The submerged prehistoric forests on Trusthorpe and Cleethorpes beaches, Lincolnshire

The aim of this post is simply to share some recent images of the underwater prehistoric forests at Trusthorpe and Cleethorpes, Lincolnshire. The submerged forest at Trusthorpe is only rarely seen, especially since beach replenishment works along the coast here; however, an unusually low tide on Monday 13th August, 2018, exposed at least two of the tree stumps and I was able to take the following pictures of these.

One of the tree stumps exposed on Monday, 13th August 2018 at Trusthorpe, Lincolnshire; click here for a larger version of this photograph (image: C. R. Green).

Top view of the submerged prehistoric tree stump exposed at Trusthorpe, Lincolnshire, in August 2018, showing its tree rings; click here for a larger version of this photograph (image: C. R. Green).

Another of the prehistoric tree stumps exposed by an exceptionally low tide at Trusthorpe, Lincolnshire; click here for a larger version of this photograph (image: C. R. Green).

The tree stumps and trunks that are revealed by such very low tides and in excavations all along the Lincolnshire coast from Immingham to Ingoldmells have their origins in a drowned prehistoric forest that once stretched out over what is now the floor of the North Sea after the last Ice Age, when global sea-levels dropped to around 120 metres below their current levels. For the early part of the Mesolithic era, beginning c. 9600 BC, the actual coastline lay a significant distance to the north-east and eastern Lincolnshire represented part of an upland district rather than a coastal zone. However, from about 8,500 years ago, this situation began to change as the inexorably rising sea-level due to the melting of the glaciers pushed the coastline ever nearer. Sometime around 6200 BC, the land bridge connecting Britain to the continent was severed, perhaps being finally destroyed by the Storegga Slide tsunami, and by approximately 6000 BC the flooding of what remained of Doggerland had advanced sufficiently that the coastline probably lay just to the seaward of its present position along much of east Lincolnshire. As this process continued, the trees that are now found submerged off the Lincolnshire coast were first subject to waterlogging as the water-table rose and were then submerged by the rising tide. The date of this waterlogging and submersion varies from site to site, depending on the elevation of the land on which the forest grew: at Immingham and Theddlethorpe the waterlogging of the prehistoric landscape has been dated to 5840–5373 BC and 6205–6012 BC respectively, whilst at Anderby Creek and Cleethorpes the trees on the foreshore were submerged in 3514–3349 BC and 2912–2299 BC, as determined by the radiocarbon dating of their wood.

The extent of Doggerland about 12,000 years ago at the end of the last glacial era, with possible reindeer migration routes shown (drawn by C. R. Green for Origins of Louth, based on Barton, 2005 and Shennan et al, 2000, with permission).

The last stages in the drowning of Mesolithic Doggerland, from the perspective of Lincolnshire and the Fens (drawn by C. R. Green for Origin of Louth, based on Shennan et al, 2000, with permission). Louth is marked to help in understanding the changes; darker blue indicates areas permanently under water, light blue the inter-tidal zone and low-lying marshland.

The photographs of submerged trees at Trusthorpe included above were taken at approximately 14:30 in the afternoon, when the tide was at its lowest point of 0.4 metres above chart datum, equivalent to around 3.35 metres below Ordnance Datum. Unfortunately, this wasn't quite low enough to expose more than a handful of tree stumps, especially after beach replenishment works along this coast, although wading a short way out beyond the shoreline revealed a number of additional tree stumps lying just below the water's surface. A number of photographs are available online of the more dramatic exposures in the Mablethorpe to Huttoft area visible in previous decades, especially those in 1984 and 1992, although none of these in turn seem to approach those recorded in previous centuries, leading to the suggestion that the drowned forest remains have been subject to recent erosion as well as being covered up by beach replenishment schemes. In particular, the outcrop of exposed forest seen in 1796 by Sir Joseph Banks and Joseph Correa de Serra was around 1 mile wide just to the south of Trusthorpe at Sutton-on-Sea (something also apparent on Robert Mitchell's 1765 coastal sailing chart, where the forest 'islets' are marked as a wide belt of 'Clay Huts' between Sutton and Anderby Creek), whereas in 1923 it was only 150 yards wide. According to A. J. Clapham, 'even allowing for the shifting pattern of the sand covering the foreshore and the fact that the tides might not have fallen as low in 1923 as on the 1796 visit, this is evidence for considerable erosion of the outcrop in a century and a quarter'.(1) With regard to the 1796 exposure, it is worth quoting Joseph Correa de Serra's 1799 description of the 'submarine forest' at length as an indication of what was visible in the eighteenth century:

