Case Study – River Avon

Unraveling the Geological and Archaeological History of the River Avon Valley

The Avon Valley, with its complex Quaternary deposits, offers a wealth of information about past environmental changes and human activity. These deposits include clay-with-flints, head, gravelly head, river terrace deposits, brickearth, alluvium, and occasional peat. The clay-with-flints, in particular, are residual deposits formed by the dissolution of underlying chalk and the reworking of Palaeogene sediments, predating the river terrace deposits. Found predominantly on hilltop flats, these deposits likely date back to the Pleistocene (Gallois, 2009). Older head deposits, associated with clay-with-flint sediments, are products of solifluction and bedrock solution, commonly occurring on upper valley slopes, while gravelly head and head deposits result from fluvial transport, hill wash, and solifluction processes (Barton et al., 2003; Hopson et al., 2007).

The Avon Valley River Terraces

The Avon Valley is renowned for its 14 distinct river terraces, which rise to heights of up to 100 meters above the valley floor and span widths of up to 12 kilometers. These terraces exhibit consistent thickness, indicative of sediment overloading from upstream sources, lateral erosion, and sediment redeposition (Blum and Tӧrnqvist, 2000; Brown et al., 2009a, b). While these terraces provide a unique stratigraphic record, their chronological framework has been a subject of intense debate. Clarke and Green (1987) suggested that the deposition of these terraces draped over the landscape, complicating correlations with specific climatic events. (Case Study – River Avon)

Inconsistent Dating Methods: Radiocarbon and Optical Dating

Efforts to date the terraces have yielded conflicting results, particularly when comparing optical dating (OSL) with radiocarbon dating. For example, Egberts et al. (2019) highlighted discrepancies in OSL results, where terraces T7 (58m OD) appeared to predate T10 (102m OD). Such results challenge earlier assumptions about terrace chronology. Additionally, sediments from T4 and the undifferentiated Loess Terrace (77m OD) were dated to the Last Glacial Maximum (LGM), further complicating traditional terrace formation models.

Radiocarbon dating has similarly revealed inconsistencies. Gaigalas (2000) observed discrepancies of up to 30%-40% between radiocarbon and OSL dates, such as sands overlying peat layers. For instance, organic detritus dated by radiocarbon at 24,430 ± 210 years contrasted sharply with OSL dates of 39,000 ± 4,000 years for the overlying sands. These variations highlight the challenges in establishing reliable chronologies for terrace sequences. (Case Study – River Avon)

The Role of Holocene Flooding

Holocene flooding has further influenced the Avon Valley’s stratigraphy. Macklin’s studies identified over 100 significant flood events, with 12 lasting for centuries. These events would have redistributed sediments, eroded terraces, and contributed to the inconsistencies in dating sequences. For instance, older terraces may have been overlaid or modified by later flood deposits, complicating interpretations of stratigraphic continuity. Such flooding could explain the lack of significant alluvium or colluvium deposits in certain areas, such as Stonehenge Bottom. (Case Study – River Avon)

Revisiting Terrace Models and Uplift Hypotheses

Traditional models of terrace formation, such as those proposed by Bridgland (2000), linked terrace sequences to Marine Isotope Stages (MIS). However, recent studies challenge this straightforward correlation. For example, Maddy et al. (2000) and Westaway et al. (2006) suggested that the uplift-driven terrace formation model might not account for the complexities observed in the Avon Valley. The uplift rates inferred from terrace altitudes also conflict with sea-level reconstructions, which show lesser ice extent during the period 389–243 ka compared to the LGM, implying reduced terrace impact rather than increased erosion. (Case Study – River Avon)

Sedimentary Evidence and Anomalies

Egberts et al. (2019) further examined terrace sediments using 3D modeling and borehole data. Their findings revealed significant anomalies in sediment thickness and depositional rates. For example, sediment accumulation rates varied drastically within the same stratigraphic unit, with one layer accumulating at 1.33 cm per 1,000 years and another at just 0.23 cm per 1,000 years. Such disparities raise questions about the depositional mechanisms and the accuracy of OSL dating. (Case Study – River Avon)

