Cryosphere – portion of hydrosphere and groundwater that is perennially frozen Glacial formation – occurs at north/south poles, high hi gh elevations (mountain ranges) Glacier – large persistent body of ice that rests on land or floats on sea, and in i n which accumulation exceeds ablation (melting/subliming) ablation (melting/subliming) Mass balance/budget – difference between accumulation and ablation Two main techniques for studying mass balance: Probing – placing poles at various points in ice during beginning of ablation/accumulation period and later studying change in the height of the ice along the poles Crevasse stratigraphy – observing number of layers formed in crevasses to determine how much snow accumulated Névé – accumulation of snow that has been partially melted, refrozen, and compacted Firn – intermediate recrystallized state between snow and ice; névé that survives a full season of ablation; weight of snow on top compresses snow on bottom, turning it into ice (blue from lack of oxygen) Two forms of glacial movement – spreading and spreading and basal slip (pressure slip (pressure causes ice on bottom to melt, reduces friction and allows slide) Less pressure on upper layers > more brittle – fracture and form crevasses Glaciohydraulic supercooling – process that allows water at base of gl acier to remain in liquid state below freezing temperature Accumulation area/zone – cold temperatures, snow collects and adds mass; larger in winter Ablation area/zone – warm temperatures, glacier melts; larger in spring/summer Snow/firn line – separates zones of accumulation and ablation Icebergs – chunks of ice that fall off glacier/ice shelf into ocean from calving; calving; tabular – flat-topped Moulins/potholes – vertical tubes that carry meltwater down through the glacier Seracs – jagged columns/blocks of ice; intersection of multiple crevasses or when softer ice falls off denser ice; can easily collapse; found within icefall Icefall – place where glacier moves over cliff; part of gl acier with rapid flow and chaotic crevassed surface Ogives – alternating dark/light bands of ice occurring on glacier surfaces, only below icefalls Two types – alpine/valley glaciers (high glaciers (high elevations, basal slip) and ice sheets/continental glaciers (continental masses of glacial ice, ex. Antarctica, Greenland, Arctic Ocean) Ice shelves – occur when ice sheets extend over the sea and float on water Ice caps –dome-shaped ice shelves that cover area of less than 50,000 km 2 and completely bury underlying landscape Ice streams – channelized glaciers that flow more rapidly than surrounding ice Icefields – extend in elongated patterns over mountainous regions Piedmont glaciers – occur when steep valley glaciers gl aciers spill out into relatively flat plains; spread out into bulb-like lobes Hanging glacier/ice apron – wide glacier that clings to walls of glacial valleys; often causes avalanches Glacial valleys: U-shaped valley/glacial trough – originally V-shaped river valley that was eroded by alpi ne glacier that moved through and removed rock from the sides through plucking and abrasion Tunnel valley – large, long U-shaped U -shaped valley originally cut under glacial ice near ice sheet margins; formed by subglacial erosion through water; served as drainage pathways carrying meltwater; appear as dry valleys, lakes, seabed depressions, and sediment-filled areas; most run from north to south Urstromtal/meltwater Urstromtal/meltwa ter valley/ice-marginal v alley/ice-marginal valley – broad glacial valley formed during Ice Ages by meltwaters parallel to ice region; appear in front of gl acier, unlike tunnel valleys, which appear below Tidewater glaciers – valley glaciers that flow far enough to reach the sea; high acceleration rates; calve rapidly Outlet glaciers – channels of ice that flow out of ice sheet, constrained by bedrock on sides Valley glaciers – provide drainage for icefields; surrounded by exposed bedrock and slopes, which provide snow and ice to accumulate via avalanches; fjords are formed after valley glaciers retreat and water fills the depression Catchment/snowdrift/drift Catchment/snowdrift/drift glaciers – semi-permanent masses of firn formed by drifted snow behind obstructions or in the ground Isostatic depression – glacier forces liquid in mantle out of the way Isostatic rebound – slow process in which mantle refills space and pushes crust back up i nto original
position after glacier recedes Fjord – long, narrow inlet with steep sides; formed when glacier cuts U-shaped valley by ice segregation and abrasion of surrounding bedrock Misfit stream – stream/river that is too large/small to have eroded the valley i n which it flows Overfit stream – too large; underfit stream – too small Hanging valley – tributary valley with floor at higher elevation than main channel into which it flows; often has waterfall through outlet Glaciers act like conveyor belts, picking up rocks along the way and l ater depositing them Sometimes rocks are crushed by glacier weight into rock flour (which sometimes appears in thick, grayish meltwater) Glacial erratics – large rocks transported by glaciers into prominent locations Striations – scrapes in bedrock caused by rocks being transported by glaciers Chatter marks – intermittent scrapes Till – unsorted, coarsely graded sediment (part of glacial drift deposited directly by gl acier) Moraines – glacially formed accumulation of unconsolidated debris (soil and rock); depositional Lateral moraines – parallel ridges deposited along sides and on top of glacier Ground/dump moraines – till-covered areas with irregular, rolling (usually gentle) topography and no ridges; often found between two lateral moraines in alpine glaciers; deposited between glacial ice and underlying bedrock, behind end moraines; may change into drumlins by overriding ice Rogen/ribbed moraines – form series of ribs in ice sheet; sometimes filled with water End/terminal moraines – deposited at end of glacier, marking maximum advance; reflect shape of glacier’s terminus/snout; size and shape determined by whether glacier is advancing, retreating, or at equilibrium; more accumulation the longer the terminus stays in one place Recessional moraines – series of ridges running across valley behind terminal moraines; reside between and are perpendicular to lateral moraines Medial moraines – ridges that run down center of valley floor; formed when two glaciers meet; debris join and are then deposited Supraglacial moraines – accumulated on top of glacial ice Washboard moraines – shaped like washboards Veiki moraines – hummocky (cross-bedded) moraines that form i rregular landscapes of ponds and plateaus surrounded by banks Outwash – sediments deposited by glacial meltwater Outwash plain/Sandur – plain formed of glacial sediments deposited by meltwater outwash at terminus of glacier Outwash fan – fan-shaped body deposited by braided streams Esker – long, winding ridge of outwash (stratified sand and gravel) deposited in streams that flow through base of glacier Kame – irregularly-shaped hill or mound composed of till that accumulates in depression on retreating glacier; associated with kettles; depositional Roche moutonnée/Sheepback – asymmetrical rock formations and hills; indicates glacier flow from one side, which is smooth, to the other side, which is jagged ; results from abrasion on “stoss” (up -ice) side of rock and plucking on “lee” (down -ice) side Drumlins – elongated, oval-shaped hills; narrower side indicates direction of glacier flow; depositional Pyramidal peak – mountaintop created by erosion of multiple glaciers on central point; extreme form called glacial horn Aréte – narrow ridge of rock usually formed when two glaciers erode parallel U-shaped valleys Col/Saddle/Spillway – lowest point of aréte between two peaks/cirques Cirque/corrie/cwm – bowl-shaped depression created when glaciers erode backwards into mountainsides; cirque glaciers may be created in these Tarn/Corrie loch – mountain lake or pool formed in a cirque Ribbon lakes – long and narrow lakes usually found in glacial troughs Kettle lakes – form, often from melting cirque glaciers, when pieces of ice break off and become buried by till; small and pond-like; depositional Paternoster lakes – series of glacial streams connected by single stream or braided stream system, li ke a rosary; occur in alpine valleys; created by end moraines Jökulhlaup – sudden flood that occurs when glacial lake is rel eased Theories of glacial advance and retreat (glacial periods): Milankovitch Cycles (eccentricity – deviation of orbit shape from perfect circle, obli quity – tilt of
axis, precession – wobble of axis); shifting of tectonic plates; particles expelled by volcanoes or meteoric impacts; atmospheric composition; solar variability; insulation; dust; atmospheric composition; ocean current circulation; sea ice; and atmospheric circulation Periglacial – relating to conditions, processes, and landforms associated with cold, non-glacial environments; includes geomorphic processes related to freezing of water Permafrost – condition where layer of soil, sediment, or rock below ground surface remains frozen for more than a year Continuous permafrost – exists over landscape as uninterrupted layer Discontinuous permafrost – has numerous, scattered, small thawed areas Sporadic permafrost – consists of small islands scattered in unfrozen areas Alpine permafrost – found in higher elevations Subsea permafrost – exists below seawater Active layer – upper zone of soil that experiences daily and seasonal freeze-thaw cycles Taliks – unfrozen layers located on top, underneath, or within masses of permafrost Frost heaving – upward and outward movement of ground surface resulting from formation of ice beneath surface of soil; ice grows in direction of heat Frost-susceptibility – determined by size of voids in soil (grain-size distribution) Periglacial processes: Weathering – operates in repeated cycles of freeze-thaw; responsible for rock fracturing Ground/anchor ice – bodies of ice in ground surface of permafrost layer Pore ice – found in spaces that exist between particles of non-frost-susceptible soil/sediment Needle ice – groups of small, narrow ice slivers; formed in moist soil; loosens soil for erosion and moves small rocks up to soil surface; enhances soil creep Ice wedges – downward, narrowing bodies of ice that form from seasonal cracks in the ground and grow; cycles of ice addition can be identified as f oliations, or layers; called sand wedges when accumulation of wind-blown sand occurs Segregated ice – masses of almost pure ice that grow in frost-susceptible soil as a result of liquid water diffusion from unfrozen parts of soil Ice lenses – layer of horizontal accumulation, usually of segregated ice Mass movement – downslope movement of sediment, soil, and rock material Solifluction – characterized by freeze-thaw action, water-logged soil, slow movement, and formation of U-shaped features (solifluction lobes) Gelifluction – form of solifluction in which material slides over slick permafrost layer Frost creep – initiated by frost heaving and thawing with small amounts