6 - Glacial Processes Flashcards

Question

Answer 1

we first calibrate for a few glaciers where measurements have been made.

Answer 2

* Glaciers are a natural reservoir, storing water in high precipitation, cold years; releasing it in low precipitation, warm years. * Glacier hydrology modulates effects of surface melting on stream runoff. * Controls quantity and quality (sediment, chemistry) of water in glacier-fed streams. * May increase risk of flooding – ‘jökulhlaups’, Glacier Outburst Floods (GLOFs). * Implications for water resource management. * Controls spatial & temporal distribution of water pressure beneath glaciers, & therefore glacier movement (sliding/sediment deformation).

Answer 3

supraglacials, englacial and subglacial hydrology

Answer 4

an erosional feature which occurs on the surface of a glacier. formed by erosion by meltwater, creating circular inlet down that meltwater can enter the body of the glacier

Answer 5

deep crack that forms due to movement and resulting stress of the moving ice

Answer 6

time domain reflectrometry

Answer 7

probes are installed in snow in the accumulation area they measure two way travel time through the snow of EM waves - this time is affected by the water content of snow when EM pulse encounters a change in material properties (such as boundary between ice and water) part of the signal reflects back to surface. time delay is measured to determine distance to and nature of material change

Answer 8

in small pipes or larger conduits fed by crevasses / moulins

Answer 9

study of caves/cave like structures within glaciers

Answer 10

1. incision of surface streams or base of crevasse followed by roof closure 2. hydrologically driven ice fracturing 3. exploitation of pre existing permeable structures within the ice gulley et al 2009

Answer 11

theoretical direction of water flow calculated by considering hydraulic potential throughout ice this is the sum of gravitational potential (height above sea level) + pressure potential (overburden pressure).

Answer 12

a passageway within which water flows

Answer 13

it is uniform, at 0 degrees C

Answer 14

conduction, infiltration of water, refreezing and release of latent heat

Answer 15

a fraction where 1 is when max pressure potential and 0 atmospheric pressure

Answer 16

wherever ice at a glacier bed reaches the pressure melting point

Answer 17

is when ice melts at a given pressure.

Answer 18

radio-echo sounding use of artificial tracers monitoring manipulation of conditions via boreholes monitoring runoff properties

Answer 19

surface, englacial and basal melt, subglacial meltwater

Answer 20

climatic regime at ice surface, temperature of glacier ice ice flow dynamics nature of glacier bed

Answer 21

the surface temps never reach above the freezing point, but the ice temps reach pressure melting point near the glacier bed.

Answer 22

distributed or slow channelised or fast

Answer 23

smaller fluxes can be stable in cavities, as it rises the effective pressure drops. inverse relationship between discharge and effective pressure more water going through increases water pressure - this causes cavities to become unstable, behave like channels, meaning water pressure drops, and effective pressure rises

Answer 24

ice overburden pressure - water pressure

Answer 25

direct- as discharge increases the water pressure decreases as channels widen, leading to greater effective pressure

Answer 26

* Water pressure will rise, due to piling water from above * this will increase sliding which increases cavity XSA * increase in WP means effective pressure falls, lowering the creep closure rate * however on net cavity has enlarged less than discharge did * as discharge is velocity times XSA and discharge went up more, velocity must have too * this raises water pressure

Answer 27

snow - 90% coarse grained snow - 50% firn - 20-30% glacial ice - 20% as bubbles

Answer 28

the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.

