Coastal cliff system instability – a natural disturbance or manmade?
The lack of wildness in Britain is my “nature-deficit disorder” (1). I don’t think I ever suffered anything like it until the penny dropped about the underlying pathology of land use here (2,3). Apparently, the “eco-anxiety” it engenders in me is a “psycho-terratic syndrome” attributable to the degraded state of my physical surroundings, or at least that it is what “ecopsychologists” may say (4). My “ecotherapy” is thus to seek out and walk the wilder places, tapping into my “ecological unconscious” (5). Well, this is perhaps an over analysis of what is fundamentally a seeking out of an emotional fulfilment from wild nature (6) but it does require a bit of forethought, especially if I want to submerse myself in the stunning wild nature of a rocky coast at low tide, a location that is mostly free of human domination (7,8). Thus the tide times were an important element of planning when I headed off a few weeks ago for the N. Yorkshire coast. While there are large areas of sandy beach at Whitby and Scarborough, I am wanting to walk the extensive rocky terraces uncovered at low tides. These are the wave-cut platforms backed by high, often sheer cliffs, and with the odd pocket beach of sand and/or pebble between headlands. The pocket beaches are often cut off at high tide, as are the bases of the cliffs, and so you have to escape back to your access point to the foreshore as the tide rises.
It’s not just a case of ensuring walking access - you have to choose a few days when the low tides reasonably coincide with a time span across midday, but also that the tide sequence over those days coincides with the extreme high and low waters of Spring Tides and thus the largest tidal range (9). It is the lows of these Spring Tides that can be up to two metres lower than the Neap low tides, and which reveal the nodding heads of the kelp forests (Laminaria spp.) of the infra-littoral fringe just beyond the extent of the intertidal or littoral zone (10). Their disappearance heralds a turn in the tide as it begins to come in, and provides a warning not to get trapped by the rising tide. What I am looking for though are the areas of rocky platform near the infra-littoral fringe that are only uncovered with these Spring lows, a world that while it is revealed twice a day, is only revealed for two periods totalling about 10 days in any month. The light levels there range from 100% exposure at low tide to as low as 0.1% at high tide, the five metres or so of sea water covering at Springs high tide markedly reducing light penetration. If you think about it, the nature of the bedrock, the extent of wave action, the potential for desiccation, and the diurnal extent of light penetration, are key factors in determining the species present and their abundance in the community structures on these rocky habitats (11,12). Community structure is additionally modified by biological factors such as inter-species competition for space, grazing, and predation, between the plants (seaweeds) and animals (anemones, dogwhelks, limpets and other shellfish, barnacles, sponges - the herbivores and carnivores). Thus there are distinct horizontal bandings or zonations of species that vary within the littoral zone from alternate immersion in water and drying in air, and which depend also on the extent of exposure to wave action (see Fig. 2 in (13)).
The inquisitiveness of seals
The few days I had staying in Robin Hoods Bay were graced with good weather when the advance forecasts had looked grim. There was not much wind, but the waves breaking onto the platform edges were tremendous on North Batts near Saltwick Nab (S of Whitby) and on Naze Craze just past Homerell Hole (N from Robin Hoods Bay). These were the largest waves I have ever seen there, even to the point of breaking and curling over into translucent tubes before crashing over into foam. I got a bit wet from misjudging how close I could get to the waves as they broke onto the rock platforms. I walked along the platforms of High Scar, Flat Scar, Billet Scar and Wine Haven (S from Robin Hoods Bay) to see the seal colony hauled out on the rock strewn platform at Old Peak under the cliffs at Ravenscar. It seems like a mixture of mostly grey seals and a few common seals, ranging from first years to adults, with probably over a hundred scattered amongst the boulder field on the platform, or up on the shale beach. I worked out how to get close and sit amongst them without their scattering. They have beautiful eyes, and their rear flippers are like infinitely flexible wings that seem to be an expression of how relaxed they are when they are clasped together and curled over at the end. A few adults stay in the water off the elongated platform at Peak Steel, their heads bobbing up and down. Astonishingly, they will follow you as you walk along the edge! It’s not a trait I have ever seen before, as if they were expecting to be fed. I have since read that this inquisitiveness is a common phenomenon, but I haven’t seen any convincing explanation of why they do it. Considering the persecution seals have suffered, it seems an unwise habit.
