Ugo Sauro

Evidence of recent surface faulting and surface rupture in the Fore-Alps of Veneto and Trentino (NE Italy)

Abstract The Fore-Alps of western Veneto and Trentino regions belong to the central Southern Alps (NE Italy), in which there is little evidence of very fresh surface ruptures or surface faulting. This does not seem to match historical data about earthquakes, some of which have been very intense. The strong influence of the inherited structures makes it difficult to detect a direct link between morphotectonic features and present-day stress fields. In the present study, four areas (Orsara, Scandole, Naole and Soran) with surface faulting and surface rupture features were examined, and models of morphotectonic evolution are discussed. In the Lessini Mountains, the Orsara graben and Scandole ridge show examples of surface faulting and surface rupture, respectively, reactivating Paleogene normal faults and fractures. Within the Orsara graben, rocky bluffs displace the previous morphological features. The bluffs are some decimetres to some metres high and are practically devoid of evidence of either physical or chemical weathering; on the slopes above them are steep areas which may be interpreted as the remnants of previous strongly weathered bluffs. The Scandole ridge has many trenches, some with rocky walls, which may be the result of several episodes of morphotectonic rupture. In the Giudicarie Belt, the Naole and Mt. Soran surface faulting landforms are details within large frontal culmination walls of Neogene thrusts. The Naole ridge corresponds to the southeastern sector of Monte Baldo. Here, inside a fault angle valley, a sinuous scarp originating from surface faulting marks the base of the fault scarp slope. Ridge splitting is the expression of the backward migration of separation niches due to slope tectonics, also evidenced on the slope by several terrace-like features and by a lower belt of very thick slope breccias. On Mt. Soran, in the Gruppo di Brenta massif, the surface faulting scarp faces uphill, giving rise to a trench-like feature. Downvalley of the scarp, there is the niche of a large landslide dated to 3 kyears B.P. All these landforms are consistent with slope tectonic movements caused by intense earthquakes. Whereas the morphostructures in the Lessini Mountains are the result of responses by sensitive structures, the Naole and Mt. Soran features express the evolution of frontal culmination walls of thrusts, with clear evidence of present-day tectonic activity. On the basis of the weathering of the scarps and associated features, the relative seismotectonic episodes probably occurred between the Bronze and Middle Ages.

Solution and recrystallisation processes and associated landforms in gypsum outcrops of Sicily

Abstract Four small areas of Messinian (Upper Miocene) age gypsum, outcropping in western Sicily, are described. Messinian age evaporites are found in Sicily over a 1000-km 2 area. Here, gypsum outcrops extensively as a consequence of soil erosion induced by human impact. Geomorphological maps show how the rocky surfaces are characterized by a wide range of forms. There are large, medium, small, and microsized forms, which can be identified as belonging to different morphotypes. The morphotypes can be classified into two main categories: those that originated by solution and those that originated through recrystallisation. Four areas, illustrated by geomorphological maps, were specifically chosen to describe a type of medium-sized form: dome-like hills. These medium-sized forms are covered by a mosaic of smaller forms, related to both the previous categories: different types of karren and of “expansion” forms. The types of karren can be explained as the results of the solution process under different hydro-dynamical behaviour; the dome-like hills and other related “expansion” forms are more difficult to understand. These “expansion” forms can be explained by the same process that leads to the development of gypsum tumuli. The outcrops of gypsum lacking soil cover and influenced by alternating seasonal water conditions of surplus and deficit are affected by both solution and recrystallisation processes. During the wet season, the water soaks into the rocky mass, filling all the fissures and pores of the outer rocky layer from a few centimetres to some metres below the surface. During the dry season, there is a capillary upward motion of the water solution. Near the surface, gypsum precipitates from the oversaturated solution, increasing the crystal size or forming new crystals. In this way, during the dry season, there is a pressure increase in the outer gypsum layers, which is responsible for the development of a “gypsum weathering crust” and characterised by many different forms such as gypsum tumuli, pressure ridges, pressure humps, and other related small forms. The crust may also lead to the development of mega-tumuli and dome-like hills. From the morphostructural point of view, the dome-like hills do not seem to be controlled by the strike, dip, or fissuring of the gypsum beds. Their evolution seems to be linked to the fact that on most of the dome surfaces, the weathering crust is evolving through a nearly isotropic field of stresses, resulting in volume increase in the outer gypsum layer.

Geomorphological aspects of gypsum karst areas with special emphasis on exposed karst

1. Mediumand large-sized forms Mediumand large-sized gypsum karst landforms are similar in many respects to those found on carbonate karst. However, there are also some differences. This chapter will review the typical landforms of gypsum karst, stressing the similarities and the differences when compared with carbonate karst forms, and discussing their morphogenetic peculiarities. In gypsum karst areas it is also commonly possible to recognise landforms produced by erosion due to surface flow and the effects of fluvial deposition, both of which are to some degree related to the presence of lenses and layers of other rock types. Landforms produced by different types of landslides are also present. Among the typical karst landforms, the following have been recognised: 1) dolines, 2) blind valleys, 3) polje-like depressions, 4) subsidence and collapse basins in rocks that overlie gypsum.

Closed Depressions in Karst Areas

Closed depressions are a defining feature of karst areas. Closed depressions occur on many size scales from meters to kilometers. The smaller depressions, known as dolines or sinkholes, are important inputs to the karst drainage system. At the intermediate scale are compound dolines, uvalas, and blind valleys, also formed by and related to the input of precipitation and surface water into the aquifer. Largest are the great poljes, complex features on a size scale of tens of kilometers. Most closed depressions form by a combination of bedrock dissolution and soil piping although some form by cavern collapse or by upward stoping from deep-seated cavities.