Answer 29

massive ice and glacial ice

Answer 30

elastic, viscous, plastic

Answer 31

how a material responds to an applied stress

Answer 32

a stretch goes back to where it came from

Answer 33

permanent deformation, not going to snap back, will continue oozing out speed is proportional to the stress being given

Answer 34

elastic at first until a critical stress is met, then permanent movement

Answer 35

between viscous and plastic- viscoplastic

Answer 36

in terms of strains

Answer 37

measured in pressure. Newtons/Metres2 = pascals

Answer 38

how much change since original position (end position - start) / start it is a proportion, a unitless ratio

Answer 39

strain keeps increasing as stress is applied

Answer 40

pure shear and simple shear

Answer 41

an object that squishes in one direction, onto the sides extension and compression

Answer 42

parallel surfaces moving past each other material deforms in a way that layers slide over each other. this results in a change in angles between lines that were originally perpendicular

Answer 43

glens flow law

Answer 44

logarithmic scales, it is not linear exponential scale strain rate = ice hardness*stress^usually 3

Answer 45

when we plot it is the most fitting value for the viscoplastic movement , but some think it should 4. works most of the time with n=3

Answer 46

increases significantly with fall in temp ice hardness increase by factor of 1000 from 0 to -55 degrees

Answer 47

water content impurities

Answer 48

10^15 times (massive number)

Answer 49

primary - initially drops under applied stress, due to stiffening, as ice grains redistribute secondary - then softens due to recrystallisation and rotation of crystals tertiary - reaches a steady state

Answer 50

stress is a measure of how hard a material is being compressed, stretched or twisted as the rest of applied forced strain measures the amount of deformation that occurs as the result of stress

Answer 51

toothpaste comes out due to deformation (strain) resulting from an higher pressure on the surface than the nozzle (stress)

Answer 52

the physical influences which change the state of motion of a mass mass times acceleration

Answer 53

force per unit area

Answer 54

pascal (newton/metres squared)

Answer 55

stress acting at right angles to the surface (normal stress) acting parallel to the surface (shear stress)

Answer 56

either pressing together across the surface *compressive stress* or pulling away from it *tensile stress*

Answer 57

parallel but act in opposite directions

Answer 58

mostly due to weight of overlying ice

Answer 59

force per unit area on a surface of a specified orientation - a measure of force intensity

Answer 60

a pair of equal and opposite tractions acting across a surface of specified orientation

Answer 61

a pair of tractions acting parallel to a surface

Answer 62

a pair of tractions acting at right angles to a surface

Answer 63

elastic (recoverable) permanent (irrecoverable)

Answer 64

brittle failure - where the material breaks along a fracture ductile deformation - where material undergoes flow or creep

Answer 65

the accumulation area of a glacier reduces in volume while increasing in density

Answer 66

it is essentially incompressible. after snow is condensed to ice

Answer 67

comparing the shape and size before and after deformation.

Answer 68

pure shear simple shear

Answer 69

flattening or stretching of a material under compressive and tensile deviatoric stresses

Answer 70

strain rate - amount per unit of time cumulative strain - net amount that takes place in a given time interval

Answer 71

the way in which strain rate varies with applied stress for a given material

Answer 72

the value of the applied stress at the onset of permanent deformation, measured in Pascals

Answer 73

permanent deformation will happen at any stress, no matter howsmall

Answer 74

cohesion, friction

Answer 75

how much deformation do you get if you increase the force on ice

Answer 76

E (strain) = A * T^3 (ice hardness*stress cubed)

Answer 77

strain is hardness * stress cubed

Answer 78

ice density x gravity x thickness of ice x sin of ice gradient weight x sin of ice surface gradient

Answer 79

if it was flat, there would just be normal stress crushing the ice down as it increases shear stress increases how much of the weight of the ice that is generated through shear stress rather than normal stress depends on that gradient

Answer 80

key component of landscape evolution - mountains, valleys, fjords sediment flux to oceans and global cycles palaeoclimate insights from landslides hazards

Answer 81

glaciers are a natural water reservoir hydrology modulates effects of surface melting on runoff quality and quantity of water (due to influence of sediments, chemistry) GLOF risk water resources controls pressure and deformation of subglacial sediments

Answer 82

supra glacial, englacial, subglacial

Answer 83

has to be 0 - it is uniform

Answer 84

conduction, infiltration of water, refreezing and release of latent heat

Answer 85

an optical satellite, its data used for DEMs for glacier mass

Answer 86

special report on oceans and cryosphere and changing climate

Answer 87

we need a DEM - as we need elevation

Answer 88

A: It is an empirical model that estimates glacier melt based on the sum of positive air temperatures over a given period.

