Isostatic Rebound

 

Isostatic Rebound

 

  

Isostatic Rebound is explained in detail in the following quote from Encyclopedia Galactica. Briefly though it is the response of the earth's crust to the additional weight of ice sheets laid upon it in the last ice age, and the continuing response of rising land as ice sheets are removed.

In my discussion of this enormously influential scientific discipline I am not trying to disprove the existence of Isostatic rebound,  but I am questioning some of the evidence for it.

Quoted from:- Encyclopedia Galactica

"Introduction to Isostatic Rebound

Isostatic rebound represents one of the most profound yet subtle processes shaping our planet’s surface—a slow vertical dance of the Earth’s crust in response to changes in surface load. At its core, isostatic rebound describes the gradual rising of land previously depressed by the immense weight of ice sheets during glacial periods. This phenomenon operates on the principle of isostatic equilibrium, a state of gravitational balance analogous to an iceberg floating in water, where the Earth’s lithosphere “floats” on the denser, more plastic asthenosphere beneath. When heavy ice masses accumulate, they push the crust downward, much like adding weight to a ship causes it to ride lower in the water. Conversely, when these ice masses melt, the crust gradually rebounds upward, seeking to restore its equilibrium position. This process must be distinguished from eustatic sea level changes, which represent global changes in ocean water volume rather than local vertical movements of the crust. The interplay between isostatic and eustatic processes creates complex patterns of relative sea level change that vary dramatically across different regions of the globe.

The recognition of isostatic rebound as a geological phenomenon emerged gradually through careful observation and interpretation of landscape features. In Scandinavia during the late 19th century, Swedish geologist Gerard De Geer meticulously documented elevated shorelines and marine deposits far inland, realizing they represented ancient coastlines that had been uplifted following the retreat of the Fennoscandian Ice Sheet.

His development of varve chronology—counting annually deposited sediment layers—provided crucial timing information about this uplift process. Around the same time, Scottish scientist Thomas Jamieson was puzzling over raised beaches in his native country, proposing in 1865 that the weight of glaciers had depressed the land, which subsequently rose after their melting. These early observations were revolutionary, challenging established geological thinking and requiring scientists to reconceptualize the Earth’s crust not as rigid and unchanging, but as responsive and dynamic. The intellectual journey from these first recog- nitions to our modern understanding spans nearly two centuries, involving contributions from geologists, geophysicists, geodesists, and many other specialists who gradually pieced together this global puzzle.

The scale and significance of isostatic rebound are truly remarkable when viewed across both space and time. Vertical movements of hundreds of meters have occurred in regions once buried beneath the thickest ice, with the center of the former Laurentide Ice Sheet around Hudson Bay still rising at rates exceeding 10 millimeters per year today. In Fennoscandia, the Gulf of Bothnia continues to emerge from the sea at similar rates, with the land having risen nearly 300 meters since the peak of the last glaciation. These movements operate on timescales ranging from immediate elastic responses to complete viscous relaxation spanning tens of thousands of years. The geographic footprint of significant rebound extends across vast areas of North America, northern Europe, Siberia, Antarctica, Patagonia, and numerous other regions glaciated during the Pleistocene epoch. Beyond its direct effects on land elevation, isostatic rebound influences global sea level patterns, triggers earthquakes, alters drainage systems, shapes ecosystems, and continues to impact human societies in profound ways."

Isostatic Rebound has become interwoven into the fabric of our understanding of Quaternary Science. It is assumed to be real because the assumptions that are used to qualify the processes of glaciation and deglaciation are accepted as factual.

Until recently I also accepted Quaternary Science as it is because, fact or not , it had no bearing on my life. That changed when I sought to understand how early humans were able to walk from Europe to Britain. 

It is difficult to see the link there, between Quaternary Science and neolithic Britain,  but I found one, (or two!)

A childhood experience also taught me that the most significant feature of the deglaciation of Britain and Scandinavia was that the melting of ice sheets in those places caused the draining of huge amounts of water off from high ground out to coastal waters.

The meltwater carried sediments and boulders, dumping them as they slowed, or as they reached water.

In my recent research i discovered that when meltwater reached coastal waters it raised sea-level locally. This raising of local sea levels was particularly pronounced when complex coastlines prevented the free flow of meltwater away from land.

In the published literature about relative sea-level around our coasts the evidence is found in seabed borings underwater, and in raised beaches, morainal dumps, and isolated lagoons on land.

Mollusc shells are markers, giving environmental, and carbon dating information, usually for a marine context.

Diatoms are markers for marine and brackish water in raised lagoons, and twigs, leaves, and peat samples tend to imply a terrestrial environment. 

The following locations have been surveyed for various research purposes. 

Kattegat 

  

The Kattegat is a semi enclosed basin between Denmark and Sweden. It is largely shallow sea with narrow waterways leading south into the Baltic Sea. 

North of the Kattegat is the Skagerrak, which in contrast to it, is very deep. North of the Skagerrak is southern Norway.

A boring was driven into the seabed here from a bed depth of 38 metres, and at about 41 metres below sealevel a group of mussels were found, a species that lives in groups on shorelines down to 5 metres below sealevel.  This group of mussels would have been living in shallow water at this location in about 10,000BP.

On top of that, an additional 3 metres thick layer was dumped, in which were found random molluscs that were derived from deeper waters. The nearest deep water to the Kattegat is the Skagerrak, and it is most likely that a melt period occurred at around 10,000BP causing meltwater to enter the Skagerrak from Norway with enough force to scour out sediments and molluscs to dump them on the Kattegat. 

This demonstrates that water and sediments were being moved around southern Scandinavia with considerable force. Also, as far as the floor of the Kattegat is concerned there is no evidence of isostatic rebound. 

Tromsø

 

At Tromso in West Troms, North West Norway great deposits of mollusc bearing sediments have been described and recorded in detail by Bjorn Andersen. He has drawn sketch sections, and produced photographs for sources at over 70 metres above sealevel. These deposits contained huge bolders and molluscs from deep sea locations.

The mountains around Tromsø are huge....

....and the narrow inlets that incised the area would have channelled any sediment loaded meltwater deeply enough to leave molluscs and boulders on high ground. 

Kola Peninsula 

At the Kola Peninsula a group of four lakes were surveyed. The dating for the contents of the lakes, the highest of which was 54 metres above sealevel was provided by the carbon dating of mussel shells and algae, ie seaweed. 

The seaweed growing in the intertidal region of coastline would have been attached to seabed ballast, including stones and molluscs at times and locations where sea-level was low,and when meltwater was not running. Evidence of a time when meltwater runoff was comparatively low is from Kattegat above, at about 10,000BP, when mussel beds were growing at a level equivalent to global sea level at the time.

Seaweed growing in fjords and inlets would have formed seaweed rafts, which would have been raised by the influx into the fjords of meltwater from elsewhere in Scandinavia. The seaweed would then have been pushed across the landscape until it arrived at the lagoon where it settled.

Seaweed rafts are a common feature of North Atlantic coasts, and they typically carry mussels with them that they have attached themselves to on the seashore, and that have been ripped up with them in winter storms.

Many other land based lagoons on coastal areas of Norway are similarly over-topped by the influx of seawater pushed into fjords and inlets by meltwater surges. These surges have left evidence of diatoms that are common to marine and brackish waters. The diatom population in these locations is one of the commoner means for establishing the relative sea-level of Northern European Coastlines. 

Jeffery Nicholls 

Orkney 

Kattegat

 Kattegat 

Information from:- Late glacial to early Holocene development of southern Kattegat, by Carina Bendixen et al

 

"Two lithological units presumably of Holocene age were also found in sediment core no. DGU 561118.10 collected at 56°23.165´N, 11°22.0´E from a water depth of 38.0 m.

