Application of Geographical Information Systems to Lahar Hazard Assessment on an Active Volcanic System

Lahars (highly dynamic mixtures of volcanic debris and water) have been responsible for some of the most serious volcanic disasters and have killed tens of thousands of people in recent decades. Despite considerable lahar model development in the sciences, many research tools have proved wholly unsuitable for practical application on an active volcanic system where it is difficult to obtain field measurements. In addition, geographic information systems are tools that offer a great potential to explore, model and map hazards, but are currently under-utilised for lahar hazard assessment. This research pioneered a three-tiered approach to lahar hazard assessment on Montserrat, West Indies. Initially, requirements of potential users of lahar information (scientists and decision-makers) were established through interview and evaluated against attainable modelling outputs (given flow type and data availability). Subsequently, a digital elevation model, fit for modelling lahars, was used by a path of steepest descent algorithm and a semi-empirical debris-flow model in the prediction of lahar routes and inundation areas. Limitations of these established geographical information system (GIS) based models, for predicting the behaviour of (relatively under-studied) dilute lahars, were used to inform key parameters for a novel model, also tightly coupled to a GIS, that simulated flow routes based on change in velocity. Importantly, uncertainty in model predictions was assessed through a stochastic simulation of elevation error. Finally, the practical utility of modelling outputs (visualisations) was assessed through mutual feedback with local scientists. The new model adequately replicated past flow routes and gave preliminary predictions for velocities and travel times, thus providing a short-term lahar hazard assessment. Inundation areas were also mapped using the debris-flow model to assist long-term planning. Ultimately, a GIS can support ‘on the ground’ planning decisions, but efficacy is limited by an active volcanic system which can restrict feedback to and from end-users. *[The appendices for this thesis were submitted as separate files which could not be uploaded to the repository. Please contact the author for more information.]

A tool for assessing error in digital elevation models from a user’s perspective

A Digital Elevation Model (DEM) is a representation of geographic reality. The elevations recorded within DEMs have been shown to contain errors pertaining to sampling, measurement and interpolation (Fisher, 1998). Even a small amount of elevation error can greatly affect derivative products (Holmes et al., 2000). This can potentially have a significant impact on the application of DEMs in Geographical Information Systems (GIS) where first and second order derivatives are considered

Sediment-charged flash floods on Montserrat : the influence of synchronous tephra fall and varying extent of vegetation damage

On 20th May 2006 the Soufrière Hills Volcano on the Caribbean island of Montserrat experienced a large dome collapse and intense rainfall generated flash floods. The floods had very high loads of volcanic debris derived both from this and previous eruptions and can thus be classified as lahars. The floods reached unusually high water levels and caused substantial geomorphic change in the Belham Valley. Detailed rainfall and geomorphological data, coupled with the precise timing of events and yewitness accounts have facilitated an assessment of the relative importance of rainfall volume and intensity, older volcanic debris, pre- and syn-flood tephra fall and the extent of pre-flood vegetation damage for the behavior of this and subsequent sediment-laden floods in this setting. The change in runoff behavior was controlled by preexisting vegetation damage and synchronous tephra fall and this was critically important in controlling the impact of these flash floods. Although rainfall intensity and volume have some control on flood occurrence they are not the critical control on flash flood impact on the geomorphology in the Belham Valley. A significant conclusion of this study is that the extreme nature of the flash floods was not caused by extreme rainfall (as is commonly believed to be the primary cause of flash floods) but rather it was the result of changed runoff behaviour caused by the widespread syn-flood tephra deposition and importantly the widespread vegetation damage by volcanic-associated acid rain in the preceding weeks

A tool for assessing error in digital elevation models from a user’s perspective

A Digital Elevation Model (DEM) is a representation of geographic reality. The elevations recorded within DEMs have been shown to contain errors pertaining to sampling, measurement and interpolation (Fisher, 1998). Even a small amount of elevation error can greatly affect derivative products (Holmes et al., 2000). This can potentially have a significant impact on the application of DEMs in Geographical Information Systems (GIS) where first and second order derivatives are considered