It was a common report in Lincolnshire, that a large extent of islets of moor, situated along its coast, and visible only in the lowest ebbs of the year, was chiefly composed of decayed trees. These islets are marked in Mitchell's chart of that coast, by the name of the clay huts... In the month of September, 1796, I went to Sutton, the coast of Lincolnshire, in company with the Right Hon. President of this Society [Sir Joseph Banks], in order to examine their extent and nature. The 19th of the month, being the first day after the equinoctial full moon, when the lowest ebbs were to be expected, we went in a boat... and soon after set foot upon one of the largest islets then appearing. Its exposed surface was about thirty yards long, and twenty-five wide, when the tide was at its lowest. A great number of similar islets were visible round us, chiefly to the eastward and southward... These islets, according to the most accurate information, extend at least twelve miles in length, and about a mile in breadth, opposite to Sutton shore... The channels between the several islets [representing the eroded lines of drainage from wave backwash], when the islets are dry, in the lowest ebbs of the year, are from four to twelve feet deep.(2)

Banks and De Serra examined the composition of these 'islets' on the 19th, 20th and 21st of September, 1796, and concluded that

they consisted almost entirely of roots, trunks, branches, and leaves of trees and shrubs, intermixed with some leaves of aquatic plants. The remains of some of these trees were still standing on their roots; while the trunks of the greater part lay scattered on the ground, in every possible direction. The bark of the trees and roots appeared generally as fresh as when they were growing; in that of the birches particularly, of which a great quantity was found, even the thin silvery membranes of the outer skin were discernible. The timber of all kinds, on the contrary, was decomposed and soft, in the greatest part of the trees; in some, however, it was firm, especially in the knots.... The sorts of wood which are still distinguishable are birch, fir, and oak...
     The soil to which the trees are affixed, and in which they grew, is a soft, greasy clay; but for many inches above it is entirely composed of rotten leaves, scarcely distinguishable to the eye, many of which may be separated by putting the soil in water, and dextrously and patiently using a spatula, or a blunt knife. By this method, I obtained some perfect leaves of Ilex Aquifolium [holly], which are now in the Herbarium of the Right Hon. Sir Joseph Banks; and some other leaves which, though less perfect, seem to belong to some species of willow. In this stratum of rotten leaves, we could also distinguish several roots of Arundo Phragmites [common reed].

Robert Mitchell's 1765 coastal sailing chart of Lincolnshire, showing 'clay huts' (islets of exposed submerged forest separated by deep eroded backwash channels) extending significantly offshore from Sutton to Anderby Creek.

Whilst only the tops of a few tree stumps were visible at Trusthorpe as a result of the unusually low tides this August, rather more was visible of the submerged forest at Cleethorpes on 14 August 2018 (when low tide was only 0.1 metres higher than on the previous day) and some pictures from this visit are shared below as a comparison. As was noted above, the forest at Cleethorpes is perhaps a thousand years younger than that further south at Mablethorpe–Anderby, being probably drowned in the Late Neolithic era, and both this and the lack of intensive beach replenishment as seen elsewhere on the Lincolnshire coast may explain why significantly more trees are visible here. In any case, as can be seen from the pictures below, a variety of fallen tree trunks, stumps and roots were easily to be seen on Cleethorpes beach without having to venture too far out, many well-persevered due to a layer of marine crustaceans overlying them.

A tree stump from the Late Neolithic drowned forest on Cleethorpes beach; click here for a larger version of this photograph (image: C. R. Green).

Two fallen trees from the Late Neolithic drowned forest on Cleethorpes beach; click here for a larger version of this photograph (image: C. R. Green).

Another tree trunk from the Late Neolithic drowned forest on Cleethorpes beach; click here for a larger version of this photograph (image: C. R. Green).

A tree stump from the submerged prehistoric forest on Cleethorpes beach; click here for a larger version of this photograph (image: C. R. Green).

