Dynamic Planet Study Document

THE COMPETITION: Participants will be given one or more tasks presented as an exam and/or timed stations. Topics will include the following:

a. Glacier formations

i. Properties of ice (e.g., crystal structure, density)

ii. Formation of glacial ice from snow, névé, firn

iii. Glacial budget/mass balance: ablation and accumulation, equilibrium line

iv. Glacial flow: influence of bed (e.g., basal sliding), and relation of flow to elevation and slope

b. Types of glaciers & their geographic distributions:

i. Valley/alpine (cirque, hanging, piedmont)

ii. Ice sheet/continental, including ice stream, ice shelf, ice rise, ice cap, ice tongue

c. Features in glacial ice:

i. Crevasses, ogives, icefalls

ii. Ice shelves and related processes (e.g., calving, marine ice sheet instability, ice shelf buttressing)

d. Formation of landscape features by glaciers:

i. Erosional – cirque, tor, U-shaped valley, hanging valleys, arêtes, horns, striations, Rôche moutonnée

ii. Depositional – moraines (end/terminal, recessional, lateral, medial, ground), kames, drumlins, eskers, erratics

iii. Lakes – tarns, the Great Lakes, Finger Lakes, kettles, moraine–dammed lakes, proglacial lakes

e. Periglacial processes and landforms (e.g., permafrost, pingos)

f. Sea ice (ice floe, draft vs freeboard, pressure ridge, formation (e.g., frazil ice, pancake ice))

g. Glacial hydrology: surface melt, surface lakes, moulins, drainage and subglacial lakes

h. Global connections of glaciation:

i. Atmosphere – effect of greenhouse gases & aerosols on glaciation (e.g., amplified melting due to changes in albedo, release of gases from glacial melting)

ii. Oceans – sea level change and ice sheet variation (thickness and extent)

iii. Lithosphere – isostatic effects on Earth’s crust

iv. Planetary/orbital influence on glaciation (e.g., Milankovitch cycles)

i. History of ice on Earth and its evidence (e.g., drop stones, striations, sedimentary deposits), limited to:

i. Neoproterozoic snowball Earth

(1) Late Paleozoic ice ages

(2) Eocene Oligocene Transition and the impact of opening oceanic seaways such as the Drake Passage

ii. Pleistocene Northern Hemisphere glaciation (e.g., Laurentide Ice Sheet retreat & melting history)

iii. Recent records of cryospheric change (e.g., Larsen B, Thwaites Glacier, Amundsen Sea Embayment)

j. Sedimentary sequences produced in glacial environments (e.g., varves, outwash vs till)

k. Methods of studying glaciers & interpretation of related data:

i. Altimetry, radar, optical imagery, seismology, and gravimetry

ii. Ice cores as archives of past environments, including the use of gases, aerosols, and stable isotope compositions

l. Glacial hazards, including but not limited to ice avalanches and glacial lake outburst floods

https://www.soinc.org/dynamic-planet-c

https://scioly.org/forums/viewtopic.php?t=28699

https://scioly.org/wiki/index.php/Dynamic_Planet/Glaciers#Movement 

https://www.youtube.com/live/wwLsKCEFGTs?si=JccacHz7Q-UOITSN (SciOly Study Tips)

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Glacier Formation

Properties of Ice 

• less dense than water

• can assume large number of crystalline structures

• Hexagonal crystal lattice

• The ice crystal commonly takes the form of sheets or planes of oxygen atoms joined in a series of open hexagonal rings.

• solid substance produced by the freezing of water vapor or liquid water. At temperatures below 0 °C (32 °F), water vapor develops into frost at ground level and snowflakes (each of which consists of a single ice crystal) in clouds. Below the same temperature, liquid water forms a solid, as, for example, river ice, sea ice, hail, and ice produced commercially or in household refrigerators. 

