Chapter 17 Outline

Chapter 17 Outline - Chapter 17: Glacial and Periglacial...

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Chapter 17: Glacial and Periglacial Processes and Landforms Introduction ~77% Earth’s freshwater frozen; =>frozen record of earth’s climatic history; worldwide, glacial ice in retreat; paleoclimatology - science of methods used to decipher past climates; ~25% earth’s land area subject to freezing conditions/frost action char’ic of periglacial regs; =>evidence of last ice age Rivers of Ice Glacier - lg mass ice resting on land/floating as ice shelf in sea; form by cont’s accumulation of snow that recrystallizes under own weight into ice mass; move slowly under pressure of own weight/gravity- in streamlike patterns, merging as tributaries into lg rivers of ice; cover ~11% earth’s land area Form in areas of permanent snow- high lats/elves; snowline - lowest elevation where: snow can survive yr-round/where winter snow accumulation persists thru summer; vary w/equatorial mtns (5000 m), midlat mtns (2700 m) etc; glaciers varied; based on form, size, flow chars, fall w/in 2 general grps: Alpine Glaciers Glacier in mtn range= mountain/ alpine glacier ; svrl subtypes: valley glacier - river of ice confined w/in valley orig formed by stream action; range 100m – 100 km length; as flows downhill, mtns, cyns, river vllys under it altered- debris created by glacier moved ice=>dark streaks/bands being moved: For deposition elsewhere; debris also carried w/in/along its base; most form in mtn snowfield, confined in bowl-shaped recess- cirque ; glacier that forms here=> cirque glacier ; may jointly feed vlly glacier; piedmont glacier - forms whn svrl vlly glaciers pour out of confining vllys, coalesce @base of mtn range: Spreads freely over lowlands; tidewater/ tidal glacier ends in sea, breaking off to form floating ice- icebergs - usu form whenever glaciers meet ocean Continental Glaciers On lgr scale than indv alpine glaciers, continental glacier - cont’s mass of ice; extensive form= ice  sheet - most earths glacial ice exists as these in Greenland, Antarctica (92% glacial ice on planet)- both have such huge mass of ice sheets that landmass under ice isostatically depressed below sea lvl: Each ice sheet deep as 3000+ m; more cont’s ice cover of mtn locations: 1) ice cap - ~circular, covers area of < 50K km 2 ; completely buries underlying landscape; 2) ice field - extends in char’ic elongated pattern in mtn’ous reg; ridges, peaks ( nunatak ) visible above buried terrain Cont’s ice sheets/ice caps drained by quickly moving, solid ice streams tht form around thm, moving to sea/lowlands; outlet glacier flows out fr ice sheet/ice cap but is constrained by mtn valley/pass Glacial Processes Glacier mass budget consists of net gains/losses of glacial ice- determine if glacier expands/retreats Formation of Glacial Ice Essential input to glacier- snow that gthrs in snowfield (glacier’s accumulation zone)- usu at highest elev of ice sheet/ice cap/head of valley glacier in cirque; as snow accumulates=>incr’d weight/pressure
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This note was uploaded on 06/24/2008 for the course GEOG 1 taught by Professor Okin during the Fall '06 term at UCLA.

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Chapter 17 Outline - Chapter 17: Glacial and Periglacial...

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