Soils formed in volcanic ash or other volcanic ejecta.

Make up less than 1% of soils globally.

Unlike other soil orders, are dominated by glass and short-range-order colloidal weathering products.

As a result, Andisols have unique chemical and physical properties that include:

  • high water-holding capacity
  • very fertile








Bonner, Colorado


This area saw repeated flooding from glacial Lake Missoula, more than 13,000 years ago.

Soils are formed on outwash deposits.

Periodic ash-falls have mixed into the upper profile.

The soils are used for:

  • timber harvest
  • pastureland
  • irrigated cropland


The rapid permeability of the soil and underlying sediment have created aquifer contamination issues.




Iceland Andisol Landscape


Many highland landscapes of Iceland originally consisted of deep Andisols overlying glacial till

Centuries of overgrazing and the high susceptibility of these soils to wind erosion have exposed the glacial till promoting desertification.

An Andisol about 1.5 meters thick can be seen in the middle part of the photo.

It has been estimated that vegetative cover has been reduced by 60% since settlement because of overgrazing and erosion.

Desertification in Iceland



Iceland Andisol Near Thingvellir National Park


Formed in volcanic ash and eolian deposits.

High organic content.

Lacks soil horizon development.

Soil structure is weak.

Volcanic ash particles are mostly silt- and sand-sized, making the soil highly susceptible to wind erosion.