Landscapes developed on ignimbrites

Abstract

This paper analysesthe landforms and landscapes developed on ignimbrites outcroppingin different regions of Argentina: Portezuelo (province of Mendoza), LihuelCalel (province of La Pampa), Pilcaniyeu (province of Río Negro), BardaColorada (province of Chubut) and Chon Aike (province of Santa Cruz). Some of theselocalities show clear resemblance to landforms which are typical ofsedimentary rock landscapes, whereas others expose landforms typicalof granitic rocklandscapes. Systems of macro- and micro-landforms have been observed, such asinselbergs, bornhardts, nubbins, castle koppies, tors, crests and pinnacles, lowcliffs, whale backs, and many other, associated minor features. Landforms ofmicro-modelling are shown at the base of vertical slopes, as cavities of the alveolarhollows and tafoni types, with subsequent evolution to caves, caverns and rockshelters. Besides, sometimes peculiar landforms such as yardangs, mushrooms andhoodoos are observed. The dominant agents that are responsible for these features arechemical and physical weathering and aeolian erosion. The micro-modellingaffecting the different ignimbrite units is a direct consequence of their particulartextural and structural conditions, on which a varied set ofprocesses and erosionmechanisms have acted and defined their shape. In other cases, the orientation of theprevailing winds and the exposure of the ignimbrite flows have a decisivecontribution to their genesis and ensuing development. It is hereinconcluded that theheterogeneity of these rocks, mostly due to changes in the welding degree, generatesdiverse types of macro- and micro-landforms.p { margin-bottom: 0.25cm; line-height: 120%; }