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Evaluation of the use high resolution satellite Imagery to map slope instability in a tropical environment: St. Thomas, JamaicaLandslides are a major natural hazard in Jamaica, and have resulted in loss of life, major economic losses, social disruption and damage to public and private properties. There is a need to delineate areas that are prone to slope instability in order to mitigate their effects. The first and most important stage for the creation of a landslide risk maps is the collection of accurate landslide data in a timely manner. However the type of terrain makes landslide mapping particularly difficult. Aerial Photographs have proven to be an effective way of mapping landslides but acquiring new photographs to map recent landslides is very expensive. High resolution satellite imagery were evaluated for their effectiveness in delineating landslides. The landslides on a whole had no distinctive spectral property; hence no one classification technique could be used to identify them. This research developed integrative methods utilising a combination of: edge enhancement to delineate the scarps area; Wetness Index to identify back titling blocks and debris flow lobes where moisture is higher; shape classification (to distinguish from e.g. ground cleared for agriculture); and slope curvature to map scarps. The information from the image classification was combined in a GIS and automated to determine the probability of the presence and or absence of a landslides. Data derived was validated against detailed field mapping at a scale of 1:5000. For more recent landslides, the modelling proved to be effective, accurately identifying 91% of the landslide both in terms of the location and extent. For the older landslides Pre 2000) the mapping was less effective, with misclassification as high as 24% particularly for smaller landslides. However, the use of these imagery does have great potential as they prove useful for mapping new landslides quickly and efficiently after landslide disaster and are much cheaper and quicker to acquire.
Landslides in Jamaica: Distribution, Cause, Impact and ManagementJamaica has one of the highest natural hazard risk exposures in the world, with more than 90% of the population exposed to two or more natural hazards. The island of Jamaica is particularly prone to multiple hazards, including hurricanes, earthquakes and slope instability, due to its geographical position (within the track of Atlantic hurricanes and its location on the Caribbean ‘tectonic’ plate) and its topography and geology (steep slopes with highly weathered material). Of these hazards, slope instability is the most common, affecting not only mountainous areas but also the coastal plains, where submarine landslides have been known to generate tsunamis. One such tsunami contributed to the destruction of the then capital city of Port Royal in 1692. Landslides are predominantly triggered by seismic activities and heavy rainfall associated with hurricanes and tropical depressions. These landslides have caused loss of lives, widespread destruction to the built and natural environment and long-term damage to the socio-economic development of the country. The slope instability problem is compounded by the lack of awareness of the impact by the general public, developers and planners, as well as uncontrolled and unplanned urbanization on marginal lands susceptible to slope failure.