Another piece of the drowned Late Neolithic forest visible on Cleethorpes beach; click here for a larger version of this photograph (image: C. R. Green).

Notes

1.     See A. J. Clapham, The Characterisation of Two Mid-Holocene Submerged Forests (Liverpool John Moores University PhD Thesis, 1999), pp. 62–4, for a brief discussion.
2.     This and the following quotation are taken from J. C. de Serra, 'On a submarine forest, on the east coast of England', Philosophical Transactions of the Royal Society of London, 89 (1799), 145–56.

The content of this post and page, including any original illustrations unless otherwise stated, is Copyright © Caitlin R. Green, 2018, All Rights Reserved, and should not be used without permission.

The prehistoric evolution of the coastline of north-eastern Lincolnshire

The following post offers a brief look at the evolution of the coastline of north-eastern Lincolnshire and Spurn Head from the Mesolithic through until the start of the Roman era, a period that saw dramatic changes as an inland forested region was gradually flooded by the rising tide to become the new coastal zone. Included below are a series of palaeogeographic maps that offer reconstructions of the coastline at various points in prehistory, along with some brief commentary on the changes and developments that each map shows.

The extent of Doggerland in around 10,000 BC, towards the end of the last glacial era, along with suggested reindeer migration routes in that period (drawn by C. R. Green for Origins of Louth, based on Barton, 2005 and Shennan et al, 2000, with permission). Ahrensburgian tanged points, or arrow tips, of this period have been found in north Lincolnshire, which are identical to finds associated with reindeer hunting in northern Germany then. 

The Mesolithic landscape of Doggerland, now the floor of the North Sea, as revealed by 3D seismic data collected by the North Sea oil and gas industry (image source: Vincent Gaffney).

The landscape and outlook of the present-day Lincolnshire coast was dramatically different in the Mesolithic period (9600 BC onwards). The formation of massive ice sheets during the last 'Ice Age' led to global sea-levels dropping to -120 metres OD, with the bottom of the North Sea consequently becoming dry land as far north as Shetland. Although this exposed landscape, known as Doggerland, began to be submerged once more as the ice melted and sea-levels rose, this process took millennia. As a result, the modern Lincolnshire coast was covered by a mixed deciduous forest that extended out over what is now the floor of the North Sea for much of the Mesolithic, with the actual coastline lying 50 km or more to the north-east at the start of this period and eastern Lincolnshire representing part of an upland district rather than a coastal zone. Such a situation appears to have persisted throughout the earlier Mesolithic, with the coastal zone still lying well outside this region in c. 7000 BC:

A reconstruction of the Mesolithic coastline as it existed around 7000 BC, with Louth in eastern Lincolnshire marked to aid with location (image drawn by C. R. Green, based on data from Shennan et al, 2000). 

The landscape of north-eastern Lincolnshire and south-eastern Holderness in around 6500 BC; at this point in the Mesolithic, the coastline still lay outside the region under consideration in the present post (image drawn by C. R. Green, after Berridge & Pattison, 1994). Note, the present-day coastline from approximately Saltfleet in Lincolnshire to Easington in the East Riding of Yorkshire is shown in grey.

From about 8,000 years ago, this situation began to change. Sometime around 6200 BC, the land bridge connecting Britain to the continent was severed, perhaps being finally destroyed by the Storegga Slide tsunami, and by approximately 6000 BC the flooding of what remained of Doggerland had advanced sufficiently that the coastline probably lay just to the east of edge of our study area. The next 500 years saw continued flooding, with the result that the coastal zone moved decisively into this region, as can be seen in the following maps:

A reconstruction of the Mesolithic coastline as it existed sometime around 6000–5500 BC, with Louth in eastern Lincolnshire marked to aid with location (image drawn by C. R. Green, based on data from Shennan et al, 2000, with modifications). Note, the marine flooding had reached Theddlethorpe by c. 6000 BC; it also created offshore islands from former higher ground to the east and north of the modern Lincolnshire and Norfolk coastlines in approximately this period — these islands are thought to have persisted until the later thirteenth century AD, before they were finally destroyed by storms and flooding.

