Enhanced rock‐slope failure following ice‐sheet deglaciation: timing and causes

Abstract

The temporal pattern of rock-slope failures (RSFs) following Late 12Pleistocene deglaciation on tectonically stable terrains is controversial: previous 13 studies variously suggest (1) rapid response due to removal of supporting ice 14 ('debuttressing'), (2) a progressive decline in RSF frequency, (3) a millennial-scale 15 delay before peak RSF activity. We test these competing models through 10 Be Stadial glacial limits, but that runout debris was removed by LLS glaciers. 36Keywords: Rock-slope failure; paraglacial; surface exposure dating; stress release; 37 palaeoseismicity. 2002; Leith et al., 2011; McColl, 2012 Cormier et al., 2005; Agliardi et al., 2009; El Bedoui et al., 2009; Hippolyte et al., 58 2009), to constrain the extent of Pleistocene glacier advances 59 2011), to determine the level of hazard at former landslide sites (Welkner et al., 2010), 60to estimate long-term rates of pre-failure sliding (Hermanns et al., 2012) and to 61 determine the contribution of RSFs to postglacial denudation and landscape evolution 62 (Barnard et al., 2001; Antinao and Gosse, 2009; Seong et al., 2009; Hewitt et al., 63 2011; Shroder et al., 2011). The timing of individual dated RSFs has been variously 64 related to deglacial unloading and stress release (Cossart et al., 2008; Shroder et al., 65 Gosse, 2009; Sanchez et al., 2010; Stock and Uhrhammer, 2010; Hermanns and 67 Niedermann, 2011; Hewitt et al, 2011; Penna et al., 2011) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 that dip ESE at 25-40° and are locally intruded by doleritic dykes (Walker, 1961; 132 Anderton, 1976 132 Anderton, , 1977 132 Anderton, , 1985. 134When the last British-Irish Ice Sheet reached its maximum extent at ~27-26 ka, 135westwards-moving ice crossed Jura and extended to the Atlantic shelf edge, 195 km 136 west of the island (Hubbard et al., 2009; Clark et al., 2012 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 to 7% younger. Where citation of both ages is necessary, the age derived using LL 288LPR is cited first, followed in brackets by the age derived using NWH11.6 LPR. 290An additional advantage of using LPRs is that the variability amongst different 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 ...

Geomorphological evidence and 10Be exposure ages for the Last Glacial Maximum and deglaciation of the Velká and Malá Studená dolina valleys in the High Tatra Mountains, central Europe

“…If the glacier wasted out of the trough at an average rate of 0.9 ± 0.5 m yr À1 , this failure occurred around 1400 years after the ice retreat. Although this lagtime is relatively long, it falls within the typical range of response times reported for large glacially conditioned slope failures (Prager et al, 2008;McColl, 2012;Ballantyne et al, 2014aBallantyne et al, , 2014b. Therefore, all the sampled rockfalls may be considered as resulting from (paraglacial) stress release following deglaciation (Ballantyne, 2002;Geertsema and Chiarle, 2013).…”

Two early Holocene rock avalanches in the Bernese Alps (Rinderhorn, Switzerland)

“…However, a growing number of dated post-glacial landslides show lag times (i.e., time between deglaciation and slope failure) of thousands of years (e.g., Ivy-Ochs et al, 2009a;Prager et al, 2009;McColl, 2012;Ostermann et al, 2012;Ballantyne et al, 2014a;2014b), contradicting this hypothesis.…”

“…Post-glacial isostatic rebound has been suggested to be the driver of these seismic episodes (Monecke et al, 2006;Strasser et al, 2013). Related studies in Scotland and Ireland exclude debuttressing as a direct trigger for the majority of dated rock slope failures, but further support stress release and uplift caused by glacial unloading as a predominant cause of landslide activity (Ballantyne et al, 2014a;2014b). Periods of isostatically induced seismicity trail deglaciation, possibly explaining observed lag times of early Holocene landslide clusters (McColl, 2012).…”

Beyond debuttressing: Mechanics of paraglacial rock slope damage during repeat glacial cycles

“…Field evidence of squeezed glaciers adjacent to active slope failures supports this hypothesis [ McColl and Davies , ]. Meanwhile, frequently observed large lag times between deglaciation and large‐scale slope instability [e.g., Prager et al , ; Ivy‐Ochs et al , ; Ballantyne et al , , ; Zerathe et al , ] cast doubt on the importance of glacial debuttressing as a direct failure trigger and point to the need to further understand time‐dependent effects. These results underscore the importance of additional research into the mechanics of the paraglacial rock slope response and specifically how stress cycles imposed by the changing weight of glaciers generate rock mass damage as a first‐order control on slope failure processes.…”