Pedogenesis in Andisols of Craters of the Moon National Monument and Preserve Karen L. Castenson 1 , Paul A. McDaniel 1 , and Dave Hoover 2 1 University of Idaho, Moscow; 2 Natural Resource Conservation Service, Boise, Idaho. 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 9.5 to 10.9, 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. Objectives 1. Determine the extent and distribution of tephra in the Craters of the Moon area. 2. Identify the major the sources and elemental compositions of tephra. 3. Assess tephra weathering and resultant secondary mineral phases. 4. Examine the influence of tephra on ecologically important soil properties such as water-holding capacity and nutrient sorption. Classification of volcanic glass identified at Craters of the Moon (adapted from Dahlgren et al., 1993) Clear 62.8 - 75.6% Rhyolitic, dacitic, and andesite. 1.49-1.51 Non-colored Light brown, red, & dark brown. 48.1 - 59.6% Basaltic andesite and basalt. >1.52 Colored Glass Colors Silica Content Parent Rock Composition Refractive Index Type of glass NaF pH v ersus AOD Al + 0.5Fe y = 0.4188x + 8.9365 R 2 = 0.4973 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 0.0 1.0 2.0 3.0 4.0 5.0 AOD Al + 0.5 Fe (%) NaF pH 0 cm 25 cm 50 cm Low Total Cover 0 cm 25 cm 50 cm High Total Cover Landscape displaying the unique vegetation pattern observed on some cinder cones. The limber/antelope bitterbrush (high total cover) community is on the left and the cinder garden (low total cover) community is on the right. Soil Formation on Cinder Cones and Cinder Gardens: Cinder fragments, or scoria, eject from an erupting volcano and are deposited on the surrounding landscape. A number of soils have formed in these materials resulting in the following classifications: •Ashy-skeletal over fragmental or cindery, aniso, glassy Xeric Vitricryands •Medial-skeletal, amorphic, frigid Lithic Vitrixerands •Medial, amorphic Xeric Vitricryands •Medial, amorphic, frigid Typic Vitrixerands Unique vegetation patterns have been observed on cinder cones and cinder gardens. Areas dominated by limber/antelope bitterbrush (high total cover) are composed of large, block type lava remnants interspersed with cinder gardens (low total cover). NaF pH relationship with poorly crystalline minerals (oxalate-extractable Al + 0.5Fe (%)) in soils sampled throughout the Preserve. (Soil Survey Staff, 1998). NaF pH measured ranged from 8.5 to 10.9. 0 10 20 30 40 5 Kilometers Legend COM Data Points % Alox + 0.5 Feox 0.23 - 0.40 0.41 - 1.00 1.01 - 2.00 2.01 - 3.69 ¯ 0 10 20 30 40 5 Kilometers ¯ Legend COM Data Points NaF pH 7.00 - 9.00 9.01 - 9.40 9.41 - 10.9 0 20 40 60 80 100 120 0.0 0.5 1.0 1.5 2.0 2.5 % depth (cm) Alox Feox Siox a 0 20 40 60 80 100 120 0.0 0.5 1.0 1.5 2.0 2.5 % depth (cm) Alox Feox Siox b 0 20 40 60 80 100 120 0.0 0.5 1.0 1.5 2.0 2.5 % depth (cm) Alox Feox Siox d 0 20 40 60 80 100 120 0.0 0.5 1.0 1.5 2.0 2.5 % depth (cm) Alox Feox Siox c Ammonium oxalate-extractable Al, Fe, and Si with depth at (a) site 1 low total cover, (b) site 1 high total cover, (c) site 2 low total cover, and (d) site 2 high total cover. Preliminary data suggests that andic soil properties are more abundant in the northern portion of the Great Rift that runs the length of Craters of the Moon. (a) NaF pH values greater than or equal to 9.4 indicate an abundance of poorly crystalline minerals and are assumed to be influenced by volcanic ash (Fieldes and Perrott, 1966). (b) Oxalate- extractable Al + 0.5Fe (%) is used to determine the presence of amorphous Al and Fe. Depending on percent volcanic glass, soils with oxalate-extractable Al + 0.5Fe (%) greater than 0.4 may be classified as andic soil materials (Soil Survey Staff, 2003). Due to the severe terrain, a representative sample of all landscapes in the Preserve has yet to be collected. Electron microprobe data for Ca, K, and Fe (sum=100%) in glass shards from soil sampled (a) in an aspen grove on a south aspect within the northern park boundary and (b) on a cinder cone in the northern part of the Preserve. Unlabeled points are tephra from unidentified events. CaO K 2 O Fe 2 O 3 0% 100% 0% 100% 0% 100% Tephra from local source Tephra from Cascade range (a) Tephra from local source CaO K 2 O Fe 2 O 3 0% 100% 0% 100% 0% 100% (b) Maps showing (a) the state of the Idaho outlining Craters of the Moon lava flows, (b) closer Landsat image of Craters of the Moon, and (c) Craters of the Moon National Monument and Preserve boundaries. References Dahlgren, R., S. Shoji, and M. Nanzyo. 1993. Mineralogical characteristics of volcanic ash soils. P.101-143. In S. Shoji et al. (eds.) Volcanic ash soils – Genesis, properties, and utilization. Elsevier, Amsterdam. Fieldes, M., and K.W. Perrott. 1966. The nature of allophane in soils. Part 3. Rapid field and laboratory test for allophane. N.Z. J. Sci. 9:623–629. Soil Survey Staff. 2003. Keys to soil taxonomy. 9 th ed. U.S. Gov. Print. Office, Washington, DC. ID MT Soil Formation on Lava Flows: Lithic Torrifolists have been described on lava flows that surround the cinder cones in the northern part of the Preserve. These soils are found under woody vegetation that have been able to root deep into the cracks in the lava. Organic material accumulates at the base of these plants and aids in the collection of wind-blown mineral material. Weathered volcanic ash with NaF pH of 10.3-10.7 was found on a lava flow with a radio carbon age of 2,076 years BP. The amount of time necessary for this ash to weather is greater than the age of the lava flow. It is hypothesized that this material has been deposited by wind after weathering elsewhere. The ash is protected from further translocation by a desert pavement of basalt that covers the soil surface. Volcanic ash protected under pieces of Blue Dragon lava. Organic materials accumulating below a limber pine growing on a recent lava flow. Black line measures 20 cm. Colored volcanic glass from soil located on Broken Top, a cinder cone in Craters of the Moon. 25μm 25μm