ice age
(not recommended) use Pleistocene.

ice-contact slope
a steep escarpment of predominantly glaciofluvial sediment that was deposited against a wall of glacier ice, marking the position of a relatively static ice-margin; an irregular scarp against which glacier ice once rested. compare - head-of-outwash. SW & GG

ice-marginal stream
a stream drainage along the side or front of a glacier. relict ice-marginal streams are used to trace the former position of a glacier; also called ice-marginal drainage. SW & GG

ice-margin complex
an assemblage of landforms constructed proximal to a relatively static, rapidly wasting continental glacial margin. constituent landforms can include fosse, head-of-outwash, ice-contact slope, ice-contact delta, kame, kame moraine, kettle, outwash fan, small outwash plain, glacial sluiceway, and small proglacial lake. Moraines, if present, are of limited occurrence (except kame moraines which can be extensive). glaciofluvial sediments dominate but glaciolacustrine sediments, till, and diamictons can be present in minor amounts. SW

ice-pushed ridge
an asymmetrical ridge of local, essentially non-glacial material (such as deformed bedrock, with some drift incorporated in it) that has been pressed up by the shearing action of an advancing glacier. it is typically 10 - 60 m high, about 150 - 300 m wide, and as much as 5 km long. examples are common on the Great Plains where such ridges occur on the sides of escarpments formed of relatively incompetent rocks that face the direction from which the ice moved. GG

ice-rafting
the transportation of rock fragments of all sizes on or within icebergs, ice floes, or other forms of floating ice. compare - dropstone, erratic. GG

ice segregation
the formation of ice by the migration of pore water to the frozen fringe where it forms into discrete layers or lenses. it commonly ranges in thickness from hairline to more than 10 m and often occurs in alternating layers of ice and soil. NRC

ice wedge
a massive, generally wedge-shaped body with its apex pointing downward, composed of foliated or vertically banded, commonly white, ice. NRC

ice wedge cast
a filling of sediment in the space formerly occupied by an ice wedge. NRC

ice wedge polygon
patterned ground in areas of ice wedges. these polygons are commonly in poorly-drained areas and may be high-centered or low-centered. NRC

igneous rock
rock formed by solidification from a molten or partially molten state; major varieties include plutonic and volcanic rocks. examples: andesite, basalt, granite. compare - intrusive, extrusive. HP

impact crater
a) [anthropogenic] a generally circular or elliptical depression formed by hypervelocity impact of an experimental projectile or ordinance into earthy or rock material. compare - caldera, crater, meteorite crater. SW;
b) (not recommended - use meteorite crater) a generally circular crater formed by the impact of an interplanetary body (projectile) on a planetary surface. GG

inselberg
a prominent, isolated, residual knob, hill, or small mountain, usually smoothed and rounded, rising abruptly from an extensive lowland erosion surface in a hot dry region; generally bare and rocky although the lower slopes are commonly buried by colluvium. compare - monadnock, nunatak. GG

inset fan
(colloquial; southwestern USA) the flood plain of an ephemeral stream that is confined between the fan remnants, ballenas, basin-floor remnants, or closely-opposed fan toeslopes of a basin. FFP & SW

integrated drainage
a general term for a drainage pattern in which stream systems have developed to the point where all parts of the landscape drain into some part of a stream system, the initial or original surfaces have essentially disappeared and the region drains to a common base level. few or no closed drainage systems are present. SW

interbedded
Said of beds lying between or alternating with others of different character; especially said of rock material or sediments laid down in sequence between other beds, such as "interbedded" sands and gravels. GG

interdrumlin
the concave to relatively flat bottomed, roughly linear depressions ranging from small saddles or swales to small valleys that separate drumlins or drumlinoid ridges in drumlin fields. streams, if present, have not had a dominant impact on the formation of the depression. compare - drumlin, drumlinoid ridge. SW

interdrumlin swale
see interdrumlin.

interdune
the relatively flat surface, whether sand-free or sand-covered, between dunes. GG

interfluve
a landform composed of the relatively undissected upland or ridge between two adjacent valleys containing streams flowing in the same general direction. an elevated area between two drainageways that sheds water to those drainageways. compare - divide. GG & FFP

interfluve [geomorphology]
a geomorphic component of hills consisting of the uppermost, comparatively level or gently sloped area of a hill; shoulders of backwearing hillslopes can narrow the upland (e.g., ridge) or merge (e.g., crest, saddle) resulting in a strongly convex shape. compare - crest, side slope, head slope, nose slope, free face, base slope. SW

interior valley
a large, flat-floored closed depression in a karst area whose drainage is ultimately subsurface and its floor is commonly covered by alluvium. some interior valleys may become ephemeral lakes during periods of heavy rainfall, when sinking streams that drain them cannot manage the runoff; also called polje (not preferred). compare - karst valley, sinkhole. GG

intermediate position [gilgai]
a nearly level area, including the lower part (footslope) of a micro-high, that is a transition zone between the slightly elevated micro-high (i.e. microknoll; mound in Russia) and the outer edge of an adjacent micro-low (i.e. microbasin, microtrough; depression in Russia) in gilgai. where present, it can make up a majority of the ground surface area in gilgai; called slope in Russia. compare - gilgai. SW

intermittent stream
a stream, or reach of a stream, that does not flow year-round (commonly dry for 3 or more months out of 12) and whose channel is generally below the local water table; it flows only when it receives a) base flow (i.e. solely during wet periods), or b) ground-water discharge or protracted contributions from melting snow or other erratic surface and shallow subsurface sources. compare - ephemeral stream. HP

intermontane basin
a generic term for wide structural depressions between mountain ranges that are partly filled with alluvium and called "valleys" in the vernacular. Intermontane basins may be drained internally (bolsons) or externally (semi-bolson). FFP

interstream divide
a) (not preferred) a synonym for divide.
b) (colloquial - esp. southeastern USA). broad interstream divide - a wide, relatively level area between incised drainageways; a broad, nearly level "summit" or interfluve. compare - broad interstream divide, interfluve. SW

intramorainal
said of deposits and phenomena occurring within a lobate curve of a moraine (e.g. within the area occupied by a glacier). compare - extramorainal. GG

intrusive
denoting igneous rocks derived from molten matter (magmas) that invaded pre-existing rocks and cooled below the surface of the earth. compare - extrusive. HP

island
a) an area of land completely surrounded by water;
b) an elevated area of land surrounded by swamp, or marsh, or isolated at high water or during floods. compare - barrier island. GG

joint [geology]
asurface of actual or potential fracture or parting in a rock, without displacement; the surface is usually planar and often occurs with parallel joints to form part of a joint set. HP

jokulhlaup
an Icelandic term for a glacial outburst flood, especially when an ice dam impounding a glacial lake breaks. such breaks drained glacial Lake Missoula and created the Channeled Scablands in the Pacific Northwest. (Pronounced: yo-kool-loup, the last syllable as in "out".) compare - glacier outburst flood, scabland, giant ripple. SW & GG