Robert J. Allison

Terrestrial laser scanning for monitoring the process of hard rock coastal cliff erosion

Hard rock cliffs represent approximately 75% of the worlds coastline. The rate and nature of the mechanisms that govern the retreat of these cliffs remain poorly constrained, primarily because conventional approaches employed to monitor these processes are generally inadequate for describing cliff erosion processes directly. These techniques are usually centred upon the interpretation of data collected periodically from aerial sensors, including stereographic aerial photographs and more recently air-borne LIDAR. These methods are generally not capable of assessing the pattern of erosion on the cliff face due to the oblique viewing angles, and hence tend to concentrate upon the resultant recession of the cliff top rather than change on the cliff face. Thus, processes of undercutting and small scale iterative failures of localized sections of the cliff face are generally not recorded. It is only when a failure affects the cliff top that any retreat is recorded. It is therefore unsurprising that cliff erosion is commonly deemed to be episodic. This paper presents a new approach to detailed cliff process monitoring using terrestrial laser scanning (TLS), which directly monitors changes on coastal cliff faces. The method allows the quantification of failures ranging in scale from the detachment of blocks of a few centimetres in dimension through to large rock, debris or soil, falls, slides and flows over 1000 m3. The collection of data is on-site and rapid and hence cost effective, providing a detailed description of the nature of coastal cliff erosion. This paper describes the methodological approach and demonstrates the range of results which can be generated, here shown for 16 months of monitoring data collected for a near-vertical cliff section on the coast of North Yorkshire, UK. The results demonstrate that terrestrial laser scanning can be used to quantify cliff failures to a previously unobtainable precision. The results reveal a strong spatial and temporal pattern of cliff collapse which contradicts commonly held perceptions of the nature of coastal cliff development.

The Dynamics and Environmental Context of Aeolian Sedimentary Systems

Recent studies of aeolian deposits have made it possible to test hypotheses which relate major phases of aeolian activity to changes in climate and sea-level. Dust deposits in ocean sediments, and thick sequences of aeolian sand, loess and palaeosols have revealed some of the most complete and detailed evidence of the environmental changes which affected continental areas during the Quaternary and earlier.

Patterns of precursory rockfall prior to slope failure

In this paper we examine data generated using high-resolution three-dimensional laser scanning monitoring of coastal rock cliffs. These data are used to identify spatial and temporal patterns in rockfall activity behavior prior to slope failure. Analysis of the data suggests that given sufficient measurement precision precursory behavior, here manifest as the rate of rockfall activity prior to failure, can be detected, measured, and monitored. Environmental conditions appear to have a diminishing influence on the occurrence of increasingly large slope failures. The monitoring data implies a time-dependent sequence in the occurrence of smaller rockfalls in the period leading to the largest failures recorded. This behavior is attributed to the mechanisms of strain accumulation in the rock mass resulting from brittle failure of the slope. The implication is that combining these data with models of failure mechanisms may allow failure time to be forecast from wide-area monitoring of precursory behavior. These findings have implications for the management of potentially unstable slopes, the understanding of slope failure mechanisms, and the generation of a new type of slope failure warning systems.

The effects of fire on rock weathering: some further considerations of laboratory experimental simulation

Fire in the natural environment is a widespread agent of geomorphological and biological change. Temperatures can exceed 1000°C. There is often a rapid rise from ambient conditions through a steep thermal gradient, promoting rock disintegration. Laboratory simulation studies have established that temperature changes which are representative of natural fires affect rock material properties, which can then be related to weathering susceptibility. This study extends previous work by more closely replicating the natural environment, (a) through the simulation of rainfall and (b) by encasing samples to reflect the exposure of a single rock face to a passing fire event. Rock samples collected on Cyprus were prepared and tested following previously reported procedures. Change in modulus of elasticity was monitored using a non-destructive ultrasonic method. The data corroborate previous work but with somewhat different degrees of change. The new results are more likely to be representative of natural conditions and real-world change. The rate of rock disintegration and effects such as case-hardening appear to be a function of rock thermal characteristics, material properties and environmental constraints such as diurnal temperature range. Copyright

Post-Depositional Modification of the Linear Sand Ridges of the West Kimberley Area of North-West Australia

Late Quaternary linear dunes of the west Kimberley area of tropical north-western Australia exhibit an extensive degree of post-depositional modification. Evidence for modification includes degraded overall morphology in cross profile, severe reddening, high (typically 20-25 per cent) silt and clay contents, and complete pseudomorphic replacement of some mineral components. All the modification took place subsequent to the emplacement of the dune ridges which, based on luminescence dating, occurred since latest Pleistocene and earliest Holocene times. Accelerator radiocarbon dating of particulate charcoal from discontinuous, sub-horizontal lenses within the dunes was found to produce ages inconsistent both with the chronology erected using luminescence methods and stratigraphic inferences. A combination of petrographic, SEM and XRD investigations suggests that much of the dune reddening is the result of in situ hematite crystallization within kaolinitic grain coatings, which are responsible for the high fines content of the dunes.