The core was 518 cm long and consisted of 136 cm sand with abundant shells of the common blue mussel Mytilus edulis characteristic of shallow water, overlain by 328 cm of mud with shells of Turritella communis, Arctica islandica, Pecten s.l. sp. and other marine molluscs that are characteristic of deeper water. The marked lithological change 382 cm below the core top probably corresponds to the boundary between units H1 and H2 (Bendixen 2012). We suggest that the sand was deposited during the early Holocene when sea level was low, whereas the mud was deposited after the relative sea level had increased. Radiocarbon dating of Holocene sub-littoral sand deposits in the region has yielded ages of c. 11–10 cal. ka BP (Bennike et al. 2000; Jensen et al. 2002a)."

The sealevel  curve for the North Sea west coast of Denmark (Hijma et al) indicates that the date that mussels were living in the Kattegat was around 10,000BP. 

  

Jeffery Nicholls 

Orkney 

Kola Peninsula

 

Kola Peninsula 

Source:-

"Postglacial relative sea-level history: sediment and diatom records of emerged coastal lakes, north-central Kola Peninsula, Russia" by Jeffrey Snyder et al

The maps below indicate the location for the Kola Peninsula, and for the group of lakes surveyed. 

  

There are four lakes featured, sites 54, 41, 22, and 7. "The sediment character and diatom flora in the basal unit in cores 54,41, and 22 indicate a near shore marine environment."

and, "The diatoms present in these units is consistent with a protected bay with seasonal freshwater influx and perhaps higly variable salinity. "

"In contrast to the other three basins the basal core sediments from core 7 is rich in organic and carbonate material. The diatom flora contains a diverse polyhalobous (marine) and mesohalabous flora, minor halophobous diatom eg eunotia and plant fossils such as betula and empetrum indicate inwashing from terrestrial environments. "

   

The laboratory number, and radiocarbon dates for the lowest levels of the four lakes are detailed here. Additionally the material that was tested to provide the date is stated, and the height of the sample above sealevel. 

Site 54

"GX20140 10,910BP, algae, 54 metres

GX20139 10510BP, algae, 54 metres

Site 41

AA16845 11845BP, algae, 40 metres 

Site 22

GX20141 8820BP, shell, mytilus edulis, 20m

AA16846 9945BP, algae filaments, 20m

AA15619 9765BP, laminated algae mtl, 20m

Site 7

AA20502, 4855BP, shell, mytilus edulis, 10m"

The authors describe the algae as marine algae and it is probable that the algae and the shells came together here as floating rafts.

Molluscs and Seaweed 

The materials dated at Kola Peninsula were algae, (seaweed), and mollusc shells. These components are commonly found on seashores, particularly storm battered beaches. They arrive as floating rafts of seaweed.

 

 

  

The view above is of a beach on the east coast of Orkney. A winter storm has passed over with high seas and furious winds. Everything is calm now. The seaweed that had been growing on the seabed off shore was ripped from its roots in the storm and has now been dumped on the shore.

  

Here, on another tideline, on another beach a pair of mollusc shells have become attached to and enmeshed in, a strand of seaweed washed up to the high water mark. 

Mytilus edulis, (Blue Mussel) Occurs from the high intertidal to the shallow subtidal attached by fibrous byssus threads to suitable substrata. Found on the rocky shores of open coasts attached to the rock surface and in crevices, and on rocks and piers in sheltered harbours and estuaries, often occurring as dense masses. Depth, intertidal to ca. 5m.

These rafts of seaweed would transport flotsam and jetsam wherever the winds and tides directed them

 

Jeffery Nicholls 

Orkney 

Western Troms

 Introduction. 

Troms County in North Norway is characterized by deep narrow fjords between high mountainous peninsulas. Deep valleys lead from the heads of the fjords up to a high mountain plateau near the Swedish border. Many mountainous islands lie offshore, and a narrow, shallow submarine shelf follows the coast outside the islands. 

 

Tromso

Although Troms lies well above the Arctic Circle, its climate is humid-ternperate. At Tromsø the mean annua! temperature and precipitation are respectively 2.3 °C and 940 mm (Hansen, 1960, p. 46). 

Glaciers cover the highest mountains, and the snow line Iies at altitudes between 800 m and 1200 m. 

  

Location of Tromso/Langnes

  

Detail of Tromso and Langnes in their fjord setting.

  Several sites have been recorded for evidence of glacial activity in the Tromso area, beginning at Langnes. 

  

Fig. 8. Gravel pit in shore deposits near the Skarpnes end moraine at Langnes. 

A: sand, well sorted. 

B: gravel, poorly sorted with large erratics and numerous shells of Mya truncata [1] and [2] Macorna calcarea. 

The shells were radiocarbon dated at 12,000-12,500 years R.P. (T-490 a, b, c). 

C: sand, stratified with scattered boulders. 

Scale: large boulder in "B" is l m. 

The pit Iies 7O m-78 m above sea level, immediately above the Main shore line. 

   

 

Fig. 13a. Cross-section of the proximal Tromsø-Lyngen end moraine at Giævernes on Tromsø, exposed in two grave! pits. 

A: Beach-washed gravel with several large erratics. 

B: Bouldery till with some clay. 

C: Glacio-fluvial gravel and sand, strongly folded beds in upper part. Scattered fragments of Astarte elliptica [3], Chlamys islandicus [4], Mya truncata[1] Macoma calcarea [2], Hiatella arctica [5] and Balanus sp. [6] Iie in this section. They were radiocarbon dated at 11,500 ± 350 years B.P. (T-112). 

D: Stratified marine sand, well sorted. The upper beds are folded. 

D1: Stratified silt and clay, about 0.5m, with unbroken shells of Portlandia arctica [7], Leda pernula ]8], Thyasira flexuosa [9] and Nucula tenuis ]10]. Section D1 is Probably younger than bed E. 

E: Glacio-marine blue clay with scattered cobbles and shells of the same species that were found in bed C. The shells were mostly unbroken. 

They were radiocarbon dated at 11,480 ± 150 years B.P. (T-436 B). 

F: Medium sand. 

Filled circles: stratigraphic positions of radiocarbon dated samples. 

Frame: Beds in fig. 13 b Iie within the frame. 

 

Sketch of the two Tromsø--Lyngen end moraines and the marine terraces on the eastern side of Tromsøsund. 

A: Sand (Yz m-1 m) with shells of Mya truncata [1] and Macoma calcarea. [2].

B: Glacio-marine clay with scattered pebbles to boulders and shells of Macoma calcarea,[2] Macoma torelli,[11],  Nucula tenuis,[10] Yoldiella (Portlandia) lenticula, [12], Yoldia hyperborea [13] etc. About 4 m of clay was exposed. Shells from the middle part of the section ( x) were radiocarbon dated at I0,200 ± 35O years B.P. (T -113) . 

Altitudes in metres above sea level. 

  

Fig. 16. Cross-section of the outwash delta at Bjorelv. 

Beds exposed in the gravel pit: 2 m topset beds, mainly of gravel with boulders. 20 m foreset beds, mainly of well sorted sand. However, beds of poorly sorted bouldery sand to gravel exist particularly 6m-10m below the exposed part of the topset beds. The foreset beds dip 20°-25° NW. Unbroken shells of Macoma calcarea [2] and Mya truncata [1] Iie within several beds. I, Il and Ill show the statigraphic positions of collected shell samples radiocarbon dated at respectively 10,500 ± 400 years B.P. (T-50), 11,250 ± 319 years B.P. (T-511 B) and 11,200 ± 500 years B.P. (T-174). 

Altitudes in metres above sea level

  

Fig. 18. Cross-section of the Tromsø-Lyngen end moraine at Rensaa. 

