lacustrine deposit
clastic sediments and chemical precipitates deposited in lakes. HP

lagoon
[coast] a shallow stretch of salt or brackish water, partly or completely separated from a sea or lake by an offshore reef, barrier island, sand or spit. GG. [relict landform] a nearly level, filled trough or depression behind the longshore bar on a barrier beach and built by a receding pluvial or glacial lake. compare - sewage lagoon. FFP

lahar
the process, associated sediments or resultant landform characterized by a mudflow composed chiefly of volcaniclastic materials on or near the flank of a volcano. the debris carried in the flow includes pyroclastic material, blocks from primary lava flows, and epiclastic material. thick flows can exhibit a crude (poorly sorted) upward-fining sediment sequence. compare - mudflow. SW & GG

lake [water]
an inland body of permanently standing water fresh or saline, occupying a depression on the Earth's surface, generally of appreciable size (larger than a pond) and too deep to permit vegetation (excluding subaqueous vegetation) to take not completely across the expanse of water. GG

lakebed
a) [relict] The flat to gently undulating ground underlain or composed of fine-grained sediments deposited in a former lake.
b) The bottom of a lake; a lake basin. GG

lake plain
a nearly level surface marking the floor of an extinct lake filled by well-sorted, generally fine-textured, stratified deposits, commonly containing varves. GG

lakeshore
the narrow strip of land in contact with or bordering a lake; especially the beach of a lake. GG

lake terrace
a narrow shelf, partly cut and partly built, produced along a lake shore in front of a scarp line of low cliffs and later exposed when the water level falls. GG

lamella
a) [soil] a thin (< 7.5 cm thick), discontinuous or continuous, generally horizontal layer of fine material (especially clay and iron oxides) that has been pedogenically concentrated (illuviated) within a coarser (e.g. sandy), eluviated layer (several centimeters to several decimeters thick). compare - lamina. SW & ST
b) [mineralogy] a thin scale, leaf, lamina, or layer, e.g. one of the units of a polysynthetically twinned mineral, such as plagioclase. GG

lamina
(noun) the thinnest recognizable layer (commonly < 1 cm thick) of original deposition in a sediment or sedimentary rock, differing from other layers in color, composition, or particle size. several laminae constitute a bed. compare - lamella. GG

lamination
(not recommended) see lamina.

landfill
(see sanitary landfill). compare - dump.

landform
any physical, recognizable form or feature on the earth's surface, having a characteristic shape and range in composition, and produced by natural causes; it can span a wide range in size (e.g., dune encompasses both parabolic dune, which can be several tens-of-meters across, as well as seif dune which can be up to 100 kilometers long. landforms provide an empirical description of similar portions of the earth's surface. SW & GG

landscape [soils]
an assemblage, group, or family of spatially related, natural landforms over a relatively large area; the land surface which the eye can comprehend in a single view. SW & GSST

landslide [mass movement]
a general, encompassing term for most types of mass movement landforms and processes involving the downslope transportand outward deposition of soil and rock materials, caused by gravitational forces and which may or may not involve saturated materials. names of landslide types generally reflect the dominant process and/or the resultant landform. the main operational categories of mass movement are fall (rockfall, soil fall, topple), slide (rotational landslide, block glide, debris slide, lateral spread), flow [rock fragment flow (especially rockfall avalanche), debris avalanche, debris flow (e.g., lahar), earthflow, (creep, mudflow)], and complex landslides. compare - solifluction. SW & DV

land-surface form
the description of a given terrain unit based on empirical analysis of the land surface rather than interpretation of genetic factors. surface form may be expressed quantitatively in terms of vertical and planimetric slope-class distribution, local and absolute relief, and patterns of terrain features such as interfluve crests, drainage lines, or escarpments. HP

lapilli
non or slightly vesicular pyroclastics, 2.0 to 76 mm in at least one dimension, with an apparent specific gravity of 2.0 or more. compare - ash [volcanic], block [volcanic], cinders, tephra. KST

lateral moraine
a ridge-like moraine carried on and deposited at the side margin of a valley glacier. it is composed chiefly of rock fragments derived from valley walls by glacial abrasion and plucking, or colluvial accumulation from adjacent slopes. GG

lateral spread [mass movement]
a category of mass movement processes, associated sediments (lateral spread deposit) or resultant landforms characterized by a very rapid spread dominated by lateral movement in a soil or fractured rock mass resulting from liquefaction or plastic flow of underlying materials; also called spread. types of lateral spreads can be specified based on the dominant particle size of sediments (i.e. debris spread, earth spread, rock spread. compare - fall, topple, slide, flow, complex landslide, landslide. SW, DV & GG

lava channel
see lava trench.

lava field
an area covered primarily by lava flows whose terrain can be rough and broken or relatively smooth; it can include vent structures (e.g., small cinder cones, spatter cones, etc.), surface flow structures (e.g., pressure ridges, tumuli, etc.) and small, intermittent areas covered with pyroclastics. compare - lava plain, volcanic field. SW

lava flow
a solidified body of rock formed from the lateral, surficial outpouring of molten lava from a vent or fissure, often lobate in form. compare - a'a lava flow, pahoehoe lava flow. GG

lava flow unit
a separate, distinct lobe of lava that issues from the main body of a lava flow; a specific outpouring of lava, a few centimeters to several meters thick and of variable lateral extent, that forms a subdivision within a single flow. a series of overlapping lava flow-units together comprise a single lava flow. also called flow unit. compare - lava flow. GS & GG

lava plain
a broad area of nearly level land, that can be localized but is commonly hundreds of square kilometers in extent, covered by a relatively thin succession of primarily basaltic lava flows resulting from fissure eruptions. compare - lava plateau, lava field, volcanic field. SW & GG

