Chapter 9

Cirque

A bowl shaped basin carved by a glacier (erosional)

Ground Ice Formations

ICE WEDGES: vertical forms that develop where ice gathers in deep cracks in the sediment Only occur in permafrost, below the active layer Sorted circles (Norway) Ice wedge polygons (Nunavut) Many usual surface formations common in periglacial terrain due to freeze-thaw and frost-heave process ICE LENSES: horizontal ice layers that form as the active layer freezes at end of warm season

firn

as snow ages over the winter and loses intricate crystal forms, changes to larger more rounded and compact grains. over melt season, this snow further compacts --> with time and under pressure of overlying snowpack, firn consolidates to glacial ice, gradually becoming denser and less porous

glaciation stages

before glaciation --> region has smoothly rounded divides and narrow, V-shaped stream valleys active glaciation --> when glaciation has been in progress for thousands of years, new erosional (aretes, horns, cirques) and depositional (moraines) forms develop. later glaciation --> The disappearance of ice begins to expose a system of glacial troughs (U-shaped valleys) and depositional features

Glaciers transport and deposit vast quantities of materials

• Large blocks directly transported by glacier ice (e.g. erratics) • Fine grained material transported and sorted by subglacial streams • Unconsolidated materials deposited directly from glacier as till • Materials carried away from the glacier snout by proglacial (outlet) streams deposit outwash plains

Solifluction

→ slow movement saturated material downslope; common in periglacial areas as infiltration inhibited - Upper layrs of frozen ground thaw in summer - soil/rock in active layer saturated and unfrozen - Saturated material moves downslope over frozen sub-layer - Slopes of 5-20 degrees (steeper slopes = better drained)

Permafrost Distribution

- Continuous Permafrost - areas where permafrost exists under almost all areas (except under rivers, lakes) - Discontinuous permafrost - areas where permafrost exists under only somoe parts of an area year round (eg seasonal melt on slopes facing sun) ~50% of Canada with permafrost Southward progression: continuous >> discontinuous >>>> isolated Geothermal heat increases as we move towards equator

ice caps

-found on high portions of mountain ranges or on elevated plateaus smaller than ice sheets, flow largely independent of topography -are smaller than ice sheets (covering <50,000km2) and form primarily in polar and sub-polar regions that are relatively flat and high in elevation.

glaciers as agents of erosion

-quarrying varies spatially, reflecting differences in the intensity and character of erosion processes such as abrasion, quarrying, and glaciofluvial activity as well as the character of the rock below the ice, particularly the spacing of joints -warm-based glaciers in areas with high precipitation rates erode rock at rates between 1 and 1000 mm/yr while areas with less precipitation erode more slowly

glacial abrasion

Underlying bedrock worn smooth (grinding) by rock tools carried in the overriding ice or from bedload carried in sub-glacial meltwater streams produce some of most distinctive and characteristic evidence of glaciation including striations (long, straight scratches), grooves (deep), glacial polish, loess and rock flour grooves, striations and gouges routinely used as flow direction indicators for now-vanished ice sheets

Retrogressive thaw slump

Unique form of mass wasting in permafrost terrain Develops where erosion exposes the ice-rich upper layer of permafrost Typically occurs along eroding river banks or lakes and ocean shorelines.

glacial distribution overtime

Variable extent of glaciers over last 2 million yrs; last glacial maximum extent (~25,000 yrs ago) ice covered 25% of Earth's total land area

Thermokarst lakes

formed in depression as permafrost thaws Permafrost beneath prevents water from percolating into the soil which contributes to abundant surface water even though precipitation levels are typically low.

temperate glaciers

have ice at pressure melting point throughout

continuous permafrost vs. discontinuous permafrost

Continuous permafrost: areas where permafrost exists under almost all areas (except under rivers, lakes) Discontinuous permafrost: areas where permafrost exists under only some parts of an area year round (e.g. seasonal melt on slopes facing sun) Permafrost can be continuous or discontinuous. Above the permafrost, the active layer, which is decimeters to meters thick, thaws every summer. Unfrozen material under the permafrost or within permafrost is known as a talik. Talik depths increase under lakes and rivers. The temperature profile in the upper active layer of permafrost varies seasonally, freezing in the winter and thawing in the summer. Temperature in the permafrost generally increases with depth because of geothermal heat.

