Lesson 6 Snow avalanche & Glacier - CDEEP-IIT Bombay

GNR 639

Prof. R. Nagarajan, CSRE , IIT Bombay

GNR 639 : Natural Disaster And Management

Lesson 6

Snow avalanche & Glacier

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GNR 639 : Natural Disaster And ManagementSnowfall - precipitation that falls from the clouds over higher altitudes which consists of snowflakes, in a variety of sizes and shapes. Snow is composed of small ice particles in the form of granular material. It has an open and soft structure, unless packed by external pressure.

Powdery Snow is fluffy, granular when it begins the cycle of melting and refreezing, and eventually iceonce it packs down. After multiple melting and refreezing cycles, snow becomes a dense mass called

snow pack. Powdery snow moves with the wind from the landing location forming deposits called snowdrifts.

The water equivalent of a given amount of snow is the depth of a layer of water having the same mass and upper area. The snow covering a given area has a water equivalent of 50 cm, when it melt into a pool of water 50 cm deep covering the same area.

Once the snow is on the ground, it will settle by its own weight due to differential evaporation until its density is approximately 30% of water.

Snow avalanche - are the moving masses of snow that contain rock, soil or ice, caused by direct loading of snowfall from large-scale weather system of the mountains. Precipitation patterns and intensity, wind direction and wind speed, and radiation heating or cooling on snow are important in snow avalanche..

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Courtesy: realaspen.com) (courtesy: colorado.edu)

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Trigger which causes the avalanche Start zone from which the avalanche originates

Crown fracture at the top of the start zone of slabavalanche

Flank fractures on the sides of the start zones. crownand flank fractures are vertical walls in the snow

Shallow staunch fracture at the bottom of the start zone

Slide path along which the avalanche flows

Run out where the avalanche comes to rest

Debris deposit which is the accumulated mass of the avalanched snow once it has come to rest (source courtesy: ffden-2.phy-vaf.edu)

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Wet snow avalanche or isothermal avalanche occurs when the snow pack becomes saturated by water. When the percentage of water is very high they are known as slush flows and they can move on very shallow slopes.

Powder snow avalanches are the largest, most powerful of avalanches that can exceed speeds of 300 km/h.Masses of 10,000,000 tonnes. Turbulent suspension of snow particles then flows as gravity current.

Slab avalanches are generated when an additional load causes a brittle failure of a slab that is bridging aweak snow layer. This failure is propagated through fracture formation in the bridging slab. It accounts foraround 90% of avalanche-related fatalities, and occur when there is a strong, cohesive layer of slab snow.

Loose snow and isothermal avalanches are generated when a stress causes a shear failure in a weakinterface, either within the snow pack, or at the base. When the failure occurs at the base they are knownas full depth avalanches.

Spin drift avalanches occur when wind lifted snow is funneled into a steep drainage from above thedrainage. It occurs in freshly fallen snow that has a lower density and is most common on steeper terrain.

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Schematic diagram of Slab avalanche formation

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Source courtesy.avalanche.org

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(Source courtesy: avalanche.org)

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Criterion Characteristics

Type of Rupture Starting from a line: slab avalanche(soft

slab avalanche, hard slab avalanche)

Starting from a point : loose snow

avalanche

Position of sliding surface Within snow cover: surface layer

avalanche(new snow fracture ,old snow

fracture)

On the ground: entire snow cover

avalanche

State of humidity Dry snow: dry snow avalanche open, flat

track: unconfined avalanche

Wet snow : wet snow avalanche

Form of track Open, flat track: unconfined avalanche Channeled track: Channeled avalanche

Form of movement Whirling through air: airborne powder

avalanche

Flowing along ground: (sliding

avalanche, flowing avalanche)

Triggering action Internal release: Spontaneous avalanche External trigger: (natural, artificial)

Avalanche classifications (UNESCO 1981:29-30)Classification scheme of the international commission on snow and ice

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Movement Snow type Conditions for

occurrence

Scale Characteristics

Primary (during

snowfall)

Dry Slope steeper than

friction

Small Surface runs of snow

Secondary (after

snowfalls)

New snow on

crust

External trigger Small to

intermediate

Snow block debris

Crusted surface External trigger Intermediate Large slab

Wet surface layer Solar radiation warm

wind, rain

Small Wet mass, slow velocity

Depth hoar Constructive

metamorphism

Intermediate to large Large blocks, entire layer

Wet snow Warm weather, weak

base

Intermediate to very

large

Large blocks, slow to

medium velocity

Primary and secondary avalanching

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Terrain Factors

Snow can accumulate deeply and quickly in mountain areas, increasing the possibility of an avalanche. You can offer clues about avalanche likelihood. Terrain traps serve as accumulation points for snow and debris

Altitude - risk factor increases with increases in altitude. Tree line is an imaginary line, above which conditions become too harsh for trees to grow, and avalanches start above the tree line.

