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reticulate cryostructure

the cryostructure in which horizontal and vertical ice veins form a three-dimensional, rectangular or square lattice.

reticulate ice

a network of horizontal and vertical ice veins forming a three-dimensional, often rectangular or square lattice.

reticulate-blocky cryostructure

the cryostructure in which horizontal and vertical ice veins form a three-dimensional, irregular rectangular lattice.


when a mountain glacier's terminus doesn't extend as far downvalley as it previously did; occurs when ablation surpasses accumulation.
Muir Glacier, Glacier Bay National Park and Reserve's White Thunder Ridge as seen on August 13, 1941 (left) and August 31, 2004 (right). (2004 USGS photo courtesy of B. Molnia; 1941 photo courtesy of W. Field. Archived at the Long-Term Change Photograph Pairs Special Collection in the Glacier Photograph Database.)

retreating glacier

a glacier whose terminus is increasingly retreating upvalley compared to its previous position due to a higher level of ablation compared to accumulation.

retrogressive thaw slump

a slope failure resulting from thawing of ice-rich permafrost.


in meteorology, an elongated area of relatively high atmospheric pressure, almost always associated with and most clearly identified as an area of maximum anticyclonic curvature of wind flow.

ridge ice

piled ice formed by ridging.
Ridged sea ice. (Photo courtesy of Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory.)


process that occurs when wind, ocean currents, and other forces push sea ice around into piles that rise and form small mountains above the level sea ice surface; ridges are initially thin and transparent with very sharp edges from blocks of ice piling up; also see keels.
Ridged sea ice. (Photo courtesy of Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory.)


a white or milky and opaque granular deposit of ice formed by the rapid freezing of super-cooled water drops as they impinge upon an exposed object; it is denser and harder than hoarfrost, but lighter, softer, and less transparent than glaze.

ripple marks

corrugation on a snow surface caused by wind (as on sand).

river ice

floating ice formed in rivers.

river talik

a layer or body of unfrozen ground occupying a depression in the permafrost table beneath a river.

rock flour

a fine powder of silt- and clay-sized particles that a glacier creates as its rock-laden ice scrapes over bedrock; usually flushed out in meltwater streams, causing water to look powdery gray; lakes and oceans that fill with glacier flour may develop a banded appearance.

rock glacier

looks like a mountain glacier and has active flow; usually includes a poorly sorted mess of rocks and fine material; may include: (1) interstitial ice a meter or so below the surface (“ice-cemented”), (2) a buried core of ice (“ice-cored”), and/or (3) rock debris from avalanching snow and rock.
Frying Pan Glacier, Colorado, is almost entirely covered by rocks and debris in this photograph from 1966. (Photo courtesy of George L. Snyder, archived at the World Data Center for Glaciology, Boulder, CO.)

rotten ice

floating ice which has become honeycombed in the course of melting, and which is in an advanced state of disintegration.


the part of a ridge above sea level; like a sail on a sailboat, it catches wind and moves the ice.

saline permafrost

permafrost in which part or all of the total water content is unfrozen because of freezing-point depression due to a high dissolved-solids content of the pore water.


(1) a general property of aqueous solutions caused by the alkali, alkaline earth, and metal salts of strong acids (Cl, SO4 and NO3) that are not hydrolyzed (2) in soil science, the ratio of the weight of salt in a soil sample to the total weight of the sample.

sand wedge

a wedge-shaped body of sand produced by filling of a thermal contraction crack with sand either blown in from above or washed down the walls of the crack.

sand-wedge polygon

a polygon outlined by sand wedges underlying its boundaries.


complex, fragile shapes of snow on top of sea ice that resemble sand dunes; they form parallel to the prevailing wind direction; sastrugi can also form on snow cover over land.
Sastrugi at South Pole Station, Antarctica. (Photo courtesy of Fred Walton, NOAA Corps Collection.)


the condition in which the partial pressure of any fluid constituent (water in the atmospheric air) is equal to its maximum possible partial pressure under the existing environmental conditions, such that any increase in the amount of that constituent will initiate within it a change to a more condensed state; evaporation ceases under such conditions.

saturation vapor pressure (water)

the maximum amount of water vapor necessary to keep moist air in equilibrium with a surface of pure water; this is the maximum water vapor the air can hold for any given combination of temperature and pressure.


(1) a series of marks at regular intervals for the purpose of measuring (scale of an instrument, for example, a thermometer) (2) system of units for measuring ( 3) proportion between the size of something and the map, diagram, etc. which represents it (4) order of magnitude of a phenomenon or of a meteorological parameter.

sea ice

any form of ice found at sea which has originated from the freezing of sea water.

sea ice development stage

A phrase used to classify sea ice for operational purposes using the age of the ice as a proxy for its thickness. Specific terms such as new ice, nilas, young ice, and multiyear ice are used for each stage of sea ice development.

sea ice extent


sea ice maximum extent

the day of the year when the sea ice covers the largest area of the Arctic or Antarctic.

sea ice minimum extent

the day of the year when the sea ice covers the smallest area of the Arctic or Antarctic

sea smoke

evaporation fog formed when water vapor is added to air which is much colder than the vapor's source; most commonly, when very cold air drifts across relatively warm water; also called steam fog.

sea surface temperature

temperature of the water film at the sea surface.

sea-level pressure

the atmospheric pressure at mean sea level, either directly measured or, most commonly, empirically determined from the observed station pressure.


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seasonal freezing index

the cumulative number of degree-days below 0 degrees Celsius, calculated as the arithmetic sum of all the negative and positive mean daily air temperatures (degrees Celsius) for a specific station during the time period between the highest point in the fall and the lowest point the next spring on the cumulative degree-day time curve.

seasonal frost

the occurrence of ground temperatures below 0 degrees Celsius for only part of the year; see also active layer.