One of the Department of Defense's most pressing environmental problems is the efficient detection and identification
of unexploded ordnance (UXO). In regions of highly magnetic soils, magnetic and electromagnetic sensors often detect
anomalies that are of geologic origin, adding significantly to remediation costs. In order to develop predictive models for
magnetic susceptibility, it is crucial to understand modes of formation and the spatial distribution of different iron
oxides. Most rock types contain iron and their magnetic susceptibility is determined by the amount and form of iron
oxides present. When rocks weather, the amount and form of the oxides change, producing concomitant changes in
magnetic susceptibility. The type of iron oxide found in the weathered rock or regolith is a function of the duration and
intensity of weathering, as well as the original content of iron in the parent material. The rate of weathering is controlled
by rainfall and temperature; thus knowing the climate zone, the amount of iron in the lithology and the age of the surface
will help predict the amount and forms of iron oxide. We have compiled analyses of the types, amounts, and magnetic
properties of iron oxides from soils over a wide climate range, from semi arid grasslands, to temperate regions, and
tropical forests. We find there is a predictable range of iron oxide type and magnetic susceptibility according to the
climate zone, the age of the soil and the amount of iron in the unweathered regolith.
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