fjords

Deep valleys along the coastline cut by glaciers

ice flow velocity depends on

Distance from bed/valley sides (friction) Surface slope/gradient (steepness) Temperature of ice (cold/warm based glaciers) Free water at bed (basal lubrication) Material at base (till, bedrock) Snow mass accumulation (weight) (Does Sarah Try For Me Sure)

pingo

Dome shaped mound with ice mass at core ice core slowly grows in height (up to 90 m) as ice accumulates & forces overlying sediment upward Formation process • Draining of shallow lake underlain by wet, sandy sediments • Draining water moves downwards and forms ice lens that expands • Advancing permafrost generates upward pressure (hydrostatic) on mass of unfrozen soil and ice • Pushes the overlying material upward as it expands

periglacial environments

Environments that are not permanently ice-covered but experience below freezing temperatures for much of the year Climate of cold permafrost regions: • Mean annual temperature is < 0°C Dominant geomorphic processes: • Seasonal Freezing/ Thawing Periglacial Features & Landforms: • Permafrost & Patterned ground Permafrost not only in arctic areas, in both HIGH LATITUDES and HIGH ALTITUDES

outwash plains (sandur)

Form in front of the ice margin; smooth, gently sloping feature accumulated from stratified drift (layers of sands and gravels) sorted by lateral shifting of braided meltwater streams issuing from the ice. -Because they develop beyond the margin of an ice sheet, an outwash plain is classed as a proglacial deposit (developing along the front of glaciers)

Describe two ways in which glaciers move

Glacial ice moves in several ways as it responds to the shear stress induced by gravity --> ice deformation (creep) --> basal sliding (sliding at bed/ice interface) --> deformation of mobile bed rate of ice deformation or the strain rate varies with shear stress

Glaciers grounded on land vs. floating on water

Grounded glaciers: forms moraines, marginal position marked by a moraine and extent of glacier changes only slowly, increases resistance to flow, slowing delivery of ice to margin glaciers terminating in marine environments: affected dramatically by rising sea level or changes in mass balance, ocean water floats ice once grounded, ice margin degrades rapidly by calving and sheds mass in form of massive icebergs and sediment, leaving substantial submarine deposits in temperate environments, less grounded ice, flow speed increaes, increasing rate at which ice is delivered to margin

Dynamism of glaciers

1. due to phase transitions 2. ice melts when pressure on it increases (pressure melting) 3. b/c ice weak near it's melting point, easily deforms

Movement mechanisms vary for cold vs. warm based glaciers:

(i) ice deformation (slow creep due to slippage between crystals) (ii) basal sliding (relates to water at base, pressure melting) (iii) mobile bed deformation (soft, weak sediment beneath glacier)

Ice wedges

- vertical forms that develop where ice accumulates in deep cracks in the sediment >> patterned ground - only occur in permafrost, below the active layer - as cycle of thawing and freezing continues, year after year the wedge grows 1. Freeze-thaw expansion- contraction as water changes phase (liquid, ice) 2. Start from soil cracks filled with ice 3. Ice expands as it freezes and opens crack further (exerts pressure) 4. Next summer (thaw) water fills cracks and subsequently freezes 5. Freeze-thaw cycle continues > growth in ice wedge ice wedge casts: indicate where permafrost used to exist; form when ice melts away and sediment fills the resulting void

glacier movement

-Glaciers flow downslope because they accumulate mass (ice) in their upper portions (from precipitation and from wind-blown snow) and ablate (melt, sublimate and calve ice bergs) in their lower portions. -glaciers move in response to internal ice deformation called ice creep (cold based glacier) -some glaciers slide at bed/ice interface, called basal sliding (warm-based glacier) --> warm-based ice is not forzen to the bed, thus can slide over bed in addition to deforming internally, esp in summer with more meltwater strain rate varies with shear stress, can be approximated using experimentally derived equation known as Glen's flow law

geomorphic mapping

-indicates extent of now-vanished ice sheets & glaciers -demarcates margins of ice sheets that covered high lattitudes and mountain ranges -indicates glacial cycles -extent of ice sheets before last glaciation poorly known because glaciers usually destroy evidence of prior glaciations by overrunning, eroding and incorporating older sediments as they advance

global distribution of ice sheets

-large continental glaciers (ice sheets) cover Antarctica and Greenland -Greenland Ice Sheet: ~1.7 million km2 (approx. 3x times the size of Texas); occupies 90% of island of Greenland -Antarctic Ice Sheet: ~14 million km2 (approx. area of United States & Mexico combined); contains 30 million km3 of ice; thicker than Greenland ice (maximum accumulations of 4000m) -Average ice thickness (in Antarctica): 2 km Maximum ice thickness: 5 km 86% of ice in East Antarctica

