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The southernmost terrestrial extent of the Irish Sea Ice Stream (ISIS), which drained a large proportion of the last British-Irish Ice Sheet, impinged on to the Isles of Scilly during Marine Isotope Stage 2. However, the age of this ice limit has been contested and the interpretation that this occurred during the Last Glacial Maximum (LGM) remains controversial. This study reports new ages using optically stimulated luminescence (OSL) dating of outwash sediments at Battery, Tresco (25.5 AE 1.5 ka), and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on Scilly Rock (25.9 AE 1.6 ka), which confirm that the ISIS reached the Isles of Scilly during the LGM. The ages demonstrate this ice advance on to the northern Isles of Scilly occurred at $26 ka around the time of increased ice-rafted debris in the adjacent marine record from the continental margin, which coincided with Heinrich Event 2 at $24 ka. OSL dating (19.6 AE 1.5 ka) of the post-glacial Hell Bay Gravel at Battery suggests there was then an $5-ka delay between primary deposition and aeolian reworking of the glacigenic sediment, during a time when the ISIS ice front was oscillating on and around the Llŷn Peninsula, $390 km to the north.

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 ...

The deglacial history of the central sector of the last British-Irish Ice Sheet is poorly constrained, particularly along major ice-stream flow paths. The Tyne Gap Palaeo-Ice Stream (TGIS) was a major fast-flow conduit of the British-Irish Ice Sheet during the last glaciation. We reconstruct the pattern and constrain the timing of retreat of this ice stream using cosmogenic radionuclide ( 10 Be) dating of exposed bedrock surfaces, radiocarbon dating of lake cores and geomorphological mapping of deglacial features. Four of the five 10 Be samples produced minimum ages between 17.8 and 16.5 ka. These were supplemented by a basal radiocarbon date of 15.7 AE 0.1 cal ka BP, in a core recovered from Talkin Tarn in the Brampton Kame Belt. Our new geochronology indicates progressive retreat of the TGIS from 18.7 to 17.1 ka, and becoming ice free before 16.4-15.7 ka. Initial retreat and decoupling of the TGIS from the North Sea Lobe is recorded by a prominent moraine 10-15 km inland of the present-day coast. This constrains the damming of Glacial Lake Wear to a period before $18.7-17.1 ka in the area deglaciated by the contraction of the TGIS. We suggest that retreat of the TGIS was part of a regional collapse of ice-dispersal centres between 18 and 16 ka.