On a walk north along the extensive platform from Runswick Bay, over Cobble Dump and on, I got out further than usual on the platform below Lingrow Cliffs before Rosedale Wyke, and found a beautiful world of shallow crevices with the only just submerged, but sparse, brown seaweed saw or toothed wrack (Fucus serratus) along with a short, densely tufted dark green seaweed (Cladophora rupestris) the delicate filigree of pink coral weed (Corallina officinalis) and what looked like a beautiful pink coral or aquatic lichen that I have now found out is actually a calcified rock encrusting coralline seaweed (it may be Lithophylum incrustans, but is often referred to as just Corallinaceae in habitat descriptions because its species are difficult to differentiate – see that for coralline crusts and coral weed of shallow rockpools in (14)). You just don’t expect a seaweed to manifest like that. This encrusting seaweed can also be found in the shallows at the edge of the infra-littoral fringe on the southern side of the platform at North Batts, as well as in crevices in the platform between Ness Ruck and Ness Point, N of Robin Hood’s Bay, and where the plateau itself is strewn with delightfully shaped fixed rocks, eroded to look like squat mushrooms. The undersides of these and other rocks have colonies of bright yellow and pale green breadcrumb sponges (Halichondrea panacea) accompanied by pepper dulse (Osmundea pinnatifida) a short, tough, reddish-brown seaweed. The spreading mass of sponge is punctuated with pores, small holes through which sea water enters into inner cavities where food particles are filtered out, making these an unlikely invertebrate animal, in the same way that the encrusting corallines are unlikely aquatic plants. Where they can get a foothold, brown seaweeds dominate many of the platforms, but the pink coralline seaweed is common on large areas of platform that don’t completely drain, especially either side of Saltwick Nab, where it is found on its own, and in many other places where it is sometimes in accompaniment with cladophora and sea lettuce (Ulva Latuca) another green seaweed. (Photographic examples of various UK rockpools, their species and habitat classification, can be seen in (15))
The climatic, biotic and trophic interactions of terrestrial habitats seem to pale in comparison to the rigours of life on these rocky shores. Even so, coastal cliff habitats are subject to a greater disturbance from a range of conditions of extreme exposure when compared to inland areas. I have written before about how the cliff vegetation of the Pembrokeshire coast varies with the twists and turns so that some stretches feel the full fury of winter gales and are soaked by salt spray carried up from the waves, while other lengths are tucked around corners and are fully sheltered from this buffeting (16). The differences don’t stop there as geomorphology and geology also vary from sheer cliffs to gentle slopes, and both exposed and sheltered lengths may be in full sunshine or deep shade for part or most of the day. All this gives rise to a gradation of vegetation from bare rock to sparse, low cover on thin, sharply drained soils, maritime grassland in damper areas, to wind-pruned shrubs and then woodland.
Soft cliff slumps and mudslide systems
It is the same for the N Yorkshire coast, where the cliffs themselves have also been structured by disturbance. Thus the rocky platforms I walk have arisen from erosion by wave action at the base of the coastal cliffs, formed initially after sea level rise some 7,000 years ago, that creates a notch that enlarges, undermining the cliff face so that it collapses, with the fallen material being washed away by the tides (17). This process will have been repeated over time as the cycle starts again, the cliff face continuing to retreat so that the wave-cut platform enlarges. Other drivers of coastal instability, erosion and cliff recession exist along this coast, such as the percolation of ground water within the land leading up to cliff so that it appears as seepages, its freezing and thawing in harder cliffs giving rise to rockslips, and as flows causing mudslides or landslips in the softer, overlaying areas of clay deposited as glacial tills. These slumps or slips in the soft cliffs may resist woodland vegetation if they are still active, but may take on pioneer species associated with disturbed bare earth, or open wetland habitats. Undercliff shelves at Hayburn Wyke and Beast Cliff are wooded, as are the slopes at Runswick Bay, Cayton Bay and Cornelian Bay (18,19) although slumping is still active at the latter (see later). It is not surprising that this stretch of the N Yorkshire coast and continuing up past Whitby is clearly shown as the main area of nett erosion on our North Sea coast in a map of coastal erosion patterns in Europe (20).
