gap
a sharp break or opening in a mountain ridge, or a short pass through a mountain range; e.g., a wind gap. GG

gelifraction
(not recommended) use frost shattering.

gelivation
(not recommended) use frost shattering.

geomorphic component
a fundamental, three dimensional piece or area of a geomorphic setting (i.e., hills, mountains, terraces, flat plains) that has unique and prevailing kinetic energy dynamics and sediment transport conditions which result in their characteristic form, patterns of sedimentation and soil development. SW

geomorphic component - flat plains:
a group of fundamental, three dimensional pieces or areas of flat plains. In descending elevational order, the geomorphic components of a simple, flat plain (e.g. lake plain, low coastal plain, etc.) are the rise [a broad, slightly elevated area with comparatively greater gradients (e.g., 1-3% slopes], and the talf [a comparatively level (e.g., 0-1% slopes), laterally extensive, non-fluvial area], and dip [a slight depression that is not a permanent water body nor part of an integrated drainage network]. compare - geomorphic component - terraces. SW

geomorphic component - hills:
a group of fundamental, three dimensional pieces or areas of hills. In descending elevational order, the geomorphic components of a simple hill are the interfluve (roughly analogous to the summit); crest (converged shoulders); 3 variations of the hillslope, each distinguished by the surface shape and the nature of overland flow: head slope (converging surface or overland flow, especially at the head of a drainageway), side slope (parallel surface flow), nose slope (diverging surface flow) and free face (rock outcrop),; and the base slope (colluvium / slope alluvium apron at the bottom of the hill). SW

geomorphic component - mountains:
a group of fundamental, three dimensional pieces or areas of mountains. In descending elevational order, the geomorphic components of a simple mountain are the mountaintop (roughly analogous to the crest or summit); mountainflank (the long slope along the sides of mountains which can be further subdivided into three portions based on the relative slope location: upper third-, middle third-, or lower third mountainflank); free face (rock outcrop); and the mountainbase (colluvium / slope alluvium apron at the bottom of the mountain). SW

geomorphic component - terraces, stepped landforms:
agroup of fundamental, three dimensional pieces or areas of terraces, flood-plain steps, and other stepped landforms (e.g. stacked lava flow units). in descending elevational order, the geomorphic components are the tread (the level to gently sloping, laterally extensive top of a terrace, flood-plain step, or other stepped landform); and the riser (the comparatively short escarpment forming the more steeply sloping edge that descends to another level or a channel). SW

geomorphic surface
a mappable area of the earth's surface that has a common history; the area is of similar age and is formed by a set of processes during an episode of landscape evolution. a geomorphic surface can be erosional, constructional or both. the surface shape can be planar, concave, convex, or any combination of these. compare constructional, erosional. RR

geomorphology
the science that treats the general configuration of the earth's surface; specifically the study of the classification, description, nature, origin, and development of landforms and their relationships to underlying structures, and of the history of geologic changes as recorded by these surface features. the term is especially applied to the genetic interpretation of landforms. GG

geyser
a type of hot spring that intermittently erupts jets of hot water and steam, the result of ground water coming in contact with rock or steam hot enough to create steam under conditions preventing free circulation; a type of intermittent spring. compare - mud pot, hot spring. GG

geyser basin
a valley that contains numerous springs, geysers, and steam fissures fed by the same ground-water flow. GG

geyser cone
a low hill or mound built up of siliceous sinter around the orifice of a geyser. GG

giant ripple
a ripple that is more than 30 m in length; e.g., the jokulhlaup derived giant ripples in Camas Prairie, MT.; it usually exhibits superimposed megaripples. compare - ripple mark. GG

gilgai
a microfeature pattern of soils composed of a succession of microbasins and microknolls on level areas, or of microtroughs and microridges parallel to the slope on sloping areas, and produced by expansion / contraction and shear / thrust processes with changes in soil moisture. found in soils containing large amounts of smectitic clay that swell and shrink considerably with wetting and drying. various types of gilgai can be recognized based on the dominant shape of micro-highs and micro-lows: circular gilgai, elliptical gilgai, and linear gilgai. also referred to, in part or in total, as crabhole, Bay of Biscay, or hushabye in older literature. SW & GSST

glacial (adjective)
a) of or relating to the presence and activities of ice and glaciers, as in glacial erosion.
b) pertaining to distinctive features and materials produced by or derived from glaciers and ice sheets, as in glacial lakes.
c) pertaining to an ice age or region of glaciation. GG

glacial drainage channel
a channel formed by an ice-marginal, englacial, or subglacial stream during glaciation. GG

glacial drift
(not recommended) use drift.