A: Beach grave!, 0.5m-1.5m. 

B: Foreset beds, mainly gravel with large boulders. 

The beds dip 15°-20°. 

Shell fragments of the following species lie scattered within the beds: Mya truncata,[1] Hiatella (Saxicava) arctica, [5], Chlamys (Pecten) islandicus [14], Arctica (Cyprina) islandica [15] and Astarte elliptica. [3]. The shells fragments probably originale from older beds. They were radioarbon dated at 11,100 ± 300 years B.P. (T-111) and 11,650 ± 220 years B.P. (T-437 B). 

C: Stratified marine sand and silt. 

D: Interbedded silt and clay, with scattered pebbles and cobbles. Shells of Portlandia arctica [7] Iie in some of the beds. The shells were radiocarbon dated at 11,100 ± 800 years B.P. (T -17 5). 

E: Marine blue clay, well sorted with no stratification. 

F: Glacio-marine clay, 2m exposed. Numerous pebbles to cobbles and unbroken shells exist. The shells were of the same species as the shells in section B. They are large, and their radiocarbon age is 11700 ± 21O years B.P. (T -43 8 B); 11,990 ± 250 years B.P. (T-438 A). 

Filled circles: radiocarbon dated samples. 

  

Fig. 19. Cross-section of the ice-contact outwash delta at Storm o in Balsfjord 

( rough sketch). 

A: Marine blue clay, mostly unstratified. 

B: Marine silt and clay, partly laminated. 

C: Marine silt and fine-sand, stratified. 

D: Foreset beds of sand and grave!. 

E: South-dipping sand and grave! beds. 

F: Topset beds of grave! with large boulders. 

A1: Marine clay, mostly unstratified. 

B1: Marine silt and clay, partly laminated, with shells of Macoma calcarea [2] and Mya truncata. [1]

D1: Gravel

x: Location of shells radiocarbon dated at approximately 9,150 years B.P. 

(T-510 A, B). 

Altitudes in metres above sea level.

  

Fig. 20. Cross-section of the terraces immediately inside (east of) the moraine at Moen in Gratangen Fjord (rougb sketch). 

A: Sand and gravel

B: Silt and fine-sand, stratified with scattered pebbles. Small shells of Mya truncata [1] and Macoma calcarea [2] were collected and radiocarbon dated at 9,520 ± 190 years B.P. (T -63 O). 

C: Bouldery gravel, poorly sorted~ in parts till-like, with many large striated erratics. 

D: Stratified silt and sand, about 4 m. Pebbles and cobbles lie in some of the sand beds, pariicularly in one bed which is very fossiliferous. Shells of Macoma calcarea, [2] Mya truncata, [1] Hiatella (Saxicava) arctica, [5], Chlamys islandicus [4] were collected and radiocarbon dated at 9,740 ± 160 years B.P. (T-512 B). 

E: Bouldery gravel,  l m. 

Altitudes in metres above sea level

Conclusion 

The photograph of the town of Tronso at the head of this article demonstrates the proximity of the high mountains of northern Norway with their snow cover, towering over the region. In addition the plan of the local area presents the fjords that criss-cross the region, each with higher ground either side of them.

No evidence is presented that the molluscs that were catalogued were live in-situ. These are therefore likely to be redeposited, along with the the material in which they were found.

It is demonstrated elsewhere that when the ice sheets melted they did so producing meltwater in quantities measurable in cubic kilometres per day. These volumes would have literally moved mountains, and churned up neighbouring fjords bringing up deep dwelling molluscs to the surface and dumping them on land that is now above sealevel. 

[1] Mya truncata, A deep burrower in sand and sandy mud. From low in the intertidal to shallow shelf depths of about 70m.

[2] Macoma calcarea, A burrower in muddy sands, offshore. Subfossil in North Sea and off northern Scotland. Living in Norway, Iceland and circum-Arctic Depth Range, Continental Shelf (to 200m)

[3] Astarte elliptica, Lives in a range of clean, silty and muddy sands and gravels from the near sub-littoral towards the mid-shelf, depth range c.5m - >150m, but most frequently in depths <50m.

[4] Chlamys (Pecten) islandicus, Byssally attached to stones and rocks from low in the intertidal to shelf edge. Present here only as post glacial subfossil shells. Living in Faroes, Iceland and Norway south to Bergen. Intertidal Continental Shelf (to 200m)

[5] Hiatella arctica, A nesting species attached by a weak byssus in crevices on hard substrates and among coarse ground and Modiolus beds and in kelp holdfasts. From the low intertidal to the shelf edge and upper slope. Widespread. Continental Shelf (to 200m), Continental Margin Zone (200 - 500m)

[6] Balanus sp. (Barnacles)

Balanus crenatus is primarily a sublittoral species that can sometimes be found under stones or overhangs on the lower shore. Balanus crenatus colonizes cobbles, shells, bedrock, molluscs and artificial substrata. It is found at a wide range of wave exposures and it can tolerate salinities as low as 14 psu

[7] Portlandia arctica, A high arctic species living in Greenland, Svalbard and northern Norway but not in Iceland. Records further south are most likely subfossil. The status of the single record from the Minch, NW Scotland (see NBN Gateway) is uncertain.

Continental Margin Zone (200 - 500m), Bathyal (500 - 2000m), Abyssal Rise (2000 - 4000m)

[8] Leda ( nuculana) pernula, northern species ranging south to to the northern North Sea at outer shelf and shelf edge depths. Also recorded from greater depths on the slope off Ireland but these may be based on valves only or subfossil shells. Depth Range, Continental Shelf (to 200m), Continental Margin Zone (200 - 500m)

[9] Thyasira flexuosa, Widely distributed from the intertidal and shelf to over 150m.

[10] Nucula tenuis. Occurs all around Britain and Ireland but is absent from the English Channel and southern North Sea. Mud and substrates such as sand and gravel which have a muddy element. Occurs from inshore in c. 10m to the outer continental shelf in depths of up to 200m.

[11]Macoma torelli, burrower in muddy sands, offshore. Not in the British fauna. Circum-Arctic Greenland and Svalbard. Continental Shelf (to 200m)

[12] Yoldiella (Portlandia) lenticula, Known from the West European basin mostly from a small geographic area from 43° to 48° N and 3° to 10° W in depths from 1400-2245m.

Panarctic, south to northern Norway and Iceland in depths of 10-300m. Also known from deep water north Atlantic basins (West European and Canary) in depths from 1400-2245m.

This species displays “equatorial submergence” being found at much greater depths in the south of its range. 

[13] Yoldia hyperborea. A subarctic species extending southward to Iceland. Mostly taken from outer shelf depths beyond 100m. Not yet recorded from the British area. Continental Shelf (to 200m)

[14] Chlamys islandicus, Byssally attached to stones and rocks from low in the intertidal to shelf edge. Present here only as post glacial subfossil shells. Living in Faroes, Iceland and Norway south to Bergen

[15] Arctica (Cyprina) islandica, Arctica islandica is found at extreme low water level but predominately on sublittoral firm sediments including level offshore areas, buried (or part buried) in sand and muddy sand that ranges from fine to coarse grains. Depth range, 4-482 m

Mytilus edulis, Occurs from the high intertidal to the shallow subtidal attached by fibrous byssus threads to suitable substrata. Found on the rocky shores of open coasts attached to the rock surface and in crevices, and on rocks and piers in sheltered harbours and estuaries, often occurring as dense masses. Depth, intertidal to ca. 5m.

Turritella communis (Turretellinella Tricarinata). Abundant on muddy sediments in shallow water, more or less buried but maintaining contact with the water. This species is slow moving and sits on the seabed filtering seawater for particles of food. It may be gregarious, occurring in large numbers. It can be found down to 200 m.