Vegetation - 90% of avalanches occur on terrain with a green cover and average ground cover height is lower than 2 m. during avalanches, trees and rocks catch debris and cause excessive snow pile-up, as well as provide lethal obstacles for anyone caught in an avalanche. Smooth surfaces, such as a rock face or grassy slope may cause avalanches during the spring melting season.

Slope Aspect - slope orientations are much more affected by wind-loading, particularly northeast, east, and southeast. Most of the avalanches run on slopes facing north, east, and northeast because the sun is at such a low angle, particularly during the winter, a colder and deeper snowpack develops.

Slope steepness – Avalanches most frequently occur on natural slope of 300 to 450, but their release is from 25 to 650 slopes. Avalanches can occur on any slope angles under the right conditions.

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Slope profile – Disastrous avalanches are more likely to begin on convex slopes but may also begin on concave slopes. Short slopes may be as dangerous as long slopes

Meteorology Rapid weather changes in wind, temperature, snow, rainfall cause changes in the stability of the snowpack.

Wind Direction - The wind can deposit snow ten times more rapidly than snow falling directly from the sky. Wind drifted snow is always found on steep slopes. A cornice or icy overhang at the top of a mountain or ridge is a telltale sign of wind scouring.

Wind Speed- The snow that is fallen on the mountain terrain is redistributed by wind drift. From high crests snow is blown to cause excessive deposition in depression, zones of avalanche formation and on leveled ground where snow drift glaciers may form. Wind speed over 10 km/hr can transport crystals of diameter 1-2 mm to a distance of 100 to 500 m on an average.

Air Temperature is the most important element responsible of metamorphic changes in snow cover.

Temperature-Gradient (TG) layer may gain strength by sintering and instability may reappear during spring by melting of the sintering bonds. This condition can be significantly warmer on the bottom of the snow pack than at the snow's surface.

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Storms – Avalanches are most likely to run either during or immediately after a storm where there has been significant snowfall. The 24 hours following a heavy snowstorm are the most critical period.

Snow Cover Recent snowfall puts extra stress on the existing snowpack, especially if it does not adequately bond to the pre-existing surface layer. The extra weight of new snow alone can cause a snow slab to break off and fall down the slope in storm-induced avalanches. Snowfall amounts of one foot or more create the most hazardous situations.

Snow-Depth - New snow layers more 25-30 cm thick most frequently lead to soft slabs. It has been found out that risk factor increases with increases in snow depth.

Snow Temperature - Avalanche generally occurs when snow temperature is in and around <-70 C due to formation of weak TG layer.

Snow Grain Size- A difference in grain size greater than 0.5 mm and a large difference in hardness indicate instability, as does a depth to the interface between 20 cm and 85 cm.

Depth hoar forms in areas of a snowpack where temperature gradients are greater than 10ºC per meter. Depth hoar is often the weakest layer in the snowpack and is a potential sliding layer for avalanches.

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Snow Density - The stability of the snowpack is influenced by many factors, but two of the mostimportant is the strength of the weak layer and the load it has to support. The fresh snow depth, typeand density also offer clues to stability.

Grain Type of weak layer - Persistent grain types (facets, depth hoar and surface hoar) as well as icelenses, crusts and grain type anomalies raise suspicion in any snow profile.

Snow layering – Testing of the layering and bonding of the snow structure by using ski or probe poleindicate the strength of the various snow layers. The strong layers may act as a sliding surface foravalanches, especially if overlaid by a weak layer.

Wet snow – A rainfall can rapidly weaken surface snow and overload, weak layers. During sustainedrainfall a series of avalanches may occur on the same slope as progressively deeper snow layers areweakened and stressed.