The coastline of north-eastern Lincolnshire and south-eastern Holderness sometime around 5000 BC (image drawn by C. R. Green, based on underlying till-surface contour data reported in Berridge & Pattison, 1994, with additions and modifications). As before, the present-day coastline from approximately Saltfleet in Lincolnshire to Easington in the East Riding of Yorkshire is shown in grey. By this point, the coastal zone lay well within our region, with the Lincolnshire coast being protected by offshore islands; the sand body that underlies the North Somercotes–Saltfleet storm beach appears to have first formed in this period too, based on borehole records, and a very notional representation of this is included above.

This flooding had a dramatic effect on the vegetation of the region, with the mature mixed deciduous forest that had once stretched out onto the North Sea plain being replaced by wetlands and a coastal landscape. The tree stumps and trunks that are revealed at very low tides and in excavations all along the Lincolnshire coast from Immingham to Ingoldmells have their origins in this lost prehistoric forest, which was first subject to waterlogging as the water-table rose and was then submerged by the rising tide. The date of this death and submersion varies from site to site depending on the elevation of the land on which the forest grew, but at Immingham and Theddlethorpe the waterlogging has been dated to 5772–5346 BC (recalibrated) and 6174–5961 BC respectively.

With regard to the resultant Late Mesolithic coastal landscape of northern Lincolnshire and Holderness, several features need noting. First, a comparison of both of the above maps with the preceding pair show that it was in this period that the peninsula of Holderness began to take on a recognizable form, although its south-eastern tip had a rather different profile to that which it has today. Second, the higher ground that had previously lain to the east and north of the present-day coastlines of Lincolnshire and Norfolk is thought to have been gradually surrounded by the rising tide, becoming coastal barrier islands that seem to have persisted through until their final destruction by the sea in the late thirteenth century AD. Initially, at least, this high ground off the Lincolnshire coast may have become a single island, and it is shown as such on the above reconstruction, before later splitting into a number of smaller islands as the sea-level continued to climb. Third and finally, a cross-section of the Lincolnshire Outmarsh running east–west through Marshchapel and Donna Nook (North Somercotes) created from borehole records indicates that the coastal sand body that underlies the current storm beach on the Lincolnshire coast from Donna Nook to Saltfleet formed directly on top of the Mesolithic land surface and must have been in existence from the first arrival of the sea in this area; as such, a notional representation of it is included on the above map.

A very small, partially polished Neolithic axe, found at Grainthorpe, Lincolnshire (image: PAS).

The coastline of north-eastern Lincolnshire and south-eastern Holderness in the Neolithic era, sometime around 3000 BC (image drawn by C. R. Green, based on underlying till-surface contour data reported in Berridge & Pattison, 1994, with additions and modifications). As before, the present-day coastline from approximately Saltfleet in Lincolnshire to Easington in the East Riding of Yorkshire is shown in grey.

The coastline of north-eastern Lincolnshire and south-eastern Holderness in the Early Bronze Age, sometime around 2000 BC (image drawn by C. R. Green, after a map in Berridge & Pattison, 1994, with some modifications). As before, the present-day coastline from approximately Saltfleet in Lincolnshire to Easington in the East Riding of Yorkshire is shown in grey.

The next two maps offer possible reconstructions of the coastline of north-eastern Lincolnshire and south-eastern Holderness in the Neolithic and Early Bronze Age. Continued—albeit now significantly slower—sea-level rise is thought to have a led to further coastal areas being submerged by the rising tide, with the result that by around 2000 BC or so the Lincolnshire coastline lay significantly inland of its current position. It is also possible that the offshore coastal barrier had been divided up into several smaller islands by this point. Whether these offshore islands were inhabited or visited by people in this era is entirely unclear due to their subsequent destruction by the sea in the medieval period, although it seems inherently likely that they were. Certainly there may well have been some activity within the coastal zone on areas of dryer land closer to shore, such as the small island of glacial till that was probably surrounded by coastal marshes visible on the Neolithic map at Grainthorpe. For example, not only is a Mesolithic axe or pick known from Grainthorpe, testifying to an earlier human presence, but there are also a number of Neolithic flint objects (including a knife and a possible votive axe) from the area of this island, and beaker sherds have been found from a spot to the north that have been seen as indicative of the presence of a Late Neolithic/Early Bronze Age barrow here in the coastal zone.

