Glaciers and Glaciation

Introduction to Glaciers and Glaciation

Benn, D.I. and Evans, D.J.A. (2010) Glaciers and Glaciation. Routledge, London. • Glaciers have shaped the landscape by scouring rock and sediment and depositing thick accumulations of glacial debris = provide information on past glacier activity and also climate change. Ice in Greenland, Antarctica and smaller glaciers and ice caps contain rich archives of former environmental conditions. • MASS BALANCE: Seen as a SYSTEM: - INPUTS = snow, avalanches and rock debris which have potential energy due to higher elevation. Referred to as accumulation. - OUTPUTS = Inputs release energy in the form of melting, evaporation or breakaway ice blocks = ABLATION. So must be dissipated from the system as heat or water - Glaciers grow where the conditions allow accumulation to exceed ablation. - Energy exchanges between the atmosphere, the glacier and the solid earth below also modify temperature so that the total energy stored can change even if mass stays the same. - ACCUMULATION ZONE: Upper zone where accumulation exceeds ablation. - ABLATION ZONE: Lower zone where ablation exceeds. - EQUILIBRIUM LINE: annual levels of mass are both equal; also called the equilibrium line altitude (ELA) and is dictated by local and regional climate and topography. • MELTWATER: Flows from glacier margins towards the sea and shapes the land by carving gorges and depositing gravel, silt and sand. - Beneath the glaciers and ice sheets, it controls rates of glacier flow and influences the processes and rate of erosion and deposition. • GLACIER MOTION: Snow and ice are transferred from areas of accumulation to areas of ablation by glacier flow. Occurs through sliding, deformation of ice and deformation of glacier bed. - Rates and patterns depend on balance between driving forces (downslope gravitational acceleration) and resisting forces (drag at bed/margins). - If in balance: Rates of flow match those of snow and ice accumulation and ablation. Reach a dynamic equilibrium. • SEA LEVEL CHANGE: Glacier fluctuations directly affect SL due to storage of liquid. Also influences loading on the Earths crust due to changes in ice volume and distribution of mass around the planet. • EROSION AND DEBRIS TRANSPORT: Glaciers are the most effective at eroding and also transporting debris such as gravel and silt. - GLACIAL SEDIMENTS, LANDFORMS AND LANDSCAPES: Leave behind corries, troughs, drumlins and moraines after deglaciation. Can help reconstruct past environments • GLACIER MORPHOLOGY: Form taken is a function of climate and topography – unique to its own location on earth. Convenient to assign these into different types e.g. niche glacier, ice fringe, ice dome • ICE SHEETS AND CAPS: These submerge the landscape. An ice cap becomes an ice sheet at 50,000km2. Greenland and Antarctica are ice sheets where as Ellesmere Island is an ice cap. • ICE DOMES: Broad upstanding area on an ice sheet/cap. Underlying area is either a topographic high or low. Occur in the accumulation zone. • ICE DIVIDES AND DISPERSAL CENTRES: Mass that is evacuated outwards from a central ice dome acts as a dispersal centre. ICE DIVIDES: flow is directed in 2 opposing directions. Ice sheets usually don’t have simple domes and so divides change due to development and decay of glaciers. Velocity is 0 unless vertical flow occurs due to compaction and deformation. • MOVEMENT WITHIN ICE SHEETS/CAPS: Sheet flow occurs within ice dome areas; Stream flow = in outlet glaciers and ice streams – these are rapidly moving that radiate out from interior. Movement accounts for the majority of discharge and are responsible for most icebergs and ice rafter debris reaching the oceans.

GLACIERS CONSTRAINED BY TOPOGRAPHY

• ICE FIELDS: Different to ice caps as don’t have simple dome like surface and flow is influenced by underlying topography. Form in gentle topography and altitude sufficient for ice accumulation e.g. Columbia Ice Fields in Canadian Rocky Mountains. Less than 50,000km2 of ice. • VALLEY GLACIERS: Ice that is discharged from an ice field/cap/sheet in streams that flow between steep walled valleys. Single branched or dendritic networks dependant on the bedrock lithology and structure. Slopes either side are important sources of snow and ice accumulation through avalanches and rock debris. • TRANSECTION GLACIERS: Interconnected systems of valley glaciers which occur where mountains landscapes are deeply dissected. Glaciers flow down several directions but cause overspills from existing drainage divides. Form web like patterns where ice flow splits and sends branches down a number of channels and also confluences. • CIRQUE GLACIERS: Armchair like shaped bedrock allows accumulation to occur in dome shaped depression, which is often wind driven snow. Avalanching from steep sided walls common. • PIEDMONT GLACIERS: Glaciers that travel out from bedrock troughs from steep valley glacier, onto a relatively flat surface and spread out to form a lobe (FAN) shaped structure. Large amounts form under the ELA and so fall into the ablation zone, but normally enough accumulation from ice fields to maintain. • ICE APRONS: Smallest glacier ice masses. Thin snow and ice accumulations adhering to steep mountain sides, particularly summits. Often source of avalanches. ICE FRINGES: Similar to aprons but occupy small depressions along coasts, no further than 1km inland. • NICHE GLACIERS: Controlled by a shallow recess (niche) within gullies/hollows on north sides of steep sided mountains (shaded). Very small sections of ice. These and ice aprons are different to large snow patches as they undergo significant movement due to internal deformation or basal sliding – movement initiated by forces imposed by weight and surface gradient of the ice overcomes internal resistance (Ballantyne & Benn, 1994a). • ICEFALLS: Steep zones on a glacier where ice flow is rapid. The acceleration creates extreme extending flow where the ice thins and stretches under tensile stresses, opening up crevasses and breaking the ice into unstable ice blocks called seracs. Deceleration creates a compression flow where crevasses close and ice thickens. Ice flow is in the form of avalanches due to seracs collapsing. Can be open rock where accumulation is separated. • ICE SHELVES: Low gradient, floating glaciers ‘tongues’ and are produced where glaciers flow offshore or when the sea ice thickens due to accumulation and bottom growth. Occur in high polar settings and most extensive around the coast of Antarctica • ICE RISES: Floating ice shelves thicken to the point where they can ground offshore shoals. Form by ice flow over an obstacle, local thickening due to accumulation or a combo.

PRESENT DISTRIBUTION OF GLACIERS

• LATITUDE AND ALTITUDE: Higher altitude = more glaciers due to temperatures and air density decreasing. Glacier ELAs rise from the poles towards the equator but this alters with local precipitation. • RELIEF AND DISTANCE FROM MOISTURE SOURCE: - Slope is important due to the solar radiation and precipitation received. Lowest snowlines in northern hemisphere are in NE facing basins as they receive the least solar radiation and are in the lee of south westerly winds and so trap snow. - Shape = If a high mountain has narrow top but steep sides then there won’t be enough space for snow accumulation, instead causes avalanches, benefitting below glaciers. - Distance to moisture source: if far away then unable to sustain a glacier e.g. Antarctica continental interior is very arid and accumulation occurs near coast.

Glacial landsystems

• Landsystem: area of common terrain attributes, different to those of adjacent areas. Recurring patterns of topography, soils, vegetation reflect underlying geology, past erosional and depositional processes and climate (Eyles, 1983). • Process form model: conceptual model emphasising the genetic interrelationships of specific landform-sediment associations at both local and regional scales. • Holistic approach: geomorphology and sediments characterise the landscape and are genetically related to processes that generated them; individual landforms can be grouped in land facets. Clayton and Morain (1974): North Dakota – emphasised spatial temporal landform sediment associations during advance and retreat. Recognised importance of suites of landforms not just in isolation e.g. marginal, transitional. Linked glacial stratigraphy to landforms.