I saw evidence of this landslip erosion while walking along the coastal cliff path at Wheatcroft Cliff, south of Scarborough, where it overlooks the large wave-cut platform of Black Rocks. My arrival at midday over at the coast was such that access to Black Rocks from Scarborough was already blocked from the rising tide, and so I was instead walking the cliff path to White Nab with the intention of then getting access down to the foreshore that was still partly uncovered at Cornelian Bay. The soft boulder clay of this coastal slope below the path quickly gives way from low woodland to gorse scrub, and then increasingly losing its vegetation cover as you approach White Nab, with some large areas of bare earth slump on the slopes above the final drop of the cliff. For an understanding of cliff recession, there is a classification into Cliff Behaviour Units (CBU) that is based on the geomorphology and its likely erosion pattern, given that erosion is a transfer system of material from the cliff top through the mass of the cliff face/slope and down onto the foreshore (21). A range of types of cliff system can be recognised on the basis of the throughput and storage of material within the system. Simple, composite and complex cliffs react in different ways, the CBU for this eroding section of Wheaton Cliff fittingly being classified as “Composite cliffs comprising shallow mudslide systems developed in interbedded mudrocks and sandstones capped by glacial till above a vertical sea cliff developed in bedrock” (see Composite cliffs in the main CBU types in Fig. 1.5, and Fig. 3.3 in (21)). By contrast, just past White Nab, the cliff system is much wider at Frank Cliff above Cornelian Bay, so that there is failure at more than one level in this Complex cliff (see Fig. 1.5 in (21)). It is classified as “Deep-seated mudslide systems developed in interbedded mudrocks, sandstone and overlying glacial till” (see Fig. 3.3 in (21)). If there is a final transfer of material onto the foreshore there, then it can be seen in the balled lumps of clay and the wet clay seepages that infiltrate parts of the sandy beach where water run-off through the wooded slope exits over the final low edge of eroded channels of bare earth. However, erosion along that low edge is probably more contributed to by wave action at Spring high water than by run off.
Given the attention to characterising cliff recession and coastal landsliding along this coast (eg. see (22)) you would think that this hydrological disturbance of cliffs is the result of natural processes, and it is the case that the cliff top and slope between South Bay, Cornelian Bay and Cayton Bay are designated in a Site of Special Scientific Iinterest (SSSI) as “Neutral grassland” (23). The designation citation says that the “bare and eroding boulder clay on the more unstable areas of the cliff also support a rich invertebrate fauna”, later implying that the cliff seepages and wet grassland, the bare earth and the seasonal accumulation of dislodged boulder clay blocks at the foot of the unstable cliffs are “Naturally disturbed, open wetland habitats” and which are “generally scarce in lowland areas” (24). And yet one of the largest areas of bare and landsliding earth on the southern end of Wheaton Cliff occurs where a 20cm diameter blue drainage pipe protrudes out near the top of the slope, pouring water down the slope. The land behind this area of the cliff top is the manicured grass of a golf course (Scarborough South Cliff Golf Club) and where it is easy to believe that drainage measures have been taken over the years to ensure a good playing surface for the golfers. I have to say that the length of the golf course along the cliff top does appear, from an aerial view, to coincide with a greater instability of the coastal slope and a reduction in vegetation cover.
