Scottish landform examples 45: Sgriob na Caillich: a landslide-sourced medial moraine on the Isle of Jura

Colin K. Ballantyne, Alastair G. Dawson

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Medial moraines deposited by former glaciers and ice sheets are rare in Scotland. The most prominent example is the Sgriob na Caillich moraine, which consists of two to four parallel belts of angular quartzite boulders that extend northwestwards for over 3.5 km from the SW flank of Beinn an Oir on the Isle of Jura. The boulder belts extend to within 300 m of the present coastline, where they are truncated by a low bluff and raised marine terrace. The source of the moraine coincides with bedrock gullies and cliffs that represent the scars of former rock-slope failure(s), indicating that the moraine debris was sourced by one or more rockfalls or rockslides onto the ice surface after Beinn an Oir had emerged from the thinning ice cover as a nunatak. Exposure dating of boulders on the moraine indicate that it formed at 16.6 ± 0.8 ka, consistent with the timing of ice-sheet retreat in this sector. The alignment of the moraine indicates ice-margin retreat to the SE; as regional ice-sheet retreat across the adjacent offshore shelf was to the NE, this anomaly implies that a residual icefield became stranded on Jura during ice-sheet retreat.

Original languageEnglish
Pages (from-to)139-149
Number of pages11
JournalScottish Geographical Journal
Issue number1-2
Publication statusPublished - 3 Apr 2019



  • Isle of Jura
  • last Scottish Ice Sheet
  • Medial moraines
  • rock-slope failure
  • rockfall

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