• Concept development: 1970-80s: styles of glaciation e.g. subglacial, supraglacial (Eyles, 1983); 1990s – present: continuum of glaciation styles and dynamics e.g. surging glacier, ice stream, plateaux icefield (Evans, 2003) – suggests land systems change over time. Important of topography and thermal regime continuum (e.g. temperate glaciers – entirely warm based, slide over bed or deform underling till; poly thermal – largely frozen to bed around margin, produces lots of debris, can’t melt out as too much, clearly warm and cold based zone) (example S4) – Recent applications of landsystems are qualitative characterisations for reconstructing paleo-glaciology. Resulted in development of specific landsystems models relating to specific ice dynamic e.g. surging glaciers from wide range of glaciated environments. Prediction of whats is beneath surface by looking at surface and landforms. • ACTIVE TEMPERATE glaciers: Have strong seasonal climatic control (respond quickly to) and a predominantly warm bed. Active: flow maintained during advance and recessions due to forward flow from mass balance (constant accumulation even when ablation exceeds); produces push moraines e.g. maritime locations Iceland, Alaska, Norway. 3 Components (Evans and Twigg, 2002) Iceland: - Marginal morainic: areas of extensive low amplitude push and squeeze moraines derived from material on glacial foreland, recording annual recession of ice. But also sub glacial imprint domain with other landsystems - Glacioflvial/lacustrine: incised and terraced glaciofluvial forms e.g. recessional ice contact fans; eskers and pitted outwash. - Subglacial: flutes, drumlins and overridden push moraine located between ice marginal glaciofluvial depo-centres. - Lack of supraglacial sediment in active glaciers prevents the widespread development of chaotic hummocky moraine. Tills across foreland produced by subglacial deformation and lodgement; comprise of pre existing stratified material and abraded rock from lake sediments. - Laurentide IS margin: (Evans, 2014): used modern analogue to reconstruct: spatial variability in landform type reflects changes in paleo ice stream activity and snout basal thermal regimes which potentially linked to regional climate controls. Spatially variable landform assemblages in southern Alberta consistent with palaeoglaciological reconstructions proposed for other ice stream lobate margins of the S Laurentide IS where alternate cold, polythermal and temperate marginal conditions caused dynamic, surging activity. • SURGING glaciers: characterised by short rapid advance phases followed by longer quiescent phase (downwasting). Linked to reorganisation of the subglacial drainage system e.g. extensive crevasses, catastrophic meltwater discharges, rapid snout advance. Produces consistent and predictable landsystem. Observed in forelands of modern glaciers e.g. Iceland and in marginal record of Pleistocene IS e.g. S Laurentide IS. - Landsystem: Evans and Rea (1999): No single landform identifies. Landforms produced during surging: thrust moraines, zig zag eskers (concertina) and subglacial crevasses squeeze ridges. Sedimentary sequences: multiple stacked diamictons and stratified interbeds which display glaciotectonic faulting. Also associated with hummocky moraine where large supraglacial and englacial debris entrained in the surge event have melted. Example: Alberta, Canada. Also found surging paleo ice stream (S Laurentide IS) - Use modern analogues to reconstruct former surging glaciers. • PLATEAU ICEFIELDS: cold based plateau ice; topographical constrained outlets and niche (shallow) glaciers (suggests warm based?). - Summit breadth concept: Manley (1955): critical concept. If summit too narrow, then snow would blow off but if snow stays produce plateaux snow hold. - Subtle summit landsystem: summit blockfields and abraded bedrock with lateral ice marginal meltwater channels. Prominent depositional features in surrounding valleys: continuum of subglacial landforms, Glacitectonic moraines and boulder moraines (debris volume dictated by ice flux). However, misidentification in the palaeoglaciological record can occur. - Spatial/temporal continuum: Critical role of ice flux. Plateau summit: If debris rich ice, low ice supply and so ice moves slowly, produces terminal moraines? Composed of boulders from underlying blockfield; if high ice supply and low debris then lateral moraines deposited – sediment from rockfall debris. At plateau margins, strain heating/frictional heat widespread producing tills and flutings from abrasion, lodgement and deformation. Valleys surrounding mostly fine grained diamictons. - Modern analogues to reconstruct ancient: Lake District: Original valley and cirque glacier reconstruction based on depositional evidence but no evidence of accumulation zone (Sissons, 1980). - McDougall (2001): evidence of plateau icefileds in central fell of Lake District during the YD. Geomorphological impact minimal on summits where survival of blockfields and frost weathered debris suggest protective cold based ice. Prominent moraine systems produced by outlet glaciers which descended into surrounding valleys where margins become traps for supraglacial debris/inwash. Ice marginal moraine records show successive positions of outlet glaciers that actively backwasted towards plateau source. Differs from alpine style glaciation which constructed glaciers emanating from valley heads (Manley, 1959; Sissons, 1980). So former plateau icefields may have been reconstructed incorrectly as cirque/valley glaciers adjacent to ice free summits. • ICE STREAMS: relatively fast move streams of ice within IS. Landsystems model for this is based on characteristics of modern day ice streams. Used to be based on non modern analogues. - Margold (2013): Mapping inventory of ice streams. New remote sensing and DEMs permitted glacial landform mapping. Identified 117 ice streams dependant on: bedform imprint, topographic constraints (limits of glacial troughs), major sedimentary depo-centres; subglacial till or edge of bedform imprint where lateral shear margin moraine (where no topography). Multiple types of evidence for some ice streams but others just 1; strength of evidence varies. - Stokes and Clark (1999): geomorphological criteria included characteristic shape; convergent flow patterns; abrupt lateral margins; lateral shear moraine; glaciotectonic evidence of deformed till. Highly elongated bedforms e.g. Artic Canada - Stokes and Clark (2003): Canadian Shield major ice stream reconstruction from Laurentide IS 9ka BP: high convergent onset zone, abrupt lateral margins, where flow fastest MGSL 13km long. Flow pattern not steered topographically; located on hard bedrock, surprisingly as soft sediment would have lubricated the bed over bedrock downstream; oposes view that only arise in deep bedrock troughs or thick deposits of soft sediment. Though inititated by velocity increase through calving.

Glacial sediments

• Basically material caused by glaciers. Need to reconstruct past glacial environments but complexity. UK 70-80% glaciated and so environment formed by glaciers. • Debris cascade: Glaciers can carry material outside the drainage system and can deposit miles away from the source. - Size of material: tells us about the depositional environment and the energy of it. Clast morphology: tells what geomorphic medium had done to it. Fabric and structure: see patterns of directional properties - Source: lithology and clast morphology and size important; Transport: clast morphology, size, fabric and structure e.g. subglacial, Englacial; Deposition: bedding, structure and grain size. Can see type of deformation. • CLASSIFICATION: Tills - Sediment deposited directly by ice. Far too many classifications of till but 3 main types. - PROCESSES: - 1. Lodgement: plastering of debris onto bed by sliding ice. As dragged across causes striation; increasing bed angle results in more friction and stops boulder moving, moving against frictional resistance, more sediment clusters behind as acts as obstacle; - 2. Melt out: Subglacial release of debris by melting ice. Debris rich ice undergoes volume reduction due to ice melt and drainage. Amount of consolidation depends on the debris concentration i.e. large if little debris. If drainage not easy, pore water pressure increases during melt out, decreasing frictional strength of deposited debris, increasing likelihood of failure and remobilization. Remobilization also more likely if bed slopes. Easier if cavity as just collects here. - 3. Deposition by gravity: into sub glacial cavities, in the lee or below ice overhangs at margins. If basal melting high, debris melts out from roof of cavity and fall to floor. Slurries of saturated debris can flow into cavities from ice bed interface. Below thicker ice, clasts extruded from basal ice into cavities by excess ice pressure (Boulton, 1982). Till curls: curved masses of debris rich ice, spall off due to different strain response of debris rich and clean ice going into cavity = stress release. All cavity deposits may accumulate and re couple the glacier base as frozen or subglacial deforming layer. - Subglacial (primary glacigenic deposition): Combo of lodgement, bed deformation (stress too large as moves over), ploughing (large boulder ploughs through bed until lodges) and melt out, but complex interactions between these. Till very variable. - Sliding bed deposits: Deforming soft bed which it slides over, changes due to meltwater pressure i.e. water pressure in cavities creates high pressure, sediment deforms, increases meltwater, pore can’t handle volume and ice detaches causing it to slide = produces sand and gravel lenses. If water pressure drops, re couples – daily basis – lenses found with diamictons reflects sliding to deformation changes. - Glacitectonite: Sediment deformed by subglacial shearing (deformation) but retains structural characteristics of original material (igneous, metamorphic, sedimentary etc). Type A: banded and laminated tills, show penetrative deformation; Type B: non penetrative deformation so pre deformational sediment structures are folded/faulted. Previously referred to as deformation till but this is included in sub glacial traction till. - Subglacial traction till: Sediment deposited by a glacier sole either sliding over/deforming its bed, releasing sediment directly from ice by pressure melting/detached from substrate and disintegrating and homogenised by shearing (Evans, 2006). Shearing zone created by shearing structure in diamictons called partings which produce a fault gauge between upper ice sheet and lower deformable substrate = produces deformed sediment. Previously labelled lodgement/deformation till. - Meltout till: Sediment released by melting of stagnant/slowly moving debirs rich ice; directly deposited without transport or deformation (Benn and Evans, 2010). Preservation low due to likeliness of debris flow resulting from high pore pressure pile of sediment. • Subglacial Till Mosaic: Below modern glaciers can see glacier beds consist of mosaics of deforming and sliding bed conditions that vary in space and time. - Characterised by changes in till properties over short distances dependant on the predominant process at time depositional system shut down. - May be possibility of superimposition on parts of till layer due to difference temporally and spatially (Piotrowski, 2004). - Tills show complex histories showing combos of cycles of lodgement, deformation and melt out. Difficult to reconstruct. - Show less sediment in soft bedrock; melt out till in hollows; zones of glacitectonite; pseudo stratification - CASE STUDY: Alaska (Ham and Mickelson, 1994): Till known to have frozen onto glacier sole and then melted out. Characteristics indicate not just melt out till; 1. Shear surfaces present; 2. Stoss and lee boulders common at the upper surface indicating modification of till below sliding ice. 3. Clasts don’t show particular mode of deposition. Suggest gone through many cycles of erosion, transport and deposition beneath the glacier – repeated Meltout and freezing. READ SUMMARY IN BENN AND EVANS • GLACIOFLUVIAL ENVIRONMENTS: Sediments deposited from flowing water. Can be deposited in subglacial and Englacial conduits; supraglacial and proglacial streams; meltwater portal, therefore important to many landforms. Characterised by stratification reflecting migration and creation of bedforms. - Have steep head gradients and so have high energy as ice is constantly pumping; high discharge which is temporally variable (melt only occurs at seasonally); high magnitude events e.g. Jokulhlaup - Landform-sediment assemblages: 1. Sandur: braided outwash plains; 2. Kame and kettle: sand and gravel collapses as meltwater occurs; 3. Esker: river within, beneath ice constrained by ice walls, winding through ice. Cut and fill caused by abrupt changes in grain size and sediment structure. - Hyperconnected flow: saturated debris flow, deposited rapidly. - Bedforms: Formed in the traction zone between water and bed. Different bedforms from different flow velocities e.g. lowest velocities produce sand ripples; highest produce dunes/plane bed deposits. FROUDE number: less than 1 = subcritical flow (deep and slow); more than 1 = supercritical flow (fast and shallow). - 1. Ripple cross lamination: Sand facies deposited by migration and vertical accretion. Form depends on balance between down current migration and suspension sedimentation. Ripples on top of one another. Type A: more sediment eroded from stoss sides during ripple migration than is added from suspension. Lee side preserved as cross laminae that dip down current but stoss eroded, so lee side laminae sets separated by erosion surfaces that dip up current; Type B: Cross lamination on stoss and well as lee, recording net deposition from suspension over whole bedform; Type S: sinusoidal cross lamination. Small variations in thickness between stoss and lee side laminae with steep angle of climb (shows amount of deposition from suspension), so suspension dominates. Weakly symmetric or asymmetric. Shows weak current flow. - 2. Plane bed deposits: Net deposition of flat, sandy stream beds produce beds of horizontally bedded or laminated sand. Laminae record minor fluctuations in flow velocity/sediment supply. In upper flow: bedding planes thin, linear grooves and ridges parallel to former flow direction in response to instabilities in boundary layer of water flow (parting limitation) e.g. sandstone. Lower flow: sand is coarser and no parting limitation. - 3. Gravel sheets: form by clast by clast accretion on low relief parts of riverbeds. Sediment movement and deposition occur only during floods and waning flows; between floods normally exposed. Bedded class supported gravels – fine grain gravel become trapped in spaces between large clasts = poorly sorted deposits. Horizontal stratification can occur during fluctuating flow. - 4. Hyperconnected flow: Debris slurry, in jokhulaup like floods. Deposits can be extensive, consist of matrix supported gravels/diamictons reflecting mass transport and rapid deposition. Stratification can occur from surges in flow. Upward increase in structures and sediments indicating fluvial processes e.g. better sorting – transition to normal stream flow during falling discharge - 5. Silt and mud drapes: Reduction in flow, leaves stagnant water in abandoned channels, allowing fine suspended sediment to settle. Forms drapes of mud and silt, thickest in middle. • SUBAQUEOUS GLACIAL SEDIMENTS - Dictated by: 1. Water body characteristics: water stratification i.e. top layers warmer and lower cooler and salinity, means different sediment transported at different times of year; bathymetry i.e. depth of water body as dictates where sediment deposits; tides, currents i.e. mix and movement, also Coriolis effect deflect sediment. 2. Glacier/water interface: ice contact i.e. floating and calving in the water; glacier fed i.e. goes across meltwater stream. - WATER INFLOW: overflow, interflow and underflow – water carries sediment at different levels dependant on stratification. Overflow: water is less dense even with sediment than below. Through ice: underflow mainly or interflow. Sediment starved further away from interflow point. TURBIDITES: underflows. Particles kept afloat by turbulent suspension; make flow denser than the surrounding water causing it to move downslope along the bed. Turbulent head moves downslope mixing with water and requires transfer of denser fluid from the tail to maintain momentum. Sediment is suspended or bedload (if velocity drops). - Iceberg drop, dump and grounding structures: 1. Drop: Rupture of the stratum underneath, deformation varies with size, shape. 2. Dump: Mounds of gravel/diamict formed by break up of dirt laden icebergs, causing release of large quantities of debris to lake floor; 3. Grounding structure: Grounding of icebergs (Thomas, 1985). - Proximal-distal sequences: Proximal: coarse grained gravel mass flow, turbites and foreset beds; Distal: finer, glacimarine lamination e.g. varves and glacilacustrine rhythmites e.g. varves and turbidites; dropstone, dump etc. - Deformation structures: Principal includes shear, compressional and vertical deformation. Clastic dykes: injection of sediment; Hydrofracture fills: fracture and injection due to elevated water pressure. (table in lecture) - Syn-sedimentary deformation: Deformation ongoing during sedimentation; driven by increased density. - Gravitation mass movement deposits: Debris flows the stiffest> hyperconnected flow>turbidity flow (surge). - Reconstructing depositional environments: Shown by complex sedimentary sequences; glacitectonite; subaqueous mass flows.