Answer 89

Glacier melt is primarily driven by air temperature, which serves as a proxy for available energy.

Answer 90

Melt = Degree Day Factor × Positive Degree Days Where: Degree Day Factor (DDF) is an empirical coefficient (mm/day/°C) Positive Degree Days (PDD) is the sum of daily mean temperatures above 0°C

Answer 91

It is an empirical value that represents how much snow or ice melts per degree above 0°C per day.

Answer 92

Different surfaces have different melting efficiencies: Fresh snow: ~2-5 mm/day/°C Firn: ~4-7 mm/day/°C Glacier ice: ~6-10 mm/day/°C DDFs are also influenced by location, radiation, and debris cover.

Answer 93

By summing daily mean air temperatures above 0°C over a specified period.

Answer 94

Simple and requires limited data ✅ Useful for large-scale glacier melt estimations ✅ Good for historical reconstructions

Answer 95

❌ Ignores other energy sources (e.g., solar radiation, longwave radiation) ❌ Requires calibration for different glacier types ❌ Less effective in maritime climates with frequent temperature fluctuations

Answer 96

: Rising temperatures lead to higher Positive Degree Days, increasing glacier melt and accelerating mass loss.

Answer 97

It is a model that calculates glacier melt by considering all energy fluxes affecting the glacier surface, including radiation, heat fluxes, and conduction

Answer 98

Q_m = SW_in - SW_out + LW_in - LW_out + Q_H + Q_L + Q_G Where: Q_m = Energy available for melt SW_in, SW_out = Incoming & outgoing shortwave radiation LW_in, LW_out = Incoming & outgoing longwave radiation Q_H = Sensible heat flux Q_L = Latent heat flux Q_G = Ground heat flux

Answer 99

Solar (shortwave) radiation, which varies with latitude, altitude, season, and cloud cover

Answer 100

Incoming longwave radiation from the atmosphere contributes heat. Outgoing longwave radiation is emitted by the glacier, cooling it. Cloud cover and greenhouse gases increase incoming longwave radiation, enhancing melt.

Answer 101

represents heat transfer from the air to the glacier surface through turbulent mixing, influenced by air temperature and wind speed

Answer 102

It is energy exchange due to phase changes (evaporation, condensation, sublimation), influenced by humidity and wind.

Answer 103

It represents heat transfer from the glacier’s surface to the interior, affecting subsurface melt and refreezing

Answer 104

✅ Accounts for multiple energy sources (not just temperature) ✅ More physically realistic than degree day models ✅ Can be used to model future melt scenarios

Answer 105

❌ Requires detailed meteorological data ❌ Computationally intensive ❌ Highly sensitive to cloud cover and turbulence parameters

Answer 106

Degree Day Models are simpler but assume temperature is the only driver. Energy Balance Models account for radiation, wind, and humidity, providing more accurate melt predictions.

Answer 107

Energy first warms subsurface layers to 0°C. Once they reach this temperature, any excess energy produces meltwater, which can percolate and run off

Answer 108

Energy is conducted downward, warming subsurface layers. Once layers reach 0°C, melting begins. Meltwater may refreeze in colder layers or contribute to runoff.

Answer 109

❄️ Melt stops ❄️ Surface and subsurface layers cool below 0°C ❄️ Heat is lost to the atmosphere, causing refreezing and strengthening the ice structure.

Answer 110

Heat is transferred from the surface downward, warming colder layers before melting can occur.

Answer 111

🔹 Releases latent heat, locally warming the surrounding ice 🔹 Forms superimposed ice, which contributes to glacier mass balance 🔹 Can block further percolation, affecting runoff dynamics

Answer 112

A: The glacier acts as a heat sink, delaying surface runoff until enough energy is available to fully melt the ice.