Mud seepages flow like syrupy fudge
I’ve had an uneasy feeling for some time that the cliff process events I’ve seen on the N. Yorkshire coastline are a point disturbance arising from the outlet of field drainage, especially when I can see the ends of pipes poking out. It can be quite devastating, creating large muddy slump holes in the cliff that never get a chance to vegetate. The field drainage has probably been there for centuries, channelling water to points on the cliff edge, when what it should have done is take it to the natural water courses that do drain these cliff top areas. On that walk south around Robin Hood’s Bay to watch the seals below Ravenscar at Old Peak, I could see four waterfalls once you are past the outlet of Stoupe Beck, the beck having flowed down through a wooded valley to the foreshore (see above). They are waterfalls because they drain from the cliff top over rock faces, but it is only the southernmost waterfall that arises from a natural watercourse – Tan Beck also flows through a narrow wooded riparian corridor to the cliff top – while the others arise from field drains. In fact there are nine field drains running in parallel through the farm fields on a downward slope towards the cliff top along this 2km stretch of Peter White Cliff, and perhaps untold other pipe systems unmarked on the map. The consequences of these other drain flows onto the cliff system is seen in the denuded bare earth of the cliff slope, the slumps, gullies and mudslides, and the mounds of soil on the beach below the source outlets. There is also, just past Stoupe Beck, the unusual organ-pipe earth pinnacles left on the leading edges between gullies, sculpted by surface water and mud flow. After a few days of rain, the mud from those seepages flows over the sand of the beach like a syrupy fudge. That there has been some common sense in the past about field drainage behind this coastal slope is shown by the drains that run in parallel north to Stoupe Beck, rather than east to the cliff top, although it may just be a case of expediency in these farm fields because of the direction of the downward slope of the land goes that way.
The cliff at Robin Hood’s Bay forms part of a multiple rotational landslide system due to progressive failure of clays within the glacial tills, and is unprotected in the sense that no stabilisation work has been carried out (see Appendix 2 in (21)). The CBU is classified as a Composite cliff (see Table 1 in (25)) the cliff immediately south of Stoupe Beck where the pinnacles are, has been labelled as “active” (see Fig 4.6 in (26)) but this seems a limited observation when much of the coastal slope along the south section of the bay appears to suffer from instability. The cliff slopes along the whole of Robin Hood’s Bay are designated a SSSI, although unlike the citation of the South Bay, Cornelian Bay and Cayton Bay SSSI (see earlier) there is no mention of their instability (27). However, that this instability is recognised comes from the evaluation of the condition of Units 11, 13, 15 and 17 that cover the stretch where the field drains arrive at the cliff slope. These Units were last evaluated by Susan Wilson in January, 2010, who like many Natural England officers reuses text rather than write some unique observation about each part of this 2km stretch of coast. Thus each has it, not unsurprisingly, that the coastal cliffs are accessible at low tide, but each also says ”The cliffs are weathering and eroding naturally with localised landslip” (28-31). Well, I suppose some of the hydrological erosion may be contributed by rainfall directly onto the slopes, but considering the impact of the field drains, it is definitely not true for her to assert for each Unit that “Active geomorphological process is not affected by human activity”
Cutting across natural processes
It is self-evident that land use adjacent to cliff tops can lead to an acceleration of coastal landsliding and cliff recession by cutting across natural processes (25) especially where there is seepage erosion at drainage outlets (see the large gully formed by discharge of water from a major drainage pipe at the top of a cliff on pg. 23 in (32)). Paradoxically, drainage measures are a key part of soil stabilization schemes for unstable areas of soft cliffs. This includes the interception of groundwater, and control of surface water through collecting and preventing run-off from entering unstable areas, and through collection and safe disposal of run-off from within unstable areas (21). These decidedly interventionist measures though are often in response to highly visible instability that threatens houses or amenity areas adjacent to the cliff top, and are most likely to be mitigating the effects of existing altered hydrology from land uses, and with little thought of changing the land use itself (ie. see (32,33)). Farmland is a similar matter, the drainage of fields being an agricultural improvement, but which gives little thought to its consequences, nor to what its natural hydrology or even natural vegetation would be. It is the artificiality in its land use that in juxtaposition to cliff systems causes an artificiality in disturbance and instability there. Earlier above, I noted that the range of open wetland niches arising from this artificial instability in soft cliff systems is held in regard by the conservation industry because it has little lowland presence elsewhere. Well, there should be the blindingly obvious recognition that it is not found elsewhere because of the modification and improvement of farmland to eliminate it. Thus there has been what is in effect a transfer of these niches to the cliff system by the very mechanism that has removed them from farmland.
