Rock avalanche and mountain slope deformation in a convex dip-slope: The case of the Maiella massif, Central Italy

The Lettopalena rock avalanche occurred about 4.8 kyr BP along the SE slope of the Maiella massif, in the easternmost sector of the central Apenninic chain. The massive rock slope failure involved about 30 x 10(6)m(3) volume of well-bedded Eocene and Miocene limestone and marly-limestone, which slid onto the Aventino river valley. A comprehensive study has allowed the identification of morphological, structural and lithological constraints on slope failure style, which is featured by a break-out geometry rather than a toe rupture one. The break-out developed by cutting bedding planes and utilizing low angle shear surfaces. According to a geological model of rupture, the stress-strain analysis performed through a finite difference code, revealed the fundamental role played by the rock mass anisotropies due to shear surfaces (inherited tectonic derived surfaces). Topographic stress itself could not have been sufficient for determining significant slope deformation. Shape and dimensions of the Lettopalena rock avalanche deposit suggest a low mobility and high energy dissipative event due to the geomorphic control of the pre-existing topography and the high deformability of the outcropping Mio-Pliocene formations, despite a significant run-up on the opposite side of the Aventino valley.