lava plateau
a broad elevated tableland or flat-topped highland, that may be localized but commonly is many hundreds or thousands of square kilometers in extent, underlain by a thick succession of basaltic lava flows resulting from fissure eruptions (e.g. Columbia River Plateau). compare - lava plain, lava field. GG

lava trench
a natural surface channel in a lava flow that never had a roof, formed by the surficial draining of molten lava rather than by erosion from running water; also called lava channel. compare - mawae, lava tube. SW

lava tube
a natural, hollow tunnel beneath the surface of a solidified lava flow through which the lava flow was fed; the tunnel was left empty when the molten lava drained out. MA & GG

ledge
a) a narrow shelf or projection of rock, much longer than wide, formed on a rock wall or cliff face, as along a coast by differential wave action on softer rocks; erosion is by combined biological and chemical weathering.
b) a rocky outcrop; solid rock.
c) a shelf-like quarry exposure or natural rock outcrop. compare - structural bench. GG

lee
(adj.) Said of a side or slope that faces away from an advancing glacier or ice sheet, and facing the downstream ("down-ice") side of a glacier and relatively protected from its abrasive action. compare - stoss, stoss and lee, crag and tail. GG

levee [streams]
an artificial or natural embankment built along the margin of a watercourse or an arm of the sea, to protect land from inundation or to confine streamflow to its channel. compare artificial levee, natural levee. GG

leveled land
a land area, usually a field, that has been mechanically flattened or smoothed to facilitate management practices such as flood irrigation; as a result the natural soil has been partially or completely modified (e.g., truncated or buried). SW

limestone
a sedimentary rock consisting chiefly (more than 50 percent) of calcium carbonate, primarily in the form of calcite. limestones are usually formed by a combination of organic and inorganic processes and include chemical and clastic (soluble and insoluble) constituents; many contain fossils. HP

limestone pavement
(not preferred) refer to pavement karst.

linear gilgai
a type of gilgai dominated by parallel micro-low troughs separated by low ridges (micro-highs) and oriented perpendicular to the topographic contour (i.e., up and down slopes); the prevailing type of gilgai on sloping terrain (slopes > 8 %). compare - circular gilgai, elliptical gilgai, gilgai. SW

lithification
the conversion of unconsolidated sediment into a coherent and solid rock, involving processes such as cementation, compaction, desiccation, crystallization, recrystallization, and compression. It may occur concurrently with, shortly after, or long after deposition. HP

lithologic
(adjective) pertaining to the physical character of a rock. HP

lodgement till
a basal till commonly characterized by compact, fissile ("platy") structure and containing coarse fragments oriented with their long axes generally parallel to the direction of ice movement. compare - till, flow-till, melt-out till. GG

loess
material transported and deposited by wind and consisting predominantly of silt-size particles. commonly a loess deposit thins and the mean-particle size decreases as distance from the source area increases. loess sources are dominantly from either glacial meltwaters (i.e. "cold loess") or from non-glacial, arid environments, such as deserts (i.e. "hot loess"). [soil survey] several types of loess deposits can be recognized based on mineralogical composition (calcareous loess, non-calcareous loess). SW & GSST

loess bluff
a bluff composed of a thick deposit of coarse loess, formed immediately adjacent to the edges of flood plains, as along the Mississippi River valley or China. sometimes referred to as a bluff formation (not preferred). SW & GG

loess hill
a hill composed of thick deposits of loess, as in IA, MO, NE and the Palouse hills of WA. SW

log landing
a comparatively level area, usually with road access, constructed or cut into steeper slopes and used for sorting logs during timber harvest operations. compare - skid trail. SW

longitudinal dune
a long, narrow sand dune, usually symmetrical in cross profile, oriented parallel to the prevailing wind direction ; it is wider and steeper on the windward side but tapers to a point on the lee side. it commonly forms behind an obstacle in an area where sand is abundant and the wind is strong and constant. such dunes can be a few meters high and up to 100 km long. compare - seif dune, transverse dune. GG

long run-out landslide
(not recommended; see rockfall avalanche).

longshore bar [relict]
a narrow, elongate, coarse-textured ridge that once rose near to, or barely above, a pluvial or glacial lake and extended generally parallel to the shore but was separated from it by an intervening trough or lagoon; both the bar and lagoon are now relict features. GG

louderback
a hill or ridge composed of a lava flow remnant that caps or is exposed in a tilted fault block and bounded by a dip slope. used as evidence of block faulting in Basin-and-Range terrain (western USA). compare - hogback. GG

low-center polygon
a polygon whose center is depressed relative to its boundary. compare - high-center polygon. NRC

low hill
a generic name for an elevated, generally rounded land surface with low local relief, rising between 30 meters (100 ft.) to as much as 90 m (approx. 300 ft.) above surrounding lowlands. compare - high hill, hill, hillock. SW

lowland
a) (not preferred) a generic, imprecise term for low-lying land or an extensive region of low-lying land, especially near a coast and including the extended plains or country lying not far above tide level.
b) (not preferred) a generic, imprecise term for a landscape of low, comparatively level ground of a region or local area, in contrast with the adjacent higher country.
c) (not recommended - use valley, bolson, etc.) a generic term for a large valley. compare - upland. SW

low marsh
(refer to mud flat). the flat, usually bare ground situated seaward of a salt marsh and regularly covered and uncovered by the tide; e.g., a mud flat. GG

lowmoor bog
a bog that is at or only slightly above the water table, on which it depends for accumulation and preservation of peat (chiefly the remains of sedges, reeds, shrubs, and various mosses). compare - highmoor bog, raised bog. GG