KINEMATICS OF THE CERCA DEL CIELO, PUERTO RICO LANDSLIDE DERIVED FROM CONTINUOUS GPS OBSERVATIONS

Global Positioning System (GPS) technologies have been increasingly employed to monitor landslide movements. We demonstrate the use of high-precision GPS to study kinematics of a creeping landslide in the Cerca del Cielo community, Ponce, Puerto Rico. Both campaign and continuous GPS surveying methods were applied over a 2-year period. The landslide is mostly composed of chalk colluvium that formed at the base of a Miocene chalk cliff and extends down to depths of about 26 m. The slip surface lies beneath the chalk colluvium within a highly plastic, clayey residual soil that developed over the underlying weathered mudstone unit. The initial movements of this landslide were first manifested in the summer of 2007. GPS monitoring of this landslide started in March 2008. Our GPS observations suggest that the landslide’s continuous creep movement and accelerated surges are controlled by accumulated rainfall. A tropical disturbance in September 2008 dumped 50 cm rain on the landslide area over a 4-day period and temporarily accelerated the sliding, which generated a rapid displacement of 1 m horizontally and 0.5 m vertically. The landslide creep rate slowed markedly after this major surge and displacement. A prolonged moderate rainfall in November 2009 also temporarily accelerated the landslide movement. The southeast direction of the continuous sliding has remained steady over the past two years. The average rate of creep during 2009 was 0.5 cm/month. The landslide creep appears likely to continue in the future with periodic surges with rapid displacement induced by heavy rainfalls.