The Physical Geography of North America

By Antony R. Orme | Go to book overview

9
Weathering and Soils
John C. Dixon

The landscape of North America is mantled with varying types and thicknesses of unconsolidated materials collectively referred to as regolith. Although much of the regolith has been transported, some of it has been derived in situ. This residual material is the product of the combined effects of chemical, physical, and biological weathering processes. These processes operating synergistically have transformed unstable primary minerals in rocks at and near Earth's surface to secondary products. The weathering residua accumulate under favorable geomorphic conditions to give rise to a wide variety of weathering-dominated landscapes.

Regolith is variably modified by a complex set of processes operating at and near the boundary layer. These processes encompass the addition, translocation, transformation, and removal of materials from the regolith, resulting in soil horizons with diagnostic physical, chemical, and biological characteristics. Spatial variability in the degree of soil development is determined by the variability of the soilforming factors of climate, organisms, relief, parent material, and time. These factors operate at different spatial and temporal scales, but at the continental scale reflect their influence in the mosaic of diverse soils of North America.

This chapter examines the weathering mantles of the North American landscape and discusses the major soil types, their origins, and their distributions across the continent.


9.1 Weathered Landscapes
of North America

Weathering-dominated landscapes, reflected in the occurrence of thick weathering mantles, occur extensively across large areas of North America (Hunt, 1986). The first section of this chapter focuses on the evolution of some of the distinctive landscapes in which weathering processes have dominated their development.

When the rate of weathering exceeds the rate of removal and transportation of weathered waste, then transportlimited landscapes develop with characteristic accumulations of weathered debris. These landscapes are not limited to the stable core of the continent but can also be found associated with mobile mountain belts and ancient collision zones.


9.1.1 Weathering Mantles of Arctic
and Alpine North America

Arctic North America Expansive areas of far northern North America are characterized by the accumulation of vast amounts of both unconsolidated, weathered bedrock debris known as felsenmeer and grus associated with deeply weathered continental basement bedrock. Throughout the

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