Michael Lim - Academia.edu (original) (raw)
Papers by Michael Lim
The application of Terrestrial Laser Scanning (TLS) to monitor and quantify rock slope change has... more The application of Terrestrial Laser Scanning (TLS) to monitor and quantify rock slope change has enabled significant improvements, at both the temporal and spatial scale, of understanding of rock slope change behaviour. However understanding the errors and accuracy ...
Remote Sensing of Environment, 2015
Eroding coastlines composed of sequences of till, carbon rich peat and sand layers are characteri... more Eroding coastlines composed of sequences of till, carbon rich peat and sand layers are characteristic of many formerly glaciated coastlines due to the interplay of relative land and sea levels. Dune cliffs cut into these materials represent one of the most sensitive systems to the processes of coastal change. Establishing appropriate scales for the quantification and analysis of change in coastal dune cliffs remains limited by the speed and nature of change, the intensity of environmental processes and the challenges of achieving adequate survey control. This paper presents the results from multi-scale analyses into the behaviour of dune cliffs on the northeast coast, UK, over a 118 year period. Repeat unmanned aerial vehicle (UAV) survey differences have been used to identify and quantify system behaviour, set in context with historic map comparisons. At the landform scale, monthly dune cliff dynamics have been analysed over the course of a year with terrestrial laser scanning (TLS) in order to gain insights into the drivers of contemporary dune cliff behaviour. Finally, pseudo three-dimensional ground-penetrating radar (GPR) data are used to trace subsurface stratigraphy from which the potential extent of stored carbon (in excess of 100 t over 50 m of monitored dune cliff) at risk of release by coastal erosion over the next 50 years can be calculated. The consideration of multi-scale changes over time periods relevant to well-constrained sea level change has revealed a complex combination of failure mechanisms that have resulted in an acceleration in dune cliff recession (particularly over the last decade) and a form change to shallower, divergent profiles. This potential acceleration in contemporary dune cliff response holds significant implications for both coastal management and the contribution of this poorly quantified input to the coastal carbon flux.
Journal of Geophysical Research: Oceans, 2013
Michael (2013) Coastal cliff-top ground motions as proxies for environmental processes.
Geology, 2013
Despite much research on the myriad processes that erode rocky coastal cliffs, accurately predict... more Despite much research on the myriad processes that erode rocky coastal cliffs, accurately predicting the nature, location and timing of coastline retreat remains challenging, confounded by the apparently episodic nature of cliff failure. The dominant drivers of coastal erosion, marine and sub-aerial forcing, are anticipated in future to increase, so understanding their present and combined efficacy is fundamental to improving predictions of coastline retreat. We capture change using repeat laser scanning across 2.7 x 10 4 m 2 of near-vertical rock cliffs on the UK North Sea coast over 7 years to determine the controls on the rates, patterns and mechanisms of erosion. For the first time we document that progressive upward propagation of failure dictates the mode and defines the rate at which marine erosion of the toe can accrue retreat of coastline above; notably a failure mechanism not conventionally considered in cliff stability models. Propagation of instability and failure operates at these sites at 10 1 year timescales and is moderated by local rock mass strength and the time-dependence of rock fracture. We suggest that once initiated, failure propagation can operate ostensibly independently to external environmental forcing, and so may not be tightly coupled to prevailing subaerial and oceanographic conditions. Our observations apply to coasts of both uniform and complex lithology, where failure geometry is defined by rock mass strength and structure, and not intact rock strength alone, and where retreat occurs via any mode other than full cliff collapse.
Despite their widespread occurrence, the behaviour of coastal rock cliffs, and in particular the ... more Despite their widespread occurrence, the behaviour of coastal rock cliffs, and in particular the balance between the marine and subaerial conditions that promote erosion, is poorly understood. This is mainly due to a lack of direct, quantitative data on process and response in this type of environment. This paper investigates how nearcliff environmental processes can be associated with the occurrence of rockfalls, which we argue contribute the majority of material lost from coastal cliffs. A detailed recent history of rockfall volumes, dating back to 2003, has been collected using repeat terrestrial laser scans of a 70 m high cliff section on the North Yorkshire coast, UK. This dataset is complimented with a bespoke environmental monitoring system installed upon the cliff face, which allows the influence of weathering and erosion processes on the magnitude and frequency of rockfalls to be analysed. This system is comprised of three instrument clusters at nodes that correspond to three main lithological units of the cliff, hard wired to a communications unit at the top of the cliff face. Data is collected on air temperature, humidity, irradiance, wind and precipitation. Within the near surface of the rock mass we also measure temperature, rock moisture, surface wetness and strain, to allow the direct physical response of the rock to be quantified. The cliff (local) environment monitoring system demonstrates that the rock undergoes significantly greater variability than can be identified from more generic regional weather and tide datasets, predominantly as a function of the angular geometry of the cliff face, resulting in rapid gradients of change. For example, daily variations in temperature and moisture can be seen to have a significant and direct effect on the strain responses of the rock. We seek to establish this as a long-term dataset, to provide a new quantitative assessment of the links between regional and hinterland weather conditions and those found on the cliff face, and to assess the efficacy of these conditions as drivers of sub-aerial weathering and its relative contribution to rock cliff retreat.
