The Post-Glacial Flooding Hypothesis – 1/11

Posted on August 14, 2026 by admin

Chapter 1 – The Legacy of the Ice Age

Book Extract

1. Introduction

Roughly twenty-six thousand years ago, the Earth entered the final phase of the last ice age, when more than 30 million square kilometres of the northern continents were mantled by ice. Sea level dropped by over a hundred metres, continents expanded, and the atmosphere became drier and dustier. When the climate warmed, that frozen water returned to the ocean basins, transforming every river and shoreline on the planet. Understanding the magnitude and tempo of this transition is fundamental to reconstructing the landscapes that Holocene societies inherited. (The Post-Glacial Flooding Hypothesis)

The scientific history of sea-level research stretches back more than a century. Fairbridge (1961) first proposed that global “drowned terraces” recorded former sea levels. Oxygen-isotope analysis later provided a direct measure of global ice volume (Shackleton & Opdyke 1973; Chappell & Shackleton 1986). By the 1990s, uranium-thorium dating of coral reefs (Bard et al., 1990) and glacio-isostatic models (Lambeck & Chappell 2001) produced continuous global sea-level curves for the late Quaternary. Satellite altimetry and GRACE gravimetry now track present-day mass exchange between ice sheets and oceans with millimetre precision (Watkins et al., 2015; Cazenave et al., 2018).

These cumulative datasets reveal that the transformation from the Last Glacial Maximum (LGM) to the modern interglacial was neither instantaneous nor globally uniform. The following sections examine the evidence for the magnitude of the LGM, the deglacial rise in sea level, and the feedbacks that coupled ice, ocean, and atmosphere into a single dynamic system.

2. The Last Glacial Maximum

The LGM, dated between ~26 000 and 19 000 years BP, represents the maximum combined extent of Northern Hemisphere ice sheets. Reconstructions by Ehlers et al. (2018) show the Laurentide Ice Sheet extending south of the Great Lakes, the Fennoscandian complex covering Scandinavia, northern Britain, and the Baltic, and separate domes over the Barents and Kara Seas. In the Southern Hemisphere, the Patagonian, New Zealand, and Antarctic ice sheets expanded simultaneously. Global mean air temperature was about 5–6 °C lower than today (Tierney et al., 2020).

Cosmogenic-nuclide dating of moraines indicates near-synchronous maxima in both hemispheres within 1–2 kyr (Balco et al., 2009). Ice cores from Antarctica record atmospheric CO₂ concentrations of only ~190 ppm, the lowest of the last 800 kyr (Lüthi et al., 2008). The increased planetary albedo and reduced greenhouse forcing locked the Earth into a radiative imbalance until orbital precession increased summer insolation at high latitudes around 21 ka BP, initiating melting.

Sea level at the LGM stood 134 ± 5 m below present (Rohling et al., 2009; Lambeck et al., 2014), implying an extra ~52 × 10⁶ km³ of continental ice—roughly triple modern Antarctic volume. The load depressed the lithosphere by up to a kilometre and generated a peripheral forebulge hundreds of kilometres wide. When deglaciation began, these distortions created regional variations in relative sea level (RSL) of tens of metres—a problem that still complicates correlation between sites.

3. Quantifying Global Ice and Sea-Level Change

High-resolution oxygen-isotope records from the Red Sea (Rohling et al., 2009) and global benthic stacks (Lisiecki & Raymo, 2005) define the eustatic component of sea-level change. Grant et al. (2014) extended the Red Sea curve to 500 kyr BP and confirmed an approximately linear relation between δ¹⁸O and global mean sea level within ±140 m. Combined with coral-reef U/Th dates (Peltier & Fairbanks 2006) and glacio-isostatic modelling (ICE-6G v2; Peltier et al., 2015), these data yield the following deglacial sequence:

Stable minimum (26–19 ka) — Sea level constant near −130 m; ice volume at maximum.
Deglacial rise (19–7 ka) — Global mean increase ~120 m; average rate ~1.2 cm yr⁻¹.

Waelbroeck et al. (2019) and Gowan et al. (2021) further improved resolution, showing that roughly 70% of the total rise occurred before 10 ka BP and that rates exceeded 4 cm yr⁻¹ during short meltwater pulses. These figures quantify the pace of global hydrological reorganisation that followed the LGM.

