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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/nhess-2018-211
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/nhess-2018-211
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Aug 2018

Research article | 13 Aug 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Natural Hazards and Earth System Sciences (NHESS).

Changes in ground deformation prior to and following a large urban landslide in La Paz, Bolivia revealed by advanced InSAR

Nicholas J. Roberts1, Bernhard T. Rabus2, John J. Clague1, Reginald L. Hermanns3,4, Marco-Antonio Guzmán5, and Estela Minaya6 Nicholas J. Roberts et al.
  • 1Department of Earth Sciences, Simon Fraser University, 8888 University Drive, Burnaby, Canada, V5A 1S6
  • 2School of Engineering Science, Simon Fraser University, 8888 University Drive, Burnaby, Canada, V5A 1S6
  • 3Geological Survey of Norway, P.O. Box 6315 Sluppen, Trondheim, Norway, 7490
  • 4Department of Geoscience and Petroleum, Norwegian University of Science and Technology, Trondheim, Norway, 7491
  • 5Instituto de Investigaciones Geológicas, Universidad Mayor de San Andrés, Pabellon 3, Campus Universitario Cota Cota, La Paz, Bolivia, 35140
  • 6Observatorio San Calixto, Indaburo 944, La Paz, Bolivia, 12656

Abstract. We characterize and compare creep preceding and following the 2011 Pampahasi landslide (∼40Mm3±50%) in the city of La Paz, Bolivia, using spaceborne RADAR interferometry (InSAR) that combines displacement records from both distributed and point scatterers. The failure remobilised deposits of an ancient landslide in weakly cemented, predominantly fine-grained sediments and affected ∼1.5km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8cm/a and localized parts of the scarp area showed displacements of up to 14cm/a. Changes in deformation in the 10 months following the landslide are contrary to the common assumption that stress released during a discrete failure increases stability. During that period, most of the landslide toe and areas near the headscarp accelerated, respectively, to 4–14 and 14cm/a. The extent of deformation increased to cover most, or probably all, of the 2011 landslide as well as adjacent parts of the slope and plateau above. The InSAR-measured displacement patterns – supplemented by field observations and by optical satellite images – indicate that kinematically complex, steady-state creep along pre-existing sliding surfaces temporarily accelerated in response to heavy rainfall, after which the slope quickly achieved a slightly faster and expanded steadily creeping state. This case study demonstrates that high-quality ground-surface motion fields derived using spaceborne InSAR can help to characterize creep mechanisms, quantify spatial and temporal patterns of slope activity, and identify isolated small-scale instabilities. Characterizing slope instability before, during, and after the 2011 Pampahasi landslide is particularly important for understanding landslide hazard in La Paz, half of which is underlain by similar, large paleolandslides.

Nicholas J. Roberts et al.
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Short summary
Landslides risk is high in La Paz, Bolivia, due to topography, geology, and urban growth. We quantify creep before and after the city’s largest modern landslide using spaceborne InSAR. Creep of ancient landslide deposits forming the slope increased in rate and extent following failure, calling into question the common assumption that slopes stabilize after failure. Landslide risk in La Paz, which is underlain by many large ancient failures, may be even greater than previously thought.
Landslides risk is high in La Paz, Bolivia, due to topography, geology, and urban growth. We...
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