Answer 113

Positive energy balance → Melting & runoff Negative energy balance → Refreezing & ice accumulation Transition periods → Subsurface warming/cooling without immediate melt

Answer 114

Cold glacier: Most meltwater refreezes internally. Temperate glacier: Meltwater drains freely as runoff. Polythermal glacier: Combination of refreezing and drainage occurs.

Answer 115

is often simplified using empirical relationships based on annual mean air temperature (Tₐ) and limited field observations

Answer 116

R (cm) = -0.69 Tₐ + 0.0096 Where: Tₐ = Annual mean air temperature (°C) R = Refreezing depth (cm)

Answer 117

They used it to estimate global glacier refreezing rates for 2000-2100, providing a large-scale assessment of meltwater retention.

Answer 118

Meltwater refreezes within the glacier until cumulative melt exceeds R—at which point, excess meltwater becomes runoff

Answer 119

Delays runoff, affecting hydrology Enhances glacier mass balance by retaining water as ice Regulates seasonal meltwater availability

Answer 120

❌ Based on limited field data ❌ Does not account for spatial variations in glacier type, snow depth, or internal heating ❌ Assumes a linear relationship with temperature, which may not hold for all conditions

Answer 121

Meltwater is no longer retained within the glacier and instead contributes to runoff.

Answer 122

🌡️ Warmer temperatures → Lower R → More meltwater lost as runoff 🌨️ More snowfall → Higher R → Increased meltwater retention

Answer 123

It is a modified version of the classic Degree Day Model that incorporates additional radiation-based factors to improve melt estimates.

Answer 124

It assumes melt is only controlled by temperature (T) and does not account for shading, cloud cover, or radiation effects

Answer 125

1️⃣ First variant: Includes potential clear-sky radiation (I) to account for shading effects. 2️⃣ Second variant: Includes actual cloud cover effects using measured global radiation (Gₛ).

Answer 126

Accounts for spatial melt variability (shading & cloud cover) ✅ Variant 1 requires no extra field measurements ✅ More accurate than the classic Degree Day Model ✅ Less computationally expensive than Energy Balance Models

Answer 127

❌ Variant 2 requires global radiation (Gₛ) measurements, which are not always available ❌ Depends on empirical coefficients, making application to other glaciers difficult ❌ More computationally expensive than the classic Degree Day Model

Answer 128

Accumulation is usually treated as a linear function of elevation, with precipitation increasing at higher altitudes

Answer 129

They use an air temperature threshold, typically around 1°C, to distinguish between snowfall and rainfall

Answer 130

Because on average, precipitation increases with altitude, and temperature-based thresholds can approximate seasonal snow accumulation

Answer 131

❌ Works less well at smaller spatial or temporal scales ❌ Does not account for local topography (e.g. valley effects, wind-sheltered zones) ❌ Ignores snow redistribution by wind, avalanches, or sublimation

Answer 132

🌬 Wind redistribution (snowdrift transport & deposition) 🏔 Local topography (e.g. ridges may lose snow, basins may accumulate more) ☀ Solar radiation effects (e.g. melting on exposed slopes) ⏳ Sublimation & compaction over time

Answer 133

Wind direction & strength Orographic lifting & rain shadows Cloud cover & storm tracks

Answer 134

✅ Using higher-resolution climate models ✅ Including wind redistribution algorithms ✅ Incorporating remote sensing data to validate snow depth estimates

Answer 135

Using Automatic Weather Stations (AWS) placed on or near glaciers, then extrapolating meteorological variables over a Digital Elevation Model (DEM)

Answer 136

By assuming a standard atmospheric lapse rate of 6.5°C per km of elevation

Answer 137

By applying a regionally measured precipitation gradient to estimate precipitation at different elevations.

Answer 138

❌ Glaciers are often in remote locations, making AWS installation difficult. ❌ Data gaps occur due to harsh weather conditions affecting equipment. ❌ AWS data only represents a single point, requiring extrapolation across the glacier.