4. Meltwater Pulses and Deglacial Chronology

Superimposed on the long-term trend are several abrupt accelerations known as Meltwater Pulses (MWPs). MWP-1A (14.6–14.3 ka BP) raised global sea level by 14–18 m in < 400 years (Deschamps et al., 2012). Coral cores from Tahiti and Barbados capture the event as a distinct change in growth depth and isotope composition. MWP-1B, centred near 11.5 ka BP, added another 6–10 m (Liu et al., 2019). A later, smaller pulse (~8.2 ka BP) corresponded to catastrophic drainage of pro-glacial Lake Agassiz into the North Atlantic (Teller et al., 2002).

Numerical models (Gregoire et al., 2012) indicate that collapse of the Laurentide ice saddle triggered MWP-1A, releasing freshwater at ~0.3 Sverdrups—enough to disrupt the Atlantic Meridional Overturning Circulation (AMOC) and cause short-lived cooling across the Northern Hemisphere (Liu et al., 2009). Geomorphic evidence of megafloods, such as the Missoula outburst channels in North America (Bretz 1969; Baker 2013), provides analogues for the required discharge scale.

MWPs demonstrate that deglaciation was a series of threshold events rather than a steady retreat. The timing of pulses aligns closely with abrupt climatic shifts seen in Greenland ice cores (NGRIP Members 2004), underscoring the tight coupling between ice dynamics and global climate.

5. Isostatic Rebound and Crustal Adjustment

Once surface loads were removed, the lithosphere began to rebound. The process is governed by viscoelastic relaxation of the mantle with characteristic times of 1–5 kyr (Milne et al., 2006). Modern GPS and tide-gauge data show uplift of 10 mm yr⁻¹ in central Fennoscandia and subsidence of 1–2 mm yr⁻¹ in southern England and the Netherlands—the collapsing forebulge. Modelling (Lambeck et al., 2014; Peltier et al., 2015) reproduces these patterns when mantle viscosities of 3–5 × 10²¹ Pa s are used.

Rebound created ephemeral basins along glacial margins where meltwater ponded before marine incursion. The Baltic Ice Lake and the Champlain Sea are classic examples, forming as differential uplift temporarily dammed drainage routes (Saarnisto & Salonen 1995; Parent & Occhietti 1999). Many present-day estuaries owe their origins to these basins. Sediment cores from the Humber, Thames, and Rhine estuaries contain alternating freshwater and brackish layers that track the balance between isostasy and eustasy (Shennan et al., 2018).

6. The Rebirth of the Oceans

Between 19 ka and 7 ka BP, the oceans absorbed roughly 4.5 × 10⁸ km³ of meltwater, raising mean sea level by ~120 m. Coral records from Tahiti, Huon Peninsula, and the Sunda Shelf show a remarkably consistent transgression curve (Deschamps et al., 2012; Hanebuth et al., 2000). By 7 ka BP, sea level stabilised within a few metres of the modern datum.

The redistribution of this mass altered Earth’s rotation and gravitational field, increasing the length of day by 0.5 milliseconds (Mitrovica & Munk 2003) and displacing the geoid by several decimetres. More tangibly, flooding of continental shelves expanded shallow-marine habitats and enhanced nutrient exchange between land and sea, fuelling mid-Holocene marine productivity (Haug et al., 2001). The creation of new estuarine and lagoonal systems also provided nursery grounds for species that later became critical to human subsistence.

7. Climate Feedbacks During Deglaciation

Ice-core and modelling studies reveal that the deglacial rise in greenhouse gases both responded to and accelerated warming. CO₂ increased from 190 ppm at the LGM to 270 ppm by 11 ka BP (Lüthi et al., 2008). Methane doubled from 350 to 700 ppb (Loulergue et al., 2008). The combined radiative forcing of ~2.5 W m⁻² produced a global temperature increase of ~4 °C (IPCC AR6 2021). Shakun et al. (2012) demonstrated that Antarctic warming led the CO₂ rise by several centuries, implying that oceanic outgassing initiated the feedback loop.

