GeoWord of the Day

The GeoWord of the Day is a free service of the American Geosciences Institute. All of the terms and definitions are from the Glossary of Geology, 5th Edition Revised.

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base surge . A ring-shaped cloud of gas and suspended solid debris that moves radially outward at high velocity as a density flow from the base of a vertical explosion column. It accompanies a volcanic eruption or crater formation by a hyrovolcanic explosion or hypervelocity impact.

intermittent stream . (a) A stream or reach of a stream that flows only at certain times of the year, as when it receives water from springs or from some surface source. The term "may be arbitrarily restricted" to a stream that flows "continuously during periods of at least one month" (Meinzer, 1923, p.68). (b) A stream that does not flow continuously, as when water losses from evaporation or seepage exceed the available streamflow. Cf: ephemeral stream. Syn: temporary stream; seasonal stream.

ice front . (a) The floating vertical cliff forming the seaward edge of an ice shelf or other glacier that enters water, ranging in height from 2 to more than 50 m above sea level. Cf: ice wall. Syn: ice barrier; front [glaciol]. (b) Less preferred syn. of ice cliff in the sense of "any vertical wall of ice". (c) The snout of a glacier.

outlet (out'-let). (a) The relatively narrow opening at the lower end of a lake through which water is discharged into an outflowing stream or other body of water. Syn: outflow. (b) A stream flowing out of a lake, pond, or other body of standing water; also, the channel through which such a stream flows. (c) The lower end of a watercourse where its water flows into a lake or sea; e.g. a channel, in or near a delta, diverging from the main river and delivering water into the sea. (d) A crevasse in a levee.

divide [streams] . (a) The line of separation, or the ridge, summit, or narrow tract of high ground, marking the boundary between two adjacent drainage basins or dividing the surface waters that flow naturally in one direction from those that flow in the opposite direction; the line forming the rim of or enclosing a drainage basin; a line across which no water flows. An "anomalous" divide is one that does not follow the crest of the highest mountain range of a mountain chain. See also: continental divide. British syn: watershed. Syn: drainage divide; height of land; topographic divide; watershed line. (b) A tract of relatively high ground between two streams; a line that follows the summit of an interfluve. (c) The highest summit of a pass or gap. (d) groundwater divide.

brachyome (brach'-y-ome). The short arm of an anomoclone or ennomoclone of a sponge, or the different fourth ray of a trider of a sponge.

cascandite (cas'-cand-ite). A pale pink triclinic mineral: CaScSi3O8(OH) .

mammillary hill . A smooth, rounded, more or less elongate drumlin having an elliptical base.

thoroughfare (thor'-ough-fare). (a) A tidal channel or creek providing an entrance to a bay or lagoon behind a barrier or spit. (b) A navigable waterway, as a river or strait; esp. one connecting two bodies of water.

greenschist facies . The facies (set of metamorphic mineral assemblages) in which mafic rocks are represented by albite+epidote+chlorite+actinolite (Eskola, 1939). Chlorite, white mica, biotite, and chloritoid are typical minerals in pelitic rocks. It is believed to correspond to temperatures in the range 300°-500°C.