Philip E.F. Collins

Late Devensian river and floodplain dynamics and related environmental change in northwest Europe, with particular reference to a site at Woolhampton, Berkshire, England

Marked fluctuations in Late-glacial climate are correlated with significant changes in river behaviour and floodplain environment across much of northwest Europe. Evidence from a new site in the Kennet Valley provides a rare comprehensive picture of varying fluvial regime and local vegetation during this interval. Chronological control for the site is provided by biostratigraphical and morphostratigraphical correlations with other sites in the region, and by radiocarbon dating of carefully selected material. Preservation of the sedimentary sequence was facilitated by its occurrence within a large depression in the underlying bedrock. The origin of this depression is uncertain, perhaps reflecting subsidence or scour. Following the Last Glacial Maximum, a nival regime braided river dominated by floods deposited sandy gravels under stadial conditions. A large channel infilled by fine sediments during the latter part of the Windermere Interstadial indicates a fall in flow competence at a time of increased floodplain vegetation, most notably the appearance of tree birch. Variations in sediments and vegetation suggest fluctuations in the floodplain environment, reflecting complex vegetation dynamics and possibly climate forcing. During the Loch Lomond/Younger Dryas Stadial, a nival, braided regime was re-established, accompanied by the disappearance of tree birch.

Dendrochronological evidence for a lower water-table on peatland around 3200-3000 BC from subfossil pine in northern Scotland

Tree-ring analysis of subfossil Pinus sylvestris L., from nine new peatland sites located beyond the species’ current northern limit in Scotland, established a regional chronology called WRATH-9. The chronology has been provisionally dated against Irish pine chronologies and provides the first annual resolution picture of Scots pine expansion from c. 3200 BC and subsequent demise from c. 3000 BC. Pine germination and growth is suggested to be associated with a widespread fall in bog water-tables that indicates a regional climatic control. Bog pines progressively declined in number, rather than died out in a single event, reflecting their growth in a marginal habitat, close to a critical ecological threshold. The use of tree-ring sequences from in situ bog pine macrofossils provides a higher resolution insight into past conditions than possible with existing radiocarbon and pollen-based chronologies.

100 years of environmental change in a coastal wetland, Augusta Bay, southeast Sicily: evidence from geochemical and palaeoecological studies

Abstract Recent (post-1950 ad), industrial development in southeast Sicily has resulted in extensive modification of the coastline (port construction) and a potential for persistent, chronic pollution (oil refinery and petrochemical developments). High resolution radio-metric dating (210Pb and 137Cs) and palaeoenvironmental analysis of a short saltmarsh core from the Mulinello estuary (Augusta Bay) provides a record of change over the period 1880–1995 ad. Palynological data indicate expansion of halophytic vegetation across the study area between c. 1880 and 1945 ad. An increase in sediment accumulation occurred between 1945–1965 ad, with an associated rapid change in saltmarsh vegetation occurring at the beginning of this period. Palynological and geochemical data indicate that this increase in sediment accretion is probably due to an enhanced input of catchment-area derived material. This ante-dates the main period of industrial activity in the area, and probably reflects fluvial/catchment processes rather than local anthropogenic changes. Port and industrial developments, in comparison, have had a less significant impact on marsh vegetation and sediment supply, despite large-scale disturbance at the rear of the marsh. Trace element analyses show little input of industrial effluent to the Mulinello despite its location in a heavily-industrialized area. This, combined with preliminary diatom studies, indicates that the Mulinello receives most of its sediment from inland and local sources. The rapidity of local environmental change revealed in this sequence illustrates the dynamic nature of wetlands in microtidal settings and emphasizes their potential sensitivity to both local and regional disturbance. This study also demonstrates the use of combining palaeoecological with geochemical analyses to reconstruct environmental change in fluvial and estuarine wetland settings.