Freshwater discharges into the North Atlantic weakened the AMOC and triggered millennial-scale climate reversals. The Younger Dryas (12.9–11.7 ka BP) involved a 5–7 °C drop in Greenland temperatures followed by rapid recovery within a few decades (Severinghaus et al., 1998). Numerical experiments show that such shifts require freshwater fluxes of 0.05–0.1 Sverdrups (Liu et al., 2009). Once meltwater routing shifted southward and AMOC strength recovered, interglacial stability was achieved.

8. The Transformation of North-West Europe

Retreat of the British–Irish Ice Sheet began near 22 ka BP and concluded by 15 ka BP (Clark et al., 2012). Deglaciation exposed outwash plains and periglacial lakes that evolved into estuaries and wetlands as sea level rose. Seismic and core evidence from the southern North Sea shows basal peats overlain by brackish and marine sediments between 9 and 8 ka BP (Hijma & Cohen 2011). These sequences chart the drowning of Doggerland—a vast lowland linking Britain to Europe. Pollen and macrofossil data indicate temperate woodland colonisation prior to submergence (Gaffney et al., 2009).

Regional RSL curves diverge sharply due to GIA: western Scotland has risen > 40 m since 10 ka, while southern England has subsided by ~10 m (Bradley et al., 2020). Raised beaches in the north and submerged forests in the south reflect this differential motion. In the English Channel, fluvial erosion during early deglaciation carved the “Channel River,” later flooded by 8 ka (Mellett et al., 2013). Similar sequences occur along the Irish and Danish coasts, documenting the progressive marine transgression of northwest Europe.

9. Towards a Global–Regional Synthesis

By combining isotopic, coral, and geodetic datasets, modern reconstructions achieve decimetre precision for Holocene sea level (Gowan et al., 2021). Three principles emerge:

Proportionality — Sea level and global ice volume vary linearly during deglaciation.
Pulsation — Superimposed meltwater pulses mark thresholds in ice-sheet stability.
Regionality — Local deviations result from isostasy, tectonics, and sediment compaction.

Shennan et al. (2018) synthesised over 500 Holocene RSL indicators for the British Isles, demonstrating that once GIA corrections are applied, regional curves converge on the global mean within analytical error. These findings provide a quantitative baseline for analysing river-terrace altitudes and groundwater histories in later chapters.

Equally important, comparison with modern sea-level observations highlights the extraordinary pace of contemporary change. Satellite altimetry records a mean rise of 3.4 ± 0.4 mm yr⁻¹ since 1993 (Cazenave et al., 2018)—an order of magnitude faster than the late-Holocene background rate (Kopp et al., 2016). The processes that ended the last ice age therefore remain relevant to current climate dynamics.

10. Conclusion

The end of the last ice age was a planetary event in which ice, water, and rock interacted on colossal scales. Between 26 ka and 7 ka BP, sea level rose more than 120 m, ice sheets vanished from most temperate latitudes, and the hydrological cycle intensified. The evidence—oxygen-isotope curves, coral terraces, basal peats, and glacio-isostatic models—forms a coherent narrative of gradual yet punctuated change.

These quantitative reconstructions define the environmental backdrop for all Holocene landscapes. They also establish a principle crucial to later chapters: that elevation within fluvial and coastal systems encodes time, because each terrace or peat horizon corresponds to a known fraction of global ice volume. The following chapter therefore turns from global physics to the mathematical description of flooding itself—the equations that translate ice-volume change into measurable hydrological response.

Plain-Language Conclusion

The ice age was like the planet putting a huge amount of the world’s water into giant freezers on land. When those freezers started to melt:

All that stored water went back into the oceans.
The seas rose by about 120 metres.
The weight of the ice came off the land, so some places bounced up, others sagged down.

Scientists can see this story in:

tiny shells on the sea floor,
old coral reefs now sitting at the “wrong” depths,
layers of mud and peat around coasts.

Put simply:

We froze the oceans on land, then poured them back in. The combination of rising seas and bouncing crust rearranged coastlines everywhere, and we can measure it.

