Assessing Landslide Hazard in the High City of Antananarivo, Madagascar (UNESCO Tentative Site)

Abstract

Built on the hilltop of a granite ridge rising above the Ikopa River valley (the Analamanga Hill), the High City of Antananarivo (Madagascar) is renowned for its baroque-style palaces the Rova royal complex and gothic cathedrals dating back to the nineteenth Century, and therefore is part of the UNESCO Tentative List. Due to the frequent cyclonic heavy cyclonic rain, geological and geomorphological conditions, and a general lack of urban planning the study area is particularly prone to landslides (as shown by events of the winter of 2015, 2018 and 2019). As a first step towards understanding quantitative landslide risk, the geological, geomorphological, geotechnical features, as well as landslide phenomena were defined in an integrated landslide hazard assessment. Results show that the main factors affecting landslides are slope, lithology, creek-gully erosion and anthropogenic activities, while most of the landslide events are clearly triggered by heavy rainfall events. Thematic maps produced by this study are fundamental land-use management tools to be applied as a first step towards a geo-hydrological risk reduction strategy by the institutions and actors involved in the protection and conservation of the High City.