Volcanic soils of Iceland

The parent materials of all Icelandic soils are volcanic in origin, and most of the soils are classified as Andosols. Iceland has the largest area of Andosols in Europe, and may have >5% of all Andosols in the world. A new classification scheme based on the World Reference Base (World Reference Base for Soil Resources. World Soil Resources Reports 84, FAO, Rome) is used to provide an overview of Icelandic volcanic soils. The data were acquired as part of a recently initiated effort to build a database for Icelandic soils, but are also partly based on data from the EU COST-622 action, a literature review and unpublished Icelandic research. The main soil types in Iceland are Histosols, Histic Andosols, Gleyic Andosols, Brown Andosols, Vitrisols and Leptosols. In the Icelandic language, a single term is used to refer to each soil type. This system reflects the dominant influence of eolian deposition and drainage conditions on the formation of Histosols and Andosols. The parent materials of Icelandic soils are mixtures of tephra layers and eolian sediments consisting mostly of volcanic glass. The steady flux of eolian sediments from unstable sandy deserts constantly recharges the surface with basaltic tephra materials. The Histosols (>20% C) have appreciable amounts of andic materials because of the eolian deposition. The Andosols (Histic, Gleyic and Brown Andosols) show characteristic properties of soils dominated by andic materials with allophane contents of up to 30%. Ferrihydrite commonly accounts for 5-15% of the soil. The contents of both allophane and ferrihydrite generally decrease with increasing organic C content of soil horizons, as organic matter inhibits allophane formation and iron tends to become reduced and lost in poorly drained locations. The Vitrisols are soils of desert surfaces with low organic content, but they usually meet criteria for andic materials with >30% glass and (Al+1/2Fe)(o)>0.4%. Cryoturbation is intense in Iceland, resulting in a range of geomorphic surface features. The cryoturbation is related to both climatic factors and the andic soil properties including high water retention and rapid hydraulic conductivity. (C) 2003 Elsevier B.V. All rights reserved.