Landslide occurrence above the city of Philipsburg, Sint Maarten, Lesser Antilles

Abstract:

In the northern part of the Lesser Antilles volcanic arc, the island of Saint Martin/Sint Maartin is a remnant of the Eo-Oligocene “ancient arc”. It is constituted of Oligocene granodiorites intruding Eocene tuff deposits and andesitic lava flows. The eastern and western parts of the island are covered with Miocene limestone (Terre-Basses and Tintamarre islet). The igneous rocks outcrop in the central part of the island. As a response to tropical weathering, the coarse grain granodiorites are deeply eroded and form depressions. The very fine-grained tuffs are on the contrary forming crests and hilltops. At Fort Hill, immediately west of Philipsburg city, the metamorphised tuffs are extending North-South, following the direction of the contact with the granodiorite that form the base of the hill. The granodiorite is quartz bearing and its magmatic prismation is well developed. It shows fractures in both directions, parallel and perpendicular to the contact (i.e. north-south and east-west). Being in the hill-slope orientation, the contact parallel fractures are re-activated into normal faults. Several blocks are individualized, sliding downhill towards the first houses. In this work, we present a geological sketch of the Fort Hill landslide and its applications with regard to disaster mitigation. We also present ongoing satellite survey of deformation through time. The aim being to decipher in the signal the average quantity of sliding from the transient, hurricane related part.