  • Mechanical Properties

• Like any other crystalline solid, ice subject to stress undergoes elastic deformation, returning to its original shape when the stress ceases. However, if a shear stress or force is applied to a sample of ice for a long time, the sample will first deform elastically and will then continue to deform plastically, with a permanent alteration of shape. This plastic deformation, or creep, is of great importance to the study of glacier flow. It involves two processes: intracrystalline gliding, in which the layers within an ice crystal shear parallel to each other without destroying the continuity of the crystal lattice, and recrystallization, in which crystal boundaries change in size or shape depending on the orientation of the adjacent crystals and the stresses exerted on them. The motion of dislocations—that is, of defects or disorders in the crystal lattice—controls the speed of plastic deformation. Dislocations do not move under elastic deformation.

• The strength of ice, which depends on many factors, is difficult to measure. If ice is stressed for a long time, it deforms by plastic flow and has no yield point (at which permanent deformation begins) or ultimate strength. For short-term experiments with conventional testing machines, typical strength values in bars are 38 for crushing, 14 for bending, 9 for tensile, and 7 for shear.

  • Thermal Properties

• The heat of fusion (heat absorbed on melting of a solid) of water is 334 kilojoules per kilogram. The specific heat of ice at the freezing point is 2.04 kilojoules per kilogram per degree Celsius. The thermal conductivity at this temperature is 2.24 watts per meter kelvin.

• Another property of importance to the study of glaciers is the lowering of the melting point due to hydrostatic pressure: 0.0074 °C per bar. Thus for a glacier 300 meters (984 feet) thick, everywhere at the melting temperature, the ice at the base is 0.25 °C (0.45 °F) colder than at the surface.

• Optical Properties

• Pure ice is transparent, but air bubbles render it somewhat opaque. The absorption coefficient, or rate at which incident radiation decreases with depth, is about 0.1 cm^-1 for snow and only 0.001 cm^-1 or less for clear ice. Ice is weakly birefringent, or doubly refracting, which means that light is transmitted at different speeds in different crystallographic directions. Thin sections of snow or ice therefore can be conveniently studied under polarized light in much the same way that rocks are studied. The ice crystal strongly absorbs light in the red wavelengths, and thus the scattered light seen emerging from glacier crevasses and unweathered ice faces appears as blue or green.

  • Electromagnetic Properties

• The albedo, or reflectivity (an albedo of 0 means that there is no reflectivity), to solar radiation ranges from 0.5 to 0.9 for snow, 0.3 to 0.65 for firn, and 0.15 to 0.35 for glacier ice. At the thermal infrared wavelengths, snow and ice are almost perfectly “black” (absorbent), and the albedo is less than 0.01. This means that snow and ice can either absorb or radiate long-wavelength radiation with high efficiency. At longer electromagnetic wavelengths (microwave and radio frequencies), dry snow and ice are relatively transparent, although the presence of even small amounts of liquid water greatly modifies this property. Radio echo sounding (radar) techniques are now used routinely to measure the thickness of dry polar glaciers, even where they are kilometers in thickness, but the slightest amount of liquid water distributed through the mass creates great difficulties with the technique.

Formation of glacial ice from snow, névé, firn

• Snow: individual ice crystals that grow while suspended in the atmosphere

  • Four main types 

• Névé: granular type of snow that has been partially melted

  • This type of snow can contribute to glacier formation through the process of nivation

  • Névé that survives a full season of ablation turns into firn

  • Minimum density of 500 kg/m, which is roughly half of the density of liquid water at 1 atm

• Firn: partially compacted a type of snow that has been left over from past seasons

  • been recrystallized into a substance denser than neve

  • ice that is at an intermediate stage between snow and glacial ice

  • older and slightly denser than neve

  • eventually becomes glacial ice

  • density generally ranges from 0.35 g/cm3 to 0.9 g/cm3

Glacial budget/mass balance: ablation and accumulation, equilibrium line

• So, glacier mass balance is the quantitative expression of a glacier’s volumetric changes through time.In the figure below, Panel A shows how temperature varies with altitude. It is colder at the top than it is at the bottom of the glacier. This is crucial, as surface air temperature strongly controls melting and accumulation (as in, how much precipitation falls as snow or ice).

