Paper No. 9
Presentation Time: 10:20 AM
THE TIMING AND STRATIGRAPHY OF A LARGE COASTAL SAND INVASION: SHETLAND ISLANDS, NW EUROPE
Large sand dunes are common on many beaches in Western Europe. In the past, disturbances led to breakdown of coastal dunes and “sand invasions” moved inland, burying communities. At Quendale, in the Shetland Islands (Scotland, UK), a productive valley on the main island was inundated by coastal sand in the late 17th Century. We conducted ground-penetrating radar surveys of the dunes in Quendale to assess the magnitude of the most recent eolian event, and to establish timing of past events through OSL dating. A LIDaR survey was used to classifiy the dunes: 1) a foredune ridge (9 m high, 50 m wide, about 2 km long), 2) a back dune sloping 100 m landward from the foredune; 3) small dunes (< 3 m high) continuing several km landward from the backdune; 4) a dune complex (> 10 m thick, a hundred m wide) against the eastern valley of the field; 5) a sheeted sand region (< 1 m thick in the most landward area and burying 16th and 17th century buildings), and 6) old dunes (2-4 m high) on the eastern side of the valley but on a rock cliff seaward of the beach and no longer connected to the eolian system. No erosional blowouts were recognized in the fore or back dune areas, suggesting accumulation with little erosion. An eroded core was observed within the small dunes, implying erosion and then deposition. The dune complex possessed a soil layer throughout, and a paleosol was seen at the base of the old dunes. OSL dates indicated that the sand sheet was deposited in the 17th Century during the historic invasion. The frontal dune was deposited entirely since 320 BP. The dune complex yielded a date of 3520 BP 3.8 m beneath the surface and about 2 ka BP at the soil layer. The outer dunes, no longer in contact with a sand source, yielded dates at their surface of 290 and 980 BP, with a basal date of 4.4 ka BP. This suggests shoreline migration landward with loss of large volumes of sand during eolian events. The late 17th Century event eroded all of the fore and back dunes and stripped sand from the smaller dunes as the sand sheet migrated onto distant hillsides. The tops of the old dunes were reworked by this event, but their bases, the cores of the small dunes and the thick dune complex retain a record of at least one older event. The most recent sand invasion coincides with the Little Ice Age and may have resulted from enhanced storminess, as well as human modification.