Anomalous buried hollows in London: development of a hazard susceptibility map

Engineering works carried out in central London over many decades have revealed a number of buried hollows that exhibit curious characteristics. Some extend deep into the bedrock geology and are in-filled with disturbed superficial deposits and reworked bedrock. Others are contained within the superficial deposits. They can be up to 500 m wide and more than 60 m in depth. As the infill material often has different behavioural characteristics from the surrounding deposits failure to identify them during an initial site investigation can prove costly. This paper considers their common characteristics and describes the method used to develop a buried hollow hazard susceptibility map. This map provides planners with a broader awareness of the potential location of difficult ground conditions associated with them, thereby reducing the potential for unforeseen ground conditions through effective site investigation design. The paper continues with a discussion of some of the likely processes associated with their formation, which are attributed to cryogenic processes, and concludes with potential future research directions.

The geomorphological context of the Brimpton Late Pleistocene succession (south central England)

Mapping of the area surrounding the site of the important Brimpton succession shows that it aggraded in a c . 10 m deep depression beneath the low 2 m (Beenham Grange) terrace of the river Kennet system. This is contrary to the previously published account by Bryant et al . (1983) which claimed that the depression underlay the 8 m terrace of the Kennet. The latter situation implied a large magnitude aggradation and incision cycle during the Late Devensian (post 25 ka bp ) and this factor had led to doubts as to whether the 2 superposed interstadials in the lower part of the depression were of early Devensian age. Geomorphological reaffirmation of a Devensian age plus new data makes the Brimpton-Woolhampton Gravel Pit sequence one of the most complete onshore Devensian records yet identified in Britain.

Geomorphological evidence for a changing tectonic regime, Pasinler Basin, Turkey

The Pasinler Basin, in the ‘East Anatolian Contractional Province’, features a suite of geomorphological zones, visible in the field, air photographs and Landsat and Shuttle Radar Topography Mission (SRTM) digital elevation model imagery. These zones reflect past and current tectonically influenced processes. Relicts of the Erzurum–Kars Plateau representing Mio-Pliocene volcanism, associated with transtensional tectonics, have been modified by two stages of drainage development: an earlier, shallow valley network, which was modified following uplift and tilting to form the present system characterized by deep narrow valleys that supply alluvial fan complexes. These fans discharge onto the present, aggradation-dominated basin floor. Initial normal faulting induced massive slope failures on the basins northern margin. This extensional phase within the basin was reversed by the Late Pleistocene, with thrust faults modifying and producing landforms, and affecting sediment sequences, along both its northern and southern margins. The shift from a transtensional regime, and the associated volcanism, to normal faulting in the Pliocene to Early Pleistocene, and then to the present regime of compression-induced thrusting appears to correspond to a regional tectonic shift resulting from the collision of the Eurasian and Arabian plates and the subsequent westwards movement of the Anatolian microplate.

Superficial Hollows and Rockhead Anomalies in the London Basin, UK: Origins, Distribution and Risk Implications for Subsurface Infrastructure and Water Resources

Recent findings in London show that the subsurface is much more complex than expected, with a number of apparently anomalous features that present a direct hazard to infrastructure development and a risk to ground water management. Of these features, one of the least understood are the large superficial hollows which occur in the rockhead—in much of the London Basin, this is the top of the London Clay Formation—and which are infilled by a range of Quaternary deposits, principally alluvial sands and gravels deposited by the River Thames and its tributaries. The hollows range in size and shape. Several are a few hundred metres across and can be up to 40–50 m deep, though determining their exact form is problematic. The soil and sediment infill of the hollows differs substantially from the surrounding ground in terms of strength and drainage, as well as some differences in chemistry. This presents a real hazard to infrastructure as there is a potential for vertical and horizontal movement, flooding, as well as increasing the risk of contamination of the deeper aquifer. In the paper, the locations and characteristics of known hollows and deformed strata are reviewed and evidence for how they formed is reassessed, systematically considering different hypotheses (scour, ground ice, karst subsidence, seismo-tectonic). From this we consider the implications for continued development of subsurface infrastructure development, and for water resources.

