Rock Resistance and its Influence on Landforms in Basement Terrains

Lithologic controls on knickpoint formation in Sierra Nevada bedrock channels

“…Thus, quartz content and average grain size are assumed to be two independent characteristics of granitic bedrock affecting channel slope. Similar to previous work that identified correlations between underlying geology and patterns of erosion (e.g., Lagasquie et al, 2012;Migon and Vieira, 2014), this study demonstrates statistically significant differences in bedrock grain size and modal mineralogy above and below channel knickpoints. While the erosional resistance of granitic bedrock is notoriously difficult to quantify, geomorphic field studies in granitic environments reveal several trends.…”

“…This study demonstrates that bedrock channel knickpoints are often coincident with local transitions in rock grain size and quartz content, implying a correlation between knickpoint formation and instances of unequal bedrock resistance. This study finds evidence that erosion rates may be partially controlled by the matrix grain size and relative abundance of quartz in the bedrock fabric, suggesting that unequal hardness contributes to differences in rates of erosion and are expressed in channel form as knickpoints (Lagasquie et al, 2012;Migon and Vieira, 2014). Although resistance to erosion was not specifically quantified, bedrock above the knickpoint was found to have textural and mineralogical characteristics associated with resistance to erosion, while the bedrock below the knickpoint was found to have textural and mineralogical characteristics associated with more erodible bedrock.…”

“…While the erosional resistance of granitic bedrock is notoriously difficult to quantify, geomorphic field studies in granitic environments reveal several trends. Resistant granite is generally characterized by equigranular texture, fine-grain sizes, and greater quartz content (Lagasquie et al, 2012;Sousa, 2012;Migon and Vieira, 2014). Weaker granites, prone to faster rates of erosion, usually have heterogranular textures, coarse-grain sizes, and greater amounts of biotite (Wahrhaftig, 1965;Lagasquie et al, 2012;Migon and Vieira, 2014).…”

“…Resistant granite is generally characterized by equigranular texture, fine-grain sizes, and greater quartz content (Lagasquie et al, 2012;Sousa, 2012;Migon and Vieira, 2014). Weaker granites, prone to faster rates of erosion, usually have heterogranular textures, coarse-grain sizes, and greater amounts of biotite (Wahrhaftig, 1965;Lagasquie et al, 2012;Migon and Vieira, 2014). Determining if the bedrock above and below channel knickpoints contained heterogranular or equigranular textures, while important for future research, was beyond the scope of this project.…”

The distribution of inselbergs and their relationship to geomorphological, structural and lithological controls in Southern Zimbabwe

“…Their effects include the disintegration of rocks as a consequence of the relative abundance and the dispersal and clustering of certain minerals, the differences in the permeabilities of the rocks and disintegration characteristics of individual minerals due to microcracks and crystal cleavages and the influences of fractures on the disintegration of rocks and on the geometry of the inselbergs (Pye, 1986;Coque-Delhuille, 1988;Lagasquie et al, 2001).…”