Pecten, scallops 18m Free living sitting on the surface of bottoms of sand to fine gravel. From the sublittoral to mid shelf depths, Widespread from northern Norway to Iberian Peninsula. Continental Shelf (to 200m)Hiatella (Saxicava) arctica, A nesting species attached by a weak byssus in crevices on hard substrates and among coarse ground and Modiolus beds and in kelp holdfasts. From the low intertidal to the shelf edge and upper slope. Widespread. Continental Shelf (to 200m) Continental Margin Zone (200 - 500m)

Saxicava arctica , wrinkled rock borer , and hiatella arctica. Hiatella arctica, known as the wrinkled rock-borer, the arctic hiatella or the arctic saxicave, is a species of saltwater clam, a marine bivalve mollusc in the family Hiatellidae. The white shell of this mollusc is thick and more or less rectangular, but generally irregular in shape. It is up to 45 mm long.

Hiatella arctica is widespread and found in all the oceans, ranging from the Arctic and Antarctic to the subtropical and tropical zones. It occurs from the low water mark to depths of down to 800 m. It lives on hard substrates, often attached with byssus, for instance in mussel beds or nestling among kelp holdfasts, or hiding in rock crevices and also boring itself into soft rocks.

Bathyarca glacialis , An Arctic species extending south along the shelf edge and upper slope into the Faroe-Shetland Channel. Byssally attached to gravel, stones and deep water coral debris along the continental margin and upper slope. Continental Margin Zone (200 - 500m) Bathyal (500 - 2000m)

Similpecten greenlandicus Free living on fine sediments at outer shelf and bathyal depths. An arctic species not recorded from British waters, closest are records from the Faroes and Iceland. A dwarf form was recorded from Biscay but this is now S. oskarssoni. Continental Shelf (to 200m) Continental Margin Zone (200 - 500m) Bathyal (500 - 2000m)

Modiolaria nigra black mussel rocky shores

Lyonsia arenosa, Sandy Lyonsia

Benthic; depth range 0 - 360 m (Ref. 119523). Subtropical

Members of the class Bivalvia are mostly gonochoric, some are protandric hermaphrodites. Life cycle: Embryos develop into free-swimming trocophore larvae, succeeded by the bivalve veliger, resembling a miniature clam.

Natica clausa Cryptonatica affinis

Cryptonatica affinis is widely distributed in Arctic and sub-Arctic marine environments, occurring circumpolarly from the Pacific boreal-Arctic sectors to the Northern Atlantic, including areas like the Skagerrak and Norwegian coast. It is eurybathic, found from shallow shelf depths to 2650 meters, but predominantly on continental shelves in soft sediment habitats with strong bottom currents. In the Baltic Sea region (HELCOM area), records are sparse, limited to a single deep locality in the Öresund strait (Landskronadjupet) at soft bottoms mixed with sediments, with the most recent observation from 2007. This distribution suggests it functions as a southern outpost for Arctic species in transitional zones.

 Jeffery Nicholls 

Orkney 

Ice Age Story

Glacial Prehistory 

 Ice Age Story

 

  Introduction 

This is a story of Britain, and north-west Europe, as it passed through several periods of extreme cold, Ice Ages, the formative events that created the landscape that we live with.

It is not authoritative, and may be taken with a pinch of salt, but it is my best attempt, using current evidence, to understand the ice age of Britain. 

The general territory that the story covers is very roughly the Atlantic coast of Europe, but includes the Alpine mountains of southern France, and the northern mass of Scandinavia. 

Specific areas that are covered are Britain, Norway, and the North Sea. These constitute an area that academia deems to have been covered by thick ice sheets, the British and Irish Ice-Sheet (BIIS) and the Fenno-scandinavian Ice-Sheet (FIS). These ice sheets are thought by some to have been joined across the North Sea for part of the last ice age.

The theory that is proposed, studied, taught and learned, in universities, is that the ice sheets over northern Europe, and elsewhere flowed as solid ice Formations along glacial valleys, shaping them as they progressed.

Beginning 

The evidence tells a more nuanced story that has to start several million years ago with the movement of Britain away from Europe.

As the Atlantic Ocean opened up a great chasm between Europe/Africa and North/South America developed, so that Britain pulled away from Norway. The result was that a portion of the earth's crust between Britain and Norway remained open, a vast crack in the earth's surface, to be filled by sediments from surrounding lands. 

Ultimately, as the oceans filled up with sediments, and the ice-sheets melted, the seas invaded the space between Norway and Britain, forming the North Sea. 

In the last million years, and possibly before, the planet was cold, reflecting the sun's rays off from polar ice caps. There were brief periods of warmth in which ice sheets collapsed crashing into underlying geology, cutting impact valleys and dumping huge volumes of sediments across landscapes, and eventually into offshore waters. (Impact Valleys)

This process would have raised average sealevel on a continuous basis from a million years ago right up to the present day. 

It is difficult to assess what effect this carving out of geology had on landscapes of today, but evidence of sediments in the Trent Valley confirm that some of them go back a long way into prehistory, with sand and gravel beds dated up to a million years, and more.

Nascent North Sea

The period formally assigned to the last ice age period began at 120,000BP, and lasted until about 10,000 years ago. 

Before 120,000BP, there occurred the earliest significant event that is recorded in the geology of the North Sea. An extended warm period melted polar ice sheets causing Sea levels to rise allowing an insurgence of sea water to flood the area now the North Sea. 

After this warm interglacial period snow began to fall from 120,000BP, continuing until around 70,000BP when there was a sharp thaw. At this time ice sheets on the Pennine Hill of Northern England and the mountains of Scotland collapsed, cuttimg impact valleys, and sending tidal waves across what was probably dry land in the North Sea area, to deposit huge volumes of sediments as Dogger Bank. (Dogger Bank)

Cold, but not that cold!

There followed a relatively mild period from around 50,000BP to around 23,000BP (Tattershall).

In this period the ice sheets remained at high altitude on the mountains of England Scotland, Wales and Ireland. But in the lowland regions of southern Britain and Ireland meltwater rivers flowed through a cold, and probably wooded landscape with marshy areas near the coasts. These places were home to cold tolerant creatures like the woolly rhinocerous, and to people using Upper Palaeolithic flint tools making technologies. (Dorset Barrow)

Also at this time, the ice sheet on Shetland was collapsing, and some of the meltwater from that event (Capeshore Formation) flowed south along the Scottish coast into a lagoon that had been formed by the after-wash from glacial meltwater, the Marr Bank lagoon. (Marr Bank Formation). There two additional deposits were laid with the Marr Bank Formation, the Wee Bankie Formation  and the Bolders Bank Formation. (Wee Bankie Formation) (Bolders Bank Formation)

Snowing again!

Cold weather and heavy snowfall returned to lowland Britain, possibly as late as 23,000BP,  laying a variable thickness of snow/ice across the British Isles and the North Sea. Very little snow built up on the south coast of England, though the South Downs in Kent, the east coast of England,  including London, (Levallois Flake) may have had considerable thicknesses of snow on them.

Additional thickness of snow over the pre-existing mountain ice-sheets of, Scotland, Wales, northern Ireland and northern England  raised those ice-sheets further.

The mainland ice sheets on England and Scotland extended off present coastlines a short distance and a high ridge of land joining Dogger Bank in the southern North Sea to the Atlantic Ocean at a peninsula east of, and separate from Shetland, but separated from Norway by the Norwegian Channel.

The Marr Bank lagoon lying off the Scottish coast, near Aberdeenshire remained unfrozen throughout this return to freezing conditions, supporting vegetation and wildlife. 