Glacier and ice sheet modelling

• WHY?: Predict future change i.e sea levels; reconstruct past change for insight into longer term behaviour; understand controls such as feedbacks; response to climate change in terms of thickness and flow speeds. • PART 1: Building a model of glacier flow - Ice surface evolution: quantify ice flow in terms of deformation and basal sliding. Identify accumulation, ablation and ELA. Apply climate forcing by altering net mass balance. - Flow line model (1D): Shows discrete points along a central flow line. Good for valley glaciers/constrained ice streams. Shows ice surface and bed topography. - 2D or 3D: Good for ice sheets/caps. Grid in x, y and z direction so layers vertically. Differing grid sizes due to resolution e.g. Antarctica/Greenland 40-5km resolution. More expensive. - Choice: Depends on location of interest, scientific question and resources. SIA: shallow ice accumulation. SSA: shallow shelf accumulation. Ice streams need more sophisticated model as use more complicated equations due to high speed. - Mass continuity: ice thickness = existing mass + (accumulation-ablation) + (ice flow input-flow out). If ablation increases, thins but if flow out then decreases may thicken again. - Continuity equation (conservation of mass): thickness change = mass balance – change in ice flux along flow - PART A: Ice discharge (flux) q: Need to calculate how fast and how thick it is. Ice flows by deformation and basal sliding, so use simple model which assumes no basal sliding and no longitudinal stresses (push/pull); so deformation * thickness. - Glens flow law: law describing strain response of ice when stress applied. Found deformation rate changes with ice temp (cold ice doesn’t flow as fast due to stiffness). Driving stress is unknown but easily calculated… - Driving stress: Function of thickness*ice surface slope*ice density and gravity. As ice gets steeper/ thicker should get larger driving stress. - PART B: Compute mass balance b: quantifies ablation and accumulation in m/yr. Look at data, then come up with rule. Simple option is to use data to construct mass balance parameterisation e.g. MB increases linearly with surface elevation. Steeper slope of best fit line (between accumulation and ablation) gives faster rise of b for small rise in elevation. - Alternatives: Use separate model to calculate b using energy balance models etc but need validation/calibration; use past measurements e.g. past climate/MB record using ice cores, proxies; create future scenarios for IPCC using CO2 levels to determine temperature, accumulation and ablation. - SUMMARY: Calculate equation for each section of glacier to calculate how much its likely to thin/thicken over time. Repeat for various time scales needed. Coloured output shows ice surface growing overtime. - Inputs to control model: Geometry on grid showing bed topography, reference width and thickness, ice surface. Parameters such as values for ELA, slope of best fit (net MB) and flow law values such as ice softness and n exponent (3). - Outputs generated: Glacier length and volume with time; ice thickness and surface elevation; net mass balance; flux (ice through system) and velocity - Validation and verification: needed for model. Validate by observed surface velocities, surface elevations, length record using moraines, terminus and sea level record. BUT some require mass balance history and are dependant on model parameters but can be calibrated. Re run to revalidate. • PART 2: Using a model of glacier flow: models show growth and retreat of ice sheets. • CASE STUDY 1: British-Irish ice sheet - Investigated how the ice sheet evolved over last glacial cycle and how sensitive it was to various controls. Need 3D ice sheet model; 10-2.5km resolution and multiple simulations with different inputs. - Ran model with different inputs with different combinations. Validate using land form record as these tell us about past ice flow such as how fast and what directions flowed. But different flows over time so landforms e.g. drumlins and moraines may have been overprinted. - Mass balance: Needed sophisticated model, Positive Degree Day (PDD) Model which calculated how many days were above 0oC over a year. Know from ice cores that temp fluctuated throughout time. Know precipitation was snow when temp below 1oC. Used DEM of topography to produce maps showing whether it was cold enough to snow at particular elevations. More snow on west than east. - Testing sensitivity: to different parameters such as Glens A (deformation/ice softness); PDD to temperature relation as unknown how much cooler LGM was so estimate; max temp shift and precipitation amount compared to now. - Hubbard et al (2009): Surface mass balance derived using degree day calcs based on reference climatology of mean precipitation and temperature patterns (1961- 1990). - 250 simulations explored parameter model uncertainties and sensitivities to correspond to onshore and offshore ice directional indicators and SL record. - Found series of advance/retreat cycles which correspond to alternating periods of cold based ice and wet based characterised by ice streams. - Phases of predominant ice streams coincide with periods of maximum ice extent and are triggered by abrupt transition from cold to warm climate, causing major melt discharge events into North Sea and Atlantic Ocean. - Chronology of the BIIS indicates maximum extent of 20ka BP, with fast flowing ice across the western and northern sectors that extended to the continental shelf edge. From 19ka BP deglaciation achieved in 2000 years, discharging freshwater equivalent of 2m global SL rise. Multiple readvance events from Scotland into North Sea basin from 17ka and Younger Dryas event 13-11.5ka BP. Last remnant glaciers 10.5ka BP. - Important controls: 1. Ice extent = sensitive to precipitation and temp; showed elevation, temp and MB feedback. 2. Flow patterns = dependant on position of ice divides interiorly; dynamic flow switching due to climate fluctuations and basal heat (sliding). - SUMMARY: Good fit against geomorphological data such as positions of fast flow and ice flow direction but ice extent less accurate due to max extent not at same time. Showed dynamic ice sheet which was not shown in previous reconstructions with significant margin fluctuations and ice streams. - NEED: more sophisticated models which need to account for more processes associated with marine terminating glaciers e.g. basal melting, buttressing, calving, isostatic rebound. Biggest uncertainty with predictions of SL rise if contribution from dynamic ice sheet processes (IPCC, 2007). • CASE STUDY 2: Jakobshavn, Greenland: loosing mass but controls not understood. GRACE satellite suggests area is rebounding and loosing gravity and therefore mass. - CAUSE of retreat and acceleration: Nearing terminus and speed increases, increasing retreat. Loss of buttressing from floating tongue thought to be caused by warm water. Used model to investigate as could have been coincidence. - Vieli and Nick (2011): Experiment 1: Showed melt only. Apply 20% enhanced melt caused by 1oC ocean warming. Doesn’t let ice front move. Showed large melt which initiated retreat but doesn’t explain acceleration of flow so must be another process - Experiment 2: Apply 20% enhanced melt after 1997 caused by 1oC ocean warming. Added calving model and found retreat and velocity increased similar to what we see in reality, suggesting processes important. - SUMMARY: retreat triggered by ocean melt. Dynamic change through loss of buttressing from calving retreat feedback. Less winter sea ice duration can also produce similar rapid retreat. But still not enough acceleration suggesting other processes involved. Care should be taken when interpreting such rapid dynamic changes in Greenland. Need to understand fjord circulation better. • CASE STUDY 3: Pine Island Glacier retreat (future) - Has been speeding up due to increased ocean melting over the last 40 years (Rignot, 2014). Tested future response using 3 different models which will give better confidence. Retreat experiments: Simulate until present day and then applied 4 scenarios for patterns and rates of melting beneath ice shelf, tests how much retreat could occur. - RESULTS: Retreat occurred in almost all experiments causing sea level rise. Show different rates of retreat. Model 3 showed the fastest retreat. Model 1 didn’t retreat initially but then rapidly retreated after 15 years until 25 years. Models 2&3 showed retreat initially and then kept going and continued for 50 years of prediction – unclear what will happen after this. - Later experiments: stop melting as soon as retreat begins to test whether retreat could stop. Most show retreat is irreversible suggesting PIG damage is permanent. Thought the grounding line is currently in a unstable retreat for 40km. Predicted equivalent of 3.5-10mm of sea level rise over next 20 years (Favier, 2014). - SUMMARY: Retreat due to melting beneath ice shelf. Thought it won’t stop due to MISI and so deepening slope with no topographic bumps to allow re- stabilisation • CONCLUSION: Model needs to be able to represent range of processes; have appropriate spatial framework e.g. dimension 3D; given a forcing e.g. climate; data for input, tuning and validation e.g. length variation, basal topography. Model only works within its design limitations.