Other features of note on these maps include the continued development and definition of the south-eastern tip of Holderness, although as yet there was nothing approximating Spurn Head, with the profile of the peninsula still instead following the lines first set down by the Mesolithic course of the River Humber as it flowed north-eastwards across Doggerland. Also significant is the development of a second major sand body/sand bank off the coast of Lincolnshire, running from the peninsula of glacial till at Cleethorpes down to the Marshchapel/Grainthorpe area, as evidenced once again in borehole records from this region. This sand bank seems to have developed sometime around 3000 BC (perhaps above an earlier Late Mesolithic/Early Neolithic coastline and after a period of marine flooding, to judge from the borehole data and underlying till surface contours), with tidal flat or lagoonal conditions on its landward side. It is likely that similar conditions now prevailed on the landward side of the North Somercotes–Saltfleet sand body and bank too, with the former dry land to its west having been submerged by the rising sea-level and becoming coastal marshes or the like whilst the sand body itself continued to persist and build up. Another less well-evidenced sand body on the southern coast of Holderness may similarly have its origins in this era, running south-eastwards from the islands of glacial till and gravels near Paull (not mapped).

In terms of the vegetation of the region, the continued sea-level rise led to further water-logging and submersion of the coastal woodland on sites that had been too elevated to be affected by this during the Later Mesolithic, with the drowned trees preserved at Cleethorpes and Chapel St Leonards dying off sometime around 2950–2250 BC and 3370–3020 BC respectively. The Mesolithic forest inland of the coastal zone also saw significant losses in this era. These losses appear to have begun on the high ground of the Lincolnshire Wolds, with the Mesolithic deciduous oak and hazel woodland of the Wolds cleared at Skendleby by c. 3500 BC and an open grassy landscape with indications of at least local arable agriculture having developed at Swinhope by c. 3900–3650 BC. On the lower ground, just inland of the coastal zone, the wooded landscape may well have survived a little longer, but it too was eventually lost. For example, at Butterbump (Willoughby), on the eastern edge of the dry Lincolnshire Middle Marsh, the available pollen cores indicate that the Mesolithic forest there survived the Early Neolithic through until perhaps 2900 BC, but was apparently largely cleared in the Late Neolithic/Early Bronze Age, with subsequent eras then having low levels of tree and shrub pollens and high levels of herb and cereal. Similarly, in Holderness a degree of sustained clearance began around 3600 BC, but the landscape of this area also wasn't properly opened up until the end of the Neolithic (c. 2500 BC), and only from the end of the Bronze Age (around 800 BC) did agricultural land start to dominate.

Sherds of Roman Nene Valley colour-coated pottery and imported Samian ware, found at Grainthorpe, Lincolnshire (image: PAS).

The coastline of north-eastern Lincolnshire and south-eastern Holderness at the start of the first century AD (image drawn by C. R. Green, after a map in Berridge & Pattison, 1994, with some modifications). As before, the present-day coastline from approximately Saltfleet in Lincolnshire to Easington in the East Riding of Yorkshire is shown in grey. Note, all of these maps show the approximate position of the coastline in this period; however, there would also have been an extensive zone of coastal marshes, inter-tidal flats and the like too on the seaward side of this coastline; these are not mapped here, but they clearly saw a significant degree activity in the Roman period.

The final map offers a suggested reconstruction of the coastline of this region at the start of the first century AD. As before, there are several features and points worth noting with regard to the coastal landscape in this era. First, a degree of marine regression by the Early Roman period probably led to the coastal zone moving back eastwards from its earlier westward maximum extension in the Lincolnshire Marshes area. Second, the coastal marshes that continued to lie behind and close to the two major sand bodies in north-eastern Lincolnshire—despite the marine regression—saw a significant degree of activity in this era. Quantities of Roman material have been found from the Roman-era coastal marshes and margins at, for example, Marshchapel, Grainthorpe, South Cockerington, Scupholme (South Somercotes) and Saltfleetby St Peter, with some of the finds including imported pottery and box-flue tiles. With regard to the nature of this activity, the relatively substantial structure indicated by finds of pottery and building materials at Marshchapel has been interpreted as one situated within the coastal zone, perhaps on the saltmarsh itself, and probably involved in the end-stage processing and transportation of salt produced at nearby salterns.

