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Although the
area is underlain by basalt, most INEEL soil is derived from older
silicic volcanic and paleozoic rocks from the surrounding
mountains (McBride et al. 1978).
The basaltic uplands of the southern and eastern portions
of the area are covered by a thin veneer of eolian sediments.
Major episodes of loess deposition apparently occurred
between 10,000 and 70,000 years ago and between 140,000 and
200,000 years ago; little
loess has accumulated on the most recent flows of the upper Snake
River Plain, indicating that there has been no major deposition of
loess in the Holocene (Hackett and Smith 1992).
Because of the uneven, broken surface of the basalt, depths
of the silt loam and sandy loam soils vary from a few centimeters
on recent lava flows or exposed ridges of older flows to a couple
of meters in lower lying areas.
On the lee side of lava ridges, accumulation of sand on the
soil surface can improve water infiltration, increasing water
storage in the underlying fine-textured soil.
A similar phenomenon is observed north of the basalt flows
on the east side of the INEEL where numerous windrows of drifted
sand cap the underlying fine-textured ancient lake sediments.
Enhanced rates of infiltration and reduced evaporation on
the parallel dunes result in improved moisture availability to
plants compared to that of the intervening slacks (Shumar and Anderson 1986).
Changes in vegetation and surface albedo make these SW to
NE trending dunes readily apparent on the satellite image (back
cover) and the vegetation map (INEEL
Vegetation Map).
Alluvial soils
are found along the Big Lost River flood plain, on the alluvial
fans along the western side of the INEEL, and to the north where
the alluvial fan of Birch Creek extends onto the INEEL.
The alluvial fans often are covered with loess, but the
alluvial soils of the Big Lost River flood plain are often
gravelly on the surface and underlain by sandy loams.
The sandy textures of such soils resulted in the failure of
a network of irrigation canals established in the early 1900s (see
Ethnoecology). Most
eolian and alluvial soils at the INEEL are well drained.
The playas and
lakebed sediments of Pleistocene Lake Terreton generally are
fine-textured loams or clay loams with a relatively high clay
content. However,
well-drained lakebed soils derived from eolian and alluvial sands
also occur.
A comprehensive
survey of the soils at the INEEL has not been conducted;
however, the information from county surveys and numerous
other sources has recently been compiled by Olson et al. (1995).
Most INEEL soils are Aridisols, with Calciorthids being the most common great group;
Entisols, namely Torriorthents and Torrifluvents, and Mollisols,
including Calcixerolls and Haploxerolls, also are common.
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