Volcanic-ash soils in New Zealand

45 refs; 9 figs; 4 tables; 1 map

Soils formed from shower deposits of holocene age are extensive and have characteristic properties of friability, fine granular structure, deep humic topsoils, and slippery non-stick clays. The clays are chiefly amorphous, and are responsible for the notable properties of free drainage, high moisture retention, low bulk density, and critical limits of stability under pressure. The development of these characteristics increases with time up to about 15, 000 years and then decreases with the crystallisation of the clays to halloysite. Soils formed from the late Pleistocene volcanic ashes are high in halloysite clay, and with increasing age resemble soils formed frm marine sedimentary rocks. Differing degrees of development of the characteristics are shown in the soil classification. The soils from volcanic ash are widely used for crop, pasture, or forestry production. (auth)