Answer 139

Climate reanalysis datasets (e.g., ERA-40, ERA-Interim, ERA-20C, JRA55, NOAA-20CR) provide global meteorological fields at moderate resolution

Answer 140

process that ‘reanalyzes’ past observations using a weather/climate model to produce gridded global datasets of temperature, precipitation, and other variables.

Answer 141

✅ Provides consistent meteorological data for any glacier worldwide, even in remote regions.

Answer 142

They are based on models, meaning they contain uncertainties & biases, especially in complex terrain like mountain glaciers.

Answer 143

🌍 Reanalysis: Covers global glaciers but may have biases in local conditions. 📡 AWS Data: Provides accurate local data but is limited in coverage and may require extrapolation.

Answer 144

✅ Combine AWS data with reanalysis datasets for calibration. ✅ Use high-resolution regional climate models to downscale reanalysis data. ✅ Incorporate remote sensing observations to validate temperature and precipitation estimates

Answer 145

Calibration is the process of adjusting uncertain model parameters so that the model output matches real-world observations.

Answer 146

Validation is the process of testing a calibrated model against independent observations to assess how well it performs.

Answer 147

Many key parameters (e.g., Degree Day Factors, albedo, lapse rates) are not directly measured, so they must be estimated using field data or calibration methods.

Answer 148

🟠 Degree Day Factors (DDFs) – For Degree Day Models 🟡 Snow and ice albedo – For Energy Balance Models 🔵 Temperature lapse rate – For extrapolating temperature over a glacier 🟢 Precipitation gradient – For estimating snow accumulation 🔴 Rain/snow threshold temperature – To distinguish snowfall from rain

Answer 149

1️⃣ Manual tuning – Adjust parameters iteratively until model matches observations. 2️⃣ Statistical optimization – Use least-squares fitting, Bayesian inference, or Monte Carlo simulations to find best-fit parameters. 3️⃣ Machine learning – Some recent studies use ML techniques to refine parameters dynamically.

Answer 150

Remote sensing data (e.g., satellite images of glacier mass balance) 🏔 In situ measurements (AWS, stake measurements, melt sensors) 📊 Historical climate data (Temperature, precipitation records)

Answer 151

Calibration only ensures the model fits past data, but validation tests if it can predict future or unseen conditions accurately

Answer 152

❌ Indicates overfitting to calibration data ❌ Suggests wrong parameter assumptions ❌ Requires recalibration or structural model changes

Answer 153

1️⃣ Compare model outputs with independent datasets (not used in calibration). 2️⃣ Use cross-validation, splitting data into training (calibration) and testing (validation) sets. 3️⃣ Test model on different glaciers or time periods to check generalizability.

Answer 154

❄️ Glaciers are in remote areas, making field data scarce. 📊 Many processes (e.g., wind redistribution, sublimation) are hard to quantify. 🌎 Climate change affects glacier conditions, meaning past parameters may not apply in the future.

Answer 155

To compare the performance of five glacier melt models of varying complexity and evaluate their predictions for glacier mass balance under future climate conditions

Answer 156

3 Degree Day Models: 🔹 0D (point-based) 🔹 1D (elevation-band based) 🔹 2D (spatially distributed, enhanced with potential clear sky radiation, I) 2 Energy Balance Models: 🔸 1D 🔸 2D (fully distributed)

Answer 157

Storglaciären, a well-studied glacier in Sweden.

Answer 158

The models were calibrated using ERA-40 reanalysis climate data.

Answer 159

Regional climate model output, applied to project mass balance changes up to the year 2100

Answer 160

Glacier mass balance predictions and sensitivities vary significantly with model complexity—model choice matters.

Answer 161

It likely captured more spatial variability and detailed energy processes, including solar radiation and heat fluxes, leading to higher melt estimates.

Answer 162

Even when calibrated to the same glacier, different models can yield widely varying results, highlighting the need for careful model selection.