glacial lake
a) a lake that derives much or all of its water from the melting of glacier ice, fed by meltwater, and lying outside the glacier margins (e.g. proglacial lake) or lying on a glacier (e.g. ice-walled lake, ice-floored lake) and due to differential melting.
b) a lake occupying a basin produced by glacial deposition, such as one held in by a morainal dam.
c) a lake occupying a basin produced in bedrock by glacial erosion (scouring, quarrying); e.g., cirque lake, fjord.
d) a lake occupying a basin produced by collapse of outwash material surrounding masses of stagnant ice.
e) [relict] an area formerly occupied by a glacial lake. GG

glacial-marine sedimentation
the accumulation of glacially eroded, terrestrially derived sediment in the marine environment. sediment may be introduced by fluvial transport, by ice rafting, as an ice-contact deposit, or by eolian transport. compare - glaciomarine deposits. GG

glacial outwash
(not recommended) use outwash.

glacial till
(not recommended; use till). till should only be used for describing glacial sediments, therefore "glacial till" is redundant. GM

glacial-valley floor
the comparatively flat bottom of a mountain valley predominantly mantled by till but which can grade from glacial scour (scoured rock-outcrop) near it's head to a thick mantle of till, and ultimately merging with alluvium or colluvium further down valley. some glacial-valley floors descend downstream in a series of scour-derived steps which may contain sequential tarn lakes (pater noster lakes); (not preferred: colloquial - western USA) sometimes called a trough bottom. SW

glacial-valley wall
the comparatively steep, glacially scoured, concave sides of a u-shaped, mountain valley mantled by colluvium with little or no till; (not preferred: colloquial - western USA) sometimes called a trough wall. SW

glaciation
the formation, movement and recession of glaciers or ice sheets. a collective term for the geologic processes of glacial activity, including erosion and deposition, and the resulting effects of such action on the earth's surface. GG

glacier
a) a large mass of ice formed, at least in part, on land by the compaction and recrystallization of snow, moving slowly by creep downslope or outward in all directions due to the stress of its own weight, and surviving from year to year. Included are small mountain glaciers as well as ice sheets continental in size, and ice shelves which float on the ocean but are fed in part by ice formed on land.
b) a stream-like landform having the appearance of, or moving like a glacier; e.g. a rock glacier. compare - snowfield, rock glacier. GG

glacier outburst flood
a sudden, often annual, release of meltwater from a glacier or glacier-damned lake sometimes resulting in a catastrophic flood, formed by melting of a drainage channel or buoyant lifting of ice by water or by subglacial volcanic activity. compare - jokulhlaup, scabland, giant ripple. GG

glaciofluvial deposit
material moved by glaciers and subsequently sorted and deposited by streams flowing from the melting ice. the deposits are stratified and may occur in the form of outwash plains, valley trains, deltas, kames, eskers, and kame terraces. compare - drift and outwash. HP

glaciolacustrine deposit
material ranging from fine clay to sand derived from glaciers and deposited in glacial lakes by water originating mainly from the melting of glacial ice. many are bedded or laminated with varves or rhythmites. HP

glaciomarine deposit
glacially eroded, terrestrially derived sediments (clay, silt, sand, and gravel) that accumulated on the ocean floor. sediments may be accumulated as an ice-contact deposit, by fluvial transport, ice-rafting, or eolian transport. compare - glacial-marine sedimentation. GG & GM