• Glacier mass balance is normally measured by staking out a glacier. A grid of ‘ablation stakes’ are laid out across a glacier and are accurately measured. They can be made of wood, plastic, or even bamboo like you’d use in your garden. These stakes provide point measurements at the glacier surface, providing rates of accumulation and ablation.

• The Mass Balance, the balance of accumulation and ablation, is usually therefore positive in the winter and negative in the summer. Mass balance is the total sum of all the accumulation (snow, ice, freezing rain) and melt or ice loss (from calving icebergs, melting, sublimation) across the entire glacier.

• A glacier’s mass balance gradient is critically determined by the climatic regime in which it sits; temperate glaciers at relatively low latitudes, such as Fox Glacier in New Zealand, may be sustained by very high precipitation.

• The Cumulative mass balance is the mass of the glacier at a stated time, relative to its mass at some earlier time. Some glaciers have mass balance measurements going back decades, which means that scientists can analyze how mass balance is changing over time.

• Ablation: combined processes (such as sublimation, fusion or melting, evaporation) which remove snow or ice from the surface of a glacier or from a snow-field; also used to express the quantity lost by these processes. 

• Accumulation: all processes by which snow or ice are added to a glacier. 

• The equilibrium-line altitude (ELA) marks the area or zone on a glacier where accumulation is balanced by ablation over a 1-year period. 

• Accumulation usually occurs over the entire glacier, but may change with altitude. Warmer air temperatures at lower elevations may also result in more precipitation falling as rain. The zone where there is net accumulation (where there is more mass gained than lost) is the accumulation zone. The part of the glacier that has more ablation than accumulation is the ablation zone. Where ablation is equal to accumulation is the Equilibrium line altitude.

Glacial flow: influence of bed (e.g., basal sliding), and relation of flow to elevation and slope

https://scioly.org/wiki/index.php/Dynamic_Planet/Glaciers#Movement 

• Glaciers move because of gravity

• Glaciers never flow backwards up mountain, but can have net loss of ice, making it seem to move up the mountain

• Glaciers can flow up to get over obstacles, but never towards its own head

3 Ways Glaciers Flow:

• Basal Sliding

• Internal Deformation

• Bed Deformation

• Thermal regime and other factors controlling movement

• Basal Sliding: Movement of the base of the glacier across the bedrock where its located, incorporates meltwater 

  • 3 ways this basal sliding happens:

  • • Basal slip: occurs when thin layer of water between ice and rock underneath makes the glacier smooth, making flow faster

      • Meltwater comes from pressure-melting, percolation, and water channels (like moulins)

      • Basal slip is easier to put on smoother bedrock surfaces, but still adds to the majority of basal sliding

      • If enough meltwater is there, a surge (fast glacial movement) can happen 

    • Enhanced basal creep: happens when ice faces a large obstacle, big increase in pressure makes the ice deform around obstacle

    • Regelation Flow: when ice faces a small bedrock obstacle

      • Ice does not deform around obstacle, but the ice will melt under pressure and refreeze on the other side, but ONLY happens if object is small enough to allow heat on the downhill side to quickly happen on uphill side to help with melting

• Internal Deformation: (AKA creep, internal flow, plastic flow, plastic deformation) process involves ice crystals sliding across each other within the glacier

  • Ice can deform due to how it behaves plastically with extreme pressures (standard in glaciers)

  • Glaciers flow faster near center because of internal deformation, may slide more easily against other ice than rougher rocky beds, which leads to a sagging shape can sometimes be visible

• Bed Deformation: involves movement of softer sediments to allow the glacier to go downhill

  • Fine sediments like clay and sand will deform more easily when stress is applied and also have high power-water pressure (pressure of groundwater between particles

  • Bed deformation depends on meltwater at base

  • Basal sliding is more efficient if water remains directly under surface of ice, but bed deformation is better when the sediment becomes saturated with water which reduces its strength

• Thermal Regime: the base, the temperature of a glacier determines the thermal regime,  a way of classifying glaciers

