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The Devil’s Hole blow-out (Grid Reference SD278054) has been a popular recreational attraction for generations of local children and is a spectacular viewpoint for walkers in the Ravenmeols Sandhills Local Nature Reserve (Plate 1). Blow-outs form when a sand-dune’s protective cover of vegetation is damaged; sand is then blown down-wind and an armchair-shaped hollow develops.  This may deepen until the water-table is reached, when the sand is then too wet to continue blowing.

Devils Hole 2013


by Philip H. Smith and Patricia A. Lockwood, January 2013

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Aerial photographs show that the Devil’s Hole began to form on a high dune in the early 1940s, perhaps due to a German land-mine explosion in 1940 or 1941. Instead of having an open face to windward, as in most blow-outs, it still resembles a crater, with steep slopes on all sides. Wind erosion over seven decades has created an enormous bowl at least 10m deep, with sand over-blowing the original dunes downwind and burying part of an adjacent conifer plantation. A former dune surface can be seen as a dark band of soil around the eastern sector of the bowl. The main blow-out is orientated east/west, in line with the prevailing wind direction but a later secondary (southern) basin has developed with a southeast/northwest orientation

In the early 1990s, small “proto-dunes” began to form in the floor of the northern basin. Including its downwind sand-sheet, the northern basin is currently about 317m long and has a maximum width of 104m, while the southern blow-out measures about 125 x 40m. The entire feature now covers an approximate area of 4ha, 57% larger than in 1993. Despite this, there is no risk to coastal defence or property and the minimal damage caused is more than offset by the scientific value of this feature, both from a geographic and wildlife standpoint.

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From the spring of 1993 onwards, the presence of standing water in the floor of the main blow-out attracted Natterjack Toads to spawn but, due to the rapid drying out of the shallow pools, breeding was recorded as successful only in 2006 and 2008. Another “flag-ship” species for the Sefton Coast, the Northern Dune Tiger Beetle, can be found on the bare sand slopes of the Devil’s Hole in sunny weather during the spring and summer (Plate 3).

A 1995 dissertation by S. Read shows that, from the 1940s, the Devil’s Hole grew in an easterly direction at an average rate of 4.5m per year, reaching a total area of 2.55ha by 1993.  In about 1991, the northern basin reached the water-table and began to flood in wet winters. Later photographs show surface water in 1995, 2004, 2006 and also in 2008, when the southern blow-out held water for the first time. Particularly deep flooding occurred after exceptional autumn/winter rainfall of 2012/13 (Plate 2).

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Based on recent aerial photographs and satellite imagery, the northern slack occupies about 0.44ha, while that in the southern basin covers about 0.1ha.  Relative drought conditions and a low water-table contributed to further wind-scouring from 2008 to 2011, and especially during severe gales of winter 2011/12 (Plate 4), leading to the formation of a new slack basin at the eastern end of the main blow-out.

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Plants began to colonise the slack in the main blow-out in 2003, the slack flora being recorded at regular intervals since. Only 16 different plants were identified in 2004, increasing to 70 in 2009 and 90 in 2012, about 20% of these being regionally or nationally notable. Analysis of the vegetation shows that it represents an early stage in dune-slack development and a rare community type that is declining elsewhere on the Sefton Coast and is uncommon on British sand-dunes generally

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In conclusion, the Devil’s Hole has a high and increasing scientific value and is visually dramatic. Dynamic features like this are now rare on the Sefton Coast, the dune system having become much more stable in recent decades. The floral diversity of Devil’s Hole is particularly rich, reflecting a relatively early stage in the development of slack vegetation. Several rare species add further interest. No doubt it will continue to provide a visual treat for visitors and a fascinating place for the wildlife enthusiast for many years to come.

Acknowledgements

Thanks are due to Michelle Newton for measuring the slack areas and to Peter Gateley for providing data from his vegetation survey.  Reg Yorke kindly drew my attention to early photographs and Peter Gahan provided details of Natterjack breeding

The most dramatic floristic change since 2009 is the spectacular increase in the starry white-flowered Grass-of-Parnassus, which now carpets large parts of the northern basin (Plate 5). In August 2012, its total population was estimated in the tens of thousands and is now the largest on the Sefton Coast. Indeed, it may be one of the most important UK populations of this species, which is markedly declining in southern Britain and has recently been listed as “endangered in Lancashire” by the Wildlife Trust for Lancashire, Greater Manchester and north Merseyside.