of stress Rockfall – detachment and movement of rock from cliff face to its base; fracturing of rock along natural bedding planes and joints due to frost wedging and insolation weathering (physical weathering due to thermal expansion and contraction) Erosion – removal of weathered sediment and rocks by wind, water, and ice Nivation – associated with isolated patches of snow that remain through summer season; involves processes of frost weathering at margins of snow patches, meltwater erosion, and gelifluction; often creates nivation hollows under snow patches (A)eolian erosion/deposition – processes in which strong winds move large quantities of loose sediment and soil, especially during summer months Fluvial erosion/deposition – processes in which discharge (rate of flow) of streams fluctuate; when suddenly reduced, large quantities of gravel and boulders are left behind; beaded channels develop when streams pass over ice wedges and melt them to form deep pools Entrainment – picking up of loose material by glacier from along bed and valley sides Periglacial landforms: Patterned ground – presence of ground materials arranged in a variety of symmetrical, geometric shapes; associated with frost sorting Palsas – low, often oval-shaped permafrost mounds with layers of segregated ice and peat (partially decomposed remains of plants); contain permanent ice lenses; develop in bogs from groundwater; found in areas with discontinuous permafrost; arise in groups Pingo/hydrolaccolith – ice-cored hill, usually circular in shape, which can only form i n permafrost environment by hydrostatic pressure or groundwater flowing from outside source; larger than palsas; smaller pingos have rounded tops while larger ones have exposed ice that may melt into craters Thermokarst – irregular surfaces of marshy hollows and hummocks (rounded knolls of ice) formed as ice-rich permafrost thaws; ice melting beneath thermokarst lakes cause them to deepen over time
Thufur – huge hummocks that form in seasonally frozen ground or in permafrost areas Blockfield/Everest/Felsenmeer – area covered by large, frost-shattered angular blocks of stone; created by freeze-thaw action Rock glacier – thick lobe- or tongue-shaped mass of ice and talus (coarse rock fragments) that has moved slowly downslope through deformation of internal ice; formed by ei ther glacial or periglacial processes; deposition of debris from cirque headwall is regulated by rate of headwall erosion and point of origin of debris along headwall (sometimes catastrophic rockfalls take place), which control movement of individual lobes and overall formation as well as affect morphology Active rock glacier – moves downslope or downvalley; contains substantial amounts of deforming ice; steep frontal slope; contrast with inactive rock glacier Fossil rock glacier – does not contain ice; surface is frequently covered by vegetation; gradient of front slope is less steep than that of active rock glaciers Negative mill – geyser that develops when water from conduit is forced up to surface of glacier Nunatak – rocky outcrop projecting from and surrounded by glacier or ice sheet Bergschrund – crevasse that separates flowing ice from stagnant ice at head of glacier Randkluft – fissure that separates moving glacier from headwall rock Regelation – motion of object through ice by melting and freezing due to pressure differences Sintering – bonding together of ice crystals Thomson crystal – large ice crystal found in deep, stagnant water-filled cavities Ice tongue projection of ice edge (up to several kilometers in length) out from coastline; caused by wind and currents and usually forms when valley glacier moves rapidly into lake or oc ean Constructive metamorphism – process in which snow changes shape and adds molecules to sharpen corners and edges of ice crystal Diagenesis – chemical, physical, or biological change undergone by sediment after initial deposition and during and after lithification (becoming solid rock), not counting weathering and metamorphism Groove – elongated depression carved out of bedrock by rock particles contained in base of glacier Pleistocene – geological epoch from 2,588,000 to 11,700 years ago; recent period of recent glaciations; 1st of Quaternary Period, 6 th of Cenozoic Era; at maximum, 30% of Earth was covered by ice; l arge lakes accumulated because outlets were blocked and cooler air slowed evaporation; 11 major glacial events termed glacials /pluvials, which were separated by interglacials /interpluvials; minor advances and retreats called stadials Pre-Pleistocene glacial record: Archaean (pre-2500 Ma (megaanum, or millions of years)); Early Proterozoic (2500 165050 Ma) – extensive continental glaciation and glacio-marine deposition at intervals of 3-4 Ma; Late Proterozoic (165050 590 Ma) – no glacial activity until about 1000 Ma ago; Cambrian (590 505 Ma) – welldocumented tillites few in number; Ordovician (505 440 Ma) – next major glacial event occurred late in this era; Silurian (440 412 Ma) – glacial activity waned everywhere except in South America, where it waned in Late Silurian Period; Devonian (412 365 Ma); Carboniferous (365 290 Ma) – best known of pre-Pleistocene glaciations; Permian (290 235 Ma) – more extensive distribution in Australia and less in South America; Triassic (235 192 Ma); Jurassic (192 135 Ma) – possible sea ice development Oxygen isotope ratio cycle – describes period changes in ratio of to isotopes and water temperature, which are directly linked; is the most common, followed by and –
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