1863 J. R. Green Let. 9 June (1901) 126 I have noticed..the wonderful sapping of the chalk cliffs going on here [i.e. at Margate].

1902 W. M. Davis in Bull. Mus. Compar. Zoöl. Harvard 38 328 Whatever flood plains may have been produced during the excavation of the present basin floor, the streams have now so well taken advantage of their opportunity for lateral corrosion or ‘sapping’ that terraces at high and intermediate levels are everywhere obliterated.

1932 W. H. Emmons et al. Geol. vi. 133 As the swirling water back of the falls loosens the soft, shaley formation it removes it piecemeal and undermines the capping limestone, until finally it remains as an inadequately supported overhanging ledge from which large masses of rock plunge into the pool at the bottom of the falls. This process of undercutting is termed sapping.

1936 Proc. Geologists' Assoc. 47 40 A coombe formed in jointed chalk by the sapping back of springs.

1957 Proc. Geologists' Assoc. 68 31 There remains the curious series of right-angled bends in the Ravensburgh Valley system, which has been attributed to sapping along major joints.

1970 R. J. Small Study of Landforms ii. 53 On rocks such as chalk and limestone the actual sources of streams are extended into escarpments and steep slopes by the process known as ‘spring sapping’. This involves underground chemical erosion, surface stream erosion, and slumping of moistened debris around the springhead.

1899 W. D. Johnson in Science 20 Jan. 106/1 An unrecognized process was set forth, that of sapping, whose action is horizontal and backward... The tendency of the sapping process is to produce benches and cliffs.

1938 Geol. Mag. 75 261 As the wall at the head of the cirque retreats under the action of sapping and plucking, immediately downstream the ice abrades and smoothes.

1954 Jrnl. Glaciol. 2 421 In accounting for these features [sc. roches moutonnées] the assumption ordinarily made is that rock has been removed by plucking or sapping from the downstream side, leaving that face steep and irregular.

1968 R. W. Fairbridge Encycl. Geomorphol. 741/1 The walls have been kept steep and caused to retreat by the collapse of unsupported rock faces as they have been undercut by the process of glacial ‘sapping’... The explanation of sapping appears to be found in rending and disintegration of rock by the freeze-and-thaw process.

1972 J. G. McCall in C. Embleton Glaciers & Glacial Erosion xi. 217 The term sapping, as used here, implies frost-riving on the rock slopes under the margins of a glacier. It is produced by the freezing of any water which flows in under the ‘cold’ glacier and, in the case of cirques, it results in a horizontal retreat of the headwall.