Problems with Field Recognition of Spodosol Morphology in the Northwest United States

摘要

Thin ash mantles resulting from fairly recent eruptions of Mount St. Helens are extensive in the mountainous areas of the Pacific Northwest region of the United States. The spatial distribution of such ash mantles often overlaps with the extent of podzolized soils (Spo-dosols). The visual similarities between thin, unweathered volcanic ash mantles and the light colors of albic horizons can make it difficult to distinguish between the two materials. In addition, the reddish-brown color of the weathered ash that many of the soils form in can be mistaken for reddish-colored spodic horizons. These factors can make field identification of Spodosol morphology difficult, and may be partly responsible for the lack of attention podzolized soils have receivedacross parts of the region. We analyzed morphological and chemical data from 30 pedons sampled across the mountains of northern Idaho. These data indicate that properties such as texture and pH can provide a basis for correctly differentiating albic-spodic morphology from thin, unweathered volcanic ash layers overlying other substrates. Careful attention to these characteristics can improve the recognition of spodic morphology and gain a better understanding of the spatial distribution of these soils.