Glacier Erosion Processes

• Glacier erosion: detachment, entrainment and transport of rock and sediment from the glacier bed. Difficult to observe but important as principle mechanisms of formation of landforms and linked to patterns of glacier flow and stability. Reflects balance between imposed shear stress of ice on the substrate and the strength of the glacier bed. No erosion in central ice sheet as ice stuck to bed. • Erosion controls: 1. Entrainment of fractured debris through plucking and re freezing; 2. Rock characteristics: hardness affects ability to erode and structure i.e. bedded or jointed. 3. Movement around topography: low pressure on less side due to heat of glacier as it moves over melts the ice. Water film (mm) at bottom of ice enables sliding and so get abrasion of bedrock as well as excess meltwater. • Stress and material strength: Ice exerts shear stress on debris particles in form of drag force. Frictional and cohesive forces between particle and bed act as resistance. - If shear stress greater than resistive stresses, then erosion occurs and also transport. Particle wants to rotate to move and detach from bedrock. - If shear stress less than resistive then deposition occurs. - Complexity: shear and normal stresses have gradients and so vary e.g. can be small lakes, channels, different bedrock material. Importance of stress concentrations - Material strength: determined by cohesion (chemical bonds and electrical forces) and frictional strength (interlocking proturbance between surface); also size of grains and crystals. - If crack in bedrock, stress around this influences structure around. • Coulomb ‘Boulton’ Friction Model: Assumes friction between the bed and rock particles in basal ice is proportional to effective normal pressure. - Effective pressure: pressure from ice minus water pressure (upward buoyancy, holding ice up). Basal friction: Effective normal pressure * internal friction angle (angle material is deformed at bed). Pi = overburden ice pressure – Pw = water pressure in cavities. - Predicts high friction occurs under thick ice with low water pressures. BUT ice viscous and deforms around particles, lifting them. - Not realistic but sometimes: valid for friction between 2 rigid bodies i.e. debris rich basal ice; particles in direct contact with bed (not normally due to cavities between rock and particle, so real area less than apparent area). • Hallet Friction Model (Hallet, 1979) - Unlike Boulton, regards contact forces as being independent of ice thickness and subglacial water pressure. - Instead frictional force = buoyant weight of the particle and drag force resulting from ice flow towards the bed i.e. due to melting, vertical strain or topographic bump. - Highest contact forces: large, heavy particles and where basal ice melt. Rapid ice flow towards the bed i.e. on the stoss side of bumps. - Applies to glaciers with less than 50% volume containing basal debris and so particles spaced far apart. No contact between particles; ice envelops particles; ice flowing around particles not influenced. - Debris usually entrained in dirty ice, if released through melting and dragged across surface, will cause a lot of abrasion. • Sandpaper Friction Model (Schweizer and Iken, 1992) - Modified for debris rich ice (volumes larger than 50% debris ice). Ice doesn’t flow around the debris particles and instead acts as glue between. Debris rich ice deforms and moulds itself so contacts large areas of the bed and so has lower impact of friction than Coulomb. Acts as sand paper to abrade, polish and striate the surface. - Water filled cavities still important, so considers water pressure. Uses same equation as Coulomb but includes proportion of bed occupied by particles. • Forms of EROSION: Switch in type due to pressure differences. Includes abrasion, plucking and meltwater. Meltwater important in doing erosive work at base as allows ice to always touch the bedrock and also removes debris, depositing it elsewhere. • GLACIAL ABRASION: Includes both polishing and striation (Benn and Evans, 2010) - Striation: scoring of the bedrock from asperities protruding from a particle are dragged over bedrock, scouring thin grooves. Polishing: removal of small proturbances. - Striae formed when rock particles dragged across bedrock due to cumulative effect of numerous crack growth and brittle failures (small, sudden movements in particles), promoted by transient stress concentrations below the asperity (Benn and Evans, 2010). Jerky steps, not continuous. - Striae development influenced by: Hardness of rock surface vrs overriding clast; contact forces between clast and surface; velocity of clast relative to bed; debris concentrations, 10-30% most effective; removal of the erosional product by meltwater; availability of basal debris e.g at stress concentrations. - Best developed on stoss side as pressure decreases on lee side and the glacier detaches from the bed due to meltwater so poorly developed on lee (no pressure pushing down to do work). Plucked on lee side, striated on the stoss. - Polishing: smoothing of rock surface resulting from small asperities by overriding rock particles and ice. • Glacial plucking: Involves fracture and entrainment of larger fragments (1cm). - Stress patterns govern process but pre existing weakness important. Highest normal stress over the highest part of the particle. Shear stress peaks as it passes over to lee side where a cavity has formed - Lip of rock steps there are large stress gradients develop due to falling water pressure in lee side cavities (Iverson, 1991). This increases bedrock stresses while ice adjusts, stress is vertically orientated and compressive on stoss side leading to development of tensile stresses in the direction of glacier flow so fragments will detach parallel to the back of the step. - Ice velocity is greater than particle velocity due to frictional drag and extension as the particle wants to rotate and so negative values of stress on lee side where shear stresses transferred causing tensile stress. Chattermarks (crescentic fractures) produced. - Plucking most likely at the foot of lee side cavities. Presence and pressure of water is crucial, lower pressure = higher stresses (Iverson, 1991). Cavity is full of water which pushes up against the ice, reducing effective pressure; drain water and effective pressure increases, reducing plucking. - Bedrock structure: If bedded and jointed then ice easily plucks, if tilted up then more susceptible – overdeepening in joint bounded blocks; more likely to create roche mountanees. If bed is dipping away, makes it harder to pluck but easier to abrade, therefore plucking removes joint bound blocks making step sequences (Kelly, 2014). • GLACIAL MELTWATER EROSION: effective in both subglacial and proglacial settings. In settings with high sediment load and turbulent flow. 3 main erosive features - 1. Abrasion/corrasion: Erosion by friction. Water has high sediment load which forms scallops from continuous erosion. Dependant on particle concentration/hardness/size, flow velocity and angle of incidence. - 2. Cavitation: Pressure and shock waves from bubble growth where air gets in and collapse due to turbulence. - 3. Fluid stressing: Hydraulic stresses erode rock or cohesive material. - 4. Chemical erosion (solution): Soluble components of rock and debris dissolved in meltwater, particularly rock with high carbonate value with high rainfall. Even though low temps in glacier, CO2 has increased solubility, creating acidic meltwater making easier to erode rock. Moving over bump: dissolution during melting up-bump, then precipitation of CaCO3 during refreezing. Therefore, glaciers important store of CO2 – climate change? • Rates of erosion: Difficult to measure. Need direct observation in tunnels/boreholes. Use landform evidence where preglacial landscape s reconstructed and compared to adjacent eroded landscape. - Boulton experiment (1974): Iceland and France: dug artificial tunnels with trap doors; inserted different materials to see how quickly this was eroded by the ice. Found basalt was 0.9mm a-1 and marble was 36mm a-1. - Can see lowering of glacier since the Little Ice Age and the difference between newly eroded areas in Switzerland. - Nesje (1992): found fjord in Norway only experienced 1mm a-1 over 600,000 years (6 glacial cycles); fjord may have only been full of ice for short time? - Sediment yields in meltwater streams (Hallet, 1996): Polar glaciers = 0.01mm a-1 cold at base and so not a lot of erosion; small temperate glaciers (Alps) = 1mm a- 1; Large fast flowing glaciers (Alaska) = 10-100mm a-1. Yields increase with basin size reflecting an increase in effective erosion rates. Suggests that major changes in erosion rates and therefore rates of isostatic rebound due to erosional unloading are expected in response to climatic changes. Less accurate methods based on marine records. - Few quantitative estimates of plucking. • Latitude control: Koppes (2015): Erosion rates expected to increase with decreasing latitude due to: climatic control on basal temp controlling basal meltwater and therefore sliding. This controls erosion rate and sediment transfer. - Measured erosion and ice flow from 15 tidewater glacier across 20 degrees latitude. Data shows climate and glacier thermal regime control erosion rate more strongly than ice extent, ice flux or sliding speed. • Patterns of erosion: mainly governed by basal thermal regime i.e. warm based ice meltwater allows basal sliding and therefore abrasion, plucking and meltwater erosion. Secondary controls: - Topography: steeper bed, enhanced melting and erosion; hardness of the bedrock - Ice velocity: faster, the more topography comes into contact with, so more erosion, melting and more movement. - Fluctuating pressures: localised warming and refreezing (due to regelation or uphill) and so get erosion through abrupt changes - Position along glacier: at edges particularly in low latitudes, see erosion and deposition due to thin ice being less insulating and so cold air temp can penetrate the ice and reach the bed, refreezing and limiting erosion. • CONTROVERSIAL COLD BASED: Thought to be ineffective at erosion but recent evidence: - Cuffey (2000) = evidence of debris entrainment at -17oC in Antarctica; Atkins (2002) = Found abrasion marks, deformation structures. Thought should accept cold glaciers do slide and abrade. - How?: Atkins (2002) = Erosion occurs by blocks of bedrock plucked from outcrop which is rotated and dragged causing abrasion; this causes extentional fractures and slip along weak layers from ice loading producing abraded surfaces. Deposition occurs by fragmented sandstone being plastered onto bedrock escarpments, projecting into ice mass; crushed bedrock debris on leeside of landforms; formation of ice cored debris cones from lowering of plucked blocks during retreat. • Numerical Models of erosion: Test where and how erosion happens at various scales. Use one of 3 theoretical models as basis for erosion. - Some use presence of water (sliding) as trigger to start erosion and feedbacks. - Incorporates other processes: Hydrology; sediment transport (if sediment isn’t flushed from system, can act as a buffer to erosion); tectonics; hillslope diffusion. BUT erosion rates are poorly understood. - Topographic ‘steering’ feedback: Kessler (2008): Positive feedback initiated by ice being steers towards mountain passes as enhanced erosion due to more meltwater beneath thicker and faster ice and so deepens passes further, amplifying steering towards mountains. Forms grooves which get larger and larger. FJORDS: deepest through highest topography and drain a large fraction of interior. One million years to form km deep. • FLUVIAL to GLACIAL: Jamieson (2008): Originally fluvial landscape and so not flat. Fluvial valleys guide the ice and generate glacial signal after 100ka, very quick. - Thought that erosion is controlled by presence of basal melt and coulomb type model (thick ice, low pressure). Erosion and valley over-deepening stabilise thermal regime. Suggests erosion can alter ice sheet extent. - When does it become glacial? After glaciation initiated, glacial erosion is maximised in early stages of glacial superimposition upon fluvial topography and so topography adapts so erosion minimised and glacial system expels ice more efficiently. • FLUSHING: enables more erosion, so water very important. Difficult to measure so experiments inolve glaciated fluvial valleys with or with basal hydrology. - Over deepenings were deeper with hydrology; basal water pressures are high, helps transport sediment away; water maintained bare rock vrs. Sediment laden ice contact; allows more effective erosion.