To read the rest of the book, follow this link: https://prehistoric-britain.co.uk/the-post-glacial-flooding-hypothesis-book

FREE ONLINE BOOK is available HERE: https://prehistoric-britain.co.uk/the-post-glacial-flooding-hypothesis-book

PODCAST

Author’s Biography

Robert John Langdon, a polymathic luminary, emerges as a writer, historian, and eminent specialist in LiDAR Landscape Archaeology.

His intellectual voyage has been interwoven with stints as an astute scrutineer in government and grand corporate bastions, a tapestry spanning British Telecommunications, Cable and Wireless, British Gas, and the esteemed University of London.

A decade hence, Robert’s transition into retirement unfurled a chapter of insatiable curiosity. This phase saw him immerse himself in Politics, Archaeology, Philosophy, and the enigmatic realm of Quantum Mechanics. His academic odyssey traversed the venerable corridors of knowledge hubs such as the Museum of London, University College London, Birkbeck College, The City Literature Institute, and Chichester University.

In the symphony of his life, Robert is a custodian of three progeny and a pair of cherished grandchildren. His sanctuary lies ensconced in the embrace of West Wales, where he inhabits an isolated cottage, its windows framing a vista of the boundless sea – a retreat from the scrutinising gaze of Her Majesty’s Revenue and Customs, an amiable clandestinity in the lap of nature.

Exploring Prehistoric Britain: A Journey Through Time

My blog delves into the fascinating mysteries of prehistoric Britain, challenging conventional narratives and offering fresh perspectives grounded in cutting-edge research, particularly LiDAR technology. I invite you to explore some key areas of my research. For example, the Wansdyke, often cited as a defensive structure, is re-examined in light of new evidence. I’ve presented my findings in my blog post Wansdyke: A British Frontier Wall – ‘Debunked’, and a Wansdyke LiDAR Flyover video further visualises my conclusions.

My work also often challenges established archaeological dogma. I argue that many sites, such as Hambledon Hill, commonly identified as Iron Age hillforts, are not what they seem. My posts Lidar Investigation Hambledon Hill – NOT an ‘Iron Age Fort’ and Unmasking the “Iron Age Hillfort” Myth explore these ideas in detail and offer an alternative view. Similarly, sites like Cissbury Ring and White Sheet Camp receive re-evaluations based on LiDAR analysis in my posts “Lidar Investigation Cissbury Ring through time” and “Lidar Investigation White Sheet Camp,“ revealing fascinating insights into their true purpose. I have also examined South Cadbury Castle, often linked to the mythical Camelot56.

My research also extends to ancient water management, including the role of canals and other linear earthworks. I have discussed the true origins of Car Dyke in multiple posts, including Car Dyke – ABC News Podcast and Lidar Investigation Car Dyke – North Section, which suggest a Mesolithic origin 2357. I also explore the misidentification of Roman aqueducts, as seen in my posts on the Great Chesters (Roman) Aqueduct. My research has also been greatly informed by my post-glacial flooding hypothesis, which has helped explain landscape transformations over time. I have discussed this hypothesis in several posts, including AI now supports my Post-Glacial Flooding Hypothesis and Exploring Britain’s Flooded Past: A Personal Journey

Finally, my blog also investigates prehistoric burial practices, as seen in Prehistoric Burial Practices of Britain and explores the mystery of Pillow Mounds, often mistaken for medieval rabbit warrens, but with a potential link to Bronze Age cremation in my posts: Pillow Mounds: A Bronze Age Legacy of Cremation? and The Mystery of Pillow Mounds: Are They Really Medieval Rabbit Warrens?. My research also includes astronomical insights into ancient sites, for example, in Rediscovering the Winter Solstice: The Original Winter Festival. I also review new information about the construction of Stonehenge in The Stonehenge Enigma.

Mesolithic River Avon

Posted on February 3, 2024 by admin

Rivers were higher in the past – Now UPDATED here: https://prehistoric-britain.co.uk/case-study-river-avon

At the outset, the clay-with-flints, a vestige of ancient weathering and erosion, stands as a testament to the relentless forces of nature that sculpted the landscape. Born from the remnants of Palaeogene sediments and the dissolution of chalk, these deposits serve as silent witnesses to the Pleistocene’s cold embrace. Their presence on the hilltop flats signifies a chronological anchor, predating the rhythmic succession of river terraces that stitch the valley’s quilt. (The Mesolithic River Avon)

Rivers were higher in the past (The Mesolithic River Avon)

As one descends the slopes, a mosaic of older head deposits unfolds, their genesis tied to the ancient processes of solifluction and solution. These sediments, bound to the clay-with-flint, narrate a tale of gradual descent and transformation, shaping the valley’s upper reaches with a subtle, yet profound, hand.

