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GEG 120
Peter Muller

Evolutions of Stream Valleys Functions of streams as they modify landscapes -erosion (degradation) -transportation (transfer) -deposition (aggradation) Stages in a stream's life cycle -Youth Valley deepening (v-shaped) -Maturity Valley widening Floodplain formation -Old Age Widened floodplain Meandering loops UNIT 42 DEGRADATIONAL LANDFORMS OF STREAM EROSION Study Guide Terms on Page Four are key for final exam STREAM DEGRADATION Factors that influence fluvial erosion and landscape formation -Geologic Structure -Rock formation: raw material from which streams sculpt landforms -Many examples on pp. 517-521 -Human Involvement (only temporary) -Tectonic activity (tilting and gravity) -Climate -Landscape differences between moist and arid environments is more apparent than real -Remains a contentious issue in geomorphology DRAINAGE PATTERNS -Five Distinctive drainage patterns. Each provides clues about their underlying geologic structures -Radial -Volcano (star) -Annular- Dome (fist) -Trellis (roots) & Rectangular (four square) - Ridges and Valleys -Dendritic -Mississippi Basin (dendrites) OVERCOMING GEOLOGIC STRUCTURE: SUPERIMPOSED STREAMS A. Downward eroding stream flows on surface above three buried mountain ridges B. Mountain crests now exposed but the stream OVERCOMING GEOLOGIC STRUCTURE: ANTECEDENT STREAMS Evolution of an antecedent stream which kept flowing and eroding downward as the mountain ridge was being tectonically uplifted across its path. Tectonic forces are shown by purple arrows UNIT 43 AGGRADATIONAL LANDFORMS OF STREAM AGGRADATION STREAM AGGRADATION -Through deposition, rivers can also be builders -part of the sediment load carried by the world's rivers is deposited on the land as alluvium in floodplains, deltas, and elsewhere -less spectacular landforms, but still important SPECIAL CASE: STREAM DEPOSITION IN DESERTS -Infrequent but intense rainfall -Ephemeral (intemittent) streams -High velocity and stream capacity when gradient is steep -But when base level reached, stream quickly runs dry -Alluvial fans -Fan-shaped deposit of alluvium where mountain stream emerges onto a desert plain As velocity at mouth of canyon suddenly decelerates, most of sediment load is dropped -Heaviest
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