Glacier Flow

• Balance velocities: Over long period of time, GF is function (consequence) of climatic inputs and size/geometry of the catchment. - Mass conservation theory: if glacier has constant size and shape, the ice flow through a cross section must balance accumulation and ablation. Wedge model = B shows higher MB, and more rapid turnover (Benn and Evans, 2010 pp.143). - Steeper = flow more rapidly; topography important e.g. convergent funnelling increases the velocity. Glacier driving forces and resistive forces may not be in equilibrium with climate (takes time to react) and so measured velocities differ – if flowing quicker than expected suggest out of balance e.g. Ice Stream B. - Remote sensing has allowed BV of large ice sheets to be calculated (Bamber, 2000). Found data on surface slope, ice thickness and mean surface net balance. Discovered ice tributaries far inland e.g. Antarctica 250m/yr-1 ice streams found. - Agreement between BV and measured but some diasagreement = some parts of IS not in equilibrium. • Glacier stress and strain: Able to flow as driven by stress (how much material is pushed/pulled due to external forces); strain (amount of deformation due to imposed stress). - Stress: A measure of the distributed force, force per unit area e.g. at base of ice, a lot of overhead weight (affect of gravity) and so would expect a lot of deformation (strain response). Stress increases with ice thickness (highest at bed). Force = mass*acceleration (N). Stress measured in Pascals (1=1Nm-2) or Kilopascals. Normal stress occurs at right angles to surface; Shear stress acts parallel to surface. - Normal stress: density of ice*gravitational acceleration*ice thickness - Basal shear stress: density of ice*GA*ice thickness*the surface slope (sin a). Complicated by topography (bumpy bed creates stress variation) and longitudinal stress (pushing of ice from upstream = compressive stresses; pulling of ice downstream = tensile stresses); crevasses signal high stress. - Strain: Amount of deformation that occurs due to stress applied, so higher stress, the more strain. 2 components: elastic/plastic, which removes stress and springs back; permanent, reaches critical point where ice never goes back to how it was e.g. ice fractures into crevasses. Can be ductile e.g. snow feels strain and deforms accordingly in fluid way; or brittle, deforms in chunks as it breaks and so shears. Can have constant volume of deformation of dilatancy where the material stretches and takes up a larger area. Can deform linear or non linear and deform more and more with little stress. - Ice deformation: Ice flows through deformation of the ice in response to stress. Consists of ice creep (movement within or between ice crystals) or fracture (brittle failure which produces crevasses). - Glens flow law (1955): describes strain rate of ice as (how easily ice deforms): Allows simulation of ice flow. Varies with the 3rd power of shear stress and so if doubled, strain rate increases eightfold (2*2*2). - Difficult to measure ice flow by internal deformation due to variability in ice crystals: orientated differently making them easier to be deformed; impurities within ice e.g. solutes, gas bubbles, solid debris: offer more resistance and so harder to deform. - Basal sliding: Water at the bed lubricates (water pressures reduces frictional stress) and smoothes (reduces contact to bed). Pressure melting point (PMP): due to overlying pressure, temp increases towards the base and so ice starts to melt due to so much pressure meaning it can melt below 0oC. BUT diff areas of pressure and so not all the same. 4 things slow sliding: - 1) Adhesion due to freezing: cold ice. Sticks to ice offering resistant stress and acts as barrier. Cold temps retard creep/strain rates. - 2) Bed roughness: Glacier bed not smooth and so impart form drag e.g. Antarctica mountains. Overcome by enhanced creep: larger obstacle, greater strain rate so deformation high and rapid (ice accelerates around bumps); regelation sliding: refreezing, most effective around small bumps. - 3) Lack of lubricating water: Water film needed for sliding. Increased glacier motion linked to high basal water pressures and changes in subglacial drainage (Kamb, 1987). Film (mm) can submerge minor obstacles and so form drag reduced by lee side pressurised water cavities. - 4) Debris at base of ice: Basal ice contains a lot of debris causing frictional drag against the bed. Complex and difficult to model at given stresses. 3 models: Coloumb, Hallet and Sandpaper (Benn and Evans, 1998).

• Subglacial deformation: Recently discovered material beneath a glacier undergoes permanent strain (deformation) in response to applied stresses of ice: sediment deformation (Boulton, 1986). - Boulton & Hindmarsh (1987): Dug tunnels to access bed in SE Iceland so could see some sediment exposed, inserted segmented poles, glacier flow over them to see if poles moved to investigate deformation. - Till saturated a very high porewater pressures. Upper layer 0.5m accounted for 80-95% of forward motion through ductile deformation (deforming more). Lower layer had brittle deformation due to differences in pressure. Confirmed by seismic studies (Alley, 1986) and borehole studies (Engelhart, 1990). But incompatible with observations of elastic/plastic deformation (Iverson, 2010). • Glacier surges: periods of rapid advance (months-years) followed by inactive phase of much longer duration (years to decades). - Advances transfers mass from up-glacier towards the snout, thinning the glacier, reducing the surface gradient (slope): leads to stagnation of glacier snout. Increased mass at snout, deformation at the base thrusts material upwards. Velocities 10x inactive phase. Surges and readjusts. - Clustered surge behaviour: Alaska, Columbia and Iceland. Suggests climatic influence. Trigger linked to reorgnaisation of drainage system i.e. sliding over inefficient linked cavity system at high pressure; change in water pressure alters sliding and deformation (Kamb, 1987). - Never match balance velocity, either accumulating for surge or surging. • Ice streams: Ignored until Mercer (1978). Part of inland ice sheet which moves faster than surrounding ice (Paterson, 1994). Fastest: 12,000m a-1. Large, 300km long. Dominate ice sheet discharge. - Antarctica: 90% drained by ice streams that comprise just 13% of surface area. Change behaviour of whole ice sheet. Need to understand how react to climate change as can have drastic impacts on ice sheet. - Siple Coast (Ross) ice streams: Low driving stresses but rapid velocity, low basal shear stresses as ice is almost flat. Coincide with soft deformable sediment at high porewater pressures. Flow through combo of subglacial deformation/ and or basal sliding. Erratic: rapid changes in velocity and location. - Bed conditions: ice stream flow controlled by this. Early work showed few metres of saturated deformable sediments beneath the ice streams. - Borehole techniques: confirmed basal melting, high water pressures and a porous till layer. Drilled through ice stream, found water flowed back up borehole suggesting pressurised water, conditions suited to sliding (Englehart et al, 1990). - Tethered stakes: suggests basal sliding predominant. Till deforms only in thin shear zone. Switches between sliding and deformation? (Engelhardt and Kamb, 1998). - UNKNOWN: flow mechs and morphology of ice bed interface limit ability to model ice streams. Paleo ice stream tracks can help. • CONCLUSIONS: Movement at surface of glacier is cumulative effect of internal deformation, basal sliding and subglacial deformation. Discovery of subglacial till deformation led to paradigm shift in mechanisms of fast ice flow and IS instability.

Glaciers and Climate Change

• ICE AGE EARTH: last few ice ages associated with temperature variations of around 10oC every 100,000 years. Last deglaciation took around 10,000 years, increasing sea level by 120m, sometimes in rapid pulses e.g. Meltwater Pulse 1a – 4m per century – debate over scale. - Still 10% earth glaciated. Mostly Antarctica, Greenland, Iceland, Himalayas; 198,000 glaciers; 65m sea level equivalent. Hennig and Stokes: shrunk/expanded country dependant on ice left, Canada large amounts, and Russia, Scandanavia, Iceland. Excluding ice sheets, 50cm SLE for these countries; small ice bodies, but potential to melt quicker than larger ice masses, very concerning e.g. 10cm = Thames barrier problems. - Distribution of all glaciers: Antarctica most significant contribution (58m SLE), then Greenland (6m SLE) but these have slow contribution to SLC – shows Canada as insignificant ice mass but most important. - Deglaciation not uniform all over world so hard to predict future but equator most likely to experience impacts most. • RECENT CLIMATE CHANGE: IPCC report shows hockey stick curve showing accelerated warming anomaly in Northern Hemisphere from 1960s. Instrumental and reconstructed data show past 1000 years a cooling trend. - CO2 concentrations rising: global temps start to rise 1910, with 1940s temps rising above average – CO2 correlates with this particularly with rapid increase 1940-60s. 10 warmest years all since 1998; 2014 was hottest then each year has beat this. Temps were below average 1950s,1975-80. - CO2 fits closely with temp, suggesting definite relationship. CO2 currently at 406ppm. IPCC (2013): created model attempting to recreate temps with no human impact = fit well in 1960s but not later; include anthropogenic forcings = much better fit. - Surface temp change: some areas 2.5oC rise but other have cooled e.g. North Atlantic (change in circulation). Rainfall: significant change, with less rainfall in Alaska, Patagonia – important for sustaining glaciers. - IPCC (2013): increased certainty humans have causes e.g. 2001 ‘likely’, 2013 ‘extremely likely’ shows evolution of understanding through science, models etc. • RECENT CHANGE IN MOUNTAIN GLACIERS AND ICE CAPS: Particularly in marine terminating glaciers, likely ice will melt and retreat e.g. rapid retreat of Muir Glacier, Alaska in 65 years - Smaller mountain glaciers easily monitored. Need to measure amount of melt and convert to SLE. Can measure ablation using ablation stakes (drill holes, stick in poles, measure how much is above surface; then come back and measure how much of pole is sticking out). - Combining field measurements challenging; large, global datasets estimating volume changes (mass balance) involves field measurements (stakes and pits) and area-volume scaling relationships; satellite measurements of changes in ice elevation/flow rate; detection of gravity field changes caused by glacier mass gain (stronger gravitational pull)/loss (GRACE satelites). Different techniques = different answers.

