EAST YORKSHIRE COASTAL EROSION

The cliffs of the East Riding of Yorkshire, where the plain of Holderness meets the North Sea, provide an example of coastal erosion on an observable scale. Although the situation can vary considerably from place to place, from decade to decade, year to year, and within the year, the overall loss of land through cliff recession along this coast is often quoted as being one of the fastest in Europe.

East Yorkshire coastal erosion map with rates

On the chart above, erosion rates are drawn opposite the locations to which they relate. The trend line (in dark blue) indicates that greater erosion takes place lower down the Holderness coast. It may be seen from the chart that a higher rate of erosion occurs immediately to the south of any defence structure. Seaside frontages at Bridlington, Hornsea, and Withernsea present clear examples, while rock revetments built at Mappleton and Easington produce the same effect on a lesser scale, as do defence works near Barmston and the private frontage at Ulrome.

The process responsible is known as longshore drift. Tides move material along the beach in the direction of the sea current, which for the east coast flows north to south. If movement is restricted or prevented, as at a defence structure, then a stretch of beach downdrift is starved of material and the cliffs are exposed to greater attack by the waves. Another consideration is that the cliffs themselves represent a supply of material, one that is effectively cut off behind a protective barrier.

Any proposal to limit cliff erosion at a particular location has to be viewed with a mind to high cost, typically thousands of pounds per metre for rock armour, and the strong possibility that a loss of cliff will increase elsewhere as a consequence. Of the 63 kilometres of coast from Sewerby to Spurn north, a little over 10 kilometres (about 16%) may be regarded as defended.

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an ice age legacy

In order to understand the causes for such rapid erosion it is necessary to travel back in time, to what is generally known as the ice age.

An ice age is not a single event that comes and goes but consists of major advances and retreats, with fluctuations, oscillations, and with prolonged periods of little change. Individual events are measured in thousands or tens of thousands of years.

During the most recent advance, and from the specific standpoint of the area known today as Holderness, a body of ice crept south along the dry bed of the North Sea (sea levels were low because of the volume of water bound up in ice sheets). The local coastline was determined at the time by the outcropping of a great thickness of chalk that underlies the North Sea basin.

The glacier grew and expanded laterally, extending as far as the chalk cliffs, where the higher ground stopped a further spread of ice. In time, global temperatures rose and the ice melted. The vast amount of material picked up and carried within the ice was left behind. That intraglacial load became the ground of Holderness. Geologists refer to material deposited in this way as glacial till, once called boulder clay.

With the ice gone, the North Sea began to return. Between present-day Britain and mainland Europe lay Doggerland. Over the course of a few thousand years the post-glacial territory was eroded and inundated, a process doubtlessly hastened at one stage by a massive tsunami caused by an underwater landslide off the coast of Norway. A rising sea level created an inlet between the east coast and the Dogger Hills (now submerged as the Dogger Bank).

If a start to the story of East Yorkshire’s coastal erosion is required, then the broadening of that sea inlet would serve. The North Sea continued to regain its earlier domain. In the soft tills of Holderness, an area essentially borrowed from the sea, the process goes on.

Land will be consumed at a significant rate for as long as the tides are able to wash against the foot of an unprotected cliff. At current erosion rates, and with no other influences, the sea will reach the former cliffs of chalk in about 10,000 years.

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lost places

The earliest Ordnance Survey maps record the Holderness coast as it was around 1850. Two villages are marked which no longer exist in the same form, and which were already reduced then. Overlay maps tell the ultimate fate of Great Colden (also known as Great Cowden) and (Old) Kilnsea.

Throughout the centuries, land taken by the sea has meant the removal of numerous communities. Perhaps the first ‘erosion map’ naming and depicting the sites of these can be found in Thomas Sheppard (1912), The Lost Towns of the Yorkshire Coast. A modern rendering is presented at erosion map.

For convenience, a simplified erosion map appears below. There are gallery pages for the following lost places: Great Colden, Ringbrough, Skipsea Withow Mere.

As a matter of note, the ending ‘-sea’ for an existing place name was originally ‘-sey’, meaning mere, or lake. The style is preserved in Woodmansey, a village between Hull and Beverley, and elsewhere in the East Riding. Holderness once contained a number of meres, all products of the ice age. Only Hornsea Mere remains.

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till types

Three glacial tills (or ‘members’) make up the Holderness Formation. Resting on the chalk bedrock is the Basement Till. This almost certainly dates from a previous, more extensive glacial period of 350,000-128,000 years ago. At the coast, which to all intents provides a cross-section through material left by ice, the Basement Till is (sometimes) exposed north of Bridlington and at Dimlington High Land.

Skipsea Till, from the most recent glaciation, runs the entire coastline and accounts for most of the cliff. Towards the southern end, between Aldbrough and Easington, Withernsea Till sits above the Skipsea Till and for a stretch is the dominant unit. The glacier which delivered these tills is considered composite or two-tier in that the ice originated from two sources: north and north-west. Both flows may have moved together, one overriding the other, or there could have been a readvance. Whichever the case, each flow carried its own defining till.

