Characterisation of a volcanic residual soil and its implications for large landslide phenomena : application to Tenerife, Canary Islands

Large landslides are common processes during the evolution of volcanoes and individual events can exceed several cubic kilometres in volume. Volcanic slope failures are a significant risk for the neighbouring population due to their huge volumes and great runout distances. Around the Canary archipelago, a total of seventeen deposits of large landslides have been found, and on Tenerife, seven large landslides have affected the subaerial and submarine morphology during the last ∼6 Ma. However, the causes of such mass movements are still poorly understood. This work analyses the events around the Canary Islands and focuses on the ones that occurred on Tenerife in order to obtain new insights into the mechanisms of large volcanic landslides. The study is divided into a first part that includes site investigations examining the general features favouring large-scale failures at volcanoes. The second part describes the laboratory tests used to analyse a residual soil that may be the potential slip surface of the slides on Tenerife. The site investigation revealed that regional tectonics and the climate have a significant influence on the spatial distribution of the landslides. Moreover, morphological and geological features such as deep fluvial canyons, a high coastal cliff and persistent dike intrusion may favour the initiation of slope failure. A typical residual soil sample from the lateral scarp of the La Orotava amphitheatre on Tenerife was studied by carrying out standard laboratory tests. The microstructure was analysed using environmental scanning electron microscopy and a particular bonding was found. This bonding was also detected by the geotechnical tests. Consolidation tests and direct shear tests revealed that the mechanical behaviour of the residual soil changes greatly if the bonding of the soil is broken. The bonded structure generally fails when the effective normal stress surpasses the yield strength of the bonding. In the case of large volcanic landslides with thicknesses up to several hundred meters, the high overburden easily exceeds this yield strength and generates a broken bonding. Therefore, volcanic residual soils, such as the one analysed in this study, are perfect candidates for the potential failure surfaces of large volcanic landslides. Referring to the La Orotava events, we assume that residual soil layers and morphological, geological and climatic features reduced the slope stability to critical conditions, whereas a strong earthquake associated with a caldera collapse episode may have finally triggered the landslide. The results obtained indicate that the residual soils play an important role in affecting the stability of volcano slopes and their destabilising influence significantly favours large-scale sliding. We suggest that the results obtained from this study can be applied to other locations since volcanic residual soils are common in volcanic areas.

[1]  B. Voight,et al.  Failure of volcano slopes , 1997 .

[2]  K. Wallace.  Structural behaviour of residual soils of the continually wet Highlands of Papua New Guinea , 1973 .

[3]  Robin T. Holcomb,et al.  Large landslides from oceanic volcanoes , 1991 .

[4]  J. Dieterich.  Growth and persistence of Hawaiian volcanic rift zones , 1988 .

[5]  W. Farrand,et al.  Geology of clays , 1970 .

[6]  D. Palacios.  The origin of certain wide valleys in the Canary Islands , 1994 .

[7]  T. Funck,et al.  Growth and destruction of Gran Canaria deduced from seismic reflection and bathymetric data , 1998 .

[8]  A. Ledesma,et al.  Conditions favouring catastrophic landslides on Tenerife (Canary Islands) , 1999 .

[9]  L. Siebert.  Large volcanic debris avalanches: Characteristics of source areas, deposits, and associated eruptions , 1984 .

[10]  A. Ecker.  Groundwater behaviour in Tenerife, volcanic island (Canary Islands, Spain) , 1976 .

[11]  Agust Gudmundsson,et al.  Vertical and lateral collapses on Tenerife (Canary Islands) and other volcanic ocean islands , 1997 .

[12]  D. Masson,et al.  Reply [to “Comment on “A giant landslide on the north flank of Tenerife, Canary Islands” by A. B. Watts and D. G. Masson”] , 1998 .

[13]  W. McGuire,et al.  Volcano instability: a review of contemporary themes , 1996, Geological Society, London, Special Publications.

[14]  J. Escartín,et al.  Morphometric interpretation of the northwest and southeast slopes of Tenerife, Canary Islands , 1997 .

[15]  T. L. Bas,et al.  Recurrent large‐scale landsliding on the west flank of La Palma, Canary Islands , 1999 .

[16]  L. Siebert.  Threats from debris avalanches , 1992, Nature.

[17]  Joan Martí,et al.  Stratigraphy, structure and geochronology of the Las Cañadas caldera (Tenerife, Canary Islands) , 1994, Geological Magazine.

[18]  D. Masson,et al.  A giant landslide on the north flank of Tenerife, Canary Islands , 1995 .

[19]  B. Mcguire,et al.  Volcano Instability on the Earth And Other Planets , 1996 .

[20]  A. Ledesma,et al.  Mechanical relationship between catastrophic volcanic landslides and caldera collapses , 2000 .

[21]  J. Dixon,et al.  Minerals in soil environments , 1990 .

[22]  B. Voight,et al.  Nature and mechanics of the Mount St Helens rockslide-avalanche of 18 May 1980 , 1983 .

[23]  M. Hürlimann.  Geotechnical analysis of large volcanic landslides: The La Orotava events on Tenerife,Canary Islands , 1999 .

[24]  J. Martí,et al.  Stratigraphy of the Bandas del Sur Formation: an extracaldera record of Quaternary phonolitic explosive eruptions from the Las Cañadas edifice, Tenerife (Canary Islands) , 1998, Geological Magazine.

[25]  P. Vaughan,et al.  Indexing the engineering properties of residual soil , 1988, Quarterly Journal of Engineering Geology.

[26]  T. Ui,et al.  Characterization of debris avalanche deposits in Japan , 1986 .

[27]  Juan Coello Aranda,et al.  Cronoestratigrafía del Macizo de Tigaiga: evolución de un sector del edificio Cañadas (Tenerife, Islas Canarias) , 1993 .

[28]  M. Canals,et al.  The most recent megalandslides of the Canary Islands: El Golfo debris avalanche and Canary debris flow, west El Hierro Island , 1997 .

[29]  W. Normark,et al.  Giant Hawaiian Landslides , 1994 .

[30]  David N. Petley,et al.  The mechanics of deep‐seated landslides , 1997 .

[31]  E. C. Ruddock.  Residual Soils of The Kumasi District in Ghana , 1967 .

[32]  V. Moon.  MICROSTRUCTURAL CONTROLS ON THE GEOMECHANICAL BEHAVIOUR OF IGNIMBRITE , 1993 .

[33]  M. Maccarini,et al.  A comparison of direct shear box tests with triaxial compression tests for a residual soil , 1993 .

[34]  Antonio Cendrero,et al.  Volcanic evolution of the island of Tenerife (Canary Islands) in the light of new K-Ar data , 1990 .

[35]  V. Araña,et al.  A large volcanic debris avalanche in the Pliocene Roque Nublo Stratovolcano, Gran Canaria, Canary Islands , 1994 .

[36]  N. Arnaud,et al.  REPEATED DEBRIS AVALANCHES ON TENERIFE AND GENESIS OF LAS CANADAS CALDERA WALL (CANARY ISLANDS) , 1999 .

[37]  M. Hürlimann,et al.  Evolution of the north flank of Tenerife by recurrent giant landslides , 2000 .

[38]  J. Lénat,et al.  The off-shore continuation of an active basaltic volcano: Piton de la Fournaise (Réunion Island, Indian Ocean); structural and geomorphological interpretation from sea beam mapping , 1989 .

[39]  J. Carracedo.  The Canary Islands: An example of structural control on the growth of large oceanic-island volcanoes , 1994 .

[40]  Richard M. Iverson,et al.  Can magma-injection and groundwater forces cause massive landslides on Hawaiian volcanoes? , 1995 .