Etching as a Process of Landform Development ∗

Abstract

Bedrock forms of etch origin result from the interaction of groundwaters and bedrock at the weathering front at the base of the regolith. They are significant for general theories of landscape and landform genesis because they are azonal with respect both to climate and lithology. Two stages of etch form development are recognized: one involves weathering and the formation of a regolith; the second consists of stripping of the regolith and the exposure of the bedrock forms. Although etch forms have been recognized for some two centuries, the concept of etching as a process of landform development has been neglected, particularly in North America.

Decay of ignimbrite fairy chimneys of Arizona's Basin and Range Province, USA

“…In other words, once the porosity of the weathering rind under the varnish reaches a threshold of ~25% to 30%, a vertical face provides no lateral support to slow detachment. It is also possible that a chimney top receives even less contact with moisture; a concept in geomorphic research is that contact‐time with water is a key factor in decaying rock material (Oberlander, 1974; Ruxton, 1958; Twidale, 1974, 2002; Twidale & Mueller, 1988; Wahrhaftig, 1965); water running off the tops of the chimneys might result in less time in contact with water. Regardless of this speculation on the reason for more stable tops and sides, VML data provide a general understanding of the timescale of the rates of fairy chimney flaking in the study region.…”

The origin, age, and conservation, of an ‘elevated platform’, Yarwondutta Rock, north-western Eyre Peninsula, South Australia

“…As a granite landform of etch origin (e.g. Mueller & Twidale 1988b;Twidale 2002) they are in some measure exempt from climatic control (e.g. Twidale & Lageat 1994).…”