🔍 New Evidence Supports a Post-Glacial Water Landscape at Stonehenge

Recent reanalysis of Optically Stimulated Luminescence (OSL) dates from Egberts et al. (2019) has revealed that the River Avon reached significantly higher levels than previously assumed during the last glacial cycle. In particular, sediment dated to the Last Glacial Maximum (MIS 2) was found on Terrace 8 (approximately 70 m elevation), and early MIS 2 dates appear on Terrace 7 (~92 m elevation). This challenges long-standing assumptions that post-glacial flooding only reached the lower terraces, and it suggests a much more dynamic and elevated floodplain environment during and after the ice age.

This new model supports the longstanding hypothesis that Stonehenge, situated on a chalk spur at around 100 m elevation, may have once been surrounded by water or seasonal wetlands during the early Holocene. The proximity of high terrace-level flood deposits—combined with the Avon’s documented discharge behaviour during meltwater pulses—makes it increasingly likely that the Stonehenge plateau functioned as a kind of natural promontory or island in a broader post-glacial flood basin. The elevation of Terrace 7 aligns almost perfectly with the height required to surround the base of the Stonehenge site with water, especially in combination with aquifer saturation, blocked drainage, and periglacial ponding.

This theory is further supported by the discovery of early Mesolithic postholes beneath the former Stonehenge car park, C14-dated to approximately 8300 BCE. These postholes were filled not with chalk—as would be expected from a collapsed dry trench—but with fine river silt. In a chalk-dominated landscape, silt is an unmistakable sign of waterborne deposition. This suggests the holes were created during or shortly after a period of flooding, further confirming that this area was hydrologically active and likely waterlogged in the Mesolithic.

Taken together, the elevated Avon terrace data, post-glacial sea-level model, and silt-filled Mesolithic postholes provide strong, converging lines of evidence that the landscape around Stonehenge was shaped by powerful hydrological forces. Far from being a dry ceremonial monument in an open field, Stonehenge may originally have been positioned to overlook—or even emerge from—a vast and reflective water setting. This reinterpretation dramatically shifts our understanding of the monument’s original context and underscores the need to reassess Mesolithic and Neolithic landscapes through the lens of glacial hydrology and river terrace dynamics.

📊 River Avon Terrace Model: Estimated Ice Age Impact (Ordered by Terrace Level)

Terrace	Elevation (m)	% of MIS 12 Ice Volume	Estimated MIS Stage	Affected by MIS 2 (LGM)?
T4	40	40%	Holocene or reworked	✅ Yes
T5	50	50%	Holocene or reworked	✅ Yes
T6	60	60%	MIS 2	✅ Yes
T7	92	92%	MIS 10	⚠️ Possibly (early MIS 2 or late MIS 3)
T8	70	70%	MIS 4 or 5d	✅ Confirmed (OSL sample BP02)
T9	85	85%	MIS 10	❌ Unlikely
T10	100	100%	MIS 12	❌ No

NB.“Terrace T7 sits anomalously high at 92 m compared to adjacent terraces (T8 at 70 m and T9 at 85 m). This suggests either a naming inconsistency or a unique depositional context — potentially a high flood surge or perched lacustrine event rather than a classic fluvial terrace. Despite the elevation irregularity, the OSL dates support the possibility that T7 was inundated or reworked during MIS 3 or early MIS 2.”

