Investigation of landslides along the North-West coast of Malta and related hazard issues

Abstract

The research presented in this PhD thesis deals with the investigation of landslides along the north-west coast of Malta and related hazard issues. This is the first time that landslide research is being carried out through an integrated approach, utilising innovative techniques for the Maltese Islands. Geological and geomorphological investigations, retrospective research, material testing, landslide monitoring and landslide susceptibility assessment have been carried out to achieve the aims defined for this research project. A geomorphological survey has been undertaken along the north-west coast of Malta to identify the spatial distribution of landforms and to try and understand mass movement processes and slope instability conditions. A geomorphological map has been produced at a scale of 1:10,000 for the north-west coastal region, utilising Geographical Information Systems (GIS) techniques. The geomorphological map can also be considered as a landslide inventory map since it shows the spatial distribution of the different landslides present along the north-west coast of Malta. Four different types of coastal landslides have been identified, including rock falls, block slides, rock spreading and earth flows. Moreover from the geomorphological survey, three field sites influenced by rock spreading activity have been selected to conduct further investigation. The field sites include Il-Prajjet, Rdum id-Delli and Għajn Tuffieħa Bay comprising Il-Qarraba. At these sites a detailed investigation programme has been carried out, involving geomorphological mapping at a larger scale (1 :2500), material testing and monitoring of landslide displacements through the use of the Global Positioning System (GPS) technique. These sites were chosen because they provide the best examples of rock spreading activity and also present issues of hazard and risk with regards to the location of Popeye's Village, a popular tourist resort in the Maltese Islands, and a 17th century historical tower situated at the edge of a retreating cliff. Retrospective research has also been carried out since in the Maltese Islands landslide databases and inventories do not exist. The aim has been to investigate the evolution of landslides along the north-west coast of Malta and try to build a temporal landslide record, through multi-temporal analysis for a period slightly exceeding 100 years (1900-2007). Temporal and spatial datasets have been utilised to perform this extensive task. Visual and GIS comparative analyses rave been carried out for topographic maps and aerial photographs dating from different periods. Historical data of rainfall and earthquake events were used to conduct research related to past landslide events from newspapers and online resources. Since issues of landslide hazard and risk are extremely relevant for the north-west coastal region, a landslide susceptibility assessment was carried out. In the case of the north-west coastal region, a landslide susceptibility assessment was considered to be more relevant since the temporal element necessary to elaborate landslide hazard maps is missing, due to a very limited landslide inventory. A quantitative approach has been utilised to elaborate the landslide susceptibility models using multivariate statistical techniques, through the Conditional Analysis method. The models discriminate among the different landslides and utilise different instability factor combinations to evaluate better landslide susceptibility. Due to its applied nature, involving issues of landslide hazard and risk, this study should be of interest to local institutions responsible for public safety and land planning issues, and also appeals to the wider earth science community.