Pedogenesis at Craters of the Moon National Monument and Preserve, Idaho, USA


Vaughan, Karen Lynn.. (2008). Pedogenesis at Craters of the Moon National Monument and Preserve, Idaho, USA. Theses and Dissertations Collection, University of Idaho Library Digital Collections.

Pedogenesis at Craters of the Moon National Monument and Preserve, Idaho, USA
Vaughan, Karen Lynn.
Soil formation--Idaho--Craters of the Moon National Monument
Soil Science
Soil succession on lava flows occurs as a result of the accumulation of mineral and organic material as well as the weathering of lava into smaller rock fragments and soil particles. Variations in climate, organisms, relief, parent material, and time dictate the physical and chemical characteristics of the soils that form. With only thousands of years of weathering, basaltic lava in this cool, arid climate has not had sufficient time to weather into mineral soil material. At Craters of the Moon National Monument and Preserve (CROM) in southern Idaho, organic soils are the dominant soil type covering recent lava surfaces. Unsaturated organic soils, or Folists (Folic Histosols in World Reference Base (WRB)), occupying crevices and depressions on the lava surface and support vegetation adapted for life in this harsh environment. The parent material for organic soils is biologic rather than geologic in origin with parent vegetation growing in crevices supplying the necessary organic debris capable of providing nutrients and moisture. Soil acidity is directly influenced by the type of vegetation growing in the soil, with more acidic leaf litter creating low pH soils while more alkaline plant debris generates soil with more neutral pH. Compared to Folists of wetter climates, those forming at CROM have substantially higher bulk densities with a mean of 0.41 g cm{esc}p-3{esc}s. The influence of loessial mineral material likely accounts for the increased mineral content and subsequent increase in bulk density. As lava flow age increases above 13,000 yrs, soils are dominated by windblown mineral material, not necessarily of volcanic origin. Provided is an explanation of the progression of pedogenesis on relatively recent basaltic lava flows in an arid to semi-arid environment. The most recent glacial period and subsequent recession coincides with the increase in mineral soil accumulation on basaltic lava flows. The investigation of soil evolution across a chronosequence of basaltic tephra at CROM allows for the examination of physical, chemical, and mineralogical properties as a function of time. A well-dated series of basaltic cinder cones formed approximately 2.1, 6.9, and 13.9 ka was investigated. Representative parent material, coarse fragments, and soil samples were analyzed using a variety of selective dissolutions and total elemental digests. Coupled with traditional soil laboratory analyses, a mass balance approach provides a means of relating secondary mineral formation, weathering, and elemental dynamics. Additions, losses, transfers, and transformations of elements were examined within each soil profile and across the cinder cones. The highest degree of weathering was identified on the 13.9 ka profile followed by the 6.9 and 2.1 ka soils. Short-range ordered minerals, including allophane and ferrihydrite, dominate the colloidal fraction of all soils, with greatest total amounts in the oldest soil. The dominant weathering and soil-forming processes are the accumulation of organic carbon, weathering of rock fragments, desilication and loss of bases, redistribution of Fe, Al, and Ti, and the accumulation of secondary short-range order and crystalline minerals. The results from this study will enable researchers and land managers to better evaluate the ecological importance of soils forming on lava flows and cinder cones that provide essential habitat for wildlife and vegetation adapted for life in this cool, dry climate.
Thesis (Ph. D., Soil Science)--University of Idaho, June 2008.
Major Professor:
Paul McDaniel.
Defense Date:
June 2008.
Format Original:
xvi, 156 leaves :ill., map ;29 cm.

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