Weathering characteristics of some soils formed in White River Tephra, Yukon Territory, Canada

• Published in: Canadian journal of soil science 1999-11, Vol.79 (4), p.603-613
• Main Authors: Smith, C.A.S, Ping, C.L, Fox, C.A, Kodama, H
• Format: Article
• Language: English
• Subjects: cryosols; Gelisols; holocene soils; mineralogy; permafrost; physicochemical properties; soil classification; soil formation; soil morphological features; soil morphology; tephra; volcanic ash soils; weathering
• ISSN: 0008-4271; 1918-1841
• DOI: 10.4141/S98-066

Soil formation under a cold, dry climate on two Late Holocene (approximately 1800 yr BP and 1150 yr BP) volcanic tephra deposits was examined to evaluate trends and rates of soil weathering. Presently under mature boreal forest, these soils are underlain by permafrost within 1 m of the soil surface. The soils are composed of buried forest floor materials and layers of coarse ashy-pumiceous rhyodacite tephra up to 60 cm thick. The bulk density in all tephra-derived horizons is less than 0.90 Mg m −3 , water retention values for these horizons at 1500 kPa suction are less than 10% by weight. The mineralogy of the tephra-derived horizons is dominated by volcanic glass with lesser amounts of plagioclase, microcline and amphibole. Micromorphological investigation showed minor pitting of glass and feldspar grains and some oxyhydroxide coatings and Fe and Al-humus complexes. Several soil horizons meet glass composition, P retention and oxalate-extractable Fe and Al criteria established for andic soil material. However none of the profiles meet the thickness requirement to be classified as Andisol as specified in Soil Taxonomy. It is estimated that it would take >4000 yr under present climatic conditions to achieve such a degree of weathering. Key words: Tephra, Cryosol, andic, Yukon, Gelisol, glass