Evidence of slope instability in the Southwestern Adriatic Margin

Abstract

Abstract. The Southwestern Adriatic Margin (SAM) shows evidence of widespread failure events that generated slide scars up to 10 km wide and extensive slide deposits with run out distances greater than 50 km. Chirp-sonar profiles, side-scan sonar mosaics, multibeam bathymetry and sediment cores document that the entire slope area underwent repeated failures along a stretch of 150 km and that masstransport deposits, covering an area of 3320 km 2 , are highly variable ranging from blocky slides to turbidites, and lay on the lower slope and in the basin. The SAM slope between 300-700 m is impacted by southward bottom currents shaping sediment drifts (partly affected by failure) and areas of dominant erosion of the seafloor. When slide deposits occur in areas swept by bottom currents their fresh appearence and their location at seafloor may give the misleading impression of a very young age. Seismic-stratigraphic correlation of these deposits to the basin floor, however, allow a more reliable age estimate through sediment coring of the post-slide unit. Multiple buried failed masses overlap each other in the lower slope and below the basin floor; the most widespread of these mass-transport deposits occurred during the MIS 2-glacial interval on a combined area of 2670 km 2 . Displacements affecting Holocene deposits suggest recent failure events during or after the last phases of the last postglacial eustatic rise. Differences in sediment accumulation rates at the base or within the sediment drifts and presence of downlap surfaces along the slope and further in the basin may provide one or multiple potential weak layers above which widespread collapses take place. Neotectonic activity and seismicity, together with the presence of a steep slope, represent additional elements conducive to sediment instability and failure along the SAM. Evidence of large areas still prone to failure provides elements of tsunamogenic hazard.

Bathymetry of the Adriatic Sea: The legacy of the last eustatic cycle and the impact of modern sediment dispersal

“…The Multi Beam data confirm the main features denoted by the Single-Beam data but also add relevant information to the SAM ; (B) shelf-indenting submarine slide with large blocks (Minisini et al, 2006); (C) deeply-incised Bari canyon with abandoned channel-levee complex down slope . GS: Gondola Slide; DS: Dauno Seamount; BCS: Bari Canyon System.…”

“…GS: Gondola Slide; DS: Dauno Seamount; BCS: Bari Canyon System. slope, showing: (1) the blocky nature of the mass-failure features emanating from multiple slide scars (Minisini et al, 2006); (2) the large variety of erosional and depositional bottom-current features (Verdicchio & Trincardi, 2006); (3) the Bari Canyon System (BCS), acting as the main sediment conduit since the Last Glacial Maximum ; and (4) the Dauno Seamount, the main structural feature on the slope, flanked by erosional moats recording the impact of bottom-hugging density currents .…”

“…The morphological map of Giorgetti and Mosetti (1969) was drawn with the purpose of representing a pictorial view of seafloor structures, without labels and with bathymetric contours at 20 m intervals accompanied by hatched patterns to highlight local relief. It is remarkable how the main features of the basin were correctly outlined and reported in their map; examples of features confirmed by more recent surveys include: the field of sand dunes offshore Venice (Correggiari, Field et al, 1996); the drowned coastal sand ridges found offshore Ravenna (Correggiari, Roveri et al, 1996); and the slide scars and seamounts on the South Adriatic slope (Minisini, Trincardi, & Asioli, 2006;Verdicchio & Trincardi, 2006).…”

Investigation on tsunami effects in the central Adriatic Sea during the last century – a contribution

“…We remark, however, that if the tsunami was induced by a submarine landslide, the source can very unlikely be located in the place suggested by Bedosti (1980) so close to the coast. Recent investigations show that this area is not susceptible to large offshore mass failures (Trincardi et al, 2004), while evidence for widespread failures has been found in the south-western Adriatic margin (Minisini et al, 2006) more than 100 km offshore south of Gargano, where steep slopes link the shallow Adriatic platform to the deep Ionian sea. Anomalous disturbances were also seen on the eastern coast of the Adriatic Sea: at Bar (30 cm), Dubrovnik (40 cm) and Split (45 cm) (Zoe-Armanda, 1988;Papadopoulos, 1993).…”

Tsunami hazard scenarios in the Adriatic Sea domain

“…Their contribution to tsunami generation can be conspicuous, but can be predicted only if the location and size of the landslide is known with sufficient accuracy. Minisini et al (2006) show that in the Southern Adriatic Sea slope instability could have played a relevant role in tsunami generation in historical and prehistorical times.…”