I doubt whether Susan Wilson, or any of her colleagues in Natural England, have ever made that connection, so steeped are they in externally applying disturbance in land systems everywhere else that they lose sight of what is a natural process. How much instability would there be in soft cliff systems if there was no farming right up to the edge of the cliff top? What if there was no artificial drainage, but instead a continuity in natural vegetation up the cliff slope and some way inland from the clifftop, albeit graded in response to the decreasing rigors of exposure? I pondered this continuity when I described the complex clothing of vegetation on Lister Cliff on the N Devon coast, shaped by maritime exposure and the thinness of soils (7). Small scrubby trees hug the sheer slope, hardly forming a canopy, with larger trees bent over by the wind as the cliff reaches over its apex. There is, however, a sharp transition immediately across the other side of the coastal path, where the land is predictably the tree-less improved grassland of farming. It left hanging the question of what would be the natural vegetation state of that land if it too was left to natural forces, as it does for the natural vegetation state inland from the top of Peter White Cliff at Robin Hood’s Bay? Given the likelihood that this would be woodland at the latter, the presence of woodland lining Stoupe Beck and the more exposed woodland lining Tan Beck being convincing evidence, then wouldn’t the groundwater characteristics and hydrology of this land be entirely different than they are now? It is perfectly possible in this situation that the impact of groundwater on the soft cliff there would be diminished because of this woodland coverage, leading to a virtuous circle of less bare earth from instability, greater vegetation cover of the cliff slope, and less cliff recession.
Subsidences arising from the undermining agency of water
Before going over to the N. Yorkshire coast, I had been gathering information about “one of the largest and most important active coastal landslip systems in Western Europe” (34). That is one of the descriptions given for the undercliff system on the S Devon coast between Axmouth and Lyme Regis that I wrote about some five years ago (35). Another is that the high canopy woodland – “one of the best recent examples of plant succession to be found in Britain” – along with the vegetated cliffs that developed there (36) after the massive landslips that gave rise to the undercliff, is “one of the finest wilderness areas in Great Britain” (37). Hyperbole aside, let’s go back to the beginnings of those landslips on Christmas Day, 1839, and note that the land behind the original cliff top was arable farmland, since great play is made of the 1,000 people that turned up at the ceremonial cutting in 1840 of the wheat that had been sown there, and which had continued to grow on the land that had subsided from the fields above (38). There is a remarkable, illustrated account written shortly afterwards of those landslips that rumbled on into the early months of 1840, and which sought to understand why they had happened by reference to prior landslip events in similar geomorphological settings (39). Earthquakes were discounted on the basis that “aqueous causes” had been ascribed at other recorded instances, and were the case here. The Winter of 1839-1840 had been a season of “extraordinary wetness” giving rise to an acceleration and aggravation of the “disturbances of the surface”, of “water percolating through the strata and causing dislocation and motion among them”, and of “subsidences arising from the undermining agency of water”. I wonder if the landslip would have occurred to the same extent if instead of wheat being grown on the cliff top, it had been covered with trees? The irony of course is that trees do now cover much of the subsided land of the undercliff when the land behind the cliff top above the undercliff is still pretty much treeless. Perhaps this explains why there is still active landslipping today (40).
I believe this train of thought about the causes of cliff system instability argues for our need to break the domination of land use by farming, to take back land in places where there must be a high aspiration for natural vegetation and hydrology, to see the distinctive community systems that develop in reaction to climatic and edaphic factors, the varying soils, hydrology and climate, such as the coastal cliff assemblages of vegetation that alter the further inland you go as the forces of coastal exposure recede, and which have been lost from view in our highly modified landscapes (41). It is a counter to the obsession of the conservation industry that external disturbance has to be applied to natural systems, when it is only their interests that are served by it.