The ice-sheet spread across from Norfolk, linking up with Dogger Bank, to enclose the Marr Bank lagoon from the south. 

It is likely,  but cannot be proved, that the ice sheet also lay thickly around the North edge of the Marr Bank lagoon, where the Swatchway Formation is to be found.

Everything, everywhere, melts!

From about 21,000BP the very brief cold period at the end of the ice age ended, and a 10,000 year long deglaciation began.

Between 21,000BP and 15,000BP the ice sheets retreated rapidly across all low-lying areas, causing seasonal collapse differences to leave parallel valleys across many areas.(Parallel Valleys) 

Ice sheets on the French Alps collapsed sending meltwater North to the English Channel and the southern North Sea, where the speedy retreat of ice-sheets progressed northwards at a rate of roughly a kilometre per year.

At these intial stages of the melt the Lobourg Channel of the Dover Strait was cut, the Outer Silver Pit, at Dogger Bank also, and the Norfolk Banks. The South Wales valleys were cut around this time, and the Black Mountains of Brecon and Herefordshire. 

At about 15,000BP those ice-sheets on the high mountains began to fall, the meltwater causing Ice-streams to cut wide rivers and palaeovalleys across southern England. (Ice Streams)

These ice streams, containing varying proportions of stones, sludge, ice, and meltwater flowed across England and coastal waters leaving geological features where they passed.

These include glacial lineations,  moraines, and potholes. (Striations) (Moraines) (Pot-Holes) (Erratic Boulder) (Drumlins)

An ice sheet on Dogger Bank and the peninsula that bordered the west coast of the Norwegian channel in the North Sea also retreated, leaving huge gullies in the north of the area, as the Witch Ground, and the Devil's Hole, off the Scottish coast. (Swatchway Formation)

These edge collapses would have caused the release of meltwater, possibly in the region of half a cubic kilometre of water every day, with peak melt in summer and least melt in winter. This release, repeated on several coasts around the region caused the sea levels at those local coastlines to oscillate, up and down annually, as seasons changed.().

All Melted

At around 11,000BP the last of the mountain ice sheets had collapsed, and water from that event was mostly draining away with little effect on local sea levels.

In the highland valleys that had been gouged out by the collapse of ice sheets there remained rivers of ice, valley glaciers. These, like the ice-sheets, were static, and where the sun was less able to reach in the valley floors they remained as glacial rivers of solid ice. 

The glaciers carried the stones and sands that had been gouged out of the mountains and it wasn't until about 9000BP that these began to melt.

Again local sea levels rose as the ice melted in the valleys, and the debris that had been stored within the glacier simply gravitated to the floor of the valley, remainng now as hummocky moraine. (hummocky moraine)

North Sea develops

The spine of land that divided the North Sea, north to south was available to mesolithic wildlife and people.

As sea levels rose the spine of land was gradually whittled away until in a series of collapses in the 4th millennium BC, more recent, softer sediments in the northern North Sea were easily flushed aside, opening up the whole North Sea. (Archaeology in the North Sea)

There was a coastal inlet east of Shetland that had a southern shoreline just east of Orkney.

Two tidal waves were triggered by submarine landslides in the North Sea north of Norway. The first was the Nyegga Slide in 18,000BP, the second the Storegga Slide  in around 8200BP. These may both have been funneled along this inlet, between Shetland and the extension of Doggerland from the south, to hit the Aberdeenshire coastline.

Migrations 

During the mesolithic,  and early neolithic eras, Ireland was connected to Scotland by land; England was connected to Holland; and Scotland was connected to both Orkney and Shetland. 

Forest, heaths, and marshes formed with the inward migration of animals, plants, birds, and insects from Europe. 

During the 4th millennium BC the strands of land that connected these locations were stripped away by rising sea levels. The geological anomaly at the north West coast of Europe became the British and Irish archipelago.  (Walkable Land in the North Sea)

Between Caithness in Scotland, and south Ronaldsay in Orkney, land in the North Sea was removed.

The beach that connected these two places remains, vestigially, as the island of the Pentland Skerries, and there is a submarine raised landform attached to it, called the Sandy Riddle. 

The story of how the people who watched sea levels separate Orkney from Scotland reacted to this catastrophic event is told in "Orkney Riddle"

Jeffery Nicholls 

South Ronaldsay 

Orkney 

 #BIIS #Britice-Chrono #Quaternary #glaciation #LGM #neolithic #prehistory #archaeology #Orkney #Scotland 

Swatchway Formation

 Glacial Prehistory 

Swatchway Formation 

 

In “Late Pleistocene and Holocene deposits in the Witch and Fladen Ground area, northern North Sea” by Fred Jansen, He divides each of these layers, Swatchway and Witch Ground Formations, into Upper and Lower strata. The earliest deposits are the Swatchway Formation, of which the earliest strata is the Lower SwatchWay Beds.

Jansen writes, “The Lower Swatchway Beds are heavily overconsolidated, shallow Marine sediments which form pronounced ridges, interpreted as ice Pushed ridges." (The pronounced ridges would be the peaks of ridges between valleys caused by the collapse of ice sheets as they retreated, away from warm water in the Norwegian Channel, towards Scotland.)

“A core in the Swatchway Beds nearby Old Devil’s Hole (74-J62-Z, Fig. I) contains still unidentified peaty material as an admixture in Fine sands, which was 14C dated. The section between 130 and 166 cm Below the seafloor yielded a conventional radiocarbon age of 33 800 (+2600, --2000) y BP and the sample from 248 to 251 cm of 37 500 (+ 1800, --1500) y BP.”

The Upper Swatchway Beds, filling in the hollows between the Ridges, are composed of usually normally consolidated glaciomarine Deposits, with locally some probably subglacially folded structures. The Swatchway Beds Are roughly 50 m thick.”

The Upper Swatchway Beds would be the residue of materials left behind after impact erosion formed the ridges.

"The Swatchway Formation has an amorphous, or structure-less, seismic signature, with sporadic subhorizontal reflectors. It has a lithofacies of mud and sand with scattered lithic and shell fragments, The sparse, benthonic foraminiferal assemblage is dominated by the cold-water species E excavatum var. clavatum, which suggests deposition in boreal to arctic seas (Stoker et al., 1985)." (Johnson)

Elphidium excavatum var clavatum (A most abundant calcareous foraminifer in cold-water areas (temperatures below 2°C) on the Arctic shelves; inhabits all sediment types; has a complex pattern of distribution; often dominates foraminiferal assemblages in extreme environments, such as low salinities, turbid waters, and low food supply, including sites proximal to tidewater glaciers.) ( Foraminiferal Research at Byrd Polar Research Center)

Perhaps more significantly, the foraminifera are accompanied by moderately abundant populations of dinoflagellate cysts; a limited spectrum is co-dominated by O. centrocarpum and Bitectatodinium tepikiense Wilson, indicating northern cool-temperate conditions without significant sea-ice cover (Harland, 1988a). " (Johnson)

Lower Swatchway Beds laid down in boreal to arctic seas without significant sea-ice cover after 37500BP. They are heavily overconsolidated, meaning that it was compressed under a thick ice-sheet. The Upper Swatchway Beds are the fill of erosive valleys cut into the Lower Swatchway Beds and they are generally accepted to be dated to between 18,000BP and 15,000BP. 

