Andisols
are soils that have formed in volcanic ash or other volcanic
ejecta. They differ from those of other orders in that they typically
are dominated by glass and short-range-order colloidal weathering products
such as allophane, imogolite, and ferrihydrite. As a result, Andisols
have andic properties -
unique chemical and physical properties that include high water-holding
capacity and the ability to 'fix' (and make
unavailable to plants) large quantities of phosphorus.
Globally, Andisols are the least extensive soil order and only account
for ~1% of the ice-free land area. They occupy ~1.7% of the US land
area, including some very productive forests in the Pacific Northwest
region.
Andisols are divided into
8 suborders: Aquands, Gelands, Cryands, Torrands,
Xerands, Vitrands, Ustands, and Udands.
Click here for more information
about these suborders. Click here to
view a map of their distribution in the US. |
