Cryosphere glossary
relict active layer
a layer of ground, now perennially frozen, lying immediately below the modern active layer; its thickness indicates the greater annual depth of thaw that occurred during a previous period.
relict ice
ice formed in, and remaining from, the geologically recent past.
relict permafrost
permafrost existing in areas where permafrost can not form under present climatic conditions; reflects past climatic conditions that were colder.
reprojection
Provides the user the ability to convert the data from its native reference projection to a different reference projection.
residual stress
the effective stress generated in a thawing soil if no volume change is permitted during thaw.
residual thaw layer
a layer of thawed ground between the seasonally frozen ground and the permafrost table.
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.
retreat
when a mountain glacier's terminus doesn't extend as far downvalley as it previously did; occurs when ablation surpasses accumulation.
Image
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: B. Molnia, USGS; 1941 W. Field., archived in 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.
ridge
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.
Image
Ridged sea ice.
Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory
ridging
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.
Image
Ridged sea ice.
Don Perovich, U.S. Army Cold Regions Research and Engineering Laboratory
rime
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.