Soils that form in materials that are rich in volcanic ash are called Andisols (US) or Andosols (FAO), see also www.rala.is/andosol. Andosols have unique properties, some of which are responsible for their erosion susceptibility. The soils have low cohesion but can absorb large quantities of water (>100% on dry weight basis). This high water holding capacity intensifies freezing effects that result in solifluction, landslides, needle ice formation, and the formation of hummocks ("thufur"). The lack of cohesion make the soils extremely vulnerable to rain-splash and running water, especially when the soils are water saturated. The soils tend to be super-saturated in winter and spring when a frozen layer prevents drainage. Wind erosion is further intensified by lack of cohesion, stable silt-sized aggregates, and often low density of soil grains, especially coarse tephra grains (often about 1 g/cm3).
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Volcanic eruptions are frequent in Iceland, and volcanic ash deposits are widespread. In addition, there are vast unstable sandy areas near glacial margins and along floodplains of glacial rivers. The volcanic and glacial deposits are subjected to intense eolian activity. Where vegetation stabilizes eolian materials on the surface, they accumulate on top of the soils. The surface is therefore gradually rising, commonly at the rate of 0.1-1 mm each year. Direct deposition of volcanic ash also contributes to this deposition. The rate increased dramatically at the time of settlement. As the soils gradually became thicker, they also became less stable.
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The Agricultural Research Institute has produced a soil map in 1:250 000. A preliminary version may be seen on this page. The soil information underlying the map is drawn from published literature on Icelandic soils as well as unpublished data. Some general characteristics are presented in the Table below.
The soil classes used in the map are as follows:
Histosols are dominated by organic materials. A minimum of 20% C is chosen, as is used in WRB for Andosols (FAO, 1998). The organic materials are usually fibric in nature but are often more decomposed at lower depths The Icelandic Histosols can be deep and > 7 m profiles have been identified. The Histosols also receive considerable eolian additions of andic nature in contrast to most other arctic and sub-arctic Histosols and Histic Cryosols
Histic Andosols (HA)
Histic Andosols are found in poorly drained areas with relatively small eolian additions on an Icelandic scale, but enough to reduce the organic content below the 20% C limit for Histosols. As they are often far from eolian sources and active volcanoes, the eolian materials are fine grained. Typical allophane content is 210% and all the soils meet the (Al+½Fe)ox criteria for Andosols.
Gleyic Andosols (WA)Gleyic Andosols include a variety of wetland soils that have lower organic content than 12% in surface horizons. Allophane content is quite variable, from a few percent to > 20%. Oxidation/reduction features are often well expressed, especially at the boundaries of tephra layers, with distinct textural changes between the tephra and the soil above and below. This soil type is dominant in wetland areas in the central highlands where eolian deposition is relatively rapid.
Andic soil materials carry a distinct set of attribute soil properties that separate Andosols from other soils. Wetland Andosols are separated from other Andosols in Iceland as Gleyic Andosol at the highest taxonomic level.
Brown Andosols (BA)
Brown Andosols are the classical freely drained Andosols in Iceland, and perhaps the most studied to date. They are often 0.52 m thick and have considerable allophane content, especially where the soil environment is relatively stable (1530%). Ferrihydrite is also common, with Feox ranging from 1% to 8 %. Both dark basaltic and light-colored rhyolitic tephras are often quite distinct within the profiles.
Vitrisols include a range of soils that contain less than 1% organic carbon or less than 1% Siox. The surface usually has limited plant cover, often 510%. These surfaces are desert-like, and commonly have a stone pavement caused by frost heaving of coarse fragments. The Icelandic Vitrisols are rather unique, as these deserts exist under moist climatic conditions and temperatures that otherwise sustain vegetation growth (Boreal and Sub-Arctic climate). The characteristics of the Vitrisols in Iceland were recently reviewed by Arnalds and Kimble (2001). The soils are sandy and shallow and the mineralogy is dominated by volcanic glass. The soils often occur together with Leptosols, where the Vitrisols have developed in shallow eolian deposits.
Leptosols (L)Leptosols have not been studied to date, but they include lava surfaces with shallow eolian-andic mantle and scree slopes.
Cryosols are defined as soils containing permanent ice, or permafrost. Permafrost and palsas are found in some highland areas (Thorhallsdottir, 1997), but the extent of these soils has not been surveyed. The palsa areas are associated with Gleyic Andosols in the highlands.
The classification scheme is reflected by organic content and drainage. Brown Andosols (BA) are found in relatively dry positions, regardless of eolian deposition rate. Histic Andosols (HA) and Histosols are only found in wet poorly drained sites where eolian deposition is slow (H) or moderate (HA). Gleyic Andosols (HA) dominate poorly drained sites where eolian deposition is rapid, near active eolian sources or volcanoes.
Soil Type Symbol Icelandic term1 Criteria SoilTaxonomy WRB Histosol H Mójörð >20% C Histosol (Andic) Cryic Histosol Histic Andosol HA Svartjörð 12-20% C Aquand Gleyic and Histic Andosol Gleyic Andosol WA Blautjörð 1-12% C ox/redox features Aquand or Cryand Gleyic Andosol Brown Andosol BA Brúnjörð 1-12% C Cryand Haplic Andosol Vitrisol V Frumjörð <1% C; or <1%Siox and <2% C Cryand Vitric Andosol.
Also Arenosols and Leptosol
Cryosol C Frerajörð Permafrost Gelisol Cryosol Leptosol L Bergjörð Shallow2 Entisol Leptosol
1: Icelandic term is only suggestive. 2: Includes scree slopes.
Extent of Icelandic soil types (and complexes of soil types)
Soil type Symbol Extent (km2) % of soils Histosol H 1090 1.2 Histic Andosol HA 4920 5.5 Gleyic Andosol WA 2390 2.6 Brown Andosol BA 13360 14.8 Leptosol L 7310 8.1 Cambic Vitrisols MV 17640 19.5 Arenic Vitrisols SV 4550 5.0 Cryosols WA C-WA 140 0.2 BA-WA 28080 31.1 MV-SV 6000 6.6 SV-L 4790 5.3 Total 90270 100
(Glaciers and lakes not included)
Typical range for selected soil properties
Type BD(g cm-3) C (%) pHH2O pHNaF Alox(%) Feox(%) Siox(%) Histosol (H) 0.15-0.4 20-40 4-5.5 9-10.5 0.7-1.6 0.8 0.2 Histic Andosol (HA) 0.2-0.4 13-18 4.5-5.5 9-10.5 1-3 1-5 0.4-1 Gleyic Andosol (WA) 0.3-0.8 1-12 4.5-7.2 10-11 1.3-4 1-7 1-1.7 Brown Andosol (BA) 0.5-0.8 2-7 5.5-7.5 9.5-11.5 1.3-7 1-8 0.4-5 Vitrisol (V) 0.8-1.2 <1 7-7.9 9 0.4-2 0.4-3 0.4-3
Last updated on 02.09.2004 by EG