Snow Depth and Anchoring - Large rocks, trees, and dense brush anchor the snow. Smooth, uncoveredslopes without these natural anchors are more dangerous. But avalanches can start even among trees.Weak layers deep in the snowpack can cause avalanches even if the surface layers are strong or wellbonded.

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GNR 639 : Natural Disaster And ManagementOther observations

Old slide pads - Avalanches reoccur in paths where they’ve occurred before. Look for pushed over

small trees and trees with limbs broken off. Avoid steep gullies and open slopes.

Recent avalanche activity – If you see evidence of recent avalanche’s suspect dangerous conditions

especially on other slopes with similar aspects.

Sounds and cracks – If the snow sounds hollow, particularly on a leeward slope, conditions are

probably dangerous. If the snow cracks and the cracks spread, this usually indicates slab avalanche

danger is high.

Elevation – Although avalanche danger generally increases with elevation, unusual weather conditions

combined with local topography may occasionally reverse this relationship.

Volcanic peaks – On volcanic peaks above 8000 to 10,000 feet elevation, significant avalanche hazard

may exist during any time of year.

Information – Check the local weather and avalanche forecasts. NOAA weather radio will carry these

forecasts when high or extreme hazard is expected. Contact the forest service or nearest ski area.

Depth hoar is a coarse and grainy form of snow crystal which is the culprit behind avalanches.

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Snowpack safety testsTest skiing is applied for testing the stability of the most recently deposited snow. It is the stability where a skier adds stress to the snow through his or her weight by jumping, kicking and turning.

Explosives are primarily used for avalanche control in snow safety work. It indicates fair to poor stability on the test slope. A crater created by explosive without an avalanche or cracking indicates stable snow pack.

Rutsch block test is carried out to test slopes, prior to skiing over them.

The load level failure 1- indicates the failure under the weight of the block alone; 2 – one

person on skis steps carefully on the block from above; 3- the person’s weights the skis by

making a rapid knee bend; 4 – the person on skis jumps; 5 – the person on skis jumps a

second time; 6- the person jumps onto the block without skis and 7 – no failure observed.

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Shovel shear test is to locate weak layers and interfaces. It is done by cutting a vertical column of snow to a depth below suspected weak layers. The shear force is applied by inserting the shovel blade behind the column and pulling in a down slope direction until a failure occurs. The failure is described as :

Very easy – the column fails during cutting or insertion of the shovel (shear frame index (< 100N/m2); Easy – the column fails with a very low shovel pressure (shear frame index (100 - 1000N/m2); Moderate – the column fails under moderate shovel pressure (shear frame index (1000 -2500N/m2); Hard – the column fails after a firm sustained pressure (shear frame index ( 2500 - 4000N/m2).

Fracture propagation is the sudden subsidence of the snow pack due to shear fracture propagation, when weight is added by machines or persons. Often the subsidence is accompanied by a whopping sound as air in the snowpack is compressed by the propagating shear disturbance.

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Two basic types of models are used:

topographical-statistical models and dynamic models.

Coefficients for the statistical models are based on at least 20 measured extreme run outs in paths

within a specific mountain range. The run out estimates cannot be used with confidence in other ranges.

Using regression or distribution parameters from the dataset and a reference point in the lower path

known as the Beta (β) point), it is possible to estimate the probability of a given path having a run out a

specified distance past the Beta point.

The most commonly applied types of statistical run out models are known as Alpha-Beta (α−β) and Run

out Ratio (Δx/Xβ). If the return period is known at a reference point such as Beta, and the parameters

are known for the relevant Run out Ratio model, then the run out past the reference point can be

estimated for a specific return period. Some key limitations of these models include: lack of availability

for many ranges, run-up on the opposite side of the valley, and their run out estimates are independent

of terrain anomalies, release zone area, release mass and confinement or gullies in the path to be

mapped.

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Topographical model - The run-out distance is appropriate for analysis along longitudinally concave profiles. The

run-out distance equations are found by regression analysis.

The calculated run-out is expected under a given climatic region and snow conditions favoring them. Extreme-

value model assumes that the alpha (α) & beta (β) observations are made on an average observation period of

100 years and the number of avalanches behind each extreme alpha (α) observation does not vary too much.

Dynamic models use physical laws such as conservation of mass and momentum to predict avalanche speed

down a simplified representation of the topography of the path.