1 - Mass balance estimates: Kaser (2006): Glaciological method; Increasingly negative trend since 1970s; Patagonia rapidly loosing mass whereas Europe is gaining until recently. SLE: Alaska heavily contributing (+6-7mm; 0.77mm 2001-04), Andes and Europe smaller contribution. - GRACE data: Jacob (2012): reports volume changes based on satellite gravity estimates. Lost 148 Gt/yr volume 2003-2010 contributing to 0.4mm/yr. 30% smaller than previous estimates by Kaser. Suggests Patagonia/Alaska biggest small glacier contributions; uncertainty of best method. - Different techniques: glaciological method show greatest loss, then GRACE, then ICESAT altimetry data. Attempted to combine: GRACE fit well with glaciological method but GRACE gives large uncertainties; uncertainties overlap so some agreement. ICESAT and GRACE line up well. - Comparison of different studies: reach consensus. • RECENT CHANGES IN ICE SHEETS: A signal change in polar ice sheets (larger) is dynamic thinning of outlet glaciers. Radar imagery: Greenland: can see areas of faster and slower moving ice; controlled by air temps but also ocean interactions due to changes in the terminus; can see acceleration near margins pulling ice from inland (impacts whole IS); 3 main outlet glaciers. - Outlets are thinning and retreating, sometimes accelerating. Jakobshavns Isbrae: 6km wide, flowing at 10,000m/yr. - Joughin (2004): measured speed of JI, which drains 6.5% of GrIS. Doubled acceleration from 1992-2003 (5700-12,600m a-1) due to debutressing effect and warmer temps at front of glacier; caused thinning. But questionable whether currently slowing – due to topography? - Marine terminating outlet glaciers: Carr (2013): Most observations in the Artic record retreat, thinning and accelerating flow and so not just Greenland. Causes uncertain but likely to relate to increased air temps, ocean temps and reduced sea-ice concentrations. - Feedbacks in ice: Carr (2013): increased air temps, results in more surface meltwater and basal sliding leading to dynamic thinning due to faster flow and getting rid of material from accumulation zone faster. - Feedbacks with ocean: Carr (2013): if warmer, more submarine melting at marine terminating glaciers and at grounding line, causing retreat, thinning and calving; due to large SA underneath causing further. At floating terminus also complicated processes of warm water entrainment and turbulent meltwater plumes. - Sea ice and marine terminating

2 glaciers: marine terminating glaciers are calving ice; some areas of world sea ice present all year so icebergs calving off are held by sea ice; if sea ice removed, icebergs will float off; similar to debutressing effect, if not there more calving likely. Antarctica: sea ice extent lowest ever - Sumer melt: Surface melting also important. Areas in Greenland undergoing summer melt is increasing. Mapped melting extent, until 2012 interior hadn’t undergone melting – but almost all of the GrIS underwent melt on 12 July, 2012 (only one day but on average is increasing). East Antarctica: surface melting for first time as much colder here. - Potential positive feedback: poorly understood (Zwally, 2005). Extent of basal water unknown so basal sliding unquantified. - Antarctica: Similar dynamic changes; thinning in Pine Island where warmer ocean, thinning of ice shelf, reduced debutressing and so increased calving, increased flow speed dragging more material from further back. Speeds up terminus retreat. Surface melting less so in Antarctica compared to GrIS. - CHANGE DUE TO WARMER OCEANS, not air temps (Rignot, 2014). • IMPACTS: SEA LEVEL: Can assess mass balance using different methods to determine SLE contributions. - Shepherd (2012): Found 360 Gt = 1mm sea level. East Antarctica growing with amount of snow, found negative mass balance in past due to warmer air (still cold) so more likely for snow; slight thickening signal also from slower flow and so less ice lost by melt. Greenland: Negative in 1995, sudden rise then continuous fall past 400 Gt 2010. West Antarctica: steady negative/positive MB until 2007 dropped to 300Gt but small rise in 2010. - Ice sheet & Glacier contribution to SLE: IPCC (2013): Glaciers have the largest contribution (10-17mm); Antarctica has the least despite being largest ice mass due to being so cold so less rapid discharge into oceans, W Antarctica doesn’t impact too much. - Cumulative ice mass loss (glaciers and IS): 1993-2009: 1- 1.4mm/yr; 2005- 2009: 1.2-2.2mm/yr. • IMPACTS: WATER RESOURCES: One sixth of the population rely on glaciers/snow packs for water supply during the dry season e.g. tropical glaciers and central Asia. - Kilimanjaro: melts during the summer, used water for drinking. 2012 extensive ice field but significant reduction – satellite imagery shows less than 0.5km left; thought by 2060 there will be nothing left. - Runoff scenario models: Hagg (2006): generated runoff for different climates. Found an increased flood risk at first based on current glacierization and 50% reduction in glaciers followed by more complex after glacier loss: high discharge during spring due to earlier more intense snowmelt causing water deficiency in hot summer. • IMPACTS: INCREASED HAZARDS: Glacier retreat also increases risk of geohazards caused by increased meltwater outflow e.g. debris flows, slope instability, moraine dam failure (Clague and Evans, 2000). - As air temps rise, more surface melt stored on the surface and debris acts as dams e.g. glacial lakes have been rapidly forming on surfaces of debris

3 covered glaciers during last few decades such as in Himalayas. Elevation is concerning factor. - Bhutan, Himalaya: stagnating termini of glacier. Likely chain of events: break one dam, breaks into the next system, releasing the whole system. Likely volume of water stored will increase – catastrophic outburst frequency will increase. - Caucasus, 2002: Glacier related debris flow: rockfall onto glacier occurred at the cirque headwall causing glacier to disintergrate; ice rock and snow travelled 8 miles down valley killing 125 people. Made worse as it was a straight valley, hit and went straight through town. • FUTURE CHANGES: Predictions difficult as IPCC don’t know how humans will live in future. - Create models; mitigation scenario = 421ppm at 2100 at temperature plateaus at 2040; continued growth in GGs to 936ppm, causes temp rise of 4oC; stabilisation: 2-3oC increase. Not uniform: could mean 2 oC rise in Artic and just 1 elsewhere. - Sea level: using model = mitigation: 0.4m by 2100; stabilisation: 0.5m; continued growth: 0.77m - Small glaciers contribution: Radic and Hock (2011): range of volume loss (25-75%) and in sea level (0.01-0.04m) by 2100, suggesting uncertainty. Antarctica, Scandinavia and Alaska have greatest uncertainty, need to focus more effort here. - Antarctica modelling: Golledge (2015): predicts if warming exceed 1.5-2 oC then major collapse of west Antarctica within few centuries. However more sophisticated treatment by Ritz (2015) finds this implausible; physically impossible for glaciers to flow fast enough to do this, suggested low resolution model over estimates response to warming and therefore SLR – up to 1m overestimation by 2100. - Ice stream role: analysis of ice streaming during Laurentide IS suggests they played a regulatory role and so ice sheet retreat driven by surface melt not dynamic changes (Stokes, 2016).

