| Abstract: | Although desirable for a reliable hazard assessment, rate estimates of landslide motion rarely combine a good time resolution and a sufficiently long time of observation. Here, both angles are tackled for the Manaihan landslide (East Belgium), dramatically reactivated in September 1998. I monitored the landslide displacements by repeated Global Positioning System (GPS) surveys from 1999 to 2005. Two digital elevation models were also produced, one of the landslide topography in 1999 by GPS and a second by stereophotogrammetry from aerial photographs of 1953. Subtracting one model from the other, I mapped the height changes within the landslide over the 1953–1999 period. All measurements consistently showed that, beyond the sudden ～1.5 m slip of September 1998, the landslide moved at a mean rate of c. 20 cm yr?1 since 1980. Most displacements occurred around the winter's end, when long‐lasting precipitation combined with minimal evaporation and occasional intense daily rainfall. The motions are spatially determined by seepage from a broken sewage pipe inducing local high pore pressures. Terra Nova, 18, 290–298, 2006 |