  • Cold based (Polar): frozen year round, except where there’s seasonal melting near the surface, base stays frozen though, and usually found at higher latitudes, minimal to no meltwater, only move with internal deformation without any basal slip or bed deformation, usually frozen to the rock

  • Warm-based (temperate): (AKA wet based), usually characterized by being warm enough to have meltwater, and generally or very close to melting point during the year throughout the whole glacier, found at lower latitudes, usually move though basal sliding (mostly basal slip), meltwater plays a large role in process usually coming from surface melt that’s channeled to the bottom though mouling, tunnels, crevasses, and more. During the winter, the glacier usually refreezes to bedrock, slowing the movement, the meltwater of warm-based glaciers can lead to an increase in plucking (where glaciers erode the bedrock underneath by freezing onto it and pulling away when it moves) which will cause more sediment transport

  • Polythermal (subpolar): those that have components of both warm and cold glaciers, most valley glaciers are polythermal, containing elements of both depending on the location, range from mostly cold or hot

• Other factors that control movement:

  • Bedrock conditions are usually the largest force that acts against the flow of a glacier, friction with rougher surfaces will act to slow the motion of a glacier

  • Terminal conditions like debris at the end of a glacier like terminal moraine add an extra buffer of glacial movement

  • Ice shelf buttressing happens similarly to above, happens when ice shelf prevents an outlet glacier from moving further into sea, slowing or stopping its flow, without ice shelves, outlet glaciers would drain ice sheets w/o restrictions making a severe change in mass balances

  • Tidewater glaciers empty into water without ice shelf buttressing, have higher rates of flow and calving

Types of glaciers & their geographic distributions:

Valley/alpine (cirque, hanging, piedmont)

Valley Glaciers

• streams of flowing ice that are confined within steep walled valleys

• often following the course of an ancient river valley

• the downward erosive action of the ice carves the valley into a broad U shape

• a U shaped valley with a flat floor is good evidence of the past glaciation of an area

• usually start life in either corries or ice sheets

• In large systems, valley glaciers may join and form larger glaciers with much greater erosional power than they had

Alpine Glaciers 

• a glacier that forms at high elevations within mountains

• as the glacier grows, the ice slowly flows out of the cirque and into a valley

• plucks and grind up rocks 

  • creating distinctive U-shaped valleys and sharp mountain peaks and ridges

Ice Sheet (Continental Glacier)

• mass of glacial ice that covers surrounding terrain and is greater than 50,000 km^2

• surface is cold

  • but base of ice sheet is generally warmer than due to geothermal heat

• only two existing ice sheets in the world: in Greenland and Antarctica

Features in glacial ice:

i. Crevasses, ogives, icefalls

ii. Ice shelves and related processes (e.g., calving, marine ice sheet instability, ice shelf buttressing)

• Crevasses: deep cracks or fractures in a glacier, formed when ice goes through brittle deformation, splitting because of extreme stress in short period of time

  • Water will affect dynamics of a glacier, if its deep enough it will connect the surface melt and bed, providing lots of water that can increase basal slip

  • Will preserve marks of stress and strain that allow for movements of glaciers to be deciphered

  • TYPES OF CREVASSES AND FORMATION

    • Marginal: formed near the sides of a glacier

      • formed when a glacier passes stationary valley walls

      • Ice in center flows faster which applies shear and tensional stress which leads to crevasses pointed upslope at about 45 degrees from horizontal

    • Longitudinal: form parallel to direction of flow

      • Formed when glacier expands in width of on outside edge of turn where valley bends

      • When looking at a downslope, they form a concave down shape but generally near parallel to valley walls

    • Splashing/Splay: usually formed near terminus (end of a glacier) where the flow is compressional

      • Parallel to ice flow

      • Look similar in orientation and looks to longitudinal, but form from compressional forces pushing ice out laterally

      • If glacier spreads wide enough at terminus, splay crevasses will radiate out from centerline

      • NOT THE SAME AS CREVASSE SPLAY (non glacial fluvial deposit)