glacial cycles

-periods of glaciation (ice sheets grow and spread outwards over vast areas) and interglaciation (a period of milder climate with retreat of ice sheets) -currently in period of glacial retreat (Holocene) which began about 10,000 years ago

terminal moraine

-piles of debris that accumulate at the distal end of glaciers as sediment melts at the ablation zone and as basal ice deforms and is thrust up from the bed

ice shelf

-thick suspended platform of ice that forms when glacier or ice sheets flows down to a coastline -most found around Antarctica, lose mass by calving -buttress ice upstream, reducing flow rate

Glen's Flow Law

-where A is rate parameter that increases with temp, indicating that warm ice deforms more rapidly than cold ice -T = sheer stress -model consistent with the observation that ice behaves similarly to a plastic material, deforming with increasing rapidity in response to increasing stress describes the deformation of ice. At low shear stress, ice strains (deforms) very slowly. Because the strain rate of ice increases rapidly as the shear stress increases, ice subjected to high shear stresses approximates a plastic material. In other words, small changes in shear stress cause large changes in strain rate. Once shear stress reaches a sufficient level, the ice will strain rapidly and signifcant ice flow will begin. This happens when a glacier reaches a critical ice thickness and surface slope.

Moraines

A mound, ridge, or mass of material that were left on the ground by a receding glacier.

periglacial layer

Active layer: shallow surface layer freezes/thaws each year (< 4 m thick) Permafrost: permanently frozen ground layer (soil, sediment, rock) that remains at or below 0oC for at least 2 years (1m to 1000 m thick) Talik: Unfrozen ground that lies below/ within permafrost layer or between the active layer and permafrost Ground ice: solid ice in pore spaces in soils or larger ice lenses/ wedges (usually in upper permafrost layer - geothermal influence lower down)

steepness of slope

Changes in gradient of the underlying rock surfaces also influence glacier movement. steeper gradient = glacier will accelerate and thin (extending flow) over steeper sections (eg rock steps)> large tensional cracks (crevasses) lower gradient = ice slows and thickens (compressive flow) pressure ridges deform the surface

cirque

Cirques are concave, circular basins carved by the base of a glacier as it erodes the landscape. Cirques grow steadily larger over time due to abrasion and plucking and their rough, steep walls gradually replace the smooth slopes of the original mountain

accumulation and ablation

Mass balance of glacier defined by difference between accumulation (gains from snow, wind drifting, avalanching) and ablation (losses from evaporation, sublimation, calving, melting) of a glacier over time -mid & high latitude glaciers spatial and temporal changes in glacier accumulation and ablation are seasonal and predictable -rates of accumulation and ablation are tied to elevation: b'c air masses cool as forced to rise over high elevation terrain, average air temp falls between 0.6-1 degrees Celsius for every 100 m of elevation gain, this change in temp w/ elevation is called lapse rate -thus in upper reaches, glaciers will be cooler than in lower reaches, more precipitation will fall as snow and less snow will melt

glacier

Mass of ice that has its genesis on land and that represents a multi-year surplus of snowfall over snowmelt - form in areas where annual snow accumulation is greater than snow melt = at or above lower limit of perennial snow "snowline" (function of latitude, climate) -Successive layers of snow are slowly compacted becoming more dense with depth and age

Ground instability

Permafrost environment is very sensitive to natural and human disturbances due to instability of ice layer Tilted Trees are a common sign of permafrost degradation Mechanical disturbances deepen active layer > saturation > destabilised infrastructure methane from video

Permafrost Aspect

Permafrost occurrence controlled by climate, elevation and ASPECT (direction of slope) - Aspect affects the amount of solar radiation a slope receives and influences the distribution of permafrost - Slopes facing the equator receive more sunlight, have less permafrost, and the permafrost they dO have is found at higher elevations

plucking

Removal of blocks of rock from outcrops. The glacier exploits rock weaknesses along fractures to pull the rock loose Plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the erosion and transportation of individual pieces of bedrock, especially large "joint blocks". This occurs in a type of glacier called a "valley glacier".

