Descriptionary

growler a small chunk of ice, measuring no more than 215 square feet (20 sq m), broken off from an iceberg.

hanging glacier a glacier that has positioned itself on a high shelf and hangs over a valley, posing a major avalanche danger.

hanging valley a secondary valley whose floor is much higher than the larger valley into which it leads; originally formed by a small, tributary glacier leading to a larger one.

horn a sharp, steeply descending peak formed by the headwalls of three or more cirques.

hummock a mound of broken ice, pushed up by pressure.

hummocked ice pieces of broken ice forced atop one another by pressure and forming a mound.

ice age any cold period in Earth's history marked by extensive glaciation and alternated with a period of warmth. The most recent ice age, extending from approximately 2 million to 10,000 years ago and consisting of at least four large-scale glacial advances, was the Pleistocene epoch.

iceblink a yellowish glare in the sky over an ice field.

icefall an avalanche of ice.

ice field any floating sheet of ice greater than 6 miles (10 km) across.

ice floe any floating sheet of ice less than 6 miles (10 km) across.

indicator a glacially transported rock that can be traced back to its original bedding ground.

kame mounds of stratified sand and gravel depos­ited along the edge of a glacier by glacial streams.

kettles depressions in moraines, often filling with water and creating lakes anywhere from 10 meters to 10 kilometers in diameter.

loess wind-transported silt and clay, ground fine and deposited by glaciers, and responsible for creat­ing the rich, loamy soils and billowing topography of the Midwest.

moraine a large accumulation of glacially deposited rocks and boulders (till).

moulin a whirlpool of melted water and rocks that falls through a crevasse and carves out a shaft through a glacier to the ground. Also known as a glacier mill.

neve glacial or mountain snow that becomes ice. Also known as firn.

nunatak a hill or mountain peak surrounded by a glacier.

pack ice a large slab of sea ice consisting of chunks and floes held closely together.

pancake ice evolving from frazil or slush, rounds of ice of various sizes, resembling pancakes.

permafrost permanently frozen ground.

Pleistocene epoch a period from approximately 2 million to 10,000 years ago, marked by alternating cold and warm climates and increased glacial activ­ity. Four major glacial advances—when ice covered as much as two-thirds of North America in depths reaching 3,000 meters—are recognized during the Pleistocene epoch. From oldest to youngest, these are known as the Nebraskan, the Kansan, the Illi- noian, and the Wisconsin, collectively referred to as the Ice Age.

pressure ridge a ridge of sea ice uplifted by hori­zontal pressure.

regional snow line the altitude in which more snow accumulates than melts in the summer season, thus eventually forming a glacier.

rock flour rock pulverized by a glacier and carried off by running water.

sastrugi large, sharp ridges or irregularities carved into a bed of snow by wind.

serac a pinnacle of ice upraised on the surface of a glacier by the intersection of two or more crevasses.

snow bridge an arch of snow formed over a cre­vasse.

striations scratches and grooves left on rocks and bedrock by passing glaciers.

surge a sudden or rapid advancement of a glacier, sometimes having catastrophic consequences.

till a mixture of powdered rock, gravel, and rocks carried and deposited by a glacier.

trimline the boundary between old, larger trees untouched by glacial movement and younger, smaller trees that sprouted after ice receded.

warm glacier one that reaches melting temperature during summer.

LAKES, PONDS, AND swamps

alkali lake a lake with a high content of sodium carbonate.

battery a large island of decayed vegetation and bottom material floated to the surface of a swamp by swamp gas; the island then floats, grows new vegeta­tion, and gradually roots itself to the bottom.

bayou a marshy inlet or outlet of a lake or river.

benthos the plants and animals that inhabit the bot­tom of a pond, lake, or other body of water.

bitter lake a lake with a high content of sodium sulfate.

blowup the act of swamp gas blowing bottom mate­rial to the surface of a swamp.

boatman an aquatic insect that skims the surface of water.

bog a spongy wetland characterized by peat depos­its, floating sedge or sphagnum mats, heath shrubs, and coniferous trees.

brackish describing a mixture of salt water and freshwater, such as found in coastal marshes.

caldera a crater lake formed by volcanic activity.

cirque a small circular basin lake found on the side of a mountain.