"The principal 14C samples used by HOLMES were recovered from two borings, a commercial boring at Josephine Field and the IGS boring 74/7 at roughly 60 km off Aberdeen (56058 ' N, 1°07 ' W, INSTITtrrE OF GEOLOOICAL SCIENCES, 1975). From the upper sample of the Josephine Field boring a.o. large fragments of Taxus were dated which is a thermophilic tree. An early glacial age of 23 170 y BP, as was measured, is therefore impossible for biological reasons, and the material most probably was contaminated with younger carbon. If this is the case, the older dates of the boring are also suspect." (Jansen)

The finding of Ewe Tree wood at a location near Aberdeen and off the Scottish coast requires some explanation. Initially, if the radiocarbon date is ignored the existence of the tree growing there at any date from 60,000BP to say 12,000BP, changes completely how we view the climate of northern Europe, and specifically the North Sea. 

The tree may have grown in that location , or it may have floated there, but "The lower 15 m of the Shell-Fugro boring are correlated with the Upper Swatchway Beds. The pollen spectra of this section has a considerable contribution of tree pollen." So this makes it likely that other trees were growing in the area of the Swatchway Beds both after the LGM, perhaps 18,000BP, and/or before the LGM, before 23,170BP.

The implication here, is that the period in which the Last Glacial Maximum gripped Britain was perhaps not more than 5,000 years long, enough time to add hundreds of metres of ice to the mountain ice sheets of Britain and Norway, and to dump a varying thickness of snow on southern England, southern Ireland, and much of the North Sea land area.

The cores 72-J1-Z and 72-Jg-Z, located further south (Fig. 1), were taken from the Lower Channel Fill which, at least partly, developed simultaneously with the Upper Swatchway Beds. The pollen spectrum in the lower section of 72-J1-Z also belongs to group III, a high Hystrichosphaeridae percentage pointing to a marine environment (DE JONG, 1976). The mollusc fauna lacks arctic species, suggesting that the sea was even warmer than today (SPAINK, 1973). The mollusc assemblage of core 72-J9-Z resembles the present fauna, but indicates a somewhat shallower sea level (SP.~aNK, 1976a). (Jansen)

Sources  

(Johnson) The geology of the northern North Sea. United Kingdom Offshore Regional Report By H Johnson, 

Jeffery Nicholls 

South Ronaldsay 

Orkney 

#BIIS ##Britice-Chrono #EarthSciences #LastGlacialMaximum #IceSheets #RelativeSeaLevel #Glaciers

Wee Bankie Formation

 Glacial Prehistory 

Wee Bankie Formation 

"Overconsolidated sandy and gravelly till with interbeds of fluvial sand and pebbly sand, and, less commonly, accumulations of coarse sand and gravel."

The Wee Bankie Formation rests along the east coast of northern England and southern Scotland. It also follows the southern edge of the Marr Bank Formation, and as an overconsolidated material is likely to have been overlaid by ice-sheets until deglaciation, in spite of the Marr Bank being essentially ice- free.

(Cameron) The geology of the southern North Sea. United Kingdom offshore regional report By T D J Cameron, 

 

The chart demonstrates that the Wee Bankie Formation links between the Marr Bank Formation in the north, and the Bolders Bank Formation in the south. 

Jeffery Nicholls 

South Ronaldsay 

Orkney 

#BIIS ##Britice-Chrono #EarthSciences #LastGlacialMaximum #IceSheets #RelativeSeaLevel #Glaciers

Marr Bank Formation

Glacial Prehistory 

Marr Bank Formation

The Marr Bank Formation is described as being deposited in a shallow estuarine environment in "The geology of the central North Sea. United Kingdom offshore regional report by R W Gatliff".

"Sand, fine-grained, poor- to well-sorted, soft to firm, grey to red brown with abundant lithic granules and pebbles. Locally silty."

"The Marr Bank Formation includes "muddy sediments, especially towards the north-west but it is generally formed of sands of varying grain sizes and degrees of sorting (Stoker et al., 1985). Gravelly layers contain a variety of lithic clasts of Scottish provenance, and wood fragments and clay balls occur sporadically. No dinoflagellate cysts have been recovered from the formation."

"A poor ostracod fauna and a moderately abundant population of foraminifera (Thomson, 1978) indicate that the shallow waters in which the formation was deposited were high-boreal to arctic in temperature, and inner shelf to estuarine in character." (Gatliff)

 

The chart above indicates the bathymetry of the North Sea. Generalised contours are marked on the plan. A 40 metre contour is marked around Dogger Bank in the south. Further north the 80 metre contour extends up the middle of the North Sea separating the Marr Bank Formation from the Norwegian Channel and coast. 

The base floor of the Marr Bank Formation is 100 metres below sealevel while the seabed at 80 metres below sea level is made up of outcropping formations of the MIS 6, Coal Pit Formation, and older Formations. 

This would indicate that sediments have been lost here and that Marr Bank lagoon was eroded out, initially in MIS 4 and that there was at least a 20 metre height difference between Marr Bank and the Norwegian Channel. 

North of Marr Bank is the Witch Ground, a very deep area of the northern North Sea which is likely to have been carved out by impact valleys cutting down into the Swatchway Formation, and being filled by the Witch Ground Formation.

  

 The section drawing above describes the relationship between the Wee Bankie and Marr Bank Formations. They merge together,  the Wee Bankie Formation being harder than the Marr Bank Formation. It is likely that the Marr Bank Formation was once as thick as the Wee Bankie Formation,  but, as a soft material, was winnowed away during deglaciation. 

During the Last Glacial Maximum, the Marr Bank was a shallow lagoon of unfrozen water along the British coast. It was separated from the Norwegian channel by a ridge of land that reached from dogger bank to the Atlantic ocean north of Norway

The chart demonstrates how the Marr Bank Formation links through the Wee Bankie Formation to the Bolders Bank Formation. 
 

Jeffery Nicholls 

South Ronaldsay 

Orkney 

 #BIIS ##Britice-Chrono #EarthSciences #LastGlacialMaximum #IceSheets #RelativeSeaLevel #Glaciers

Capeshore Formation

 Glacial Prehistory 

Capeshore Formation 

  

 

  

Around Shetland a deposit called the Capeshore Formation was laid approximately from MIS 5 to MIS 3.  The Capeshore Formation material is described as "Soft to firm, highly to moderately silty clay with sporadic shell fragments and pebbles." (BGS)

It overlies Ferder Formation and older layers that have been cropped by the rise of sealevel into the North Sea region. If the drawing is correct this may have been the first significant incursion of the Atlantic Ocean into the area.

Diatoms in the sediments are identified as:- "The foraminiferal assemblage is dominated by E. clavatum, Cassidulina reniforme Norvang and Protelphidium orbiculare . " (Johnson) , and the the conditions in which this organism developed are:- "The Cassidulina reniforme–Elphidium clavatum, Textularia spp. assemblage dominates the foraminifera fauna near the glacier proximal that indicates increased sedimentation and meltwater runoff." (Chatterjee)

The presence of this species suggests that meltwater was running away from Shetland probably through MIS 5, 4, and 3.

The small size of the Shetland Isles, and their closeness to the Atlantic Ocean caused an ice sheet sitting on them in MIS 5 to collapse, effectively rendering the area ice-free through MIS 3, 2, and 1.

Sources  

(Johnson) The geology of the northern North Sea. United Kingdom Offshore Regional Report By H Johnson, 

Jeffery Nicholls 

South Ronaldsay 

Orkney 

 #BIIS ##Britice-Chrono #EarthSciences #LastGlacialMaximum #IceSheets #RelativeSeaLevel #Glaciers

Bolders Bank Formation

 Glacial Prehistory 

Bolders Bank Formation 

 

"The Bolders Bank Formation characteristically consists of reddish to greyish brown, stiff diamictons that are generally massive but in places possess distinct, commonly arenaceous layering, and deformational structures. The majority of its pebbles, of which chalk is the most conspicuous component, are derived from the sedimentary rocks of eastern England. The pebble content tends to diminish eastwards. In general, the formation is less than 5 m thick, and commonly less than 1 m is preserved in deep-water areas west of the Dogger Bank, although to the east of Lincolnshire it may be 15 to 20 m thick (BGS Spurn Quaternary Geology sheet). " 

(Cameron) The geology of the southern North Sea. United Kingdom offshore regional report By T D J Cameron, 

 

The plan above demonstrates that the Bolders Bank Formation merges into the Wee Bankie Formation, which in turn merges with the Marr Bank Formation. 

