Surface and sub‐surface Schmidt hammer rebound value variation for a granite outcrop

Abstract

This study presents rock strength variations at granite outcrops and in subsurface vertical profi les in the Jizerské hory Mountains, Czech Republic. Schmidt hammer rebound values in subsurface profi les change gradually from the bedrock surface downward. An exponential relation has been observed between the R-values and depth in rock outcrops to a depth of around 4·5 m. The exponential nature of the curve indicates that rock hardness increases more rapidly with depth in the uppermost 1 m section of the rock profi le. A detailed study of rebound values obtained from both intact and polished rock exposures reveal effects of surface grinding on results of the Schmidt hammer method. The range of data collected increases after grinding, allowing more precise discrimination of rock surfaces in respect of age and weathering. The Schmidt hammer method may be used effectively as a relative-age dating tool for rock surfaces that originated during the Late Pleistocene. It is concluded that this time limitation can be signifi cantly mitigated by surface grinding before measurement.

Timing of the Northern Prince Gustav Ice Stream retreat and the deglaciation of northern James Ross Island, Antarctic Peninsula during the last glacial–interglacial transition

“…The upper limit of R-value for mediumgrained granites, which we tested here, mostly ranges between 50 and 70 (cf. Goudie, 2006;Černá and Engel, 2011), which corresponds to our results. Therefore we hypothesize that the 35 boulders used to estimate the mean R-value are considered as fresh, sometimes with striated surfaces.…”

Schmidt hammer exposure‐age dating (SHD) of late Quaternary fluvial terraces in New Zealand

“…beyond the Late Glacial re‐advances) weathering, and thus R ‐values, must inevitably reach a dynamic equilibrium. SH studies of 10 4 –10 5 year timescale features have pointed towards curvilinear relationships (White et al ., ; Engel, ; Sánchez et al ., ; Černá and Engel, ), as well as some SH studies on 10 2 –10 3 year timescales (McCarroll and Nesje, ; Betts and Latta, ; Awasthi et al ., ; Kellerer‐Pirklbauer et al ., ). Curvilinear correlations on such short timescales could be due to comparatively small datasets, uncertainty in numerical ages, exceptionally fast weathering conditions, or coincidental, non‐age related variations in rock surface hardness between study sites (Shakesby et al ., ).…”

Geomorphology and weathering characteristics of erratic boulder trains on Tierra del Fuego, southernmost South America: Implications for dating of glacial deposits

“…Rock weathering (and therefore R-values) could have reached saturation in Tierra del Fuego. However, despite agreement that Rvalues will progress toward a dynamic equilibrium over time (White et al, 1998;Engel, 2007;Sánchez et al, 2009;Černá and Engel, 2011;Stahl et al, 2013), numerous studies have effectively distinguished LGM and pre-LGM deposits using the technique on timescales of 10s to 100 s ka (Ballantyne et al, 1997;Rae et al, 2004;Černá and Engel, 2011;Stahl et al, 2013). Very high rates of weathering are required to reduce the ages of the RC 1 boulders (Table 2), yet no obvious jump in R-values occurs between these and the BI 1/BI 2 boulder trains.…”