Answer 163

To improve understanding of glacier melt processes by quantifying the role of meltwater refreezing using a detailed energy balance model

Answer 164

a full surface and subsurface energy balance model, which includes heat conduction and meltwater percolation and refreezing in the firn

Answer 165

Refreezing, often deep in the firn, accounted for approximately 20% of total modelled accumulation

Answer 166

Because most direct mass balance measurements don’t account for deep firn refreezing—they assume any meltwater not refrozen in shallow snow becomes runoff

Answer 167

A: Firn is compacted, partially melted snow that hasn't yet become glacial ice. It can store and refreeze meltwater, acting as a temporary buffer in the glacier's mass balance.

Answer 168

To model global glacier mass change and its contribution to sea level rise for all 198,000 glaciers in the Randolph Glacier Inventory (RGI), using a 0D degree day model

Answer 169

They used CRU 0.5° gridded global monthly climate data for temperature and precipitation

Answer 170

A local lapse rate was derived for each glacier using the surrounding 3 × 3 grid cell window from the CRU data

Answer 171

DDFs were calibrated for 255 glaciers with glaciological mass balance data (WGMS), and then statistically extrapolated to the remaining glaciers globally

Answer 172

They used globally derived scaling relationships from existing literature to relate glacier volume to area and length.

Answer 173

The model was forced using temperature and precipitation outputs from 15 AOGCMs in the CMIP5 ensemble

Answer 174

The greatest uncertainty came from variation within the model ensemble, not the differences between emission scenarios (e.g., RCP2.6 vs. RCP8.5)

Answer 175

They are at 0°C throughout, allowing them to store and transmit meltwater and rainwater without temperature change

Answer 176

They act as temporary reservoirs, storing meltwater and rainfall and releasing it over hours to months, smoothing out variations in surface runoff.

Answer 177

They dampen short-term fluctuations in surface melt and rainfall by delaying runoff, stabilizing glacier meltwater discharge

Answer 178

a few hours to several months, depending on snowpack structure, firn porosity, and weather conditions

Answer 179

declines, as firn and snow layers become saturated or depleted, leading to more direct runoff from the surface to the glacier base

Answer 180

It affects the timing and volume of runoff, glacier hydrodynamics, and subglacial drainage evolution, especially in models of seasonal melt.

Answer 181

They used Time Domain Reflectometry (TDR) probes installed in the accumulation area of Haig Glacier in the Canadian Rocky Mountains.

Answer 182

TDR probes measure the two-way travel time of electromagnetic waves along metal rods. The travel time increases with higher liquid water content in the snow

Answer 183

It indicates a higher volumetric water content in the snow, as the electromagnetic signal slows down in wet snow compared to dry snow.

Answer 184

There was a greater delay between surface melt and detection of liquid water earlier in the season and at greater snowpack depths

Answer 185

It suggests that early-season snow and deeper layers can temporarily store meltwater, highlighting the snowpack’s buffering capacity

Answer 186

It provides high-resolution, in-situ measurements of liquid water content in snow, helping to better understand meltwater retention and timing in the accumulation zone

Answer 187

Meltwater flows laterally through snow, firn, or over bare ice until it reaches the glacier's edge, or enters the glacier through a crevasse or moulin.

Answer 188

As the high-albedo snowpack melts, it reveals low-albedo glacier ice, increasing melt rates and enhancing runoff into moulins later in the summer

Answer 189

Thinning snowpack reduces its delaying effect on meltwater flow and increases meltwater delivery to moulins due to exposure of low-albedo ice.

Answer 190

Through conduits or small englacial pipes, as veins between ice crystals are impermeable at or below 0°C.

Answer 191

Because they are largely impermeable below or at 0°C, so water preferentially flows through larger pathways like moulins and crevasses

Answer 192

By monitoring changes in water level and electrical conductivity (EC) in boreholes drilled to the glacier bed.

