Influence of tectonic folding on rockfall susceptibility, American Fork Canyon, Utah, USA

Abstract

Abstract. We examine rockfall susceptibility of folded strata in the Sevier fold-thrust belt exposed in American Fork Canyon in north-central Utah. Large-scale geologic mapping, talus production data, rock-mass-quality measurements, and historical rockfall data indicate that rockfall susceptibility is correlated with limb dip and curvature of the folded, cliff-forming Mississippian limestones. On fold limbs, rockfall susceptibility increases as dip increases. This relation is controlled by several factors, including an increase in adverse dip conditions and apertures of discontinuities, and shearing by flexural slip during folding that has reduced the friction angles of discontinuities by smoothing surface asperities. Susceptibility is greater in fold hinge zones than on adjacent limbs primarily because there are greater numbers of discontinuities in hinge zones. We speculate that susceptibility increases in hinge zones as fold curvature becomes tighter.

Tree-ring based reconstruction of the seasonal timing, major events and origin of rockfall on a case-study slope in the Swiss Alps

“…Furthermore, there are a large number of studies on rockfall modeling (Guzzetti et al, 2002;Dorren et al, 2006;Stoffel et al, 2006b) or on long-term accretion rates of rockfall (Luckman and Fiske, 1995;McCarroll et al, 1998). In addition, research has focused on possible triggers of rockfall such as tectonic folding (Coe and Harp, 2007), freeze-thaw cycles (Gardner, 1983;Matsuoka and Sakai, 1999;Matsuoka, 2006), changes in the rock-moisture level (Sass, 2005), the thawing of permafrost (Gruber et al, 2004), the rising of mean annual temperatures (Davies et al, 2001) or the occurrence of earthquakes (Harp and Wilson, 1995;Marzorati et al, 2002).…”

Controls on Rockfall-Talus Process-Response Systems, Kananaskis, Canadian Rockies

“…The role of tectonics on rockfall susceptibility has been reviewed by several authors (Selby, 1982;Miller & Dunne, 1996;Coe & Harp, 2007). Bedrock fractures at Earth's surface are abundant and range in scale from microcracks to local joint sets, to continenttransversing fault zones.…”

“…A study of rockfall susceptibility in tectonically folded strata was conducted in the fold-thrust belt exposed in American Fork Canyon, north-central Utah (Coe & Harp, 2007).…”

“…Analysis of large-scale geologic mapping (using aerial photographs), talus production (based on field observations), rock-mass field measurements, and a compilation of historical rockfall data, led to the conclusion that rockfall susceptibility depends on the dip of fold limbs and the curvature of fold hinge zones (Coe & Harp, 2007). Rockfall susceptibility is greater in fold hinge zones than on adjacent limbs, and it increases as fold curvature tightens, whereas susceptibility is proportional to dip on fold limbs ( angle.…”

“…The inflection points mark the limits of an individual fold which can be divided into a hinge zone and fold limbs. The interlimb angle is the angle between the lines tangent to the inflection points on the profile curve and this is used to indicate the tightness of a fold (after Price & Cosgrove, 1990;Coe & Harp, 2007) Faults are another feature of structural geology that represent locations that are prone to rockfall occurrence. Butler et al (1986) found that that large rockfall avalanches were associated with thrust faults in Northeastern Glacier National Park.…”