Landform | Identification Criteria | Boundary Defined by | Significance |
| | | |
Ice-scoured bedrock | Widespread exposures of bare bedrock with smooth striated or plucked upper surfaces | Outermost extent of bare bedrock | Evidence of glacier Ice at its Pressure-melting point |
Drift Limit | the edge of the cover of a glacigenic deposit that is not also marked by a moraine ridge. Drift limit may be identified by a change in vegetation type or by change in the density of glacially deposited boulders | Outermost extent of Glacigenic deposit | Drift limit marks the extent oa a glacier advance |
Moraine Ridge | A single ridge or collection of ridges composed of glacigenic material. Typically 1-10m (but exceptionally 100 m) in height. Sharp or rounded crests and either liner, curved, sinuous or sawtooth in plan | Lower concave break of Slope. The crestline orientation can also be recorded if this is well-defined | Moraine ridge marks the lateral or terminal extent of a glacier advance (except in the case of hummocky moraine) |
Hummocky moraine | A seemingly chaotic assemblage of irregular hummocks and hollow. Hummocky moraine often shows order when viewed on aerial photographs or when mapped in detail in field | Outermost extent of Hummocky moraine. The crestline orientations of indivitual hummocks can be recorded if the scale of the map permits | Formed by the slow melting of stagnant debris-covered ice by deposition at receding glacier margins or the release of material from proglacial or englacial thrusts |
Fluted moraine | Groups of straight elongated ridges of glacigenic material. Typically 10-100 m in length and 1 m wide | Upper Convex and lower Cncave breaks of slope of indivitual features (where scale permits) | Subglacial modification of sediment. Flutes are formed parallel to the direction of ice flow |
Till sheet | A cover of glacigenic materal with no surface form or expresssion. Often associated with isolated boulders and bounded by a drift limit or moraine ridge | Outermost extent of glacigenic material | Extent of till sheet marks the extent of a glacier ice |
Drumlins | Smooth, Streamlined, Oval-shaped or elliptical hills with steep or blunt stoss (up-ice) faces. Composed of a variety of gacigenic sediments . Typically 5-50m high and 10-3000m long, with length-to-width ratios of less than 50. Occur in Swarms | Upper convex and lower concave breaks of slope (where scale permits) | Widespread subglacial modifiaction of sedimet. The steeper, blunt end usually indicated the up-ice face |
Kame terraces | Flat Topped Terrace along valley sides. Typically up to 10m in height. Usually composed of sand and gravel. Steep slopes commonly represent former ice-contact slopes. Upper Surface may be pock-marked by kettle holes | Upper Convex break of slope. Similar terrace heights can be indicated by distinctive shadings and patterns | Formed by the slow melting of stagnant debris-covered ice by deposition at receding glacier margins or the release of material from proglacial or englacial thrusts |
Kame | Sub-conical hills of segments of flat topped terraces up-to 10 m in height. Usually composed of sand and gravel. Steep slopes commonly represent former ice-contact slopes | Upper Convex break of slope. Crestline orientations of indivitual kame segments can also be recorded if the feature is discontinuous | Fragmentary features, formed in a similar manner to kame terraces, but often in ice-walled tunnels against steep valley sides or in front of a glacier |
Esker | Usually sinuous in plan and composed of sand and gravel. Some eskers are single crested, whilst others are braided in plan. Eskers can climb uphill or cross low cols. | Upper convex and lower concave breaks of slope. Crestline orientations of indivitual esker segments can also be recorded if the feature is discontinuos | Glacio-fluvial landforms created by the flow of meltwater in subglacial, englacial or supraglacial channels |
Meltwater Channels | Channels cut in rock or sediment often with abrupt inception and termination and lack of modern catchment. Subglacial meltwater channels may breach cols, displaying convex-up long profile | Thalweg of channel, location of channel inception and termination. Arrow to indicate direction of former drainage can also be recorded if known | Evidence of former meltwater discharge route |
Trimline | Line seperating areas of solifluction from extensive gullying or areas of mountain-top detritus/ weathered materal from upper limit of ice-scoured bedrock | Loer limit of solifluction or weathering and upper limit of extensive gullying or ice-scoured bedrock | Former Vertical dimensions of a glacial or englacial thermal boundary |
Friday, June 19, 2009
GLACIAL DEPOSITIONAL FEATURES
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