Answer 193

It reflects variations in water source and routing—e.g., solute-poor meltwater vs. solute-rich basal water—allowing inference of englacial and subglacial flow paths

Answer 194

It involves injecting saline (high EC) water into the borehole to trace water movement and detect englacial flow pathways

Answer 195

They help reveal hidden englacial and subglacial drainage structures and improve understanding of meltwater routing and storage within glaciers

Answer 196

Ground-Penetrating Radar (GPR), specifically using a 25 MHz antenna, was employed to image englacial conduit networks at Rhonegletscher, Switzerland

Answer 197

By transmitting radar pulses and measuring reflected signals—changes in reflection coefficients and layer impedances indicate different infill materials (e.g., water or sediment）

Answer 198

Glacio-speleology—the direct exploration and mapping of englacial passages, often by entering them through moulins or crevasses

Answer 199

Cut and closure: A surface stream or water at the base of a crevasse incises downward, followed by ice deformation closing the roof, forming a tunnel-like conduit Hydro-fracturing: Water pressure causes fractures to propagate through the ice, especially in zones of extensional or compressional flow Exploitation of pre-existing weaknesses in the glacier, such as firn pores, crevasse traces, or healed fractures, which are reopened or enlarged by meltwater flow

Answer 200

Water flows into structural weaknesses in the ice, which are more susceptible to enlargement by mechanical erosion and melting, eventually forming drainage pathways

Answer 201

By physically entering and mapping englacial passages, researchers can observe geometry, flowmarks, sediment deposits, and links to surface inputs, helping reconstruct formation processes.

Answer 202

: By calculating the hydraulic potential (f) throughout the glacier, which combines gravitational potential and ice overburden pressure

Answer 203

f=Pw gz+Pi gk(H−z) Pw = water density Pi = ice density g = gravity z = bed elevation H = ice surface elevation k = fraction of over burden pressure

Answer 204

It is a scaling factor that adjusts the ice overburden pressure term depending on subglacial water pressure assumptions: k=1: Water pressure = Ice overburden pressure k=0: Water pressure = Atmospheric pressure

Answer 205

hydraulic potential throughout ice = gravitational potential + pressure potential

Answer 206

Distributed systems: Slow, inefficient water flow over large areas Channelized systems: Fast, efficient water flow through discrete conduits

Answer 207

Thin film flow—a very shallow layer of meltwater flowing between the glacier and a hard bedrock surface.

Answer 208

Regelation: ice melts under pressure on the upstream side of bed obstacles and refreezes on the downstream side, producing localized film flow

Answer 209

The presence of secondary carbonate precipitates, which form from slow-moving, thin film water beneath the glacier, particularly in rock cavities

Answer 210

Water-filled gaps between ice and bedrock that form when sliding ice lifts off the bed behind obstacles, creating low-pressure zones where meltwater accumulates

Answer 211

✅ Rough bed topography ✅ Fast glacier sliding ✅ Presence of meltwater at the glacier bed

Answer 212

If the cavities become connected by orifices, water can flow through the entire linked-cavity network, enabling distributed drainage

Answer 213

No—they are inefficient compared to channels. They provide slow, distributed water transport and are common in early melt season or low-flux conditions.

Answer 214

They influence basal water pressure, which affects ice sliding rates and glacier motion—especially in temperate or polythermal glaciers

Answer 215

Cross-sectional area of the flow path—important for understanding flow efficiency and water velocity in subglacial conduits.

Answer 216

Because of low resistance, few constrictions, and a large XSA, allowing water to flow freely and quickly

Answer 217

✅ Large cross-sectional area (XSA) ✅ Water flows at low pressure gradients ✅ Water pressure is low ✅ High water velocity ✅ Forms channelised, discrete, arborescent networks

Answer 218

Small XSA High water pressure High pressure gradients needed to drive flow Frequent constrictions Low water velocity Forms non-arborescent, diffuse drainage networks

Answer 219

Because narrow, irregular flow paths and constrictions resist flow, requiring higher pressure to force water through.