One-dimensional (1D) models predict the velocity of the centre of mass or the front along the centre line of the

path. The earlier 1D model represents the terrain as a sequence of segments, each with constant slope angle,

down the centerline of the path. In Switzerland, AVAL-1D is currently used for hazard mapping.

Two-dimensional (2D) models estimate the flow depth or lateral extent whereas 3D models estimate both.

Using the calculated velocity and estimates of flow density based on published values and/or experience,

impact pressures along the path can be estimated.

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Run out model

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Hazard mapping benefits from runout estimates from largely independent methods such as vegetation, human records, statistical models and dynamic models

Statistical models use data sets of rare events of 100 years return periods obtained in the mountain range. Unique snow pack and snow loading conditions develop in some isolated areas in all but very winters. This model is successfully used within Western Fiords of Norway Geotechnical Institute (NGI method). It uses:-

• The alpha angle (α) measured from the crown location to a tip of the run out;

• The point where the local profile slope becomes 100 is identified

• beta (β) angle is measured from the 100 point to the crown location. Constraints is it uncertainity in α angle.

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Avalanche forecast classification • Snow and weather data measured at or above surface as numerical • Snow pack factors such as snow pit analysis as non-numerical and Stability factors using

stability test or observed occurrence.

• True forecast - probability of avalanche occurrence is determined before the incremental changes in weather and snows. Depend heavily on accurate weather forecast & subsequent stability estimate of snow pack. French SAFRAN-CROCUS-MEPRA system

• Meso-scale areas like mountain passes & Skiing areas use incremental changes that are taking place or taken place.

• Ski & Highway operation warnings based on morning observations. Stability functions could be determined and precision of prediction increased for detailed spatial forecasts and named as B1.

• Micro scale area - Predictions after incremental snow and weather conditions taken place, extensive sampling, scanning of avalanches & skiing performed.

• Helicopter is used for surveillance and increased spatial and temporal resolution of forecast.

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Avalanche Hazards Ratings assigned are

Low avalanche hazard – Mostly stable snow exists, and avalanches are unlikely except in

isolated pockets on steep, snow-covered, open slopes and gullies.

Moderate avalanche hazard – Areas of unstable snow exist, and avalanches are possible on

steep snow-covered, open slopes and gullies. travelers use caution.

High avalanche hazard – Mostly unstable snow exists, and avalanches are likely on steep

snow-covered slopes and gullies. travel is not advised.

Extreme avalanche hazard – Widespread areas of unstable snow exist and avalanches are

certain on steep, snow covered, open slopes and gullies. Large destructive avalanches are

possible. travel should be avoided.

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European Avalanche Risk

Risk Level Snow Stability Avalanche Risk

1 Low Snow is generally very stable Avalanches are unlikely except when heavy loads are applied

on a very few extreme steep slopes. Any spontaneous

avalanches will be minor (sluffs). In general, safe conditions

2 Limited On some steep slopes the snow is

only moderately stable. Elsewhere

it is very stable.

Avalanches may be triggered when heavy loads are applied,

especially on a few generally identified steep slopes. Large

spontaneous avalanches are not expected.

3 Medium On many steep slopes the snow is

only moderately or weakly stable.

Avalanches may be triggered on many slopes even if only

light loads are applied. On some slopes, medium or even

fairly large spontaneous avalanches may occur.

4 High On most steep slopes the snow is

not very stable.

Avalanches are likely to be triggered on many slopes even if

only light loads are applied. In some places, many medium

or sometimes large spontaneous avalanches are likely.

5 Very High The snow is generally unstable. Even on gentle slopes, many large spontaneous avalanches

are likely to occur.