… 2010, held 2-7 May …, 2010
Title: Cosmogenic dating of the evolution of rocky coastlines. Authors: Rosser, Nick; Barlow, Joh... more Title: Cosmogenic dating of the evolution of rocky coastlines. Authors: Rosser, Nick; Barlow, John; Densmore, Alex; Petley, David; Schnabel, Christoph; Lim, Michael. Affiliation: AA(Institute of Hazard, Risk and Resilience, Durham ...
… 2010, held 2-7 May …, 2010
Title: Change detection using terrestrial laser scanning in steep terrain and complex surface geo... more Title: Change detection using terrestrial laser scanning in steep terrain and complex surface geometry - Survey planning, data processing and validation. Authors: Schürch, Peter;Densmore, Alex L.; Rosser, Nick J.; Lim, Michael; McArdell, Brian W. ...
Journal of Geophysical Research, 2007
In this paper we examine data generated using high-resolution three-dimensional laser scanning mo... more 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.
Journal of Coastal Research, 2011
The influence of waves and tides on the development of coastal cliffs has long been recognised as... more The influence of waves and tides on the development of coastal cliffs has long been recognised as an important contributor to long-term coastline evolution. However, the relationship between the assailing force of waves and the resistance afforded by foreshore and cliff material that governs the processes through which cliff change occurs remains inadequately quantified and poorly understood. This is further confounded by a limited appreciation of the interplay between the coastal landforms and the range of processes that control their evolution. To explore this, we compare microseismic ground movements resulting from wave impacts to the occurrence of rockfalls from a section of cliffs on the North Yorkshire, United Kingdom, coastline. The results indicate that critical tide levels exist at which waves, in combination with wind directions coinciding with the greatest fetch, generate notably higher levels of energy delivery to the cliff face and that these levels, in turn, correspond to increased levels of material detachment from both within and above the cliff toe. Foreshore microtopography is shown to have a significant influence on wave energy flux and impact timing at the cliff face. The link between relative sea level and geomorphological work done by wave action is both spatially heterogeneous and tightly constrained by foreshore topography, yet local scale topographic controls are rarely considered in scenarios of future coastal change. The timing of relative increases in rockfall activity is also shown to correlate with preceding seismic events, which may indicate a lag or threshold in the geomorphic response of the cliff. Finally, the article uses modelled increases in inundation to explore the influence of topography on the distribution of changes to the tidal regime under future sea-level rise scenarios. These data highlight the need for a greater understanding of cliff behaviour if, in the context of sea-level rise, future coastal evolution is to be predicted.
The application of Terrestrial Laser Scanning (TLS) to monitor and quantify rock slope change has... more The application of Terrestrial Laser Scanning (TLS) to monitor and quantify rock slope change has enabled significant improvements, at both the temporal and spatial scale, of understanding of rock slope change behaviour. However understanding the errors and accuracy ...
Remote Sensing of Environment, 2015
Eroding coastlines composed of sequences of till, carbon rich peat and sand layers are characteri... more Eroding coastlines composed of sequences of till, carbon rich peat and sand layers are characteristic of many formerly glaciated coastlines due to the interplay of relative land and sea levels. Dune cliffs cut into these materials represent one of the most sensitive systems to the processes of coastal change. Establishing appropriate scales for the quantification and analysis of change in coastal dune cliffs remains limited by the speed and nature of change, the intensity of environmental processes and the challenges of achieving adequate survey control. This paper presents the results from multi-scale analyses into the behaviour of dune cliffs on the northeast coast, UK, over a 118 year period. Repeat unmanned aerial vehicle (UAV) survey differences have been used to identify and quantify system behaviour, set in context with historic map comparisons. At the landform scale, monthly dune cliff dynamics have been analysed over the course of a year with terrestrial laser scanning (TLS) in order to gain insights into the drivers of contemporary dune cliff behaviour. Finally, pseudo three-dimensional ground-penetrating radar (GPR) data are used to trace subsurface stratigraphy from which the potential extent of stored carbon (in excess of 100 t over 50 m of monitored dune cliff) at risk of release by coastal erosion over the next 50 years can be calculated. The consideration of multi-scale changes over time periods relevant to well-constrained sea level change has revealed a complex combination of failure mechanisms that have resulted in an acceleration in dune cliff recession (particularly over the last decade) and a form change to shallower, divergent profiles. This potential acceleration in contemporary dune cliff response holds significant implications for both coastal management and the contribution of this poorly quantified input to the coastal carbon flux.
Journal of Geophysical Research: Oceans, 2013
Michael (2013) Coastal cliff-top ground motions as proxies for environmental processes.
