturated infinite slopes.

Fallout volcanic deposits of Somma- Vesuvius (Campania, southern Italy), characterized by the presence of layers with contrasting textural and hydraulic properties, are frequently affected by shallow landslides during rainwater infiltration. The soils of the stratigraphic sequence present intra- particle pores, originated by the gases escaped during magma decompression in the volcanic conduit, thus are characterized by double porosity (i.e., intraparticle and interparticle pores), which is expected to affect their hydraulic behaviour, and to play a key role in rainwater infiltration through layered deposits. To understand the effect of double porosity on the hydraulic behaviour of the involved soils, controlled experiments have been carried out in an infiltration column. The experimental apparatus is provided with newly designed non-invasive Time Domain Reflectometry (TDR) probes, not buried in the investigated soil layers so as to minimize disturbance to the flow, allowing water content measurement during vertical flow processes. Specifically, transient flow experiments are carried out through reconstituted specimens of black scoriae and grey pumices, both loose pyroclastic granular soils from fallout deposits of Somma-Vesuvius, featuring double porosity with different pore size distributions, that were estimated by X-ray tomography and Mercury Intrusion Porosimetry. The experimental results highlight the effects of the double porosity and clearly indicate the different behaviour of the two soils during wetting and drying processes, mainly related to the different dimensions of intraparticle pores.