Until the mid-1970s, Skipsea Till was referred to as Drab Till or Clay, and Withernsea Till as Purple. There had also been a Hessle Till but this was successfully argued to be the surface layers of Skipsea and Withernsea tills subjected to weathering over thousands of years. Within the tills and between them are pockets and beds of sands, silts and gravels (especially at Dimlington High Land), as well as small and occasionally larger boulders, known as erratics. Of the two main tills, the Withernsea member is slightly the weaker.

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measurement

Following the introduction of precise mapping in the mid-nineteenth century, later revisions to the Ordnance Survey allowed for estimation of land loss by comparing changes in cliff line positions.

Linear measurement, rather than approximations from maps, became possible in 1951 by the siting of a series of erosion monitoring posts along the coast, with a few more added later. However, results were not necessarily gathered for the entire length of coast at any one time, nor on a regular basis.

A project to estimate coastal retreat after a century of erosion is described in Hartmut Valentin (1954), ‘Land Loss at Holderness’ (see references). In 1952, 307 physically selected reference points at intervals of about 200 metres were compared with the 1852 Ordnance Survey map. Results indicated that, over the span of one hundred years, the cliff line had receded 120 metres on average, losing around 720 hectares (1,780 acres, or 7.2 square kilometres) of land.

In 1999, GPS (Global Positioning System) technology was introduced, with readings recorded twice a year – spring and autumn – but not at every location. GPS was replaced in 2009 by LiDAR (Light Detection And Ranging).

Since 2003, readings have been taken every six months at all measurement points except for two included slightly later. Cliff recession is monitored along section lines, or profiles, spaced a nominal 500 metres apart and which extend a kilometre or so from a point a little distance behind the cliff to a position out to sea.

The profile approach has the limitation that it captures cliff recession only at certain points along the coast. Recently, continuous cliff line recording has been carried out, using GPS equipment. This development has its roots in the days of comparing map markings, though technology brings speed and detail.

data

Data collected from the monitoring positions are available online from the East Riding of Yorkshire Council. See profile details, results, summary, also beach profiles.

A data locator helps with prepared summaries of data 1854-2011 and from 2003. Recent data is arranged in an Excel spreadsheet.

Some degree of caution is called for when proposing an average. For example, annual averages taken through the relatively brief period 2003 to 2011 vary almost by a factor of six. Overall, the same period produces an erosion rate of 1.76 metres per year for unprotected cliff and 1.50 metres for the entire coastline. The latter figure is 25% higher than the 1.20 metres submitted by the Valentin survey (see above), which estimated loss over the century 1852 to 1952.

As regards volume of material removed by the sea, a calculation based on length of unprotected cliff and cliff height suggests that roughly one million cubic metres, weighing perhaps 2.2 million metric tonnes, are lost for every metre of recession along the coast. In fact, the tides not only erode the cliff but the beach and sea bed, too. The question of where all the washed away material is deposited awaits a complete answer.

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more on erosion of the East Yorkshire coast

wave action and cliff undercutting (1-6)
Waves approach the coast predominantly from a north-easterly direction and the water falls back at a lesser angle. As tides come and go, the sea can be thought of as sawing away at the cliff foot. In high winds and storms, there is also a destructive pounding.

cavities and caves (7-10)
Where a cavity forms in the clay, a combination of surging water and trapped air may enlarge it to a temporary cave. Accumulations of pebbles and stones produce abrasive ‘milling’, which accelerates the process.

detachment (11-14)
At the top of the cliff, the material of the edge has nothing to contain it on the seaward side. It begins to detach, or separate. Rainwater enters the clay more easily through the cracks, weakening it further (and freezing in winter). Detachment may continue in the cliff face on a more massive scale.

slumping, sliding, crumbling... (15-20)
A failure at the bottom of the cliff will produce slumping above. Sections of the previous land surface drop and slowly descend the cliff as if on a downwards escalator, often with a backwards tilt (called rotational sliding). Elsewhere, material may flow like slurry (because it's not only the sea), or crumble to fine pieces, or fracture along bedding planes.

...and tumbling (21-24)
In addition to slumping, which is commonplace along much of the coast, there are blocky falls when a large amount of material tumbles towards or on to the beach.

stacks (25-26)
Stack formation is rare in the Holderness clays although sometimes the potential is observed.

cliffs (27-28)
The till of East Yorkshire is generally considered to begin at the north end, where the pre-glacial chalk cliff turns inland at Sewerby. Clay also lies above the chalk where from time to time it slides or falls down the face.

(29-30)
Along the coast, lengths of cliff break to a repeated pattern of indentation. For a short depth below the surface, the clay is weathered into soil – this layer was once thought to be a separate till.

(31-34)
The Holderness cliffs display contrasts in angle of slope, also in height. A figure on the beach in the distance at the extreme right of picture 32 provides an idea of scale for Dimlington High Land (which rose even higher to the east in the past). Low cliffs are found at each end of the coast.

(35-36)
Heavy clay tills predominate, one member clearly overlying another in the cliffs to the south, but extensive sandy deposits can also be found in the cliffs.