4 Glaciofluvial environments

• Landforms assemblages: All glaciofluvial forms/sediments occupy positions on a spatial and temporal continuum. Drainage networks in receding glaciers (constantly deforming) evolve by: - enlarging drainage pathways; expand so much that tunnel system is larger than glacier system itself; spatial distribution changes (size continuum) and temporal (move) - combining drainage pathways; tunnels beneath others may collapse creating larger tunnels - changing from hydrostatic>atmospheric pressures; e.g. meltwater still present in advancing glaciers, just moves to subglacial under hydrostatic pressure and so water forced through tunnels due to over flow pressure of ice; as ice melts may cause switch to atmospheric. - R channel esker: glacier drainage network; water cutting up into ice rather than down into the bed, fills with esker sediment; atmospheric pressure produces sediments to be deposited. - H channel esker: due to pressure change; move from hydrostatic to atmospheric channel, produces widening of the tunnel with flat topped profile due to AP. - Ice walled: due to tunnel collapse. Opens up to atmosphere producing supraglacial stream running across. - Kame and kettle topography: due to ice surface drainage; ice continuously melting so anything that fills a hole is constantly changing shape and position until full melt. - Proglacial sandur progradation: final stages of meltwater produce growth of sand and gravel out in front of ice. • ESKERS: sit within low linear landscapes, esker runs through the middle where ice would have been located. Can have lots of branches, tunnels breached; find 2 types of morphology. As tunnel collapse, create ice channel fills, then glacier ice retreats and water retreats back. - R channel fills: under hydrostatic pressure. Hummocky long profiles. H channel fills: can’t move uphill and so are aligned with bed slope as ice doesn’t determine direction of travel. Includes valley eskers: subglacially engorged askers. Beaded esker: sediment deposited in large part of the tunnel, ability to change pressure as approach margin. - Characteristics: a) single continuous ridge, very rare as water normally breaches tunnels; b) single ridges with variable height and width (beaded); c) single low ridges linking numerous mounds/beads; d) complex braided systems: bumps throughout landscape. ALIGNMENT: water in tunnels follow pressure gradient and so are parallel to direction of glacier flow; transverse to flow caused by atmospheric pressure as ice is not moving the water e.g. valley eskers – moves over ridges, creates moraines. - Regional patterns (planforms): found eskers that are 100skm long; deposited in segments during retreat in the ablation zone as needed meltwater; channel system migrates towards ice sheet centre. When mapping can see long ridges with gaps between where likely to see a moraine (ice marginal features) e.g. Laurentide ice sheet divide. - Regional distribution: Storrar (2014): mapped 20,000 eskers on Laurentide ice sheet bed; found eskers became more frequent during deglaciation due to increased rates of ice margin recession and climate warming – more meltwater and so more channel infills. Meltwater becomes channelised, getting water into channels becomes increasingly important during deglaciation. Towards ice divide (of ice moving in diff directions), channels more numerous, denser network as recedes. - Incremental deposition of long eskers: - 1) Boulton (2007): eskers are complex sequences in corridors back towards ice margin. Each esker fed by a drainage basin; groundwater drains above bed, driving distribution of tunnels. Axis of tunnel remains stable showing strong coupling between groundwater and summer melt. - 2) Hooke & Fastook (2007): Laurentide ice sheet. Found eskers in straight tadpole shape segments due to: a) separate deposition of each segment in sub marginal tunnel, towards the margin tunnel gets wider due to more atmospheric pressure and so deposition; b) melt and sedimentation rates increase with increasing glacier margin surface slope as picks up energy to transport sediment; c) melt rates exceed tunnel closure rates by increasing amount towards margin and reduction in water flow deposition (less ice pressure, higher melt) – under hydrostatic pressure trying to close but closes in winter due to ice creep. - Esker sediment: Silts to boulders and diamictons. Tills also squeeze up into tunnel as less pressure there. Cut and fill sequences produced by variable discharge i.e. laminated then cut and filled with coarser material. Sediment demonstrate glacier melt patterns/tunnel constriction e.g. increased velocity of expansion of tunnel. - Formation: single tunnel shown as sinuous ridge. Become infilled with sediment after opening up of tunnel but pressure produces cut and fill sequences. Cavities: valves - water leads into causing drainage of channel, discharge drops and sediment deposited over wider area. These can be open or closed due to water pressure causing floating or decoupling of glacier = beaded esker. Mostly englacial but can be supraglacial. - Supraglacial eskers/ interlobate moraines: initially sub/englacial, evolve in supraglacial ridges (trough fills) and widening produces supraglacial lakes. At ice divide, ice downwastes leaving ice wall channel, get infill between leaving delta like feature. Later evolution: leaves kame and ice walled lake plain, chaotic areas of sediment. - Surge eskers: 1996: glacier sits over volcano, building large reservoirs, lets go every 11 years; water drains leaving esker and ice walled lake years later. - 1964 Iceland surge: Produced high catastrophic discharges; water escapes onto snout surface due to tunnels unable to carry rapidly rising volumes through crevasses on surface causing sediment to be deposited near these, can overlap; forms zig zag eskers which are crevasse infills. - Esker tunnel/lake interface: where esker enters lake, splaying of sediment into cavities due to flotation of tunnel mouth. Water loses velocity, drops sediment into deepwater column, sediment splays into centre e.g. beaded; e.g. Hooker glacier: debris covered, many tunnels full of sediment, underneath proglacial lake causes constant deposition of complex sand and gravel deposits; e.g. Oak ridge lake: moraine in deep water due to constantly filled with sediment (Barnett, 1998). • Kames: found at margins as glacier downwastes. Where large holes in ice, fill with lakes which connect to the bed (kame plateau). Tunnels where there are eskers, kame etc which collapse. • KAME AND KETTLE: fluvial deposition on wasting glacial surface. Guided by controlled ridges of debris charged ice and infilling of glacier karst (eroded limestone) but difficult to identify from pitted outwash. Heavily disturbed stratified sediments. - Kame terraces: ice marginal stream beds, accumulate sediment in a gutter between glacier and valley slope – deposited on valley slopes as more stable but collapses as melting occurs producing hummocks with flat tops. Lots of faulting and kettle holes. • Ice walled lake plains: circular plateaux (flat topped hills); surrounded by chaotic kames, eskers and hummocky moraine. Sediment is locally disturbed lake and glaciofluvial - Formation: infills of glacier karst holes, sediment accumulates in big holes, ice melts surrounding leaving upstanding plateaux with collapsed sides due to atmospheric pressure. Stable (debris charged ice) and unstable (debris poor ice). • OUTWASH SYSTEMS - Sandur: proglacial outwash fan with braided channel network e.g. Ellesmere Island, Canada - Morphology: 1) Proximal zone: few deep and narrow channels due to higher energy carrying large sediment; 2) Intermediate: complex wide and shallow braids due to less energy; 3) Distal: very shallow, ill defined channels due to low energy and so just sand and silt deposits. - Pitted sandar: Pits on surface. proximal outwash buries glacier snout forming overlap with kame and kettle (differentiation difficult); or ice blocks buried on jokulhlaup sandur. 1918 example: outwash extended coastline by 8km due to so much sediment produced, catastrophic impacts across Europe. Type of kettle relates to amount of sediment within iceberg as it melts (diagram). - Valley trains: deposition outwash confined by valleys; this is then incised producing terrace flights; individual terrace levels can be related to and paired with moraines - Architectural elements: relate to different processes within a stream and so provide evidence of discharge history e.g. braided channels. Coarser material located in proximal areas of outwash; finer located intermediate/distal. - Vertical profile models: glaciofluvial successions represent a continuum of variation (Miall, 1977).

• INTERGRATING GLACIOFLUVIAL SEDIMENTS/LANDFORMS: temporal and spatial evolution.