A tool for assessing error in digital elevation models from a user’s perspective

A Digital Elevation Model (DEM) is a representation of geographic reality. The elevations recorded within DEMs have been shown to contain errors pertaining to sampling, measurement and interpolation (Fisher, 1998). Even a small amount of elevation error can greatly affect derivative products (Holmes et al., 2000). This can potentially have a significant impact on the application of DEMs in Geographical Information Systems (GIS) where first and second order derivatives are considered

An application-driven approach to terrain model construction

Terrain is a surface phenomenon that is measured, modelled, and mapped. However, it is continuously variable and must be simulated by points or mathematical equations that are inherently approximations. The error induced by digitally represented terrain can propagate to surface derivatives and geographical information science (GIS) applications where topography is considered. This can lead to uncertainty in model predictions and the use of data that are unfit for the application to which they are intended. This article outlines the problem of uncertainty in terrain representation and demonstrates the consequences for volcanic mudflow modelling. The response of a simple least-cost single flow algorithm to input parameters was investigated in order to assess output variation from the different sources of input variation. Elevation error was modelled with a probability density function (PDF) and propagated through stochastic simulation (Monte Carlo). Such combined uncertainty and sensitivity analyses enabled a qualitative judgement of the relative significance of elevation error on the flow model prediction. Different methods for terrain model construction were considered and show that supplementing global positioning system (GPS) measurements with information from field notes and reconnaissance photographs greatly improved the model performance and reduced the uncertainty. It is concluded that in terms of validity of model results, there is no substitute for constructing an elevation model that is informed by the terrain

Framing volcanic risk communication within disaster risk reduction: finding ways for the social and physical sciences to work together

Sixteen years have passed since the last global volcanic event and more than 25 since a volcanic catastrophe that killed tens of thousands. In this time, volcanology has seen major advances in understanding, modelling and predicting volcanic hazards and, recently, an interest in techniques for reducing and mitigating volcanic risk. This paper provides a synthesis of literature relating to this last aspect, specifically the communication of volcanic risk, with a view to highlighting areas of future research into encouraging risk-reducing behaviour. Evidence suggests that the current ‘multidisciplinary’ approach within physical science needs a broader scope to include sociological knowledge and techniques. Key areas where this approach might be applied are: (1) the understanding of the incentives that make governments and communities act to reduce volcanic risk; (2) improving the communication of volcanic uncertainties in volcanic emergency management and long-term planning and development. To be successful, volcanic risk reduction programmes will need to be placed within the context of other other risk-related phenomena (e.g. other natural hazards, climate change) and aim to develop an all-risks reduction culture. We suggest that the greatest potential for achieving these two aims comes from deliberative inclusive processes and geographic information systems

Improving user assessment of error implications in digital elevation models

A digital representation of a terrain surface is an approximation of reality and is inherently prone to some degree of error and uncertainty. Research in uncertainty analysis has produced a vast range of methods for investigating error and its propagation. However, the complex and varied methods proposed by researchers and academics create ambiguity for the dataset user. In this study, existing methods are combined and simplified to present a prototype tool to enable any digital elevation model (DEM) user to access and apply uncertainty analysis. The effect of correlated gridded DEM error is investigated, using stochastic conditional simulation to generate multiple equally likely representations of an actual terrain surface. Propagation of data uncertainty to the slope derivative, and the impact on a landslide susceptibility model are assessed. Two frameworks are developed to examine the probable and possible uncertainties in classifying the landslide hazard: probabilistic and fuzzy. The entire procedure is automated using publicly available software and user requirements are minimised. A case study example shows the resultant code can be used to quantify, visualise and demonstrate the propagation of error in a DEM. As a tool for uncertainty analysis the method can improve user assessment of error and its implications

Economic values from ecosystems

No abstract available