Andosols are

soils Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by restri ...

found in

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

areas formed in volcanic tephra. In some cases Andosols can also be found outside active volcanic areas. Andosols cover an estimated 1–2% of Earth's ice-free land surface. Andosols are a Reference Soil Group of the

World Reference Base for Soil Resources The World Reference Base for Soil Resources (WRB) is an international soil classification system for naming soils and creating legends for soil maps. The currently valid version is the fourth edition 2022. It is edited by a working group of the I ...

(WRB). They are closely related to other types of soils such as Vitrosols, Vitrandosols, Vitrons and Pumice Soils that are used in different soil classification systems. The name comes from Japanese ( 'dark') and ( 'soil'), synonymous with (). In the

USDA soil taxonomy USDA soil taxonomy (ST) developed by the United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate Soil classification, classification of soil types according to several parameters (most commonly their p ...

(ST), many Andosols belong to the order of the Andisols. However, the definitions are different. Some Histosols (WRB) belong to the Andisols (ST), and some Andosols (WRB) belong to the Inceptisols (ST). Andosols typically develop in parent materials containing high proportions of

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

. If significant amounts of glasses are still present, they show vitric properties and receive the Vitric qualifier. With advanced weathering of the glasses, they show andic properties. There are two possibilities of soil formation. In more acidic tephras in humid climates, complexes of organic matter with Al ions develop, and the Andosols are characterized by the Aluandic qualifier. If the tephras are more basic or the climate is dry, amorphous

colloid A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others exte ...

al materials, including

allophane Allophane is an amorphous to poorly crystalline hydrous aluminium silicate clay mineraloid. Its chemical formula is Al2O3·(SiO2)1.3-2·(2.5-3)H2O. Since it has short-range atomic order, it is a mineraloid, rather than a mineral, and can be ident ...

and imogolite develop, and the Andosols are given the Silandic qualifier. In both cases, they contain many

ferrihydrite Ferrihydrite (Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hydro ...

and have a bulk density ≤ . Silandic Andosols are very fertile except in cases where

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

is easily fixed (this sometimes occurs in the tropics). They can usually support intensive cropping, with areas used for wet

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

supporting some of the densest populations in the world. Other Andosol areas support crops of

fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...

maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...

tea Tea is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of '' Camellia sinensis'', an evergreen shrub native to East Asia which probably originated in the borderlands of south-western China and nor ...

coffee Coffee is a beverage brewed from roasted, ground coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content, but decaffeinated coffee is also commercially a ...

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

. In the Pacific Northwest USA, Andosols support very productive

forest A forest is an ecosystem characterized by a dense ecological community, community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, ...

s. Andosols occupy ~1-2% of global ice-free land area. Most occur around the

Pacific Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a tectonic belt of volcanoes and earthquakes. It is about long and up to about wide, and surrounds most of the Pa ...

, with the largest areas found in central

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...

Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

, the

Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...

US, Japan,

and

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

North Island The North Island ( , 'the fish of Māui', historically New Ulster) is one of the two main islands of New Zealand, islands of New Zealand, separated from the larger but less populous South Island by Cook Strait. With an area of , it is the List ...

. Other areas occur in the

East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. It was formerly considered to be part of a l ...

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

and

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

. They are the most common type of soil in the

Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

Andosols are known from areas far from present-day volcanic activity and have in some cases been dated as far back as the

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of t ...

1.5 billion years ago.

Important qualifiers

*Vitric – Andosols with limited soil formation, still containing significant amounts of volcanic glasses. *Aluandic – Andosols with advanced soil formation containing many complexes of organic substances and aluminium. *Silandic – Andosols with advanced soil formation containing many allophanes and imogolites.

References

External links

Profile photos (with classification)
WRB homepage
Profile photos (with classification)
IUSS World of Soils {{Soil type Pedology Types of soil Volcanic soils

Important qualifiers

See also

References

Further reading

External links