Modelling failure mechanisms to explain rock slope change along the Isle of Purbeck coast, UK

Results are presented of distinct element computer modelling used to examine rates and mechanisms of change in rock slopes and cliffs, where material intact properties determine process and form but the most significant controls are the joint pattern and cross-joint properties. The modelling approach does not appear to have been used before in a geomorphological context and provides an alternative approach for examining cliff development. Field and laboratory data have been collected for the Portland Limestone outcrop of the Isle of Purbeck, central southern England. The Portland Limestome is a hard, shelly, crystalline sediment of the Upper Jurassic. It has a regular discontinuity pattern throughout the outcrop in Purbeck. While joint orientation remains relatively constant, bedding changes from horizontal to vertical, a consequence of the Purbeck Monocline. There are resulting implications for spatial variations in rock slope evolution. The modelling exercise enhances previous knowledge on rock failure mechanisms and slope development along the Purbeck coast and demonstrates its potential in research where landforms are developed in lithified, jointed rock masses.

Geology, geomorphology, hydrology, groundwater and physical resources of the desertified Badia environment in Jordan

This paper summarizes the information on the geomorphology and physical resources component of the Jordan Badia Research and Development Programme. The research focuses on the issue of the environment in arid lands and aims to provide practical options for sustainable development, for the benefit not only of the Hashemite Kingdom of Jordan but for other arid regions of the world. The research is significantly development driven because there is a need to identify useable natural resources and establish a framework for their effective exploitation and management in a marginal, fragile environment, which is sensitive to change.Pressure for development of the Badia stems from the fact that the great majority of the population in Jordan is compressed into less than 10% of the country by environmental constraits. It is hoped that the Jordan Badia Research and Development Programme will provide the required framework to ease current environmental pressures, encourage migration to the Badia, a sparsely populated region, and establish economically and ecologically self-supporting communities.This paper discusses the following areas that are related to the sustainable development of the Jordan Badia with special emphasis on the Safawi area in the Northern Jordan Badia; geomorphology including landform, processes and hazards, geology and physical resources, hydrology, surface water and water engineering, groundwater, soils and vegetation, sediment erosion and mobility and environmental management.

Slope form and associations with ground boulder cover in arid environments, northeast Jordan

Abstract Many studies of slope form and sediment transfer dynamics use either bounded field plots or laboratory physical hardware models to study associations between morphology and process. Results are presented here of a study which examines spatial variations in slope form, changing ground surface boulder cover between sites and at different points along slope profiles and evidence for the movement of fine-grained sediments which underlie the boulder cover. The study site is located in northeast Jordan, an arid landscape, characterised by a late Tertiary to early Quaternary basalt plateau, spreading across the foot-slopes of the Druz Mountains. Basalt age ranges from approximately 8.9 Ma to recent scoracious deposits from local eruptive centres, which are no more than 100,000 years old. The study considers whole slope profiles rather than a representative section of a slope and accounts for form differences by quantifying slope shape using a length:height integral. Slope form differs with basalt age, gradually changing from concave to convex shapes. The boulder cover can be used to examine the mobility and redistribution of underlying fine-grained sediment by establishing the degree of clast burial at points along slope profiles. Twenty-five slope profiles were surveyed and five plots, distributed between crest and toe, located at similar points on thirteen. The axial dimensions of boulders within each plot were recorded. Sorting and the preferential movement of smaller clasts is a characteristic of the steepest part of slopes, while mean clast size increases downslope for older basalts and decreases downslope for younger basalts. The degree of wadi network evolution and the development of sediment pans, known as Qa and Marab, varies with flow age. Links can be established between the age and physical nature of individual lava flows, differences in slope form and their spatial distribution. Associations also exist between changes in boulder dimensions, basalt type and the extent of clast burial between topographic highs and lows.

Weathering effects on the geotechnical properties of argillaceous sediments in tropical environments and their geomorphological implications

Outcrops of young, sedimentary, argillaceous rocks with well developed fabric display rapid changes in their properties when subject to tropical weathering. The change in the materials is often accompanied by mass movement activity and the geomorphological consequence in terms of landforms is usually the development of badlands topography. Detailed field and laboratory studies have been undertaken on the Joes River Formation, Barbados, and the Lichi Melange, Taiwan. Both are sedimentary mudrocks with well developed, scaly fabrics. Physical and geotechnical laboratory tests have been conducted on samples collected from type site locations to elucidate associations between material properties, earth surface processes and landform development. While the inherent physical properties show little or no difference in the transition from unweathered to highly weathered materials, by applying the critical state model, the mudrock geotechnical properties can be shown to change significantly. As weathering commences, material strength surprisingly increases. Only after a period of more extensive weathering do mechanical properties confirm increasingly incompetent materials. The initial strength increase appears to be due to weathering-induced modification of the fabric. The subsequent strength drop is a product of weathering-induced modification of both the fabric and the in situ, intact sediment. It is suggested that by applying the critical state model, a greater consideration can be gained of the geotechnical response of the sediments to weathering.

The geomorphology of the Napier Range, Western Australia

The Napier Range of tropical North-Western Australia is an exhumed Devonian reef in an area of intense seasonal rainfall with savanna vegetation. It is composed primarily of three types of hard limestone: a reef facies (the Windjana Limestone), a back-reef facies (the Pillara Limestone), and a foreand inter-reef facies (the Napier Formation). Slope forms, which range from near-vertical cliffs to gentle convexo-concave profiles, can be related to these facies. Foot-slope pediments are almost ubiquitous. Closed depressions are rare, and fluvial processes are important in shaping the landscape. Surface karren, especially rillenkarren, are well developed on the purer beds. Depositional forms, which include tufas and pseudo-anticlines of calcrete, are notable. Plains fringing the Range show the development of linear aligned gilgai (the orientation of which may be related to prevailing easterly winds) and of degraded Late Pleistocene dunes.