 The plan at the top of the page demonstrates that the cut for the Outer Silver Pit, at the southern edge of Dogger Bank slices into and through the Bolders Bank Formation. 

"The pebble content tends to diminish eastwards" suggests that the material of the formation is bedload for meltwater overflow around and south of Dogger Bank. 

"Stiff diamictons" may suggest that an ice sheet has rested on the formation's surface.

Jeffery Nicholls 

South Ronaldsay 

Orkney 

 #BIIS ##Britice-Chrono #EarthSciences #LastGlacialMaximum #IceSheets #RelativeSeaLevel #Glaciers

  

Tattershall

 

Glacial Prehistory 

Tattershall 

An instance of how the climate was warmed by 43,000BP, is described by Peter Kent :-

“Fluvial sand and gravel exposed in quarries near Tattershall contain evidence of a short but marked mid-Devensian climatic amelioration (Girling, 1974). An organic silt bed within involuted gravel overlying the Ipswichian peat has yielded insects indicative of a high-latitude continental tundra environment, but a slightly higher bed contains a thermophilous insect fauna—some taxa of which are now confined to southern Europe—implying summer temperatures at least as warm as those of southern England today. Radiocarbon dates from these deposits and correlatives elsewhere in England show that this warm interval, the initial phase of the Upton Warren Interstadial Complex, occurred around 43 000 years ago. It was too brief for the climatic improvement to be reflected in the flora. The overlying sand and gravel in the Tattershall area are appreciably cryoturbated and contain numerous remains of mammoth (Mammuthus primigenius), woolly rhinoceros (Coelodonta antiquatis), bison, reindeer and other tundra-favouring mammals.”

Longtown Castle

 

Glacial Prehistory 

  Longtown Castle 

 

It was 1978 when I worked at Longtown Castle, a motte and bailey medieval castle on the Welsh border in Herefordshire.

The castle is on a ridge that carries an ancient track way from Abergavenny, north to Hay- on-Wye. 

A deep valley runs parallel to the Longtown ridge, and beyond that was the Black Mountain, a high ridge, also connecting Abergavenny to Hay- on-Wye. 

The scenery, topography, and geology are difficult to ignore here, and I would sit in the site hut, sipping tea and looking out and wondering how the valley and the ridges on either side of it were formed.

Anything I might have learned at school suggested that the valley must have been formed by either a glacier sliding along it, or by water flowing along it.

Neither option looked feasible here. The valley was roughly 10 kilometres long, 1 kilometre wide, and fell 300 metres along it's length.

Looking at the valley over the rim of a cup of tea, at tea break, I could never see that the amount of rainwater falling on the valley would ever be enough to erode the several million tons of rock that was missing from the valley, not even in many millions of years.

I began to cook up an idea that the valley was actually created, not by a scraping glacier flowing along it, but by an ice sheet edge collapsing.  

This would explain most British valleys, and ribbon lakes, and the valleys that cross small islands, from sea to shining sea.

It would also explain multiples of valleys that lie parallel to each other, and that are separated by ridges like the ridge upon which Longtown Castle sits.

Gradually the idea took shape a couple of years ago, as i started to research more deeply into the recent, post-glacial geology of Britain and Norway.

I found that academia is completely locked onto the idea that mountain valleys were formed by the flow of glaciers along them.

In fact though, what is actually happening, is that ice sheet edges are collapsing, gouging out valleys as they fall, and the resulting meltwater with ice blocks, dust, and broken rocks are sliding gently down any available slope until they reach water. 

Finally, this flow of meltwater, dust, ice and rocks reach water where the ice melts out leaving a moraine at the waters edge.

The passage of the ice, dust, and rocks mixture is marked by striations in the exposed geology, being currently understood to be formed by the movement of solid glaciers rather than this looser mixture of materials. 

If my calculations are correct this melt would have supplied meltwater at a volume of over half a cubic kilometre for every day of deglaciation in that valley. This would have (did) raised sea level significantly in the brief periods when extreme temperatures and extreme melts took place.

Jeffery Nicholls 

Orkney 

Jiffynorm@yahoo.co.uk 

Impact Valleys

  

Geological Prehistory 

Impact Valleys 

 

A view of the Olchon Valley and the Black Mountain beyond. The ridge of the Black Mountain marks the Welsh border from the county of Herefordshire. 

The valleys of Britain,  particularly those in upland counties, are generally presumed, by academics and geologists to have been cut by rivers of ice or water flowing along them.

This is in spite of every indication that both schemes of valley creation are actually extremely unlikely. 

The actual erosive force that carved out these landscape features is much more likely to be by a vertical impact.

Think of a block of ice, a one metre cube, falling onto a car  from 500 metres up, at the edge of aan ice cliff face. How much damage would the ice black do to the car? Or what about falling on the roof of a house?

How much damage would the fall of a complete ice wall trimmed off the ice cliff edge do at a width of a metres, a height of 500 metres, and a length of 100 metres, if it fell onto dry ground?

Definition of a valley 

"A valley is a long depression on the Earth's surface that commonly hosts a river and lies in a relatively flat plain or between hills or mountains. Valleys can be formed through various processes, including river erosion, glacial activity, or tectonic action.

Tectonic valleys, also known as rift valleys, are formed by the subsidence of the Earth’s crust between faults. River valleys are created by the incising action of rivers. Glacial valleys, often U-shaped, are created as glaciers erode the landscape.

Valleys come in different forms, such as canyons, gorges, and rift valleys. Canyons are deep, steep-walled valleys cut by rivers through resistant rock. Gorges are narrow, deep valleys. Rift valleys are elongated troughs formed by the sinking of a segment of the Earth's crust between faults."

( Encyclopedia Britannica )

The floor of the North Sea is also composed of an undersea landscape of linear valleys which are commonly called tunnel valleys or palaeovalleys. 

Valleys forming under existing polar glaciers are apparently formed in the way described below:-

"Tunnel valleys formed when subglacial or englacial meltwaters flowing under great hydrostatic pressure, loaded with ice and rock debris, incised channels into the underlying bedrock." From "The Pennines and adjacent areas. British regional geology" by N Aitkenhead et al"

However there is no evidence that the valleys of Britain and the North Sea were created in a subglacial environment. 

There is significant evidence that these valleys, particularly on rising or high ground, were formed by the vertical impact of falling ice as described above. 

*

The Impact Valley 

The Impact Valley is the basic component of a post-glacial landscape in north-western Europe, and the "Parallel Valley Array " is an organised arrangement of impact valleys. 

These features are not yet recognised or understood by the academic community that studies glaciers and ice sheets.

They are the basic building blocks of a fundamentally novel theory for the creation of the British landscape as a result of the events in the last ice age.

 

*

Impact Valleys and Parallel Valley Arrays were created as a result of the sudden rise in temperatures that took place in periods of deglaciation at the ends of cold periods. ("Ice Ages")

Their prevalence across western Europe is due to the warm Gulf Stream waters that flowed north through the Atlantic Ocean from equatorial America. This climatic system that caused the melting, continues to maintain a "unique " climate in the northeastern Atlantic Ocean. 

Such was the speed of melt during those periods that ice sheets crumbled at speed, falling like a cliff-edge collapse, on underlying geology, gouging deep linear grooves through glacial deposits and natural bedrock alike.