Implications for Palaeolithic Archaeology

The terraces are invaluable for understanding Palaeolithic archaeology. Archaeological remains, including tools and artifacts, have been found in several terraces, offering insights into hominin activity and landscape use. However, the inconsistent dating of terraces complicates efforts to contextualize these findings. For example, the Palaeolithic site at Woodgreen (T7) has been dated to 389–243 ka, but its chronological placement remains contested due to discrepancies between radiometric and stratigraphic evidence. (Case Study – River Avon)

Sediment Composition and Water Sources

One overlooked aspect of the Avon Valley’s terraces is the role of natural springs and seasonal streams. Unlike active rivers, these water sources contribute minimal alluvium, explaining the limited sedimentary deposits in some terraces. This observation aligns with Julian Richards’ hypothesis in The Stonehenge Environs Project that seasonal streams or fluctuating water tables may have removed or thinned colluvium sediments in areas like Stonehenge Bottom. (Case Study – River Avon)

Compound Terraces and Sedimentary Mixing

The presence of compound terraces, as suggested by Egberts et al. (2019), adds another layer of complexity. These terraces likely represent mixed depositional histories, where sediments from different time periods were reworked by fluvial processes. This phenomenon may explain some of the out-of-sequence dates observed in the Avon Valley. For example, the youngest terrace (T4) showed mixed depositional behavior between the upper and lower catchments, resulting in varying OSL dates at different locations. (Case Study – River Avon)

The Importance of Multidisciplinary Approaches

Resolving the chronological uncertainties in the Avon Valley requires a multidisciplinary approach. Combining radiocarbon dating, OSL, isotope analysis, and stratigraphic modeling can provide a more comprehensive understanding of terrace formation and landscape evolution. Additionally, integrating palaeoenvironmental data, such as pollen and microfossil analysis, can shed light on climatic conditions during terrace formation and their impact on human activity. (Case Study – River Avon)

Challenges and Future Directions

Despite advancements, significant challenges remain. Dating inconsistencies, the influence of Holocene flooding, and the lack of organic remains in higher terraces hinder efforts to build a cohesive narrative of the Avon Valley’s geological and archaeological history. Future research should prioritize high-resolution stratigraphic studies, enhanced chronometric techniques, and better integration of geomorphological and archaeological data. (Case Study – River Avon)

Conclusion

The Avon Valley’s terraces offer a rich archive of environmental and cultural history but also present significant challenges due to inconsistencies in dating and stratigraphic interpretation. By leveraging advanced technologies and multidisciplinary collaboration, researchers can refine their understanding of this dynamic landscape, providing valuable insights into the interplay between natural processes and human activity over millennia. For more information, explore this video: https://youtu.be/j5LJ2sGcKOA.

UPDATE

More Empirical Evidence of Post-Glacial Flooding and a Flooded Stonehenge

 Prehistoric Levels and Widths for the River Avon

Take a close look at this illustration. It is not speculation, it is empirical science — mapped and measured river terraces from the Avon Valley, published in Egberts (2016), Pleistocene terrace formation and the Quaternary evolution of the Hampshire Basin, Bournemouth University.

What are we looking at?

• These are the terrace steps cut by the River Avon over multiple glacial–interglacial cycles.
• Each “T-level” marks a former stable floodplain where the river held its height for centuries, often millennia.
• The heights are measured in metres OD (Ordnance Datum) and tied to known quarry and pit sites (e.g. Hatchet Gate Farm, Woodgreen, Somerley, Ashley).

 How much bigger was the Avon?

• Today, the river meanders with a width of just ~50 m near Salisbury.
• At its maximum (T11), the Avon floodplain stretched ~12 km across.
• That is ~240 times wider than the river today.

 What does this mean for Stonehenge?

• Phase 1 of Stonehenge (Car Park Postholes) sits on T9 (~90 m OD).
• Phase 2 (ditch, Aubrey Holes, bluestones) cuts into T8 (~75 m OD).
• The terraces show that the palaeochannel not only flooded up to the old car park, but at times overtopped the entire Stonehenge site.

 Why this matters:

• Terraces are not theory — they are empirical geomorphological evidence.
• They prove that the Avon has flooded to multiple levels, sometimes far higher than the monument itself.
• This is not about “if” water could reach those heights — the terraces prove it already has, repeatedly, over many Ice Age cycles.

So when critics dismiss the role of high water tables or argue “the site couldn’t have been wet,” they are ignoring the most basic geological record in front of us. The terraces are the diary of the river — written in gravel, chalk, and silt — showing that water rose and fell, over and over again.