Answer 220

Channelised systems: Form arborescent (tree-like) networks with efficient flow paths Distributed systems: Form non-arborescent, irregular networks with slow, diffuse flow

Answer 221

Distributed systems: Promote high basal water pressure, enhancing sliding Channelised systems: Efficiently drain meltwater, lowering pressure and reducing sliding

Answer 222

✅ Practically: It affects water supply, river discharge, and downstream water management ✅ Scientifically: It controls basal processes, such as ice movement, sliding, and erosion

Answer 223

It can flow vertically and laterally through snow and firn, or across impermeable ice surfaces, eventually leaving the glacier or entering it through crevasses or moulins

Answer 224

They act as buffers, dampening diurnal melt cycles and delaying the timing of water reaching the glacier interior or base.

Answer 225

Through small pipes, fractures, and larger conduits (e.g. englacial tunnels), often forming networks that evolve over the melt season

Answer 226

Using Shreve’s (1972) theory, which calculates hydraulic potential based on surface elevation and ice thickness—but assumes a constant fraction of ice overburden pressure

Answer 227

Primarily the flux of water. Low flux promotes distributed systems (pores, films, cavities); high flux leads to channelised systems (canals, tunnels).

Answer 228

Distributed systems (e.g. linked cavities, films): Have higher water pressure Channelised systems (e.g. Röthlisberger channels): Have lower water pressure due to efficient drainage

Answer 229

He unified existing theories of channelised flow and linked-cavity systems into a single theoretical framework that accounts for their interactions and transitions based on water pressure and ice dynamics

Answer 230

Channels enlarge by melt from flowing water. Enlargement is controlled by: Water temperature Wall roughness Water discharge

Answer 231

Channel walls close by creep deformation, which depends on effective pressure (N), calculated as: N=pi−pw Where pi = ice overburden pressure and pw = water pressure

Answer 232

Like channels, they close by creep deformation, driven by the ice overburden pressure exceeding water pressure (N).

Answer 233

At low XSA, where closure rate exceeds opening rate. Many small cavities can coexist in a stable, distributed drainage system.

Answer 234

= (Melting caused by water flow) + (Mechanical opening due to ice sliding over bedrock) - (Closure due to ice creep under effective pressure)

Answer 235

It means the system is time-invariant—the conduit is stable, with enlargement rate equal to closure rate

Answer 236

As discharge (Q) increases, effective pressure (N) decreases This is because more water in cavities builds up pressure, reducing N

Answer 237

As discharge (Q) increases, effective pressure (N) increases This is due to more efficient drainage and lower water pressure within the channel, increasing N

Answer 238

It is the threshold discharge at which a drainage conduit transitions from a cavity to a channel. Below Qc → stable as a cavity Above Qc → stable as a channel

Answer 239

The conduit becomes unstable as a cavity and transitions into a channel, which can handle higher discharge more efficiently

Answer 240

The system reverts back to a cavity network, as channels are no longer sustainable due to low flow

Answer 241

It helps explain how and when drainage systems switch between distributed (cavity-dominated) and channelised (efficient) modes based on meltwater input

Answer 242

Because they are governed by different enlargement mechanisms: Cavities grow by sliding Channels grow by melting from water flow Each responds differently to increases in discharge (Q) and water pressure (pw)

Answer 243

discharge increases -> water pressure increases -> sliding increasing -> so XSA increases -> so creep closure decreases however cavity size increases less than proportionally to discharge -> this means water velocity has to increase -> higher pressure gradient needed -> so water pressure is higher

Answer 244

Because water pressure (pw) increases faster than ice overburden pressure

Answer 245

discharge increase -> more melting of channel walls -> XSA increases -> so slight fall in water pressure -> so creep closure slows but channel size increases more than proportionally to discharge increases -> so water velocity decreases -> sp pressure gradient must decrease -> so the water pressure ends up lower

6 - Glacial Processes Flashcards

(275 cards)