THE EFFECTS OF LATE QUATERNARY CLIMATE CHANGES ON THE STRATIGRAPHY OF THE M. ETNA VOLCANO (SOUTHERN ITALY)

At Mt. Etna Volcano, in eastern Sicily, relics of ancient volcanic edifices are largely exposed at the base of the eastern flank of the modern (< 40 ka) strato-volcano. The older volcanics are represented by subalkaline lavas, interleaved within Middle Pleistocene marine clays, which crop out along the Ionian coast of the region. In the same area, the first subaerial products, which are represented by a sequence of alkaline lavas ranging in age from 220 ka to 121 ka, are exposed. A major erosional surface grading to the OIS 5.5 (125 ka) marine terrace has been recognised within the volcanic succession. Finally, volcanic horizons showing radiometric ages from 105 to 93 ka are exposed in the walls of a large caldera depression (Valle del Bove) located along the eastern slope of the modern edifice. A major unconformity is modelled at the top of this sequence. Also the modern stratovolcano sequence is marked by a main unconformity, separating the pre-15 ka volcanics from the younger horizons.

As a whole, the volcanic succession of Mt. Etna, together with the marine terrace deposits, provides several chronological data, useful to detail the stratigraphy of the end of the Middle Pleistocene and the entire Late Pleistocene.

Recent investigation, consisting of 1:10.000 field mapping caried out on the entire eastern flank of the Volcano, integrated with information from several bore-holes, have evidenced the occurrence of distinct, several tens of meter thick, clastic horizons within the volcanic succession. These deposits exhibit textural features typical of epiclastic (debris-flow) horizons. These are made of plurimetric matrix-supported conglomerate in a well cemented muddy-sandy matrix and by fine tuff with rare centimetre-sized conglomerate elements. Generally they are associated with coarse grained, poorly sorted and unconsolidated breccias, composed of a wide range of angular to sub-rounded lava blocks and scoriae, in a poorly consolidated matrix, indicating a debris-avalanche origin. The older clastic horizons infill deeply entrenched valleys modelled on the pre-Tyrrhenian volcanics, being covered at the top by the marine terrace of the OIS 5.5. A further clastic horizons mark the unconformity at the top of the 93 ka old volcanic deposits. Finally, very thick conglomerate horizons, showing dm-sized boulders, are related to an impressive alluvial fan that conceals the topography modelled on the pre-15 ka volcanics, being covered by several historical and pre-historical lava flows.

The geometric relation between dated lava horizons and analysed clastic deposits indicates that the latter actually developed in very short periods, in the order of 1 ka, during which gravity-induced mass transport and alluvial processes have remobilised huge volumes of detritus. In this periods, coinciding with major deglaciations accompanying the sea-level rises towards the OIS 5, 3 and the Holocene, the exogenous processes were largely prevailing on lava flows accumulation. This evidence confirms that the maximum effectiveness of agents on the landscape have characterised in the past the periods of rapid sea-level rise rather than the entire periods of the sea-level highstand, thus suggesting that the increase of precipitation and the recurrence of heavy rain falls have been strctly related to climate crises induced by the main deglaciation processes.