(from Japanese ando, "black soil") 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
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.