Further down the valley, the narrative evolves with the introduction of head gravel, gravelly head, and head deposits. These characters in the valley’s story are borne of fluvial transport, hill wash, hill creep, and solifluction—agents of change that have, over millennia, contributed to the valley’s sculptural form. The river terraces, numbering fourteen, ascend like steps from the valley floor, each a plateau from which to view the passage of time. The highest terraces, perched up to 100 meters above the valley, offer a broad vista extending 12 kilometers across, while the lower terraces, more intimate in their proximity to the present-day river, mark the recent chapters of geological history.

The consistency of thickness across these terraces speaks to a dynamic equilibrium of erosion and deposition, influenced by sediment overloading and tributary contributions. This interplay suggests a complex narrative of landscape evolution, one not solely dictated by the simplistic rhythm of Marine Isotope Stage cycles but enriched by a multifaceted process of lateral erosion and sediment redeposition.

Amidst this discussion of terraces and quaternary deposits, the narrative briefly diverges to contemplate the pre-Quaternary geology, where terraces from the River Avon linger in the Hampshire basin, their ages enshrouded in mystery. The challenges of dating these terraces, and by extension, understanding the full scope of the valley’s geological history, are underscored by recent findings that question traditional dating methods. Such inquiries not only deepen the mystery but also invite a reevaluation of our understanding of the Earth’s past.

Thus, we are reminded that the study of the Avon valley’s quaternary deposits is not merely an academic exercise but a profound exploration of the human quest for knowledge and understanding. It is a journey that connects us to the very essence of the natural world, revealing the intricate interplay of forces that have shaped not only the valley but also the broader tapestry of Earth’s geological history. (The Mesolithic River Avon)

Figure 5 – OSL Results Avon River

(The Mesolithic River Avon)

The intriguing findings presented in the diagrams regarding Optically Stimulated Luminescence (OSL) dating within the Avon valley unearth a complex narrative of sediment deposition and geological processes that challenges traditional understandings. The OSL results, as depicted in Figure 5, illuminate the temporal relationship between terrace formations and Marine Isotope Stages (MIS), while Figure 6, based on a three-dimensional model constructed from borehole data, offers a visual cross-section of the valley’s superficial geology.

The OSL ages for terraces T10 through T7, indicating deposition during or before MIS10/9, including the Last Glacial Maximum (LGM), suggest a timeline that not only aligns with but also refines previously established chronological frameworks. This refinement has significant implications for interpreting the archaeological record associated with Terrace T7 and recalibrating regional uplift and incision rates, which are crucial for understanding landscape evolution over geological timescales.

However, the apparent inconsistencies in the OSL dating results, particularly the dating of Terrace T7 before Terrace T10 and the identification of a Loess Terrace laid during the LGM, introduce a paradox into the sedimentary record. These anomalies challenge the linear progression implied by the terrace hypothesis that has guided interpretations of the valley’s geological history.

The highest terrace, T10, positioned at 102 meters above ordnance datum (OD) as illustrated in Figure 6, spans an unexpectedly broad temporal range of over 200,000 years, according to OSL dating. This finding disrupts the presumed chronological order, especially when juxtaposed with the dating of Terrace T7 at 58 meters OD, which, perplexingly, predates T10. Additionally, the Loess Terrace, situated at 77 meters OD and undifferentiated in the terrace sequence, laid down during the LGM, along with Terrace T4, which harbors the youngest dates, further complicates the scenario.

These results hint at a more intricate story of terrace formation and sediment deposition than previously thought. The seeming randomness and inconsistencies in the dating challenge the traditional terrace hypothesis and suggest that other factors, perhaps related to climatic variations, tectonic activities, or both, played significant roles in shaping the valley’s geomorphology.

