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Volume 6, issue 2
Solid Earth, 6, 783-797, 2015
https://doi.org/10.5194/se-6-783-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Solid Earth, 6, 783-797, 2015
https://doi.org/10.5194/se-6-783-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 26 Jun 2015

Research article | 26 Jun 2015

Volcanic soils and landslides: a case study of the island of Ischia (southern Italy) and its relationship with other Campania events

S. Vingiani1, G. Mele2, R. De Mascellis2, F. Terribile1, and A. Basile2 S. Vingiani et al.
  • 1Department of Agricultural Sciences, University of Naples Federico II, Portici NA, Italy
  • 2National Research Council, Institute of Agriculture and Forestry in the Mediterranean (CNR ISAFOM), Ercolano NA, Italy

Abstract. An integrated investigation was carried out on the volcanic soils involved in the landslide phenomena that occurred in 2006 at Mt. Vezzi on the island of Ischia (southern Italy). Chemical (soil pH, organic carbon content, exchangeable cations and cation exchange capacity, electrical conductivity, Na adsorption ratio and Al, Fe and Si forms), physical (particle and pore size distribution, pore structure), hydrological (soil water retention, saturated and unsaturated hydraulic conductivity), mineralogical and micromorphological analyses were carried out for three soil profiles selected in two of the main head scarps.

The studied soils showed a substantial abrupt discontinuity in all the studied properties at the interface with a buried fine ash layer (namely, the 2C horizon), that was only marginally involved in the sliding surface of the landslide phenomena. When compared to the overlying horizons, 2C showed (i) fine grey ash that is almost pumice free, with the silt content increasing by 20 %; (ii) ks values 1 order of magnitude lower; (iii) a pore distribution concentrated into small (15–30 μm modal class) pores characterised by a very low percolation threshold (approximately 15–25 μm); (iv) the presence of expandable clay minerals; and (v) increasing Na content in the exchange complex. Most of these properties indicated that 2C was a lower permeability horizon compared to the overlying ones. Nevertheless, it was possible to assume this interface to be an impeding layer to vertical water fluxes only by the identification of a thin (6.5 mm) finely stratified ash layer, on top of 2C, and of the hydromorphic features (e.g. Fe / Mn concretions) within and on top of the layer. Although Mt. Vezzi's soil environment has many properties in common with those of other Campania debris-mudflows (e.g. high gradient, north-facing slope, similar forestry, and volcanic origin of the parent material), the results of this study suggest a more complex relationship between soil properties and landslides and emphasise the role of vertical discontinuities as noteworthy predisposing factors.

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An integrated soil study was carried out on landslides which have occurred on the steep northern slopes of Mt. Vezzi on the island of Ischia (Italy). The studied soils showed a substantial abrupt discontinuity in all the studied properties along a buried fine ash layer (namely, the 2C horizon). Nevertheless, only the identification of a layer of thin, finely stratified ash on the top of 2C, by optical microscopy, enabled us to assume this interface to be an impeding layer for water fluxes.
An integrated soil study was carried out on landslides which have occurred on the steep northern...
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