 The real question is not if Stonehenge was surrounded by water. It is when, and how many times it happened during its long prehistory.

Exploring Britain’s Flooded Past: The Evidence

My recent exploration into Britain’s prehistoric landscape has opened my eyes to a fascinating and often overlooked aspect of our history: the impact of post-glacial flooding. The sheer magnitude of meltwater released at the end of the last ice age dramatically reshaped the environment, creating vast waterways that are notably more significant than the rivers we see now. This realisation has sparked my curiosity to understand how these ancient waterways influenced the lives of our ancestors and shaped the landscape we know today.

Summary

The evidence for these massive, prehistoric rivers lies scattered across the British Isles, often hidden beneath soil layers and obscured by time. But with careful observation and a willingness to challenge conventional thinking, the signs become apparent. Geological maps reveal the presence of extensive superficial deposits, hinting at the scale of these ancient waterways. Peat bogs, formed in the wake of retreating glaciers, offer further clues, with their deep layers interspersed with silt and sand deposits, a testament to the cyclical nature of flooding events.

One of the most striking pieces of evidence is the presence of ancient settlements along the shorelines of these long-gone rivers. Iron Age hillforts, often perched atop strategic vantage points, offer a glimpse into the past, suggesting that our ancestors recognised the advantages of settling near these waterways. Once considered solely defensive structures, these hillforts take on a new meaning when viewed through a flooded landscape. Could they have also served as vital hubs for trade and transportation, connected by a network of navigable rivers?

The sources I’ve consulted within my books point to the limitations of traditional archaeological interpretations, which often fail to account for the significant impact of post-glacial flooding. The focus on terrestrial landscapes has usually led to underestimating these ancient waterways’ role in shaping early human settlements and cultural practices. Reexamining existing archaeological data, combined with new insights from techniques like LiDAR mapping, could unlock a wealth of information about our ancestors’ relationship with these flooded landscapes.(Britain’s Flooded Past)

Consider, for instance, the dykes of Britain, enigmatic earthworks that crisscross the landscape. While their purpose has been debated for centuries, my books suggest a compelling connection to the prehistoric river systems. The dykes, they argue, were not simply defensive barriers but intricate components of a sophisticated water management system designed to channel and control the flow of these immense waterways. The fact that every investigated Dyke shows a connection to these ancient rivers is a striking piece of evidence that supports this theory.

The implications of this hypothesis are profound. If these dykes were indeed part of a vast water management network, it suggests a level of engineering sophistication and social organisation that challenges our current understanding of prehistoric Britain. The books point to specific examples, like the dykes at Winterbourne Crossroads, which not only reveal the presence of water at Stonehenge in both the Mesolithic and Neolithic periods but also provide insights into the burial practices of that time. The alignment of these dykes with the ancient river levels paints a vivid picture of a society deeply connected to and reliant upon the waterways that shaped their world.(Britain’s Flooded Past)

The information also draws attention to post holes and mooring points at sites like Stonehenge and Durrington Walls, further solidifying the case for a significant water presence during the Neolithic period. These seemingly mundane features, often overlooked in traditional archaeological interpretations, offer a tangible link to when these sites were situated along the shorelines of prehistoric rivers. The post holes at Stonehenge Bottom, for example, not only provide evidence of a river’s existence but also suggest its use in transporting the bluestones from the Craig Rhos-Y-Felin quarry.

The books advocate for a shift in our perspective, urging us to view these prehistoric monuments not as isolated structures on a dry landscape but as integral parts of a vibrant, interconnected water world. This paradigm shift could revolutionise our understanding of ancient Britain, revealing the ingenuity and adaptability of our ancestors who navigated and thrived in this dynamic environment.(Britain’s Flooded Past)

The evidence includes numerous examples of how the post-glacial flood hypothesis can shed new light on seemingly inexplicable features of the landscape. Woodhenge, for instance, takes on a new role as a potential fire beacon or lighthouse, guiding boats along the much larger River Avon. Old Sarum’s intricate system of ditches and dykes, once interpreted solely through a defensive lens, is reimagined as a complex system of moats, highlighting the presence of a higher water table during the Mesolithic and Neolithic periods.

