LANDSLIDE EROSION IN THE CORDILLERA REAL, BOLIVIA

Troy A. Blodgett, Bryan L. Isacks, Jeff G. Masek, Arthur L. Bloom, and Andrew S. Warner (Cornell University, Ithaca, NY. 14853 USA)

Determining the area affected by landslides in regions relatively untouched by humans could help establish natural rates of erosion. The eastern escarpment of the Central Andes is topographically characterized by steep slopes. Below the treeline, landslides and mudflows represent the dominant mass wasting processes which are especially active during the rainy season. Field studies and air photos establish that below the treeline gullying also contributes to hillslope erosion, but only after vegetation is removed, as on landslide scars. Fresh landslide scars appear white on air photos from 1964, appear gray on air photos taken in 1975, yet remain distinguishable from surrounding vegetation on a Landsat Thematic Mapper (TM) image from 1987. Forest canopy closure rates of revegetating landslides are estimated to occur at between about 25 years and 40 years based on the multitemporal coverage by images and air photos and by tree ring analysis. Gaps in the canopy remain spectrally distinct from the surrounding forest during the revegetation process. A classified TM image shows that 7% of an anthropogenically undisturbed watershed on the flanks of the Cordillera Real is affected by landslides that occurred during the past 25-40 years.