Recent volcanic activity at Craters of the Moon National Monument and Preserve, in southern Idaho, has provided the ideal location to observe early soil formation. Eight volcanic periods have been documented in this area between 15,000 and 2,000 years B.P., regularly occurring no more than 2,000 years apart. Lava flows, cinder cones, and a variety of tephra, including ash, pumice, and cinders comprise the landscape. Weathering of this tephra results in the classification of these soils as Andisols, which are distinguished from other soils on the basis of their unique chemical, physical, and mineralogical properties. Many of these properties have important edaphic implications in the high-desert environment of the Eastern Snake River Plain. Samples of the iron-rich-basaltic tephra were taken from five of the eight known eruptive periods ranging from 12,000 to 2,000 years B.P. Acid oxalate extractable iron and aluminum were measured on the samples to determine the relative amount and rate of weathering of tephra in a climate with an aridic moisture regime. The NaF pH of samples collected from various aged deposits ranged from 9.51 to 10.89, indicating an abundance of amorphous iron and aluminum. Soil moisture content was measured in profiles with varying amounts and types of tephra. It appears that the abundance, amount of weathering, and type of tephra have significant effects on the soil moisture and therefore, the establishment of particular vegetational communities.
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