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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 2, issue 1/2
Nat. Hazards Earth Syst. Sci., 2, 51–56, 2002
https://doi.org/10.5194/nhess-2-51-2002
© Author(s) 2002. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

Special issue: Assessing and mapping landslide hazards and risk

Nat. Hazards Earth Syst. Sci., 2, 51–56, 2002
https://doi.org/10.5194/nhess-2-51-2002
© Author(s) 2002. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  30 Jun 2002

30 Jun 2002

Landslides density map of S. Miguel Island, Azores archipelago

P. Valadão, J. L. Gaspar, G. Queiroz, and T. Ferreira P. Valadão et al.
  • Centro de Vulcanologia e Avaliação de Riscos Geológicos, Departamento de Geociências, Universidade dos Açores, Rua Mãe de Deus, 9501-801 Ponta Delgada, Portugal

Abstract. The Azores archipelago is located in the Atlantic Ocean and is composed of nine volcanic islands. S. Miguel, the largest one, is formed by three active, E-W trending, trachytic central volcanoes with caldera (Sete Cidades, Fogo and Furnas). Chains of basaltic cinder cones link those major volcanic structures. An inactive trachytic central volcano (Povoação) and an old basaltic volcanic complex (Nordeste) comprise the easternmost part of the island. Since the settlement of the island early in the 15th century, several destructive landslides triggered by catastrophic rainfall episodes, earthquakes and volcanic eruptions occurred in different areas of S. Miguel. One unique event killed thousands of people in 1522. Houses and bridges were destroyed, roads were cut, communications, water and energy supply systems became frequently disrupted and areas of fertile land were often buried by mud. Based on (1) historical documents, (2) aerial photographs and (3) field observations, landslide sites were plotted on a topographic map, in order to establish a landslide density map for the island. Data obtained showed that landslide hazard is higher on (1) the main central volcanoes where the thickness of unconsolidated pyroclastic deposits is considerable high and (2) the old basaltic volcanic complex, marked by deep gullies developed on thick sequences of lava flows. In these areas, caldera walls, fault scarps, steep valley margins and sea cliffs are potentially hazardous.

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