Active Tectonic Risk Assessment—Problems with Soil and Soft Sediment Deformation Structures

Many sites feature soils and sediments that have undergone syn- or post-depositional deformation. Typical forms of deformation include load casts, wedges, involutions and diapirs. In studies on geologically-young (Quaternary) soils and sediments in much of northwest Europe and some other areas, such forms are frequently attributed to the former action of non-glacial freezing and thawing during past cold periods. Similar features are found in arctic and high altitude areas. They are used to help reconstruct past climate and associated ground thermal regimes, including the extent of permafrost. The identification of the features as being relict with a low likelihood of such intense freeze-thaw processes being replicated has implications for site risk assessment and, consequently, design. Features that reflect syn- or post-depositional deformation elsewhere in the world, or in pre-Quaternary rocks, are frequently attributed to strong ground motion, and are used to help reconstructed past earthquake histories, both for regions and for individual potentially-active tectonic structures. There are direct implications for risk assessment and design. In theory, since the processes related to ice growth/decay and cyclic ground motion might be expected to be different, it should be possible to differentiate between them using diagnostic criteria. Unfortunately, either because different researchers are unconsciously biased by their training (perhaps causing the difference in interpretation depending on geographical region and the age of the features), or because the criteria are inadequately defined and are equally applicable to different processes, problems remain for fully understanding site risk. This paper compares the current state of diagnostic features used for interpreting deformations and uses these to explore possible interpretations and implications of a range of features found in apparently ‘cryogenic’ and ‘palaeoseismic’ settings. It ends with a call for a renewed focus on developing a robust and testable diagnostic toolkit for site investigation of soil and soft sediment deformation structures so that the features can be understood in terms of either “fossil” ice processes or active tectonic risk.

A Modified Freeze-Thaw Laboratory Test for Pavement Sub Soils Affected by De-icing Chemicals

De-icing chemicals are the most effective and cheap method to prevent winter slipperiness on pavement surfaces in urban settings. Analysis of existing experimental studies and theoretical methods shows that solutions of de-icing chemicals run off surfaces and are deposited in adjacent soils. However, there is a lack of knowledge about the effect of de-icing chemicals on the engineering properties of pavement sub soils, where the de-icing agents may penetrate beneath the pavement surface. This is a particular issue as pavement surfaces typically cool and warm at a faster rate than surrounding areas. In particular, during seasonal freeze-thaw cycles, the lower freezing point of the chemical solution may induce moisture migration toward a freezing front within the sub soil, leading to increased heave potential, and subsequent thaw collapse.The paper describes an experimental study that simulates the movement of water and de-icing solution from the deposition area upward to the highway’s sub base. The chemical effect of de-icing solutions on the strength characteristic, water and chemical content of each 10 cm layer of tested soil column will be assessed by in situ measurement and post-experiment analysis. In the long run the impact of the de-icing chemicals precipitation on the bearing capacity and deformation of sub base soils of roads will be evaluated.

Dissolution Influences on Gypsum Rock Under Short and Long-term Loading: Implications for Dams

Dissolution of soluble substrates such as gypsum presents a major hazard to dams in many parts of the world. This research simulates hypothesised conditions beneath the Mosul Dam, northwest Iraq, where collapse of a karstic system associated with continuous fresh water supply from its reservoir is a recognised problem. Gypsum rocks from northern Iraq and similar rocks from Bantycock gypsum mine, UK, were analysed for short-term mechanical response following immersion (5–50 weeks) and long-term loading during immersion (maximum 50 weeks). New experimental devices were developed from a conventional oedometer. Cylinder samples provided a proxy for massive gypsum strata. Samples were permanently submerged at atmospheric water pressure, with groundwater recharge, flow and dissolution simulated by regular changes of water. Stress on each sample was progressively increased to a maximum of 2,688 kPa. Small increases in strain were recorded by the end of each test but no failures occurred within 60 days. However, notable failure due to atmospheric water pressure and axial stress occurred over long time periods. Visible physical changes included a decrease in sample mass and volume. Similar change was recorded in ultrasonic velocities. These indicate that gypsum collapse risk beneath dams requires prolonged exposure to dissolution. The modified device performed well and was robust, and demonstrates that such a modification can provide a simple low cost system for conducting laboratory creep tests on weak rocks.