    • Transverse: most common crevasse

      • Form in zone of extending flow where stress parallel to direction of flow

      • Tension stretches the glacier to fracture

      • Side by side across mountain, about perpendicular to flow

      • Form when valley steepens like icefall

      • Icefall: like a waterfall, a part of the glacier’s flow that has a sudden change in altitude->lots of crevassing as surface layers of ice stretched more than base

    • Randklufts and Bergschrunds: Randklufts is the gap between the headwall of a glacier and the ice under (downslope) 

      • Formed when ice is directly in contact with the rock and is melted and widened in warmer months

      • Shrund is formed between a stagnant block of ice above and a moving block of ice below, usually found at higher altitudes

  • Crevasse Depth: controlled by… compressive pressure from ice and expansive pressure from water

    • The deeper into a glacier, the higher the pressure that’s keeping a crevasse shut

      • This is why crevasses don’t become larger than 3 meters deep (internal compression from glacier is more powerful than the tensing forces pulling it apart

    • Adding water upsets the balance as water also exerts more pressure the deeper it is meaning the crevasse can grow more deep

      • Allows for crevasse to become deep enough to the base of a glacier that allows for lots of meltwater drain and more basal slip

• Ogives (forbes bands): alternating crests and valleys in glacier ice that appear as dark and light bands of ice

  • Linked to seasonal movement of a glacier

  • Distance from a light and dark band is about equal to annual movement of glacier

  • From downslope icefalls that contain large transverse crevasses

  • Will be filled with snow if not far in ablation zone (the area of the glacier that is the low altitude area, that loses ice because of ablation)

  • Dark bands don’t have air bubbles, because of the way glacier ice forms

  • Lighter bands have fresher snow, has air pockets and less dense

    • Both take on a more crescent shape because of view from downslope

  • Higher rate of flow in center of glacier, variations in height of different bands of ogives caused by uneven melting because of different colors

    • Dark bands absorb more solar radiation and melt more

  • Ogives either lack smooth forms or distinct color variations

  • Uncommon on unconstrained ice sheets, ice caps, and ice fields because of their formation

• Ice Falls: Part of a glacier with rapid flow and a chaotic crevassed surface; occurs where the glacier bed steepens or narrows

• Ice Shelves: Permanent floating sheets of ice

  • Form from ice sheets that slowly flow to sea after breaking off from glaciers or being carved by ice streams

  • Glacier outflow is the most common source of ice for larger ice shelves

  • If they don’t melt in ocean, they can continue to grow into larger ice masses

  • Typically flat and featureless

• Glacial Calving: When chunks of ice break of at the end of a glacier because of forward motion of a glacier makes the end of the glacier unstable

  • Chunks of broken ice called iceberg-> white icebergs have lots of bubbles inside, blue icebergs are very dense, greenish black ones may have broken off from the bottom, darkly striped ones carry moraine debris from glacier

• Marine Ice Sheet Instability:

  • Marine Ice Sheet: one whose bed lays below sea level, edges flow into floating ice shelves

  • Rising temperatures cause problems in West Antarctica as it led to a collapse of the west antarctic ice sheet

    • Too much of the ice sheet was below sea level

• Buttressing: surrounding topography restricts glacier movement, usually at the edges of glacier

  • Happens when physical barriers limit movement of glaciers by slowing it, usually it moves by its own weight, but when flow is redirected due to barriers, there may be a build up of pressure

Formation of landscape features by glaciers:

• Erosional:

  • Cirque (corries or cwms): large bowl shaped area carved out a mountain by moving glacier, bounded by steep cliff known as a headwall

    • Niche: a very small glacier that occupies gullies and hollows on pole facing slopes of a mountain which are covered by shadows, if conditions favor, can develop to cirque

  • U-shaped valley: a standard glacially eroded valley, contrasts v shaped valley

    • Fjords are these u shaped valleys that open up to sea and partially filled with water

  • Hanging Valley: a valley glacier that ends at a hanging valley

  • Arêtes: a sharp parallel ridge of rock that resists erosion, formed by two cirque glaciers that come together but not join