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US avalanche danger rating for Ski areas

Parameters Low Moderate Considerable High Extreme

Settlement 20% 10 % 5% 0%

24 hr snow (inches) 7-10” 11-15” 16-25” 26-30” >30 ”

12 hr snow (inches) 0-6 ” 7 -10 ” 11 - 15” 16- 25” >25”

Temperature Trend (0F) 260 26-300 30-310 30-500 >500

Wind (mph) 0-10 12-18 20-30 30-50 > 50

Intensity (inches/hr) 0.08 0.1 0.11-0.18 > 0.2

Density 5% 6-10% 11-18% >20%

Layering Low Moderate Considerable High Extreme

Natural Activity Low Moderate Considerable High Extreme

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European snow avalanche danger rating

(Source courtesy :snowheads.com)

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(Source courtesy :snowheads.com)

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Source courtesy: nwac.us

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Types of snow avalanche mapping in Canada:

1) Locator maps that identify potential avalanche terrain. 2) Avalanche atlas maps that provide illustrations of potential avalanche terrain for a series of locations in an avalanche area. 3) Risk maps that are used in numerous capacities including land-use planning for fixed facilities (occupied and unoccupied buildings or structures), linear risk mapping for highways, roads or railways, and maps for forestry applications

Risk determination for unoccupied structures (e.g. electric transmission lines, energy pipelines and ski lift towers). Risk is described in terms of expected impact pressures for appropriate return periods.

zone maps for occupied structures (e.g. residential structures, subdivisions and industrial sites). On these maps risk zones are identified in Red (high risk), Blue (moderate risk and some uses with restrictions) and White (low risk; beyond the reach of destructive avalanches with return periods of 300 years or less).

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Linear risk mapping for transportation routes. This involves formal risk calculation for roads, highways or railways, and accounts for avalanche frequency, traffic volume, waiting traffic, expected damage and path length exposed.

Forest harvest risk mapping addresses two concerns: possible avalanche initiation in future harvested terrain; and existing avalanche paths that intersect future harvested terrain.

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Conditions observed to be favorable for initiation of snow avalanches

• Time - During or immediately after a storm.

Snow fall thickness 1 to 3 inches of fresh snow – critical situation

6 to 12 inches - threat

Temperature warm front movement increases temperature & weaken layers

Wind direction wind scouring & formation of icy overhang / cornice on leeward side (NE,E & SE) @ top of ridge indicates instability of snow pack.

• Snow pack – snow flakes or crystals shape & metamorphism

• Smooth surface due to refreeze conditions due temperature rise & melt / rain

Deep weak layers but strong or well bonded surface layers

Presence depth hoar (granular, coarse snow crystals) bonds poorly forms weak layer6.42

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Avalanche avoidance

Preventative measures are employed in areas where avalanches pose a significant threat to people, such as ski resorts and mountain towns, roads and railways. The simplest active measure is by repeatedly traveling on a snow pack as snow accumulates; this can be by means of boot-packing, ski-cutting, or machine grooming.

Explosives are used extensively to prevent avalanches, by triggering smaller avalanches that break down instabilities in the snow pack, and removing over burden that can result in larger avalanches. Explosive charges are delivered by a number of methods including hand tossed charges, helicopter dropped bombs, Gazex concussion lines, and ballistic projectiles launched by air cannons and artillery.

Passive preventive systems such as Snow fences and light walls can be used to direct the placement of snow. Snow builds up around the fence, especially the side that faces the prevailing Winds.

Trees can either be planted or they can be conserved, such as in the building of a ski resort, to reduce the strength of avalanches.

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Artificial barriers can be very effective in reducing avalanche damage. There are several types.

Snow net barrier uses a net strung between poles that are anchored by guy wires in addition to their foundations.

Rigid snow fence like structure may be constructed of steel, wood or pre-stressed concrete.

Terrain management involves reducing the exposure of an individual to the risks of traveling in avalanche terrain by carefully selecting which areas of slopes is safe to travel on.

The safest routes are on ridge tops and slightly on the windward side away from cornices. Windward slopes are usually safer than leeward slopes. If you cannot travel on ridge is, the next safest route is out in the valley far from the bottom of slopes.

Avoid cornices move toward ridge tops by detouring around cornice areas. If you must cross a potentially dangerous slope stay high and near the top. If you see cracks or avalanche fracture lines in the snow, avoid them and nearby similar slopes.

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Only one person at a time should cross a potentially dangerous slope. All others should watch.

Group management Minimize the number of people on the slope, and maintain separation. Route selection should also consider what dangers lie above and below the route, and the consequences of an unexpected avalanche (i.e., unlikely to occur, but deadly if it does). Stop or camp only in safe locations.

Risk Factor Awareness about avalanche safety requires gathering and accounting for a wide range of information such as the meteorological history of the area, the current weather and snow conditions,

Avalanche safety begins even before you begin your travel and keeping an eye out for weather and terrain conditions. Proper equipment can be a critical factor in rescue efforts. Avalanche victim will either endure fatal trauma due to collisions with rocks or trees during an avalanche, or will suffocate after they are buried by snow.