glade
(colloquial - Ozark uplands, USA) a) a largely treeless, open, grassy area (e.g., oak savanna) on high, broad interfluves and hillsides, commonly with shallow soils. compare - park. SW
b) (not preferred) refer to park: an ecological term for a grassy, open depression or small valley as in a high meadow; sometimes marshy and forming the headwaters of a stream, or a low, grassy marsh that is periodically inundated. GG & SW

glauconite pellets
Silt to sand-sized, nodular aggregates with a characteristic greenish color, dominantly composed of the clay mineral glauconite; formed in near-shore marine sediments and subsequently exposed by a drop in sea level or rise of a land mass, as on a coastal plain. Glauconite pellets have a high potassium content and higher CEC and moisture retention compared to other mineral sands. compare - greensands. SW

gorge
a) a narrow, deep valley with nearly vertical, rocky walls, smaller than a canyon, and more steep-sided than a ravine; especially a restricted, steep-walled part of a canyon.
b) a narrow defile or passage between hills or mountains. GG

graben
an elongate trough or basin bounded on both sides by high-angle, normal faults that dip towards the interior of the trough. it is a structural form that may or may not be geomorphically expressed as a rift valley. compare - horst. GG

grassy organic materials
see organic materials.

gravel pit
a depression, ditch or pit excavated to furnish gravel for roads or other construction purposes; a type of borrow pit. SW

greensands
a) an unconsolidated, near-shore marine sediment containing substantial amounts of dark greenish glauconite pellets, often mingled with clay or sand (quartz may form the dominant constituent); prominent in Cretaceous and Tertiary coastal plain strata of New Jersey, Delaware and Maryland; has been commercially mined for potassium fertilizer. the term is loosely applied to any glauconitic sediment.
b) (Not Preferred - use glauconitic sandstone) a sandstone consisting of greensand that is commonly poorly cemented, and has a greenish color when unweathered but an orange or yellow color when weathered. compare - glauconite pellets. SW

grike
(not preferred) refer to cutter.

groove
a small, natural, narrow drainageway on high angle slopes which separate tertiary spur ridges or mini-interfluves and is a constituent part of rib and groove topography; common in well dissected uplands. compare - rib. SW

ground moraine
a) commonly an extensive, low relief area of till, having an uneven or undulating surface, and commonly bounded on the distal end by a recessional or end moraine;
b) a layer of poorly sorted rock and mineral debris (till) dragged along, in, on, or beneath a glacier and deposited by processes including basal lodgement and release from downwasting stagnant ice by ablation. compare - end moraine, recessional, moraine, terminal moraine. SW

ground soil
any soil at the present-day land surface and actively undergoing pedogenesis, regardless of its history (i.e., relict, exhumed). compare - buried soil. SW & RR

grus
the fragmental products of in situ granular disintegration of granite and granitic rocks, dominated by inter-crystal disintegration. compare - saprolite. SW & GG

gulch
(colloquial: western U.S.A.; not preferred - refer to ravine) a small stream channel, narrow and steep-sided in cross section, and larger than a gully, cut in unconsolidated materials. general synonym - ravine. compare - arroyo, draw, gully, wash. HP

gulf [coast]
a relatively large part of an ocean or sea extending far into the land, partly enclosed by an extensive sweep of the coast, and opened to the sea through a strait (e.g. Gulf of Mexico); the largest of various forms of inlets of the sea. it is usually larger, more enclosed, and more deeply indented than a bay. compare - bay. GG

gully
a small channel with steep sides caused by erosion and cut in unconsolidated materials by concentrated but intermittent flow of water usually during and immediately following heavy rains or ice / snow melt. a gully generally is an obstacle to wheeled vehicles and too deep (e.g., > 0.5 m) to be obliterated by ordinary tillage; (a rill is of lesser depth and can be smoothed over by ordinary tillage). compare - rill, ravine, arroyo, swale, draw. HP & GSST

gut
a) (colloquial: U.S. Virgin Islands, Caribbean Basin) a gully, ravine, small valley, or narrow passage on land.
b) [stream] A tidal stream connecting two larger waterways. GG