Appendix B: 



Glossary of Landform and Geologic Terms 



for Land Classification and Characterization 



Introduction 



This glossary of about 300 terms has been compiled to 

 provide a ready reference for biologists, plant scientists, 

 soil scientists, anu others who inventory, manage, and 

 plan the use of land and its associated resources. It may 

 be used to describe the setting of soils and vegetation. 

 Only generally accepted terms and definitions used to 

 describe the setting of a locale are included; colloquial- 

 isms have been avoided. More extensive lists are in stan- 

 dard technical dictionaries, glossaries, and encyclopedias. 

 Definitions of minerals and rocks, with few exceptions, 

 are not included; they are in technical dictionaries. The 

 purpose of this glossary is to standardize definitions used 

 by earth and biological scientists. 



A second, and equally important, purpose of this 

 glossary is to present definitions acceptable to the sug- 

 gested groups of users and other biological and earth 

 scientists. Readers are encouraged to submit proposals 

 for refined definitions and additional terms. 



Each definition is followed by a two- or three-letter 

 designation that indicates the reference work or individ- 

 ual consulted for that term. Italics signify that the source 

 definition has been modified. 



The references used most extensively for this glos- 

 sary were: Glossary of Geology (GG) edited by Bates and 

 Jackson (1980; Glossary of Selected Geomorphic and 

 Geologic Terms (HP) by Hawley and Parsons (1980); and 

 Landforms of the Basin and Range Province defined for 

 Soil survey (FFP) by Peterson (1981). The Dictionary of 

 Geological Terms (DGT) compiled by the American Geo- 

 logical Institute (1976), The Classification of Wetlands 

 and Deepwater Habitats of the United States (FWS) by 

 Cowardin and others (1979), The Glossary of Soil Science 

 Terms (GSST) compiled by the Soil Science Society of 

 America (1979), and Dr. Ray Daniels (RD) retired U.S. 

 Department of Agriculture, Soil Conservation Service 

 were also referenced. 



In addition to presenting definitions in the glossary, 

 numeric limits of slope classes have been identified. The 

 following gradient limits and slope classes have proven 

 useful in the National Cooperative Soil Survey; they are 

 suggested for use in descriptions of geomorphic features. 



Classes 



Slope gradient limits 



Simple slopes 



Complex slopes 



Lower 



Upper 

 Percent 



Nearly level 



Nearly level 







1-3 



Gently sloping 



Undulating 



1-3 



5-8 



Strongly sloping 



Rolling 



5-8 



10-16 



Moderately steep 



Hilly 



10-16 



20-30 



Steep 



Steep 



20-30 



45-65 



Very steep 



Very steep 



45-65 



None 



Diagrams depicting several landform features de- 

 fined in this glossary follow the definitions. 



Definitions 



Ablation till — Loose permeable till deposited during the 

 final downwasting of nearly static glacial ice. Lenses of 

 crudely sorted sand and gravel are common. (See glacial 

 till and moraine.) HP 



Active slope — A mountain or hill slope that is responding 

 to valley incision, and has detritus accumulated behind 

 obstructions, indicating contemporary transport of 

 slope alluvium. Slope gradients commonly exceed 45 

 percent. (See metastable slope.) HP 



Alluvial — Pertaining to material or processes associated 

 with transportation or deposition by running water. HP 



Alluvial cone — The material washed down mountain and 

 hill slopes by ephemeral streams and deposited at the 

 mouth of gorges in the form of a moderately steep, 

 conical mass descending equally in all directions from 

 the point of issue. HP 



Alluvial fan — A body of alluvium, with or without debris 

 flow deposits, whose surface forms a segment of a cone 

 that radiates downslope from the point where the stream 

 emerges from a narrow valley onto a less sloping sur- 

 face. Common longitudinal profiles are gently sloping 

 and nearly linear. Source uplands range in relief and 

 areal extent from mountains and plateaus to gullied 

 terrains on hill and piedmont slopes, (fig. B-l) HP 



Alluvial flat — A nearly level, graded, alluvial surface. FFP 



Alluvial plain — A landform comprised of the floodplain 

 or of a low gradient fan-delta built by a stream. It may 

 be modern or relict. FFP 



Alluvial terrace — (See stream terrace.) 



Alluvium — Unconsolidated clastic material deposited by 

 running water, including gravel, sand, silt, clay, and 

 various mixtures of these. HP 



Alpine — Characteristic of, or resembling the European 

 Alps, or any lofty mountain or mountain system, espe- 

 cially one so modified by intense glacial erosion as to 

 contain aiguiles, cirques, horns, etc. Implies high eleva- 

 tion, particularly above the tree line, and cold climate. 

 GG & DGT 



Anticline— A unit of folded strata that is convex upward. 

 In a single anticline, beds forming the opposing limbs 

 of the fold dip away from its axial plane. (See syncline 

 and monocline.) HP 



Arete — A narrow, jagged mountain crest, often above 

 the snowline, sculptured by alpine glaciers and formed 

 by backward erosion of adjoining cirque walls. HP 



Arroyo — The flat-floored channel of an ephemeral stream, 

 commonly with very steep to vertical banks cut in allu- 



32 



