ANDOSOLS. Dr. Selim KAPUR University of Çukurova Departments of Soil Science and Archaeometry Adana, TURKEY firstname.lastname@example.org. Volcanism is not randomly distributed over the world. It is concentrated near plate boundaries where plate subduction or seafloor spreading takes place. Other
Dr. Selim KAPUR
University of Çukurova
Departments of Soil Science and Archaeometry
concentrated near plate boundaries where plate
subduction or seafloor spreading takes place. Other
occurrences are linked to deep mantle plumes that
reach the Earth's surface at distinct `hotspots'.
Figure 1 shows the geographic distribution of major
Landforms in volcanic regions are strongly influenced by the
chemical and mineralogical composition of the materials that
were deposited during eruptive phases. Volcanic rocks and
magmas are grouped according to their silica contents in
three main categories labeled `Rhyolite' (65-75% SiO2),
`Andesite' (65-55% SiO2) and `Basalt' (55-45% SiO2).
The mineralogical properties and chemical composition
(notably the contents of K2O, Na2O and CaO) distinguish
individual rock types. See Figure 2.This influences profoundly
the character and morphology of volcanic phenomena.
Figure 1. Volcanic regions of the world
The Reference Soil Group of the Andosols holds soils developed in volcanic materials.
Common international names are:
Andosols: FAO, Soil Map of the World,
Andisols' :USDA Soil Taxonomy,
Andosols'and `Vitrisols‘: France and `volcanic ash soils'.
ANDOSOL: Black soils of volcanic landscapes
From Japan an (black), and do (soil)
and structural instability
Volcanic ash, tuff, pumice, cinders and other volcanic ejecta
a vitric@ or an andic@ horizon starting within 25 cm from the soil surface; and
no diagnostic horizons (unless buried deeper than 50 cm) other than a histic@, fulvic@, melanic@, mollic@, umbric@, ochric@, duric@ or cambic@ horizon.
Common soil units
Vitric*, Silandic*, Aluandic*, Eutrisilic*, Melanic*, Fulvic*, Hydric*, Histic*, Leptic*, Gleyic*, Mollic*, Duric*, Luvic*, Umbric*, Arenic*, Placic*, Pachic*, Calcaric*, Skeletic*, Acroxic*, Vetic* , Sodic*, Dystric*, Eutric*, Haplic*.
One or more layers within 100cm Water ret 1500kPa of 100% or more
No andic horizon overlying a vittic horizon
Dingil, 2003. Ph.D. Thesis
Andosols having permafrost within 200cm of the surface
Andosols with gleyic properties within 100cm of the surface
Andosols lacking a smeary consistance or a texture which is silt loam or finer on the weighted average for all horizons within 100cm of the surface or both
Andosols having a mollic A-horizon
Andosols having an umbric A-horizon
1. Have 10% or more volcanic glass and other primary minerals in the fine earth fraction (250-50µm); and
ı. a bulk density less than 0.9kg dm3 or
ıı. Alox + ½Feox more than 0.4%, or
ııı. Phospahte retention more than 25%, and
3. Have a thickness of 30cm or more
ANDIC: An andic horizon must have all of the following
1. A bulk density at field capacity (no prior drying) of less than 0.9kg dm3; and
2. 10 percent or more clay and an (Alox + ½Feox) value2 in the fine earth fraction of 2 percent or more; and
3. 70 percent or more phosphate retention; and
4. less than 10 percent volcanic glass in the fine earth fraction; and
5. a thickness of 30 cm or more.
Undulating to mountainous, humid, semi-arid?, arctic to tropical regions with a wide range of vegetation types.
A-C or A-B-C profile. Rapid weathering of porous volcanic material resulting in accumulation of stable organo-mineral complexes, and minerals such as allophane, imogolite (Al2 SiO3(OH), and ferrihydrite
Allophane commonly occurs as very small hallow rings or spheres having diameters of approximately 35 - 50 Å. This morphology is characteristic of allophane, and can be used in its identification.
Ferrihydrite are hydrous iron oxides. Fe2O3.2FeOOH.2.6H2O. Secondary
mineral in an oxidizing environment, strongly dependant on pH. Functions as allophane. The organically bound Fe is most probably ferrihydrite –Fe.
Imogolite occurs as very small tubes having inside diameters of 10 Å and outside diameters of 20 Å. These tubes may be several µm in length, and often form bundles of two to several hundred tubes. Occasional branching of tubes may occur.
Presence of andic (rich in allophane) and vitric (rich in volcanic glass)
Dingil, M. 2003. Ph.D thesis)
Development depends on rapid chemical weathering of porous, permeable fine grained volcanic minerals + organic matter eg. Hydrolysis of microcline and augite yieldingsufficient Al and Fe.
KAlSi3O8 + 2 H2O = K+ + Al3+ + 3 SiO2 + 4 OH-
CaFeSi2O6 + 2 H2O = Ca2+ + Fe2+ + 2 SiO2 + 4 OH-
Fe2andAl3 form stable complexes with humus. However, Fe precipitates eventually to Ferrihydrite
Aluminum alone protects organic matter against BIODEGRADATION by developing Al-Humus complexes with high metal/organic ratioof limitedmobility
This induces accumulation of organic matter in top soil ie carbon sequestration developing a melanic surface horizon
The liberated silica in the weathering products partly yield allophanes and imogolite.
Thus Andosols are of binary composition indiacting the competition between Al humus complexes and formation of allophane. Allophane stays stable in weakly acid and neutral conditions whereas the Al-humus complexes are dominant in more acid environments.
The clay contents of Andosols changes over time particularly in the subsoil as allophane and imogolite are transformed to halloysite, kaolinite and at extreme acid conditions to gibsite. Eventually an Andosol may grade into a Luvisol or Podzol depending on precipitation
Typical (?) Andosols have an AC or ABC profile with a dark Ah-horizon (20 - 50 cm thick) on top of a brown B- or C-horizon.
The average organic matter content of the surface horizon (melanic) is between5-6% but the darkest profiles may contain more.
The surface horizon is very porous, very friable, and has a crumb or granular structure.
Smeary consistence or a texture which is silt loam or finer and feels greasy within 100cm.It may become almost liquid when rubbed, presumably because of sol-gel transformations under pressure (thixotropy) in Vitric Andosols.
Figure 2. NH4+ and Cl- retention curves measured in 0.01 M NH4Cl (0.1 M NH4Cl for montmorillonite). (a) montmorillonite; (b) halloysite; (c) allophane 905 (Al:Si=2:1, containing some imogolite); (d) allophane PA (Al:Si=1:1). Wada & Okamura, 1977)