Geology, 2013
Despite much research on the myriad processes that erode rocky coastal cliffs, accurately predict... more Despite much research on the myriad processes that erode rocky coastal cliffs, accurately predicting the nature, location and timing of coastline retreat remains challenging, confounded by the apparently episodic nature of cliff failure. The dominant drivers of coastal erosion, marine and sub-aerial forcing, are anticipated in future to increase, so understanding their present and combined efficacy is fundamental to improving predictions of coastline retreat. We capture change using repeat laser scanning across 2.7 x 10 4 m 2 of near-vertical rock cliffs on the UK North Sea coast over 7 years to determine the controls on the rates, patterns and mechanisms of erosion. For the first time we document that progressive upward propagation of failure dictates the mode and defines the rate at which marine erosion of the toe can accrue retreat of coastline above; notably a failure mechanism not conventionally considered in cliff stability models. Propagation of instability and failure operates at these sites at 10 1 year timescales and is moderated by local rock mass strength and the time-dependence of rock fracture. We suggest that once initiated, failure propagation can operate ostensibly independently to external environmental forcing, and so may not be tightly coupled to prevailing subaerial and oceanographic conditions. Our observations apply to coasts of both uniform and complex lithology, where failure geometry is defined by rock mass strength and structure, and not intact rock strength alone, and where retreat occurs via any mode other than full cliff collapse.
Despite their widespread occurrence, the behaviour of coastal rock cliffs, and in particular the ... more Despite their widespread occurrence, the behaviour of coastal rock cliffs, and in particular the balance between the marine and subaerial conditions that promote erosion, is poorly understood. This is mainly due to a lack of direct, quantitative data on process and response in this type of environment. This paper investigates how nearcliff environmental processes can be associated with the occurrence of rockfalls, which we argue contribute the majority of material lost from coastal cliffs. A detailed recent history of rockfall volumes, dating back to 2003, has been collected using repeat terrestrial laser scans of a 70 m high cliff section on the North Yorkshire coast, UK. This dataset is complimented with a bespoke environmental monitoring system installed upon the cliff face, which allows the influence of weathering and erosion processes on the magnitude and frequency of rockfalls to be analysed. This system is comprised of three instrument clusters at nodes that correspond to three main lithological units of the cliff, hard wired to a communications unit at the top of the cliff face. Data is collected on air temperature, humidity, irradiance, wind and precipitation. Within the near surface of the rock mass we also measure temperature, rock moisture, surface wetness and strain, to allow the direct physical response of the rock to be quantified. The cliff (local) environment monitoring system demonstrates that the rock undergoes significantly greater variability than can be identified from more generic regional weather and tide datasets, predominantly as a function of the angular geometry of the cliff face, resulting in rapid gradients of change. For example, daily variations in temperature and moisture can be seen to have a significant and direct effect on the strain responses of the rock. We seek to establish this as a long-term dataset, to provide a new quantitative assessment of the links between regional and hinterland weather conditions and those found on the cliff face, and to assess the efficacy of these conditions as drivers of sub-aerial weathering and its relative contribution to rock cliff retreat.
… 2010, held 2-7 May …, 2010
Title: Cosmogenic dating of the evolution of rocky coastlines. Authors: Rosser, Nick; Barlow, Joh... more Title: Cosmogenic dating of the evolution of rocky coastlines. Authors: Rosser, Nick; Barlow, John; Densmore, Alex; Petley, David; Schnabel, Christoph; Lim, Michael. Affiliation: AA(Institute of Hazard, Risk and Resilience, Durham ...
… 2010, held 2-7 May …, 2010
Title: Change detection using terrestrial laser scanning in steep terrain and complex surface geo... more Title: Change detection using terrestrial laser scanning in steep terrain and complex surface geometry - Survey planning, data processing and validation. Authors: Schürch, Peter;Densmore, Alex L.; Rosser, Nick J.; Lim, Michael; McArdell, Brian W. ...
Journal of Geophysical Research, 2007
In this paper we examine data generated using high-resolution three-dimensional laser scanning mo... more 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.
Journal of Coastal Research, 2011
The influence of waves and tides on the development of coastal cliffs has long been recognised as... more The influence of waves and tides on the development of coastal cliffs has long been recognised as an important contributor to long-term coastline evolution. However, the relationship between the assailing force of waves and the resistance afforded by foreshore and cliff material that governs the processes through which cliff change occurs remains inadequately quantified and poorly understood. This is further confounded by a limited appreciation of the interplay between the coastal landforms and the range of processes that control their evolution. To explore this, we compare microseismic ground movements resulting from wave impacts to the occurrence of rockfalls from a section of cliffs on the North Yorkshire, United Kingdom, coastline. The results indicate that critical tide levels exist at which waves, in combination with wind directions coinciding with the greatest fetch, generate notably higher levels of energy delivery to the cliff face and that these levels, in turn, correspond to increased levels of material detachment from both within and above the cliff toe. Foreshore microtopography is shown to have a significant influence on wave energy flux and impact timing at the cliff face. The link between relative sea level and geomorphological work done by wave action is both spatially heterogeneous and tightly constrained by foreshore topography, yet local scale topographic controls are rarely considered in scenarios of future coastal change. The timing of relative increases in rockfall activity is also shown to correlate with preceding seismic events, which may indicate a lag or threshold in the geomorphic response of the cliff. Finally, the article uses modelled increases in inundation to explore the influence of topography on the distribution of changes to the tidal regime under future sea-level rise scenarios. These data highlight the need for a greater understanding of cliff behaviour if, in the context of sea-level rise, future coastal evolution is to be predicted.