Browsing by Autor "Reginald L. Hermanns"

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Changes in ground deformation prior to and following a large urban landslide in La Paz, Bolivia, revealed by advanced InSAR
(Copernicus Publications, 2019) Nicholas J. Roberts; Bernhard Rabus; John J. Clague; Reginald L. Hermanns; Marco-Antonio Guzmán; E. Minaya
Abstract. We characterize and compare creep preceding and following the complex 2011 Pampahasi landslide (∼40 Mm3±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 remobilized deposits of an ancient complex landslide in weakly cemented, predominantly fine-grained sediments and affected ∼1.5 km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8 cm a−1 and localized parts of the scarp area showed displacements of up to 14 cm a−1. Changes in deformation in the 10 months following the landslide demonstrate an increase in slope activity and indicate that stress redistribution resulting from the discrete failure decreased stability of parts of the slope. During that period, most of the landslide toe and areas near the head scarp accelerated, respectively, to 4–14 and 14 cm a−1. 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 optical satellite images, reveal complex slope activity; kinematically complex, steady-state creep along pre-existing sliding surfaces accelerated in response to heavy rainfall, after which slightly faster and expanded steady creeping was re-established. 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; such details are especially useful where knowledge of landslide extent and activity is limited. Characterizing slope activity 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.
Changes in ground deformation prior to and following a large urbanlandslide in La Paz, Bolivia revealed by advanced InSAR
(2018) Nicholas J. Roberts; Bernhard Rabus; John J. Clague; Reginald L. Hermanns; Marco-Antonio Guzmán; E. Minaya
Abstract. We characterize and compare creep preceding and following the 2011 Pampahasi landslide (∼ 40 Mm3 ± 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 ∼ 1.5 km2 of suburban development. During the 30 months preceding failure, about half of the toe area was creeping at 3–8 cm/a and localized parts of the scarp area showed displacements of up to 14 cm/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 14 cm/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.
Recent Landslide Activity in La Paz, Bolivia
(2014) Nicholas J. Roberts; Bernhard Rabus; Reginald L. Hermanns; Marco-Antonio Guzmán; John J. Clague; E. Minaya
Supplementary material to "Changes in ground deformation prior to and following a large urbanlandslide in La Paz, Bolivia revealed by advanced InSAR"
(2018) Nicholas J. Roberts; Bernhard Rabus; John J. Clague; Reginald L. Hermanns; Marco-Antonio Guzmán; E. Minaya
The 2011 Pampahasi landslide is one of seven historical landslides exceeding 1 Mm 3 in the La Paz area.Landslides of possibly similar size to the 2011 event happened in 1582 and 1873 in the southwest part of the La Paz valley system, but little is known of these events aside from sparse written accounts.The first event affected an area of 2 km 2 or more and buried the villages of Canoma and Ango Ango, which were likely located in Llojeta Valley (Fig. S1).This landslide claimed about 200 lives (Cabeza de Vaca, 1586; transcribed in Jiménez de la Espada, 1965, p. 342-351 andin Arispe, 2011).The second event involved extensive ground movement over an area of about 8 km 2 (Markham, 1874) and more rapid, localized movement that destroyed an area named Tembladerani (Markham, 1874) located southwest of the city centre, causing 32 deaths (Crespo, 1902).Its location may correspond to the modern area of the city called Tembladerani (Fig. S1), although Dobrovolny (1962) applies this name to a landslide deposit in Llojeta Valley.The loss of life from these two events suggests velocities exceeding several metres per second or, at the very least, a lack of prompt evacuation.Four smaller landslides happened in the twenty-first century in the Llojeta and Allpacoma valleys near the margins of the La Paz and Achocalla basins (Hermanns et al., 2012; Fig. 1B); they destroyed about 51 homes but did not claim any lives (Roberts, 2016) (Table S1).Most of these failures involved weakly lithified, fine-grained sediments of the middle part of the La Paz Formation, including large areas that had been previously mobilized by large paleolandslides.