roche moutonnee

Rock formation with a gently sloping abraded side and steeper, plucked side

striations

Scratches on rock surfaces caused by movement of debris-rich glacial ice

tidewater glacier

Terminate in a body of water, such as a fjord - (submerged glaciated valley) or lake and calves icebergs -valley glaciers that flow all the way down to the ocean -calve numerous small icebergs

alpine glaciers

The erosive power of alpine glaciers creates steep cliffs and deep basins characteristic of once-glaciated mountain landscapes. -topographically constrained by the cirques in which they originate and the valley walls that confine them, lower reaches of alpine glaciers are often bordered by moraines -constrained by topography -found in high mountains of every continent except Australia Sub-types: Cirque, Valley, Piedmont, Tidewater -respond rapidly to changes in climate; advance and retreat on yearly to decadal timescale

strong bed vs. weak bed

The height and surface slope of an ice sheet reflect basal shear strength. A strong bed (one that requires high shear stress to deform) will generate steep ice margins, whereas a weak bed will result in less steep ice margins. Cold-based ice, frozen to the bed, would also have steep ice margins. -weak beds have LOW CRITICAL SHEER STRESS result in gently sloping ice sheets; common where ice overruns weathered material high in clay and silt -strong beds only deform under higher T found in areas of scoured rock with little basal water or deformable sediment and result in STEEP ICE MARGINS

glacier mass balance

accumulation of ice (mostly by snowfall) and loss by ablation (melting or calving of large chunks into standing water) -ice added to glaciers by precipitation, both falling directly ONTO glacier surfaces AND added by avalanches and wind carrying snow from above/adjacent highlands high and mid latitudes: glacial ice originates as snow falling DURING winter months monsoon-affected areas: snow during wet season; doesn't need to be winter COMPONENTS Accumulation zone -wind drifting and avalanching -snowfall Ablation zone -sublimation and evaporation -calving and melting @ toe -meltwater

kettles

adjacent to former ice margins, small depressions that are nearly circular in plan view result from subsidence of glacial sediments where ice blocks, buried during rapid, ice-marginal sedimentation, melt out leaving large depressions in the land surface that may fill with water if the water table intersects with the depression -form when a stagnant ice body is buried by outwash & as stagnant ice ablates, collapse structures form leaving depressions on the landscape CONTINENTAL GLACIATION

Equilibrium line

boundary between accumulation and ablation zone; is controlled by climate - climate warms, snowfall decreases, ELA rises - climate cools, snowfall increases, ELA falls -can be approximated in field by measuring elevation of the firn line (boundary between melting glacial ice in the ablation zone and firn, transformed snow, in accumulation zone, on a glacier at the end of the melt season -if the ELA does not change over time, the glacier is in steady state and its mass balance is stable

calving (ice loss)

calving of ice margins into bodies of water, including lakes and ocean as by toppling failures at steep ice margins

landforms of alpine glaciers

cirque, arête, tarn, horns, as well as depositional features lateral and terminal moraines and outwash terraces -leaves distinctive character to landscape

medial moraine

concentrations of debris where two tributary glaciers merge into one larger glacier

glacial energy balance

critical to determining whether glacier will advance or retreat; energy lost and gained through sunlight, sublimation, and warming snow and ice until they melt -energy and mass balances tightly linked bc energy inputs control the melting, sublimation and calving rates of ice COMPONENTS Energy Losses: -latent heat (sublimation and evaporation) - sensible heat -longwave radiation -reflected radiation (high albedo) Energy gains -latent heat (condensation) -sensible heat -longwave radiation -incoming solar energy -geothermal energy

sublimation (ice loss)

direct transfer of water from the solid to vapor phase; driven by water vapor pressure gradients when wind moves dry (undersaturated) air over ice surfaces; thus, sublimation is v important for cold glaciers in semiarid and arid regions

eskers

elongate, sinuous ridges composted of water laid, sorted sediment capped and underlain in many cases by till thought to be remnants of subglacial drainage systems, traces of sand and gravel-filled tunnels that once drained meltwater and sediment near now-vanished ice margins (long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America) -Eskers often used for road beds as tend to be well drained, and elevated CONTINENTAL GLACIATION

cryosphere

encompasses parts of the Earth with temperatures <0 degrees C for all part of the year

albedo (glacial energy balance)

reflectivity; when glacial surface covered by fresh, white highly reflective snow, it's albedo is high when covered by black ice (sediment toppled ice) the ice instead absorbs the thermal energy and melts, creating more black ice --> feedback loop

lateral moraine

form alongside ablation zone of alpine glaciers as debris roll off and melts out of the ablating ice

