Abstract

The Central Cordillera of Luzon in the Philippines is home to some of the most complex geology, active plate margin tectonism, heaviest rainfall and steepest terrain in the world. It also hosts a thriving agricultural community that has developed its agrarian, municipal and transport infrastructure in a landscape of marginal stability and extreme geomorphological sensitivity. The village of Pilando occupies a saddle on a prominent ridge where it is crossed by the Halsema Highway. Due to landslide displacements, both the highway and the village have been subsiding for several decades and many dwellings have had to be abandoned. From topographical survey and visual observation, average rates of settlement vary between approximately 0.1 and 0.4 myr−1. The apparent depth and areal extent of ground movement are such that attempts to stabilise the area would be both impracticable and uneconomic. Realignment and relocation are options that might be considered but many adjacent slopes are unstable or have failed in the past and those that haven't are highly sensitive to earthworks and drainage disturbance. Unfortunately, there are many areas of the Central Cordillera that suffer from similar slope instability problems. The interpretation of satellite imagery available on Google Earth, supported by geomorphological field observation, can assist in the delineation and assessment of these notably unstable areas for land use planning and slope management purposes.

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