Avalanche beacons (transceivers) are the most commonly used rescue device. They are the standard equipment for ski-area patrollers and heli-ski operators.

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(Source courtesy: avalanche.org)

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View of Alps from ground based SAR

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Lesson 6.1

Glacier

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Glacier is a large persistent body of ice on land and moves slowly down the slope. It forms in a location where the accumulation of snow and sleet exceeds the amount of snow that melts. It transports rock and debris abraded from its substrate and deposits as cirques and moraines landforms. In the tropics, glaciers occur only on high mountains.

Types of Glaciers - morphology, thermal characteristics and behavior.

Alpine glaciers form on the crests and slopes of mountains and are also known as mountain glaciers or cirque glaciers. When they fills a valley is called a valley glacier. They are feed outlet glaciers, tongues of ice that extend into valleys below far from the margins of the larger ice masses.

Larger glaciers that cover an entire mountain range or volcano are known as an ice cap or ice field.

Ice shelves are areas of floating ice, commonly located at the margin of an ice sheet. As a result they are thinner and have limited slopes and reduced velocities.

Ice streams are fast-moving sections of an ice sheet that are several hundred km long.

Tidewater glaciers are glaciers that terminate in the sea. As the ice reaches the sea, it breaks off, or calve, forming icebergs.

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temperate glacier is at melting point throughout the year, from its surface to its base, while the ice of a polar glacier is always below freezing point, although the surface snowpack may experience seasonal melting.

sub-polar glacier has characteristics of both temperate and polar ice. As the snow and ice thickens, they reach a point where they begin to move, due to a combination of the surface slope and the pressure of the overlying snow and ice.

Ice sheets are the largest glaciers. These enormous masses of ice are not visibly affected by the landscape as they cover the entire surface beneath them,

Glaciers move or flow downhill due to the internal deformation of ice and gravity. Friction between ice and rock and geothermal heat from the Earth's interior also contribute to melting.

Velocity increases with increasing slope, thickness, snowfall, longitudinal confinement, basal temperature, melt water production and reduced bed hardness.

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Ablation zone is the region where there is a net loss in glacier massCirque is a theatre-like valley formed by glacial erosionAbrasion is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion.Moraine glacially formed accumulation of unconsolidated glacial debris through geomorphological processes. consist of somewhat rounded particles ranging in size from large boulders to minute glacial flour. Accumulation zone is the region that receives most of the snowfall and snowpack or superimposed ice accumulation persists

.

Source courtesy: studyblue.com

Crevasses is a deep crack, or fracture, found in an ice sheet or glacier, as opposed to a crevice that forms in rock. form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement.

Equilibrium line separates the ablation zone and the accumulation zone. At this altitude, the amount of new snow gained by accumulation is equal to the amount of ice lost through ablation. season, and a terminus with vigorous flow

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Source courtesy :www2.usgs.gov

Source courtesy :natky.in

Source courtesy :nasa.gov

Gangotri glacier

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Source courtesy:whoi.edu

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A glacial lake outburst flood is a type of outburst flood occurs when water dammed by a glacier or a moraine is suddenly released. Catastrophic failure of the containing ice or glacial sediment can release this water over periods of minutes to days. Peak flows as high as 15,000 cubic metres per second have been recorded in such events, suggesting that the v-shaped canyon of a normally small mountain stream could suddenly develop an extremely turbulent and fast-moving torrent some 50 metres deep. Glacial Lake Outburst Floods are often compounded by a massive river bed erosion in the steep moraine valleys

Source courtesy: summitpost.org

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(Source courtesy:asf.Alaska.edu)

Crevasses in Glacier

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Photo courtesy: Chandraprakash

Landslide debris & melt water through fractures

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Glacial lake formation

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Photo courtesy: Chandraprakash Photo courtesy: Chandraprakash

Dynamic weather pattern over accumulation zone

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Accumulation & movement zones of Glacier


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Thank you

Lesson 6 Snow avalanche & Glacier - CDEEP-IIT Bombay

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Transcript of Lesson 6 Snow avalanche & Glacier - CDEEP-IIT Bombay