(continental) ice sheets

glacial ice accumulation over continents leaving behind landscapes of smoothed bedrock covered in some places with till (unsorted glacial sediment) -bury peaks, deposit moraines and other glacial sediment -large enough to influence climate by diverting storms, altering wind directions, and orographically enhancing precipitation -take centuries to respond to changing climate b/c so much ice to melt

warm-based glaciers

have free water at their bed because the temperature of the ice is at the pressure melting point; melting of ice at and above the bed allows for sliding and abrasion of the rock below, as well as for the creation of fluidized sediment layers -liquid water abundant at least during melt season

subpolar glaciers

have surface melt during the summer but most of the glacier remains at temperatures colder than the pressure melting point of ice

Ice lenses

horizontal layers of ice that form as the active layer freezes again at the end of the warm season >> displacement of ground surface.

valley glaciers

ice masses that are confined to valleys and typically originate in cirques

horn

if headward erosion of cirques continues, upland surrounded by headward-retreating cirques with intervening aretes may be eroded into an isolated peak of rock known as horn -When 3 or more cirques grow together, the remnant peak is left as a sharply pointed pyramid or HORN

arête

knife-edge ridges fromed as two cirques or parallel U-shaped valleys erode toward one another, leaving only a steep-sided narrow ridge of rock between them -Where only 2 cirque walls approach from opposite sides, a jagged, knifelike ridge, or ARÊTE, is created.

stratified drift

layers of clays, silts, sands, or gravels that were deposited by meltwater streams or settled out in bodies of water adjacent to the ice.

glacial isostasy

loading and unloading of crust by glacial ice

periglacial

low temperature but not glaciated; defined by geomorphic importance of ice/water phase transition AND presence of seasonally snow-free ground -expanses of patterned ground (geometric regularity) result of thermal contraction, growth of ice lenses, and stirring of soils in periglacial terrain -permafrost, permanently frozen ground, important

meltwater streams (ice loss)

mass leaving glacier system as ice and snow melt and water drains away in meltwater streams

polar glaciers

remain below freezing, have no surface melt at any time of year

cold-based glaciers

remain frozen to their beds bc bed temperature and temperature throughout ice mass is below pressure melting point of ice; prevents melting at the base of the ice and restricts flow to internal deformation in snow and ice

crevasse fills

result of sediment carrying meltwater filling open crevasses

till

most ubiquitous sediment left by glaciers; specific type of unsorted deposit, deposited both from below the ice and from above the ice as it melts away -cover large areas that were occupied by continental ice sheets during the Pleistocene

regelation

occrus when ice flows over rock obstacles on glacier bed; pressure-melting of ice up-glacier of an obstacle releases water, which then travels down ice to areas of low pressure and consequently refreezes. this freezing may incorporate debris, and enrich the remaining solution in elements such as calcium, which precipitates and forms calcium carbonate coatings on subglacial rock surfaces. regelation facilitates meovement of warm-based glacial ice over rough bedrock beds

Ice fields

occupy highlands and in many places bury existing topography, drained by outlet glaciers that transport ice to lower elevations where it melts and deposits moraines

piedmont glaciers

occur when steep valley glaciers spill into relatively flat plains, where they spread out into bulb-like lobes.

ice fields

on the same scale as ice caps, BUT subglacial topography still exerts significant control on shape of ice field and flow of ice -Extensive ice accumulation in mountain region feeding several outlet glaciers and elongated along a mountain chain (topography differs from ice cap, lacks dome)

supraglacial

on top of ice

kame

sediment that fills voids in the ice that ice later melts away, then sediment will form a high point on the landscape. if deposit is circular in plan form, it is referred to as a kame -come from both sorted sediment and unsorted material -form when sediment is deposited on the ice surface and is subsequently lowered onto the landscape as the glacier melts away CONTINENTAL GLACIATION

drumlin

streamlined, distinctively glacial landforms -elongate hills found in many low-relief areas formerly overridden by continental ice sheets -low rounded oval hills formed under the glacier and made up of sub- glacial sediment deposits molded by its movement TEARDROP FROM THE AIR

Human Interactions with permafrost

structural instability Heat generated by buildings as well as warming external conditions have caused permafrost to thaw at an increased rate making many structures unstable

perennial ice

thickest component of sea ice

moulins

vertical conduits, where glacial streams accumulate water from surface melt in the summer, flow over the ice and plunge down moulins to become part of the englacial or subglacial drainage system

englacial

within ice