 

The huge thickness (and altitude) of the ice sheet would have tended to conserve icy conditions, both in its bulk, and in its capacity to reflect the heat of sunlight. On the ground, adjacent to the ice sheet though, the suns energy would have been absorbed, creating the conditions in which the edge of the ice sheet could be undercut. The undercut edge of the ice-sheet would then fall, causing damage to the underlying substrate.

The thickness of ice over Britain and the North Sea is believed to have varied to a maximum of 1500 metres, and in some places may have been almost nothing. 

The force of impact that falling ice would have had on any ground upon which it landed, is calculated as a quantity of joules, or kilojoules, but that unit of measure is almost impossible to relate to reality.

The Snowline 

The thickness of ice over Britain during the last ice age is believed to have varied from a maximum of 1500 metres down to nothing.

Ben Nevis, in Scotland, is the highest mountain in Britain, at 1,340 metres. 

Under present day Alpine conditions:- "The snow line appears when there is a cut between the surface and the orography. Temperature sensitivity of snow cover duration, analytically derived from the state function, is extreme at the median snow line (snow probability 0.50). Alpine-wide mean altitude of the median snow line is 793(+ / −36)m in winter and 3.083(+ / −1.121)m in summer. - The snowline climate of the Alps 1961–2010" by M Hantel et al"

An ice sheet of a kilometre thickness would make the elevation of the ice above sea level over much of Scotland and northern England, over 2 kilometres. The temperature at that elevation would be seriously low, even while warm sunny weather was keeping the ground level rivers flowing.

The height of the ice sheets during an ice age would have been maintained, and increasing, until a critical temperature environment was reached forcing the undercut and collapse of leading edges of the ice sheet.

While prehistoric creatures and environments were coexisting with early humans , in the middle of the last ice age, these ice sheets would have been both gaining height, and melting on low ground simultaneously, the high ice looming over the lowland landscapes.

The Impact 

The force of impact that falling ice would have had on the ground upon which it landed, from this height, is calculated as a quantity of joules, or kilojoules.

However, to understand the potential power of impact that this event would have had, it has to be compared to one of the largest measured man-made explosions in history, that of the atomic bomb that exploded over Hiroshima.

On August 6, 1945, Hiroshima became the first city in the world to be struck by an atomic bomb. The bomb, called Little Boy, was deployed by a B-29 bomber named the Enola Gay. The bomb was airburst at 580 meters (1,900 feet) above the city, and the explosive yield was estimated to be the equivalent of 15,000 tons of TNT.

The ton of TNT is a unit of energy defined by convention to be 4.184 gigajoules, (4,184,000,000 joules) which is the approximate amount of energy released in the detonation of a metric ton (1,000, 000 grams) of TNT. In other words, for each gram of TNT exploded, 4.184 kilojoules (or 4184 joules) of energy are released.

Assuming that the ice sheet depth was commonly 1000 metres thick over northern Britain, the impact of the collapsing ice can be calculated as follows :-

The mass of a single cubic metre of ice is 1000kg, which, falling 1000 metres, will land on a surface with an impact of 9810 kilojoules

Therefore 9810 kilojoules is the kinetic energy of impact of 1 tonne falling 1 kilometre, and the equivalent is (9810 divided by 4.184) which is 2.335 kilograms of TNT

The whole 1000 metre column of ice falling on substrate, at a total weight of 1000 tonnes would cause an estimated impact energy of (2.335 x 1000 / 2), = 1,170, kilograms of TNT

That is just over 1 tonne of TNT, which is very little compared to the atomic bomb over Hiroshima, at 15,000 tons TNT, but the column of ice that falls to create that energy is just a single one metre by one metre, thousand ton, vertical spike.

A single square kilometre of collapsing ice would cause an accumulative explosion equivalent to 66 Hiroshima sized atomic bombs.

If my science here is debatable, can we agree that the damage caused by the fall of just one cubic metre of ice , one tonne weight, falling from a height of 500 metres or 1 kilometre, would cause significant damage for the surface it landed on?

The individual palaeovalleys of Parallel Valley Arrays, are likely to be the result of high summer temperatures melting an edge of the ice sheet, and causing that edge to collapse, creating deep eroded gullies where it landed.

Over cooler periods the rate of collapse slowed, and the impact of the erosion reduced, leaving raised ridges between deep valleys. 

When the planet warmed after 21,000BP, the low level ice sheets of southern England and the North Sea collapsed, retreating north. 

Where ice sheet thickness was low, the impact of the collapse was minimal, but as the edge retreated, thickness increased and valleys were cut into ground beneath it.

Where the ground consisted of glacial sedimentary dump, from a previous ice age, the cut of the valley was deeper than it would be if it landed on harder, or older, bedrock materials. 

Where the underlying substrate was rock, that rock was pulverised and became mixed with the shards of ice that had fallen on it, at the foot of the ice sheet wall. 

The Ice Stream

This ice and rock mixture, in a soup of meltwater sludge would form a huge heap where it had fallen.

There, lubricated by meltwater, this heap of ice, rocks, and silt, would slide slowly down any sloping surface that was available to it. 

When this mixture arrived at seaside or lakeside water the ice would melt out , leaving a moraine of rocks and soils.

*

The Black Mountain Parallel Valley Array 

 

The Impact Valleys (Parallel Valley Array) for the Black Mountains (above) are on the Welsh border of Herefordshire. These are a group of valleys that run more or less parallel to each other. Some, to the west, at the Brecon Beacons, run downhill from a ridge at the North of the area. At the east though the floors of the valleys are mainly flat, horizontal. 

Current thinking would probably suggest that these features were caused by the movement of glaciers along tnem, but even if the valleys were to be filled with snow there would be no impetus for the mass of ice in its frozen state to move along them. 

The views above are taken from Longtown Castle in western Herefordshire. They both look along the Olchon Valley, and across it to the high ridge of the Black Mountain, the Welsh border. Longtown castle , from which the photo is taken stands on a ridge that runs parallel to the Black Mountains. 

The Olchon river is a small stream in the bottom of the valley. The limits of the catchment area for the stream is the horizon, in the distance of the lower view.

I suggest that the depth of ice over in this area could have been 500 metres, but it may have been more.

For the purpose of this example I suggest that the area of an ice sheet over the olchon valley is 12 kilometres long and 1 kilometre wide, 12 square kilometres. 

Because of the reduced thickness (500 metres) of ice, the impact in the Olchon valley, of the collapsing ice sheet, would be half a tonne of TNT, or 33 atomic bombs per square kilometre. 

As it seems likely that the warm period that melted the ice lasted over a summer season; 12 square kilometres, 33 bombs per square kilometre--- the valley experienced an impact equivalent to an atomic bomb, along its length roughly on every day of that deglaciation year.

This melt caused to be released 16.5 x 10^9 litres of water to find its way to the sea every single day, 16,500 tonnes.

Those 16,500 tonnes of water would have raised the level of the sea around the coast of Britain, locally, by several metres. Evidence for this is in the charts produced for the British coastline by Ian Shennan. 

  

The chart above demonstrates the change in relative sea-level for coastal locations around Britain and Ireland. 

The graphs show that at around, or just after 15,000BP the level of the sea around our coasts rises dramatically by 10 metres or more. 

This rise was caused as meltwater from fast melting and collapsing ice sheets reached coastal locations and was unable to escape due to coastal topography. 

The water that arrived at the coast from the mountains of Britain carried with it ice, rocks, gravels, sands, and silts. These were Ice Streams that traversed the landscape scouring the geology as it passed.

Jeffery Nicholls 

Orkney 

#BIIS #LGM #Quaternary #Geology #glaciation #IceAge #ice-sheet