Late-Glacial drainage in part of North-East Wales

The Late Devensian glaciation along the border of northeast Wales

“…Most of this ground is underlain by Irish Sea till and is truncated by a complex series of channels (Peake 1961;Derbyshire 1962;Embleton 1964;Thomas 1984) that fret the east side of Halkyn Mountain. The area to the west of the Alyn is largely subdued and underlain by thin Welsh till.…”

“…The succession has been fully described by Thomas (1984) who identified prograding topset, foreset and bottomset sedimentation in two classic Gilbert-style glaciolacustrine fan-deltas stacked one above the other ( Figure 5A). These deltas were fed by meltwater draining from the exit of a major subglacial channel system running parallel to the eastern flank of Halkyn Mountain (Derbyshire 1962;Peake 1962;Embleton 1964;Thomas 1984) and fed lake systems impounded at their southern ends by an Irish Sea ice-margin running southwest across the Alyn valley above Mold ( Figure 5C). The lower delta was associated with a lake level at 180 m OD.…”

Supposed Ice-Dammed Lakes in Britain with Particular Reference to the Eddleston Valley, Southern Scotland

“…(ii) The conclusions of some authors that certain meltwater channels and related deposits indicate the presence of ice from two distinct sources results from an insufficient appreciation of the significance of thinning and may well be incorrect. Embleton's (1956) conclusion that the Welsh ice and Irish Sea ice parted company in the area he studied in north-east Wales, retreating in opposite directions down two valleys heading in the same col, is more probably the result of thinning of a single mass of ice resulting in the emergence of the col while ice still occupied the valleys on either side. Trotter suggested this rather unlikely explanation to account for certain marginal channels that are simply explained in terms of thinning as having been formed solely along the margin of the Lake District-Galloway ice.…”

“…The terraces described by Embleton (1956) in north-east Wales are kame terraces, not shore features, an origin indicated by "the frequency of kettle, holes and other irregular depressions" in them. Deposits interpreted as deltas or shore-lines formed in ice-dammed lakes were laid down between the ice-margin and a hillside or deposited beneath, within or on top of the marginal zone of the ice.…”

“…Ice-dammed lakes formed as ice retreated from higher to lower ground have been described in many parts of upland Britain, for example around the Welsh uplands (Charlesworth, 1929;Jones and Pugh, 1935;Embleton, 1956), the Pennines (Dwerryhouse, 1902;Carter, 190o5;Jowett, 1914;Jowett and Charlesworth, 1929;Raistrick, 1931Raistrick, , 1933Anderson, 1940;Wray, 1948), the Lake District hills (Smith, 1912(Smith, , 1932Smith et al, 1931;Dixon et al, 1926;Eastwood, 1930), the Lincolnshire Wolds (Twidale,I956b), the Yorkshire Wolds (de Boer, I944, I958), and the Cheviot Hills (Kendall andMuff, 1901I, 1903) and in the Midland Valley of Scotland (Kendall and Bailey, 1907--08). The evidence from which these former lakes have been deduced is best considered under the four headings used by Kendall in 1902 in his paper on the Cleveland Hills (on which the studies referred to above, as well as many others, were modelled), namely beaches, deltas, floor deposits and "overflow" channels.…”