No description available.

Geomorphological and geological evidence for former Quaternary glaciation has been mapped n the Pindus Mountains of Northwest Greece. the dynamics and chronology of glaciation in this area has been established through sedimentological analysis, soil analysis and Uranium-series dating. Four glacial events are recorded in the sedimentological and geomorphological records. The more extensive recorded glaciation pre-dates 350,000 years BP and was characterised by extensive valley glaciers and ice-fields. A second glaciation occurred prior to the last interglacial, before <i>ca</i>. 127,000 years BP, and was characterised by glaciers that reached mid-valley positions. the height of the last glacial stage in Greece (30-20,000 ¹⁴C years BP) is recorded by small cirque glacier moraines and relict periglacial rock glaciers. evidence for a fourth glacial phase is recorded only in the highest cirques of Mount Smolikas (2637 m a.s.l.), the highest peak in the Pindus Mountains. This phase of glaciation is likely to have occurred during the Late-glacial Substage (14-10,000 ¹⁴C years BP). All of the glaciers during the different glacial stages were reconstructed and used alongside periglacial rock glaciers to determine palaeoclimate. During the glacial maximum of the last glacial stage mean annual temperatures were <i>ca</i>. 8-9°C lower than at present, and mean annual precipitation greater than 2000 mm - similar to modern values. Earlier glacial maxima are likely to have been colder but with mean annual precipitation still greater than 2000 mm. Maximum glacier extent in the Pindus Mountains is likely to have preceded the most severe arid phase of glacial cycles indicated in the pollen record and also global glacial maxima. this was because of the small size of the former Pindus glaciers and their rapid response to climate change, as well as the increased prevalence of aridity around the global glacial maxima. The glacial sequence in the Pindus Mountains represents the longest and best-dated recognised record of glaciation in the Mediterranean region and provides a stratigraphical framework for Quaternary cold-stage climates in Greece.

Geomorphological, sedimentological and geochronological analyses have been undertaken to decipher the effects of Quaternary environmental change on the development of the Rio Bergantes, Ebro basin, northeast Spain. Field mapping and profiling utilising large-scale aerial photography and airborne LiDAR data has identified a sequence of six river terraces. Age control, provided by luminescence dating methods, has revealed two major phases of valley floor aggradation at ~ 183 - 130 ka (Terrace BT1, elevated ~ 25 m above the modern river channel) and ~ 111- 26.8 ka (BT2, ~ 18-20 m), punctuated by ~ 20 m of incision in the intervening period. Following these two phases of large-scale aggradation, the Bergantes river system adjusted to a more sediment limited regime and responded to environmental changes through a series of smaller cut and fill cycles. This resulted in four lower elevation terraces (BT3-BT6) inset within the older (BT1 and BT2) valley fills. These lower terraces have been temporally constrained at ~ 24.5-14.2 ka (BT3); 10.6-9.8 ka (BT4); 8.3-6.2 ka (BT5) and ~ 3 ka (BT5). Field sedimentological and stratigraphic analysis of the alluvial fills, combined with sediment storage and export calculations, indicates the large influence of tributary and hillslope derived sediment supply during the aggradation of BT1 and, to a lesser extent BT2. This contrasts with the predominantly trunk river derived deposits which make up the fill of BT3-BT6, when the hillslopes and tributaries in the study area appear to be relatively de-coupled with the trunk river. A lack of lithological variation in the Bergantes catchment, combined with large amounts of carbonate, has restricted the possibility of deciphering any spatial or temporal changes in sediment source areas. However, a new and innovative methodology has been designed and implemented which calculates automatic sedimentary section-scale grain size measurements from Terrestrial Laser Scan (TLS) data. This methodology can now be applied to other ancient fluvial sedimentary successions. Data presented in this thesis suggest that the Bergantes river system has responded to, and has preserved, a record of environmental changes operating both in sync with, and at higher frequency than Milankovitch-driven glacial-interglacial cycles. Major valley floor aggradation phases (or those associated with relatively large amounts of fluvial sediment e.g. BT1 and BT2) correlate with Pleistocene glacial conditions in MIS 6 and MIS 5, when the climate on the Iberian Peninsula was cool and dry. Intervening phases of major valley incision appear to coincide with warmer and moister climates in Pleistocene interglacials. The younger terraces (BT3-BT6) are characterised by much smaller amounts of fluvial sediment. Dating control suggests that their development correlates with stadial (aggradation) and interstadial (incision) events during the Late Pleistocene and Holocene. Many phases of aggradation appear to coincide with the North Atlantic Heinrich Events, which are also recorded in marine cores off the west coast of the Iberian Peninsula, and also to other securely dated phases of aggradation elsewhere in the Mediterranean basin.

