finer particles have been removed by running water or 

 wind. (See stone line and desert pavement.) HP 



Escarpment — A relatively continuous and steep slope or 

 cliff breaking the general continuity of more gently 

 sloping land surfaces and produced by erosion or fault- 

 ing. The term is more often applied to cliffs produced 

 by differential erosion and it is commonly used synon- 

 ymously with "scarp." HP 



Esker — A long, narrow, sinuous, steep-sided ridge com- 

 posed of irregularly stratified sand and gravel that was 

 deposited by a subsurface stream flowing between ice 

 walls or in an ice tunnel of a retreating glacier, and was 

 left behind when the ice melted. Eskers range in length 

 from less than a kilometer to more than 160 km, and in 

 height from 3 to 30 m. (See glaciofluvial deposits.) HP 



Estuary — (a) The seaward end or the widened funnel- 

 shaped tidal mouth of a river valley where fresh water 

 comes into contact with seawater and where tidal ef- 

 fects are evident; for example, a tidal river, or a par- 

 tially enclosed coastal body of water where the tide 

 meets the current of a stream, (b) A portion of an 

 ocean, as a firth or an arm of the sea, affected by fresh 

 water; for example, the Baltic Sea. (c) A drowned river 

 mouth formed by the subsidence of land near the coast 

 or by the drowning of the lower portion of a nonglacial 

 valley due to the rise of sea level. GG 



Exhumed — Pertaining to formerly buried landforms, 

 geomorphic surfaces or paleosols that have been re- 

 exposed at the ground surface by erosion of the cover- 

 ing mantle. (See relict.) HP 



Extrusive — Denoting igneous rocks derived from deep- 

 seated molten matter (magmas) emplaced on the earth's 

 surface. (See intrusive and volcanic.) HP 



Facies (stratigraphy)— The sum of all primary lithologic 

 and paleontologic characteristics exhibited by a sedi- 

 mentary rock and from which its origin and environ- 

 ment of formation may be inferred; the general nature 

 or appearance of a sedimentary rock produced under a 

 given set of conditions; a distinctive group of charac- 

 teristics that distinguished one group from another 

 within a stratigraphic unit (for example, contrasting 

 river-channel facies and overbank flood plain facies in 

 alluvial valley fills). HP 



Fall line — An imaginary line or narrow zone connecting 

 the water falls on several adjacent or near-parallel 

 rivers, marking the points where these rivers make a 

 sudden descent from an upland to a lowland, as at the 

 edge of a plateau; specifically, the Fall Line marking 

 the boundaries between the ancient, resistant crystal- 



line rocks of the Piedmont Plateau and the younger, 

 softer sediments of the Atlantic Coastal Plain of the 

 eastern U.S. It also marks the limit of navigability of 

 the rivers. A synonym for fall line is fall zone. GG 



Fan apron — A sheet-like mantle of relatively young allu- 

 vium covering part of an older fan piedmont (and, 

 occasionally, alluvial fan) surface. It somewhere buries 

 a pedogenic soil which can be traced to the edge of the 

 fan apron where the soil emerges as the land surface, or 

 relict soil. No buried soils should occur within a fan- 

 apron mantle; rather, they separate mantles, (fig. B-5) 

 FFP 



Fan piedmont — The most extensive major landform of 

 most piedmont slopes, formed by the lateral coales- 

 cence of mountain-front alluvial fans downslope into 

 one generally smooth slope without the transverse 

 undulations of the semi-conical alluvial fans and by 

 accretion of fan aprons. (See bajada.) (figs. B-3, B-4, 

 and B-5) FFP 



Fan terrace — A relict alluvial fan, no longer a site of 

 active deposition, incised by younger and lower alluvial 

 surfaces. An abandoned former fan surface. HP 



Fault — A fracture or fracture zone of the earth with dis- 

 placement along one side in respect to the other. HP 



felsenmeer— Block field. GG 



Fen — Waterlogged, spongy ground containing alkaline 

 decaying vegetation, characterized by reeds, that de- 

 velops into peat. It sometimes occurs in sinkholes of 

 karst regions. (See bog.) GG 



Flood plain — The nearly level alluvial plain that borders 

 a stream and is subject to inundation under flood-stage 

 conditions unless protected artificially. It is usually a 

 constructional landform built of sediment deposited 

 during overflow and lateral migration of the stream. HP 



Flood-plain landforms — A variety of constructional and 

 erosional features produced by stream channel migra- 

 tion and flooding (for example, backswamps, braided 

 channels and streams, flood plain splays, meander, 

 meander belt, meander scrolls, oxbow lakes, natural 

 levees, and valley flats). HP 



Flood-plain playa — A component landform consisting of 

 very low gradient, broad, barren, axial-stream channel 

 segments in an intermontane basin. It floods broadly 

 and shallowly and is veneered with barren fine textured 

 sediments that crust. Commonly, a flood plain playa is 

 segmented by transverse, narrow bands of vegetation, 

 and it may alternate with ordinary, narrow or braided 

 channel segments. FFP 



Flood-plain splay — Small alluvial fans formed where a 

 flooding stream breaks through a levee (natural or arti- 



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