Irene Hernando

Landscapes Developed on Ignimbrites

This paper analyses the landforms and landscapes developed on ignimbrites outcropping in different regions of Argentina: Portezuelo (province of Mendoza), Lihuel Calel (province of La Pampa), Pilcaniyeu (province of Rio Negro), Barda Colorada (province of Chubut) and Chon Aike (province of Santa Cruz). Some of these localities show clear resemblance to landforms which are typical of sedimentary rock landscapes, whereas others expose landforms typical of granitic rock landscapes. Systems of macro- and micro-landforms have been observed, such as inselbergs, bornhardts, nubbins, castle koppies , tors, crests and pinnacles, low cliffs, whale backs, and many other, associated minor features. Landforms of micro-modelling are shown at the base of vertical slopes, as cavities of the alveolar hollows and tafoni types, with subsequent evolution to caves, caverns and rock shelters. Besides, sometimes peculiar landforms such as yardangs, mushrooms and hoodoos are observed. The dominant agents that are responsible for these features are chemical and physical weathering and aeolian erosion. The micro-modelling affecting the different ignimbrite units is a direct consequence of their particular textural and structural conditions, on which a varied set of processes and erosion mechanisms have acted and defined their shape. In other cases, the orientation of the prevailing winds and the exposure of the ignimbrite flows have a decisive contribution to their genesis and ensuing development. It is herein concluded that the heterogeneity of these rocks, mostly due to changes in the welding degree, generates diverse types of macro- and micro-landforms.