Mass movement and landscape evolution in weathered granite and gneiss terrains

Abstract

The paper assesses the contribution of mass movement to the development of landforms in weathered granite and gneiss terrain, using examples from SE Brazil, southern Mexico, SE China, and other locations. The style of slope failures varies depending on local relief and the grade of weathering, which mutually influence each other. Shallow debris slides and boulder falls are common in less weathered rock and steep terrain, whereas rotational slides appear to dominate in highly weathered rock and in more subdued topography. In certain topographic circumstances, slides may turn into debris flows or earthflows. Extreme rainfall is a typical trigger of mass movement in weathered terrain. Mapping of past landslides may considerably assist in hazard assessment, as they usually leave a clear geomorphological record.

Linking weathering and rock slope instability: non‐linear perspectives

“…Compound forms, such as rock-ice avalanches, can also occur (Schneider et al, 2011). Migon (2010) finds widespread evidence of this pattern, from a survey of deeply weathered granitic landscapes in SE China, SE Brazil and Mexico. With special reference to granitic terrains, Durgin (1977) explained the type of rock slope failure in terms of the degree of weathering (Table I).…”

“…A more nuanced view, based on dividing factors causing slope instability into preconditioning, preparatory and triggering factors (Glade and Crozier, 2005) acknowledges three roles of weathering. As an example, Migon (2010) notes that on massive granite domes in Brazil, rockfalls can occur where overhangs produced by cavernous weathering grow enough to undermine the slope. Furthermore, weathering can provide a trigger for slope failure through initiating movement and shifting the slope from 'marginally unstable' to 'actively unstable' states.…”

“…However, the boundary between rock slopes and soil-covered slopes is rather blurred. Some slopes may be composed of rocks which have been extensively and deeply weathered in situ over long periods, resulting in a complex weathering profile dominated by saprolite (as a result, for example, of humid tropical conditions as described more fully by Migon, 2010). Within such slopes, the pre-existing rock structure, mineralogy and discontinuity patterns exert a strong control on subsequent deep weathering which is isovolumetric in nature, thus preserving their designation as rock slopes (Ollier, 2010).…”

“…Weathering of granitoid rocks and characteristic mass movement types (afterDurgin, 1977 andMigon, 2010) …”

Controls on the geotechnical response of sedimentary rocks to weathering

“…Durgin, 1977;Fookes et al, 1988;Hencher and McNicholl, 1995;Migon, 2010;Thomson et al, 2014;Yatsu, 1988) and its importance for rock slope stability has been demonstrated in numerical and analogue studies (e.g. Durgin, 1977;Fookes et al, 1988;Hencher and McNicholl, 1995;Migon, 2010;Thomson et al, 2014;Yatsu, 1988) and its importance for rock slope stability has been demonstrated in numerical and analogue studies (e.g.…”