  • Horns: a pyramidal peak formed by 3 or more cirques that meet on a central

  • Roche Moutonnee: a hard bedrock bump or hill that’s been overrun by a glacier to give smooth side going up and rough surface going down

    • Up glacier often marked with striations

• Striations: long narrow channels that cut into bedrock by englacial debris

  • Parallel to adjacent grooves, indicate direction of glacial movement

  • Cut by mid to large rocks, smaller fine sediments polish entire rock surface which make a pavements

• Depositional – moraines (end/terminal, recessional, lateral, medial, ground), kames, drumlins, eskers, erratics

  • Moraines: any ridge or mound of glacial debris that is deposited in glaciated regions, can be made of boulders, gravel, sand, and clay

    • Terminal moraines: deposited at end of glacier

    • End moraine: terminal and recessional moraine because formed in same way

    • Recessional: ridges behind terminal moraine, mark where glacier has previously stopped

    • Lateral: material that's been put to the side of glaciers

    • Medial: form between two glaciers when converge

    • Ground: layer of till and other sediments under a glacier

  • Kames: irregularly shaped hill that's made of sand, gravel and till that collects in a depression on a retreating glacier which is deposited on land upon further retreat, formed by continental glaciers

  • Drumlins: Elongated, streamlined hills formed from glaciers acting on till and/or ground moraine. The gently sloped and tapered end points in the direction of glacier flow. They often resemble a crag & tail. Drumlins almost always form in large groups, known as drumlin fields. They are features of continental glaciation.

Lakes – tarns, the Great Lakes, Finger Lakes, kettles, moraine–dammed lakes, proglacial lakes

• Tarns: lakes that are formed in cirques, generally small compared to cirque its located in

• Great Lakes: 

  • Creates hydropower generation, commercial shipping in fishing industry

  • Predicting ice coverage on Great Lakes has an important role in determining climate patterns, lake water levels, water movement patterns, water temperature structure, and spring plankton blooms

  • Formed: by a fracture in the earth that ran from Oklahoma to Lake Superior that split North America from volcanic activity, lava flowed from the crack for 20 mil. Years

    • The geomorphic age made the mountains in this area in the area of Wisconsin and Minnesota, Laurentian mts. Formed in E Canada, mts eroded→volcanic activity continued

    • Molten magma that was below the highlands (area of high or mountainous land) that sunk making a mammoth rock basin that would eventually hold lake superior

  • The area went from fire to ice, and repeated, during the time of glaciation, the giant sheets of ice flowed across the land which levelled mts and carved out large valleys→encountered resistant bedrock in north, in south softer sandstones

  • When glaciers melted and receded, the leading edges left behind high ridges, and lakes formed between the ridges, the drainage from the lakes went south through the Illinois River to Mississippi, when the weight of the glaciers was heavily decreased as they left, the land rebounded, and land in the great lakes basin continues rising today

• Glaciers retreating led to water levels going through dramatic fluctuations (some in 100s of feet)

• Finger Lakes: Overdeepended U-shaped valley basins form finger lakes, can be hundreds of meters deep, capped off by moraines

  • Extreme elevation changes can lead to gorges (narrow valley between hills or mts, typically with steep rocky walls and a stream running through it) forming 

• Kettles: formed when dead ice (glacier or chunk of ice that no longer moves and melts in place) form kettles

• Moraine dammed glacial lakes: are bodies of water that’s between a moraine ridge and glacier, and can be divided into three subclasses; end-moraine dammed lakes, lateral moraine-dammed lakes, moraine thaw lakes

  • Second most common type of lake found globally, usually unvegetated, unconsolidated, and can have ice cores

  • Most lateral and terminal moraines that impound present-day glacial lakes were made during little ice age

  • Moraine dammed lakes are formed by…

    •  meltwater pooling in glacial overdeepening between moraine and glacier 

    • Coalescing of surface ponds

• Proglacial lakes: a freshwater lake, formed behind a moraine or ice dam

  • Is left by a glacier that is retreating

  • Come in different shapes and sizes

Periglacial processes and landforms (e.g., permafrost, pingos)

• Permafrost

• Pingos