Erosion in Burghead Bay
MFC Paper 10 by SM Ross 1976
The occurrence of peat under the waters of Burghead Bay was discussed by Grant and Leslie in 1798 and by Patrick Duff in 1842. Duff described the peat as having trees of considerable size embedded in it and as having different structure to normal peat in that it contained "....reeds and large leaves or fronds of aquatic plants, some exceeding a foot and a half in length." These writers considered the occurrence to be a submerged forest, but did not enlarge on their reasons. However, over the years this has been widely quoted as evidence of a period during which sea level fell to a position much lower than the present.
Grant and Leslie also discussed the ease with which the sea attacked the sandy bank forming the shoreline and mentioned that as it did, fresh exposures of peat earth were revealed some 6 to 8 feet below the sand. At the time of writing (1798) tradition had it that some time prior to 1701 the coast between Findhorn and Burghead was a straight line and that near the coast stood a conical mound some 40 fathoms (73m) high, which was known as Douff Hillock. All of this had since been eroded away in the formation of the semi-circular sweep of Burghead Bay, but Grant and Leslie commented that the mound was evidently artificial. The mound is not featured on maps of the period, but some show the Loch of Roseisle with outlets into Burghead Bay.
Writing in 1896, Wallace observed that "In the past 30 years the sea has encroached some 100 - 150 yards and a promontory called The Point near the Bessie Burn has been entirely swept away. If the present rate of erosion has been constant, the shoreline in 1701 would have been 653 yards distant from the present."
Today, in 1976, a line of coastal defences dating from the 19405 lies on the beach. These were originally built on top of the sandy cliff, and even if they were on the edge of the cliff, there has been a minimum of
25m of coastline eroded since their installation. Near the mouth of the of the Bessie Burn, (N.G.R. NJ O97 653) the sand and gravel "cliff" is being actively eroded. Over the past 10 years a large concrete protective barrier has gradually been undermined and has collapsed on to the beach some 500 m southwest of the mouth of the burn. Behind the barrier the sea has cut away some 10 - 15m of the cliff, and here the old land surface can be picked out, outlined by the change from blown sand above, to cross-bedded sand and gravel below, with a dark band representing the remnants of a thin soil at the boundary. A layer of peat 120m long and some 47 cm thick is now exposed in the cliff, lying in a depression in the old land surface just above the high water mark. Thin horizontally stratified layers of silt below the peat indicate that the depression once held a small loch. In places the sand layers have been washed out by wave action allowing large slabs of peat to slump on to the beach. From a point 60m west of the Bessie and extending southwest for 335m, another band of peat is exposed : this is up to 75 cm thick in places. Tree stumps and logs, some of which have been identified as birch, can be examined in the peat, as well as the reeds described by Duff.
From the cross-bedding, the old land surface is considered to have been entirely of glacio-fluvial deposits and would readily be eroded by wave action. The amount of material that must have been carried westwards by longshore drift to form the various bar systems across the mouth of the River Findhorn means that the deposits extended much farther seawards at one time, covering most, if not all, of what is now Burghead Bay, and would have formed a landscape like that of the present Sandur of South Iceland.
There is therefore no reason why the coastline between Findhorn and Burghead should not at one time have been a straight line. The existence of a 73 m high Douff Hillock need not be questioned when one considers that Cluny Hill in Porres and the Binn Hill of Garmouth are mounds of glacio-fluvial material of even greater height, standing on the same platform. It is also suggested that the presence of peat under the waters of Burghead Bay should not in itself be used as evidence of a period of low sea level in this area, when active slumping of peat layers from an old land surface above high water mark on to the beach can be demonstrated.
- GRANT AND LESLIE 1798 A survey of Moray, Elgin
- DUFF, P. 1842 A Sketch of the Geology of Moray, Elgin.
- WALLACE, T. 1896 Recent Geological Changes and the Culbin Sands. Trans. Inv. Sc. Soc. and Field Club. p. 116