With regard to other aspects of the first-century AD landscape, the development of the south-eastern tip of the Holderness peninsula had probably by now continued to the point where it was finally starting to take on something approaching its modern form and with a proto-Spurn Head starting to form, although the coast of Holderness and the tip of the peninsula still lay well to the east of their current position, which is the result of a further 2,000 years of coastal erosion by the North Sea. Similarly, the peninsula of glacial till at Cleethorpes that extended out into the Humber estuary had by now started to be seriously eroded away back towards its modern position, although it too continued to extend out some way beyond the current coastline. It has been suggested that this peninsula and its low cliffs were home to a Roman-era signal station or fort that stood on some of the subsequently lost land here, although it has to be admitted that the evidence is uncertain and weak—a more convincing candidate for a Late Roman fortification in this part of Lincolnshire is perhaps to be had from the area of the former Toote Hill, nr Grimsby.

The north-eastern part of the Lincolnshire Marshes in the Late Roman and post-Roman eras, taken from a map created for a previous post; note, the light blue area represents a possible reconstruction of the extent of the coastal wetlands/saltmarsh during this period of maximum marine transgression (image: C. R. Green). 

The later evolution of the coastline of Lincolnshire after the Early Roman era largely lies beyond the scope of this post, being discussed and mapped in two previous pieces on this site, one dealing with the Late Roman and pre-Viking coastline (reproduced above) and the other with the situation in the medieval era. Two points are worth noting here, however. The first is that the fourth- to sixth-centuries AD appear to have seen a significant marine transgression in the Lincoln region. This led to Romano-British sites on the Lincolnshire Outmarsh being submerged and subsequently buried under several metres of marine alluvium—for example, the Romano-British site at Scupholme, mentioned above, was found beneath more than three metres of alluvium deposited by the sea, whilst Romano-British salterns at Ingoldmells to the south were smothered by two to three metres of silt. This Late/post-Roman marine transgression also seems to have largely swamped the prehistoric Cleethorpes–Marshchapel sand body and covered it over with a thin layer of marine silt (around a metre thick at North Cotes and rather less than this at Marshchapel), to judge from borehole records, with only a few sections of the former sand bank probably being left exposed to the east of Marshchapel. The second is that the North Somercotes–Saltfleet sand body seems to have survived and remained above this marine transgression, although it too appears to have been later partly buried, in this case by storm beach deposits that are often thought to have their origin in debris thrown up on the coastline by the destruction of the offshore coastal barrier islands in the thirteenth century AD, an event discussed in more detail elsewhere.

The content of this post and page, including any original illustrations, is Copyright © Caitlin R. Green, 2015, All Rights Reserved, and should not be used without permission.

The flooding of Mesolithic Doggerland and the emergence of Lincolnshire

The following two maps will be discussed in more detail in a later post, but in the meantime I thought that I would share them both as items of interest in their own right. Both were initially created for and published in my The Origins of Louth: Archaeology and History in East Lincolnshire, 400,000 BC–AD 1086, but are presented here in full colour.

The two maps together depict Mesolithic Doggerland. The first depicts the extent of Doggerland during the Younger Dryas period, around 10,000 BC, alongside suggested reindeer migration routes across this landscape. The second shows the final drowning of Doggerland as the sea level gradually rose after the end of the last 'Ice Age', from the perspective of Lincolnshire and the Fens. With regard to the latter, I particularly like how the shape of Lincolnshire emerges as the land floods over the millennia! You can click both maps to access larger-scale versions of the images.

Suggested reindeer migration routes and the extent of Doggerland about 12,000 years ago at the end of the last glacial era (drawn by C. R. Green for Origins of Louth, based on Barton, 2005 and Shennan et al, 2000, with permission). Ahrensburgian tanged points, or arrow tips, of this period have been found in north Lincolnshire, which are identical to finds associated with reindeer hunting in northern Germany then. 

The last stages in the drowning of Mesolithic Doggerland, from the perspective of Lincolnshire and the Fens (drawn by C. R. Green for Origin of Louth, based on Shennan et al, 2000, with permission). Louth is marked to help in understanding the changes; darker blue indicates areas permanently under water, light blue areas flooded by the tides and low-lying marshland.

The content of this page, including any original illustrations, is Copyright © Caitlin R. Green, 2014, All Rights Reserved, and should not be used without permission.