Mark Fisher 6 March, 9 March 2016
(1) Louv, R. (2013) Last Child in the Woods: Saving our Children from Nature-Deficit Disorder. Atlantic Books
(2) Searching out the wildness, Self-willed land May 2010
(3) The most unnatural conservation policy possible, Self-willed land July 2010
(4) Creating a language for our psychoterratic emotions and feelings, Glen Albtrecht 8 September 2011
(5) Is There an Ecological Unconscious? Daniel B. Smith The New York Times Magazine 27 January 2010
(6) Unselfing – a selfless approach to the beauty of wild nature, Self-willed land February 2016
(7) Wild Pear Beach - how wild is it? Self-willed land April 2011
(8) The malady of conservation reliance, Self-willed land October 2015
(9) Tidal elevations for Whitby. Real-time/near real-time data display for Whitby, 24 Jan – 23 Feb. The National Tidal and Sea Level Facility
(10) Infralittoral rock (and other hard substrata) The Marine Habitat Classification for Britain and Ireland, Joint Nature Conservation Committee Version 15.03
(11) Littoral rock (and other hard substrata) The Marine Habitat Classification for Britain and Ireland, Joint Nature Conservation Committee Version 15.03
(12) Environmental influences on community structure, Shallow classification, Marine Habitat Classification, Joint Nature Conservation Committee
(13) Guidelines for selection of biological SSSIs: intertidal marine habitats and saline lagoons. Joint Nature Conservation Committee 1996 http://webarchive.nationalarchives.gov.uk/20080102105829/http://www.jncc.gov.uk/pdf/sssi_Intertidal_new_habitats.pdf
(14) Coralline crust-dominated shallow eulittoral rockpools, The Marine Habitat Classification for Britain and Ireland Version 15.03 [Online] Joint Nature Conservation Committee 2015
(15) Rock Pooling: A rock pooling blog of UK sea shores. Salty Scavenger
(16) Harting Down - obsession with conserving man-made landscapes, Self-willed land November 2007
(17) Wave cut platforms, Coasts of Erosion, The British Geographer
(18) The most natural succession of woodland, Self-willed land November 2009
(19) Rare and precious – words devalued by the conservation industry, Self-willed land June 2011
(20) Coastal erosion patterns in Europe, Coastline dynamics in Europe, European Environment Agency
(21) Lee, E. M. and Clark, A. R. (2002) The Investigation and Management of Soft Rock Cliffs. Thomas Telford
(22) Coastal Processes and Climate Change Predictions in the Coastal Study Areas, Isle of Wight Centre for the Coastal Environment LIFE Environment Project 2003-2006 ‘RESPONSE’: LIFE 03 ENV/UK/000611
(23) Cayton, Cornelian and South Bays SSSI, Designated Sites View, Natural England
(24) Cayton, Cornelian and South Bays SSSI Citation, Natural England
(25) Soft Cliffs Prediction of Recession Rates and Erosion Control Techniques, R&D Project FD2403/1302. DEFRA/Environment Agency Flood and Coastal Defence R&D Programme 2002
(26) May, V.J. (2003) Site: ROBIN HOOD'S BAY (GCR ID: 1943), Chapter 4: Soft-rock cliffs – GCR site reports. In Coastal Geomorphology of Great Britain, Volume 28: Geological Conservation Review Joint Nature Conservation Committee
(27) Robin Hood's Bay: Maw Wyke to Beast Cliff SSSI Citation, Natural England
(28) ROBIN HOOD'S BAY: MAW WYKE TO BEAST CLIFF - 11 (11)
(29) ROBIN HOOD'S BAY: MAW WYKE TO BEAST CLIFF - CLIFF: MILLERS NAB (013)
(30) ROBIN HOOD'S BAY: MAW WYKE TO BEAST CLIFF - CLIFF: BILLET SCAR (015)
(31) ROBIN HOOD'S BAY: MAW WYKE TO BEAST CLIFF - CLIFF: WINE HAVEN (017)
(32) Assessment of Coastal Erosion and Landsliding for the Funding of Coastal Risk Management Projects. Guidance Notes. Environment Agency National Coastal Team December 2010
(33) West, I.M. (2016) Barton and Highcliffe - Coast Erosion and Sea Defences: Geology of the Wessex Coast of southern England
(34) National Character Area profile: 147. Blackdowns. Natural England
(35) Walking the wild places, Self-willed land September 2010
(36) Axmouth to Lyme Regis Undercliffs SSSI citation, Natural England
(37) Axmouth to Lyme Regis Undercliffs, Devon's National Nature Reserves, Natural England
(38) Lyme’s History in Museum Objects 12: The Undercliff Model. Thea Hawksworth & Lyme Regis Museum 2013
(39) Conybeare and Dawson's Memoir and Views of Landslips on the Coast of East Devon &c. 1840, The Bindon Landslip of 1839, Lyme Regis Museum
(40) Sidmouth to West Bay Special Area of Conservation, Joint Nature Conservation Committee
(41) The free for all of trophic rewilding, Self-willed land January 2016