Regolith and Soil

Geologically, the Appalachian Mountains are the oldest on the continent. Formed more than 200 million years ago, the rocks of these mountains show the effects of folding, faulting, and metamorphosis of Precambrian and Paleozoic rock beds. Because of this geologic disturbance, Precambrian sediments were not only thrust upward and outward, they were also transformed into a number of metamorphic rocks, including slate, schist, and gneiss.

Regolith is a layer of loose, heterogeneous material covering solid rock. Different regolith characteristics exist in the different provinces of the Southern Appalachian region. Regolith weathers into soil. The most common soil type of the Southern Appalachiansis what scientists call inceptisol, an acidic, shallow soil group developed primarily on shale and sandstone beds.

• Piedmont Province
  • Regolith: Most of the regolith in the Piedmont Province is saprolite, which is formed from decomposed rock. However, there are also substantial areas of colluvium,and other transported regolith.
  • Soil: The dominant soil order in the Piedmont is the Ultisol, comprised mainly of the great group Hapludults.
• Blue Ridge Province
  • Regolith: Although thick saprolite occurs in the Blue Ridge,it is not as prominent as in the Piedmont Province, both because it tends to be thinner and because surfaces in the Blue Ridge are commonly covered by colluvium.
  • Soil: The dominant soil order in the Blue Ridge Province is the Inceptisol. This order consists of relatively young soils that lack horizons of illuvial clay.
  • Mass Wasting and Foot-Slope Deposits: The most common mass-wasting process in the Blue Ridge is probably downslope movement of colluvium and residuum induced by windthrow of trees.
• Ridge and Valley Province
  • Regolith: The flanks of sandstone-capped ridges in this province generally are covered with bouldery colluvium, whereas valley floors underlain by limestone typically are covered with thick clayey residium called terra rossa. Valley floors underlain by shale show only thin residium.
  • Soil: The sandstone ridges are dominated by inceptisols whereas the valleys show mainly inceptisols.
  • Mass Wasting and Periglacial Features: mass wasting is most prominent on sandstone ridges. The boulder colluvium on the slopes generally is quite stable, but at rare intervals may be carried downslope by debris slides set off by intense rainfalls. There is evidence that this colluvium was somewhat less stable during Pleistocene cold periods, when frost creep and solifluction were much more pronounced.
  • Karst Landscapes: The Ridge and Valley, particularly the Great Valley, is one of the major karst regions of the United States. Many areas show sinkholes, sinking streams, and caves. Many famous commercial caverns occur in the Shenandoah Valley of Virginia, for example
• Appalachian Plateau Province
  • Regolith: The Appalachian Plateau is underlain mainly by sandstone conglomerate, and shale, and residuum on these clastic rocks tends to be thin. Where hills are capped with sandstone or conglomerate, hillslopes generally are covered with boulder colluvium.
  • Soil: Soils are mainly Ultisols (Hapludults, Fragiudults, and Ochraquults) and Inceptisols (chiefly Dystrochrepts). At higher elevations limited areas of Spodosols have developed over quartz-sandstone parent materials.
  • Mass Wasting: Compared to other Appalachian provinces, the Appalachian Plateau has the greatest abundance of conspicuous slope failures. Most failures are earthflows and slump-earth flows, which generally occur in shales and mudstones.
  • Karst Landscapes: Because little limestone occurs in this province, karst features are rare. Interestingly, however, near the escarpments of the Cumberland Plateau, where sandstone overlies limestone, some of the largest caverns in the U.S. occur.