The evidence points to a dynamic and possibly non-linear process of terrace formation, where episodes of sediment deposition were influenced by a combination of environmental conditions, rather than a simple chronological succession. This complexity underscores the need for a reassessment of the methods and models used to date and interpret terrace formations, advocating for a more nuanced understanding of the interplay between geological processes and climate change over the Pleistocene.

Thus, while the OSL dating provides valuable insights into the timing of terrace deposition, it also raises critical questions about the reliability of traditional chronological frameworks and the factors driving landscape evolution in the Avon valley. These findings invite further investigation and a reevaluation of existing hypotheses, highlighting the ongoing dialogue between past and present in the quest to decipher Earth’s geological history.

Figure 6- Avon River Terrace Levels – Avon River

(The Mesolithic River Avon)

The authors’ observations highlight significant discrepancies and anomalies in the OSL dates that raise questions about the method’s reliability in certain contexts, particularly when compared to other dating methods like radiocarbon dating. These discrepancies are not merely academic curiosities; they fundamentally challenge our understanding of the temporal and environmental context in which these sediment layers were deposited.

The attempt to explain the notable discrepancy in the age estimates of Terrace T4 across different locations within the Avon valley suggests that sediment reworking due to recent fluvial processes or the presence of compound terraces exhibiting different depositional behaviors might be responsible. This acknowledgment of variability within the depositional environment underscores the dynamic nature of fluvial landscapes and the complexity of accurately dating such contexts.

The variability in OSL dates for samples taken at the same soil level (e.g., GL14039, GL14041, GL14038, GL14040) further complicates the narrative. The presence of nearly contemporaneous dates within error limits, juxtaposed with the significantly different sedimentation rates observed just below the topsoil, suggests that the depositional history of the Avon valley is more nuanced than previously understood. These findings indicate that relying solely on visual stratigraphy for dating purposes can lead to inaccuracies, reinforcing the need for a multi-methodological approach to construct a reliable chronological framework.

The comparison between OSL and radiocarbon dating, as discussed in the Gaigalas (2000) study, exemplifies the potential for significant age discrepancies between different dating methods. The observation that OSL dates can be substantially older than their radiocarbon counterparts highlights the need for caution and cross-validation when interpreting chronological data, especially in contexts where sediment exposure and reworking may have occurred.

The discussion of Holocene river flooding and its impact on the dating of river terraces introduces an additional layer of complexity. Flooding events can lead to the deposition of silt and other materials that obscure the original depositional sequence, potentially leading to out-of-sequence terrace dates. This phenomenon complicates attempts to use uplift modeling or the Palaeolithic record as reliable chronological markers, as evidenced by the discrepancies in age estimates for Terrace T7.

The passage concludes by emphasizing the potential of terrace deposits to provide a valuable chronological framework, albeit one that must be approached with caution. By integrating chronometric age control with detailed modeling of deposit height and thickness, researchers can gain a more nuanced understanding of the Avon valley’s landscape evolution. This approach not only enhances our interpretations of past hominin landscape use but also improves the predictive modeling of Palaeolithic sites. The challenges and discrepancies encountered in OSL dating underscore the importance of adopting a holistic and critically engaged approach to understanding the geological past, one that acknowledges the inherent complexities and uncertainties of dating dynamic fluvial landscapes.

Finally, archaeologists and geologists resist the fact that the river Avon was in Stonehenge Bottom during the Mesolithic and Neolithic period. They insist that there is no evidence in the form of Alluvium or Colluvium in sufficient quantities to support my hypothesis. This objection has a simple solution as Julian Richard’s suggested in his book ‘The Stonehenge Environs Project’: “colluvium sediments may have been removed or thinned by the action of seasonal streams or higher water tables in the past”.

Macklin, as we have now seen in this section has identified over one hundred Holocene river floods, twelve of which lasted hundreds of years, that would have contributed to this lack of alluvium or colluvium at Stonehenge Bottom. Moreover, the sources of the rivers that lay this sediment over the centuries of water flow, rely on massive precipitation entering the rivers, cutting through rocks and valleys making them flow at extreme levels which create this erosion and consequential sediment. However, the source of Palaeochannel water are natural springs found locally underground and therefore would not contain the same alluvium levels as active flowing rivers – resolving this dilemma.