This study investigates sediment transport processes and sediment-landform development at two small valley glaciers of contrasting basal thermal-regime. A range of innovative techniques are applied to characterize and quantify glacier structure, glacially transported sediment facies and sediment-landform assemblages at Glacier de Tsanfleuron, Switzerland, and Midre Lov ́enbreen, Svalbard. Sediment transport at Glacier de Tsanfleuron is dominated by a rockfall-derived supraglacial debris stripe and abrasion-derived subglacial debris planes. Modeled sediment transport rates are equivalent to a glacier-wide erosion rate of 0.5 mm a−1 . Subglacially transported sediment ablates to form a complex network of debris stripes, the texture and morphology of which are consistent with sediment supply from palaeokarst sinkholes. These sinkholes dominate the limestone plateau on which the glacier is situated and also restrict glaciofluvial sediment transport by rerouting much of the glacier’s meltwater though the karst system. This results in a landsystem that is atypical of valley glaciers in the Alps. Sediment transport at Midre Lov ́enbreen is strongly influenced by glacier structure, identified at the glacier surface and in digital optical televiewing borehole logs. Glacier structure is successfully reconstructed in three-dimensions, revealing several visually distinctive englacial ice properties and deformation structures. Basally derived englacial sediment layers are found to be intercalated with primary stratification, elevated into near-vertical planes around a gently upglacier dipping central fold axis by large-scale lateral folding. Sediment analysis also allows supraglacial longitudinal debris ridges to be sub-classified into two types, with a new (Type II) form experiencing secondary deformation by small-scale flow parallel recumbent folding in association with vertical displacements across arcuate shear planes near the glacier terminus. Non-structurally controlled sediment transport at Midre Lov ́enbreen is dominated by low-intensity deformation of subglacial till, and is also characterized by the formation of supraglacial debris cones and proglacial flutes. Flutes at Midre Lov ́enbreen are interpreted to form beneath warm-based ice by the squeezing of partially fluidized till into cavities where freeze-on occurs due to a ’heat-pump’ effect across subglacial boulders. The results of this investigation demonstrate that, while basal-thermal regime may exert a strong influence on glacial sediment-transport processes that operate at the small-scale, bedrock physiography ultimately defines glacier morphometry and resulting large-scale flow structures. Additionally, although some of the sediment-landform types identified in this study are exclusive to a particular set of basal-thermal conditions, the composition and morphology of these sediment-landform assemblages are such that they are unlikely to be preserved in the geological record.

The work presented in this thesis concerns the investigation of the movement and stability of the sandwaves on the Skerries Bank in Start Bay, Devon. Initially, side scan sonar records of the sea bed of Start Bay were examined and an area on the Skerries Bank was selected for detailed study. The positions of the sandwaves in this area were accurately found by echo sounder, using sextants for navigation. By repeatedly surveying the same areas, the progressive displacement of the sandwaves was found over a period of two years. The magnitude and direction of the sandwaves' displacement was predicted from tidal current measurements and there was good agreement with the measured displacement. One particular sandwave was subjected to a very detailed investigation of its reciprocative displacement, for a period of several months. A diver-operated acoustic rangemeter system was used for this work. It was found that the reciprocative displacement, predicted from tidal current measurements, was an order of magnitude smaller than the measured displacement. Reasons for this are discussed. The reciprocative motion of the dunes has also been measured. The effect of sediment grain size on sandwaves has been investigated. It has been found that sandwaves only occur when the sediment grain size lies between 0 and 2 phi. Also, the relationship between water depth and sandwave wavelength has been examined. Measurements have been made of the sediment characteristics at a number of points over a sandwave profile. The effect of storms on sandwave shape has been observed. It has also been found that the 'catback' sandwave cross-section occurs when sandwaves bifurcate. From these results a better understanding has been obtained the way in which sandwaves move and of the stability of sandwaves on a tide-swept Bank, such as the Skerries.

Earthquake-induced soil liquefaction is a major cause of damage that needs to be controlled by engineers. A popular option for protecting against liquefaction is the installation of gravel drains to relieve generated excess pore pressures. A series of centrifuge tests were carried out on level sand beds without surface structures, to investigate qualitatively the effect of changing drain parameters and the geometry of drain groups. Using these, it was possible to determine a time varying extent of drain effectiveness, and a zone of influence consisting of a conical volume of soil from which draining fluid left the ground via the drain. Increasing drain radius was seen to increase the size of this zone but not accelerate drainage time if no other drains were near. It was also seen that fluid draining from depth caused a delay in the time for near-surface soil to begin draining. Limiting the influx of fluid from regions which are not to be protected was seen to be crucial to the success of small groups of drains. Soil with low permeability fine layers at the surface had identical pore pressure response to equivalent layers without such layers. However, the quantity of ejection features were greatly reduced by the presence of drains. To aid the modelling of deeper soil deposits, a new deep dynamic centrifuge container was designed and built. Analysis of the final box demonstrated that boundary interaction still occurred when the tested soil deviated from that for which it was designed. Drains were seen to be a temperamental method of achieving liquefaction protection, requiring very careful thought if excess pore pressures are to be kept below one. However, their acceleration of post-earthquake dissipation is a benefit in all cases. This may be made more optimal by allowing for the simple considerations presented herein.

