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Permafrost and Frozen Ground |
1 Department of Geography, University of Dundee, Dundee DD1 4HN, Scotland, UK m.p.kirkbride{at}dundee.ac.uk
2 School of GeoSciences, University of Edinburgh, Drummond Street, Edinburgh EH8 9XP, Scotland, UK ajd{at}geo.ed.ac.uk
Phases of activity of four solifluction lobes at an altitude of 750–800 m are dated by tephrochronology at Snaefell, central eastern Iceland (64°48' N 15°33' E). The sample includes sorted lobes with tread gradients of 3–11° and unsorted (turf-banked terraces) in slope-foot locations. Trenches through lobe fronts reveal detailed internal structures picked out by multiple tephra layers. The tephras V1717, V1477, Ö1362, V870, Hekla-3 (2900 years BP and Hekla-4 (3800 years BP) provide isochronous surfaces of known age whose deformation and disturbance indicate mass movement and/or cryoturbation of the soil cover. Undisturbed soil including the Hekla-3 tephra indicates an absence of solifluction prior to 2900 years BP. Several centuries after Hekla-3, gravel-rich horizons mark wide-spread frost heave and solifluction of hillslopes. Later stabilization of these lobes allowed the accumulation of aprons of aeolian sediment below lee-side risers. These aprons contain in situ mediaeval tephras, dating the inception of solifluction to a considerable time prior to Norse settlement. The likely period of this first phase of solifluction is the Later Bog Period of the Subatlantic, c. 2500-1000 years BP. The aprons are currently being overridden and deformed by solifluction lobes reactivated in the Little Ice Age.
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