Relationship between morphological preferred orientations and landslides

Crystals orientation in polycrystalline natural compounds maybe either completely random or else follow preferred directions,which reflect physical processes in which the materials havebeen involved during the solidification and / or after the solidstate had been reached.The preferred orientation can be divided into two maingroups: i) preferred orientation of the crystal lattice (LPO,lattice preferred orientation) and ii) grains preferred orientation(i.e., morphological preferred orientations, MPO). Frequentlythere is a close relationship between these two groups.Geological processes that determine the formation of LPO are,for example, tectonic (regional) compressive movements; on theother hand MPO can be induced also by local stress (i.e.,gravitational movements). While tectonic (regional)compressive movements may produce LPO even on alreadylithified rocks, usually, MPO are induced only on not-lithifiedand incoherent rocks.The preferred orientation cab be observed: i)macroscopically (the rock structures) ii) microscopically, grainsorientation and morphological textures of the rock according tothe classic concept of optical microscopy, iii) with diffractionmethods (i.e., X-rays and neutrons diffraction), to study bothLPO and MPO when, this last, cannot be studied via opticalmethods because, for example, of a very small grain size.This research will investigate MPO via X-ray diffractiononly. We collected, and kept oriented, samples in severallandslide areas. In particular samples were collected both in theactive crumbling area and at the landslide margin. Sampleswere analyzed for texture using X-ray diffractometer equippedwith a phi-chi Eulerian cradle. We analyzed the preferredorientation of the hkl reflections: i) (001) and (060) in smectitiand illite; ii) (001) and (100) in caolinite; iii) (24-1) inplagioclase.Preliminary investigation demonstrated a direct correlationbetween the number of MPO and the amount of clay minerals.Texture measurements on samples collected in the crumblingarea agree with other morphological field measurements,providing, in addition to the main direction of the landslide, alsothe vertical module, thus probably defining the preferential pathfor interstitial fluids migration. Only in one case we couldobserve preferred orientation in a sample coming from a marginof a landslide, data which could testify a past movement (paleolandslide) or else a quiescent landslide.