No description available.

This thesis explores the morphology of debris flows and their role in shaping planetary surfaces. The primary objective is to assess the scale of the present martian near-surface water budget by studying recent gullies visually similar to water-carved gullies on Earth. The potential involvement of debris flow in forming these gullies is important, because it implies the action of liquid water. To assess the role of debris flow in forming martian gullies requires a better understanding of debris flows on Earth. I first performed a detailed study of unconfined debris flows in NW Iceland and developed a model to predict their path and deposition thickness using only the morphology of the previous deposits. I used this model to define areas at risk from debris flow inundation. Secondly I have used quantitive geomorphological methods to study long profiles and digital elevation models and have successfully ascertained the geomorphic “fingerprint” of mass wasting, debris flow and pure water flow on Earth. Using these methods, I then confirmed that gullies on Mars contain the signature of debris flow. In addition, these investigations revealed a strong climatic signal in gully development. Laboratory simulation experiments showed that under present martian climate liquid water can not only survive for appreciable time-scales, but can perform significant geomorphic work. Freezing at the base of the flow not only decreases infiltration, but increases the runout of the flow. These results indicate that gullies are a product of the recent action of thaw of ice on Mars. I suggest that moderate orbital spin obliquity is required to form gullies (rather than high obliquity suggested previously), because this is consistent with their distribution, the time needed for their development, and their relative youth. Thus the surface of Mars has been wetter, more recently than previously thought.

Experimental investigation of the behaviour of unsaturated soils is a key component in the analysis and design of a wide range of geoenvironmental problems. Furthermore, in some circumstances the influence of temperature variation needs to be considered in addition to the hydraulic and mechanical behaviour. Notwithstanding the significant theoretical and numerical developments, experimental determination of Thermo-Hydro- Mechanical (THM) soil properties remains a challenge. Consequently, in order to address these problems this thesis presents the design and development of two Temperature and Suction controlled Oedometer (TSO) cells with operational support. The new cells permit parallel testing of unsaturated soil over a temperature range of room temperature to 90°C. Suction control is achieved using the axis translation technique and is currently limited to 1.5 MPa. Vertical stress is applied via an air pressure controlled loading ram, operating up to a maximum stress of 2.5 MPa. The new apparatus has been calibrated in response to variations in temperature, suction and net stress. Subsequently, an experimental methodology for sample preparation and testing has been established. Speswhite kaolin has been used throughout this study due to its moderate swelling properties and the abundance of independently obtained data available. Basic geotechnical properties of kaolin have been determined via standard experimental techniques. Stress-path, temperature-path and suction-path tests have been successfully carried out using the new equipment. The results obtained have been validated in comparison to independently obtained data. From the work undertaken it is clear that temperature effects on the behaviour of kaolin are significant. Further work is now necessary to explore the behaviour of other soil types

The thesis examines the evidence for geomorphic activity of avalanches in the Cairngorm Mountains, Scotland. A typical avalanche boulder tongue morphology is developed from the literature. The form will have the following characteristics: concave slope profile, the top of the form will be in exposed bedrock, the form will be fan shaped or road bank type tongue which extends beyond the main break of slope and is raised above the surrounding surface of the valley, debris will be strewn over the tongue especially in the deposition zone and microrelief features are present on different zones of the tongue (missing boulder hole, bump holes, debris tails, scratch marks and perched boulders). The field work shows that these features do occur in the study area and furthermore that two other types of avalanche modified forms are present. These are: avalanche swept slopes where the avalanche clears the slope of debris, depositing it at the furthest extent of the avalanche activity and avalanche plunge pools where the avalanche terminates in water and deposits debris in a crescentic shape, under water, at the outer limit of the avalanche's reach. From the evidence gathered in the field the typical avalanche modified slope for the Cairngorm area is developed, describing the morphology of each subtype of form found. Other minor forms are also found in the study area: avalanche garlands. These forms are small garlands of debris that are deposited at the base of a gully along the side of the slope. These are created by snow sluffs entraining debris a short distance down the slope and clearing the area immediately surrounding the gully. The thesis subsequently examines the variables that control the formation of these forms and statistical analysis is used to examine these variables and their importance in controlling the development of the form. This data is also used to calculate the probability of avalanche modified slopes forming in the study area.