The remarkable discovery of Silbury Avenue, based solely on a few crop marks and the application of the post-glacial flood hypothesis, further emphasises the power of this new way of thinking. This finding confirms the theory of higher river levels in the past and underscores the potential for using this approach to uncover and date hidden monuments across Britain.(Britain’s Flooded Past)

Another intriguing piece of evidence is the positioning of Long Barrows, often situated on hillsides overlooking ancient waterways. These barrows, far from being random burial sites, served as navigational aids for those travelling along the vast river systems of Mesolithic Britain. Their strategic placement, offering clear lines of sight along the river routes, hints at a society that relied heavily on water transport and understood the importance of visual landmarks in navigating this complex landscape.

Conclusion

This journey into Britain’s flooded past has left me with a profound sense of wonder and a renewed appreciation for the intricate connections between landscape, environment, and human history. The evidence, though often subtle, is undeniable. By embracing the post-glacial flood hypothesis, we can better understand our ancestors’ lives, ingenuity, and deep connection to the waterways that shaped their world.(Britain’s Flooded Past)

Exploring Prehistoric Britain: A Journey Through Time

My blog delves into the fascinating mysteries of prehistoric Britain, challenging conventional narratives and offering fresh perspectives based on cutting-edge research, particularly using 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 visualizes 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, also receive a re-evaluation 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 the topic of 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, suggesting a Mesolithic origin2357. 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 to inform the 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 the astronomical insights of 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

Further Reading

For those interested in British Prehistory, visit www.prehistoric-britain.co.uk, a comprehensive resource featuring an extensive collection of archaeology articles, modern LiDAR investigations, and groundbreaking research. The site also includes insights and extracts from the acclaimed Robert John Langdon Trilogy, a series of books exploring Britain during the Prehistoric period. Titles in the trilogy include The Stonehenge Enigma, Dawn of the Lost Civilisation, and The Post Glacial Flooding Hypothesis, offering compelling evidence about ancient landscapes shaped by post-glacial flooding.

To further explore these topics, Robert John Langdon has developed a dedicated YouTube channel featuring over 100 video documentaries and investigations that complement the trilogy. Notable discoveries and studies showcased on the channel include 13 Things that Don’t Make Sense in History and the revelation of Silbury Avenue – The Lost Stone Avenue, a rediscovered prehistoric feature at Avebury, Wiltshire.

In addition to his main works, Langdon has released a series of shorter, accessible publications, ideal for readers delving into specific topics. These include:

• The Ancient Mariners
• Stonehenge Built 8300 BCE
• Old Sarum
• Prehistoric Rivers
• Dykes, Ditches, and Earthworks
• Echoes of Atlantis
• Homo Superior
• 13 Things that Don’t Make Sense in History
• Silbury Avenue – The Lost Stone Avenue
• Offa’s Dyke
• The Stonehenge Enigma
• The Post-Glacial Flooding Hypothesis
• The Stonehenge Hoax
• Dawn of the Lost Civilisation
• Darwin’s Children
• Great Chester’s Roman Aqueduct
• Wansdyke

For active discussions and updates on the trilogy’s findings and recent LiDAR investigations, join our vibrant community on Facebook. Engage with like-minded enthusiasts by leaving a message or contributing to debates in our Facebook Group.

Whether through the books, the website, or interactive videos, we aim to provide a deeper understanding of Britain’s fascinating prehistoric past. We encourage you to explore these resources and uncover the mysteries of ancient landscapes through the lens of modern archaeology.

For more information, including chapter extracts and related publications, visit the Robert John Langdon Author Page. Dive into works such as The Stonehenge Enigma or Dawn of the Lost Civilisation, and explore cutting-edge theories that challenge traditional historical narratives.

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