Landforms and Landscapes

• CONTROLS on landform of glacial erosion - Classified according to scale of size e.g. small (mm-m); large (km-10s km) and landscapes (100s km). Superimposition important as many glacial cycles impact same location. - Erosion and form controls: Glaciological = stresses, water pressure, velocity; Substratum = structure, lithology, permeability; Topography = morphology of glacier bed; Time = duration of glaciation e.g. LGM 26-18 ka BP. • Small scale erosional forms: Four main types (Benn and Evans, 2010) - Striae: Thin grooves on bedrock/clast surface. Caused by glacial abrasion. Associated with glacial polish. Created by numerous brittle failures and so not continuous, end abruptly (nailheads). Developed in fine grained, hard rocks e.g. quartzite’s where preserved, not granites (disintegrates when exposed to air). Optimum conditions (Iverson, 1990). - Cross cutting striae reconstruct changes in ice flow direction and erosion rates; but difficult to date as could be from 2 separate cycles or shift in ice dynamics over 1000s years. Also form through iceberg scour or slope processes. - Rat tails: Small tail of rock that is not eroded on the lee side, similar to large crag and tail. Differential erosion around resistant nodule. Indicate clear flow direction. - Gouges, fractures and chattermarks: Associated with grooves. Closely spaced fracture marks/cracks formed by plucking. Crescentric = concave down ice. Lunate = concave up ice. Mostly fracture planes but chattermarks: bedrock with low angle bedding and dips away; erodes through abrasion. Jerky stick-slip behaviour. - Plastically moulded forms: Smoothed depressions eroded into bedrock. Vary in size and can flow with ice flow or no trend. Originally thought produced by abrasion of plastically deforming ice. Possibly debris rich basal ice; saturated till; subglacial meltwater; ice-water mix. - P forms debate: Shaw (1988): morphology similar to scour marks eroded by water. BUT striae often on surface of P- forms suggests erosion by ice. Argues created after P forms as winding appearance, so must be meltwater. Boulton (1974): Observed debris rich basal ice in situ with ice turning corners; not formed by meltwater. Suggests P forms represent alternating forms of erosion. • Intermediate Scale Erosion Forms - 1. Roches moutonnees: Asymmetric bedrock bumps with abraded (polished) stoss and plucked lee. Vary in size. Striae superimposed on the stoss side. - Shape reflects distribution of stresses across bedrock bump – form under thin ice so easier to water to access, and fluctuating water pressure caused by cracks (Sugden, 1992). Ideal = vertical and horizontal joints are plucked more easily, spacing and hardness also critical. - Suggestion of immature pre glacial bedrock hills that have already been weathered e.g. tor covered in regolith. Only RM if glacier moves over. - Small scale erosional forms on RM: Kor (1991): Often have fluvially cut p-forms; this may reflect efficient abrasion due to high overburden pressures, high sliding velocities and large areas of ice bed contact beneath thick ice. - Whaleback: RM but without plucked lee so abraded on both sides. Rare but show differences in bedrock interface – found with thick and fast ice, potentially ice streams which supress ability of ice to lift off bed and so very high normal stress with high frictional heating due to fast movement. Ice then moulds to bed easier, sticking and preventing cavity forming and air reaching and plucking. - 2. Crag and Tails: Elongated, streamlined hills. Crag has resistance bedrock whereas tapering tail with less resistant rock. Produced by streaming of ice around obstacle, protection of tail from erosion. Length of tail suggest long pressure shadow in reflecting high sliding velocities. Need exposure to differentiate features from large flutings/cavity fills deposited in the lee of basal obstructions. Horned C & T: 2 till ridges from lateral flanks of the crag; formed by frozen ice at crag summit but melt further down, preventing till accumulation in lee. - 3. Nye channels: 10-1000sm long and 10m wide. Cut directly into bedrock following the hydraulic gradient, primarily determined by ice surface slope but local topography also e.g. valley glaciers. Interconnected channels that cross cut shallow depressions: linked cavity – high pressure water beneath ice cut into rock, move high to low pressure. Reconstruction of subglacial meltwater drainage and therefore the ice flow of ice sheet (Booth and Hallet, 1993). - 4. Tunnel channels: Similar to N channels but 100km long and 4km wide, large implying huge meltwater drainage beneath ice sheet, cutting through rock. Occur in isolation and dendritic patterns. Flat bottomed and steep sided, some filled by sediment. Moraines mark edges and large tunnel valleys mark drainage. Debate over origin: - a) Steady state meltwater drainage over deformable bed: soft sediment beneath ice, channel cuts into coupling drainage system and bed (Shoemaker, 1986) - b) Catastrophic meltwater drainage: mega flood under ice due to geothermal heat causes melt which needs to escape (Ehlers and Linke, 1989). - C) Time transgressive formation close to ice margin: super cooling. Tunnel valleys beneath ice, forces water out due to high pressure so flows up reverse slope and freezes, entraining sediment and infilling the valley. Built backwards as retreats and layers build e.g. North Sea examples. - 5. Ice marginal channels: lateral meltwater. Drain and cut channels alongside ice margin and sub-marginally (just inside margin). Preferably along cold based ice. Can reconstruct past margins and ice sheet elevation. Common in Scotland. - 6. Proglacial channels: Channels/gorges cut by proglacial streams. Discrete spillways from water escaping lakes; can exploit previously subglacial e.g. N channels. Largest formed from jokulhlaups. Process of deglaciation, common in County Durham. • Mega scale erosional forms - 1. Mega grooves: Straight and parallel troughs in bedrock. 100-1000sm long. Structurally controlled: follow bedrock structure; Structurally independent: own structure. Either cut by ice or meltwater; possibly relationship to fast flow suggesting ice streams – feedback of thick ice, friction and abrasion. - 2. Mega ridges: Straight and parallel ridges in bedrock. 100-1000sm long. Unknown but if structurally controlled, may be alternating igneous rock, softer rock eroded leaving hard. Possibly caused by glacier ice but no relationship to fast flow, thought to be controlled by normal abrasion. • Large scale erosional landforms - 1. Rock basins and Overdeepenings: Depressions/basins ranging from small hollows to large over-deepenings inside glacial cirques/troughs. Common fill by post glacial lakes. Controlled by bedrock structure and lithology. Main processes are plucking and abrasion over the same spot and enhanced meltwater pressure variations (Kor, 1991). In valley glacier, ice moves down, creates friction deepening area, extra heating from abrasion and plucking creates more meltwater to lubricate bed: enhancing feedback. - 2. Troughs and Fjords: U shaped but largely unsymmetrical. Some relate to pre existing fluvial valleys but some cut deep below sea level which rivers can’t do. Kessler (2008): Fjords reach km depths and extend 10s km inland. Ice sheets drain primarily through them, so widespread fjords may have altered ice sheet size and dynamics. Topographic steering of ice (towards mountain passes) and erosion proportional to ice discharge (thicker, faster ice towards these areas deepens and amplifies steering) are sufficient to form fjords. Fjords deepest through highest topography. Modern ice sheets more sensitive to climate change as deeper and larger. - 3. Cirques: Flat floored/over deepened basin connected to steep backwall by concave slope (Benn and Evans, 2010). Develop from hollows by progressive retreat of backwall and downcutting of the floor by plucking, abrasion, weathering and mass movement. Develop from more than 1 glacial cycle occupation. 5 types (Benn and Evans, 2010): Simple: distinct, independent features; Compound: upper part has 2 subsidiary cirques; Cirque complexes: upper part of more than 2 subsidiary sidewall/headwall cirques; Staircase: 2 or more cirques occur one above the other; Cirque Troughs: marks the upper end of a trough. • Landscapes of Glacial Erosion: Sugden and John (1976) defined 5 landscapes based on regional associations of landforms. - 1. Areal scouring: everywhere dominated by glacial erosion e.g. Canadian Shield, Scotland. Streamlined bedrock knobs, RMs, rock basins. Warm based erosion e.g. erosion and plucking in areas of low relief. Fast moving areas. - 2. Selective Linear Erosion: erosion in troughs with unmodified plateau surfaces. Fast, warm based ice in troughs and slow, cold based ice on plateau. Partitioned landscape - 3. Little/no erosion landscapes: Unmodified pre glacial landscapes, that survived glacier occupation as protected by cold based ice. Characterised by dendritic pattern of fluvial valleys, tors, blockfields; only lateral meltwater channels mark the existence of ice. Subglacial thermal organisation concept (Kleman and Glasser, 2007): composed of 4 components: frozen bed patches; ice streams; ice stream tributaries and lateral shear zones. Cold based ice can preserve but debate as to whether there was ice – exposure dating. - 4. Alpine landscapes: areas subject to repeated valley glaciation. Networks of glacial valleys and cirques separated by ice free mountain peaks (aretes). Best developed in high relief, tectonically active mountain ranges. - 5. Cirque landscapes: Independent cirques incised into upland terrain. Density, orientation and altitude of cirques used as paleoclimate indicator e.g. Evans (1977): Cirque aspect provide preferential ablation from direct solar radiation (east) as more important than wind. Decreasing glacial asymmetry with increasing glacier cover. • RECENT WORK: Landscapes of glacial erosion (Krabbendam, 2016)** - Streamlined hard beds and paleo ice streams: Mega scale glacial lineations (MSGLs) can reconstruct paleo ice streams whereas modern ice streams are mapped using satellite observations. - MSGLS usually soft deformable (till). But change attention to hard beds elongated subglacial forms – important as large parts of Northern Hemisphere Pleistocene ice sheets rest up and flow across these. Similar patterns in Antarctica and Greenland - Influence of bedrock properties (hardness, fracture spacing and bedding) important on occurrence and character of mega scale bedforms e.g. mega grooves/ridges. Look at hard beds instead of deforming and influence of ice flow velocity - Sedimentary rocks: highly susceptible to forming streamlined hard bedforms, especially if parallel to ice flow. - Erosion: dominated by abrasion or lateral plucking. - Ice reconstruction: of ice dynamics. Hard bed streamlined forms show that ice streaming does not only occur in deformable bed. - FOUND: 1. Bedrock streamlining implies fast flow ice streams whereas soft streamlining implies short term fast flow e.g. surges. 2. Ice streaming can occur due to lack of roughness on streamlined hard beds, aided by frictional melt, lubrication, facilitating basal sliding on smooth surface. 3. Evidence found from mapping hard bed landforms, identifying paleo ice stream footprints. • CASE STUDY 1: Jakobshavn Isbrae, West Greenland - Landscapes of areal scour and selective linear erosion (Sugden, 1974). - Used various scales of erosional landforms to reconstruct ice sheet and ice stream evolution (Roberts, 2005). - Found RMs evolved over multiple cycles. Have 2 plucked faces and multiple striae showing changing ice direction during end of LGM as ice thinned and became trapped into fjords. - Whaleback and RM shape changed overtime in response to changing subglacial conditions (overburden and water pressure), plucking and bedrock geology.

Marine Glaciers, Ice Shelves and Calving

• Marine Terminating Glaciers importance - Main drainage of ice sheets: fast flow. Many ice streams are marine terminating - Ocean contact: Calving. Floating ice shelf. Bed below sea level. Instability. - Calving: effective ablation mechanism. 50% in Greenland; 90% Antarctica. - Potential for rapid changes: Retreat and speed of glacier. - Collapse of ice shelves: e.g. Antarctic Peninsula Larsen ice shelf in 2002, occurred over 2 months. Causes rapid coastal thinning in Antarctica, particularly the west. Adds to sea level. • Marine terminating ice masses - Ice shelves: Like floating ice tongues. Present where mean annual air temp if <-5oC (Van der Veen, 2002). Hardly any surface melt due to large surface area beneath where water melts. Grounding line: where ice was grounded but began to float. - Tidewater margins: Occur at air temps > -5oC. Grounded ice terminus/tidewater glaciers. Surface melt occurs in Greenland and Alaska. - Flow of marine ice masses: High flux through narrow outlets of large drainage basins, therefore channelized ice discharge. Bed below sea level, forming a trough. Tidewater glacier has vertical cliff at terminus Increased flow towards the terminus due to approach of flotation where there is low basal resistance and enhanced sliding; and also soft basal sediments (less friction) e.g. Pine Island • Calving - Water depth calving model: Need grounded terminus e.g. tidewater glacier. Brown (1982): Linear relation between calving and water depth at terminus. Increased calving for deeper water due to more space to calve material. Implications if correct: Unstable retreat for reverse bed slope (end is shallow but deeper further back) as continuously getting deeper, and so more retreat. Non linear response to climate. - Problems: Data from 12 Alaskan glaciers (small) which were all stable and so slowly retreating/advancing. Causation not clear and a lack of process understanding. Columbia glacier ice flow accelerated following retreat through basal depression; expected increased calving if calving vrs water depth only control but velocity increase. Must be another process causing behaviour. Model doesn’t include feedbacks with other glacier dynamics. - Flotation calving model: Terminus position is where surface reaches critical height above flotation, everything past this is calved (Van der Veen, 1996). SO calving rate result of dynamics, i.e may be function thickness of ice which is dependant on flow, surface and mass balance. Thinning leads to retreat and enhanced calving, therefore expect terminus to move further back. - Modelling unstable retreat: Using flotation model. Retreat through basal depression (overdeepening). Shift the ELA up 50m to a warmer climate (constant climate). Glacier melts, thinning and retreats slowly. This moves the terminus in, changing the point at which floating occurs and so front calves off. Terminus comes into deeper water; the retreat accelerates causing ice surface to lower further (more calving). Reaches shallower water and it slows. So rapid retreat is a feedback: basal topography becomes important in rate of retreat after small trigger of thinning due to climatic change (mass balance). NON LINEAR RESPONSE. - SUMMARY: topography important for both models but flotation model takes into consideration adjusting the terminus where ice should no longer ground. • Topography and marine terminated glacier stability - Ice discharge increases with water depth due to more space for ice (get rid quicker, so flux increase) and more floating/calving (Weertman, 1973). - If bed deepens away from ground line: discharge reduces, accumulation causes it to grow: stable glacier. - If bed deepens behind ground line: more ice discharge causes thinning, causing even more discharge further inland. Discharges to become stable i.e if thinner, more likely to float and so continues to discharge: MISI. • Marine IS Instability (MISI) Hypothesis: If bed deepens inland, catastrophic retreat can occur (Thomas, 1979). Reverse slopes very common in Antarctica. - Water depth deeper SO: ice discharge increase and flotation occurs more easily. - If accumulation doesn’t increase to compensate for increased discharge: Ice surface will thin; more likely to float; slope becomes more gentle; ice discharge can’t keep up with that needed for stability: further retreat. - Theoretical analysis, Schoof (2007): Integrated mass balance (IMB) is all snow input minus any snow surface melt. Grounding line flux (GL) is how much ice needed to achieve stable grounding line in relation to topography. If GL greater than IMB, retreat will occur until they equalise; If GL less than IMB, advance occurs until equal. - When bed gets deeper, need more accumulation to become stable. • Tidewater cycle: cycles of slow advance, followed by rapid retreat. Climate resetting sometimes not enough. Reduce water depth by sedimentation/frontal moraine as this makes the bed higher, less deep and therefore less discharge and retreat (Nick, 2007) • Sediment flux and calving stability: Moraine banks and GL fans provide stabilisation as reduce calving rates and so margin can advance behind advancing shoal (shallow water). Sedimentation rate is therefore a control. Destabilisation of shoal margin through erosion or seal level rise results in catastrophic calving back to deep water e.g. Muir Inlet Glacier, Alaska: destabilised bank by earthquake. • Ice shelves and floating tongues: influence stability. Provide lateral resistance and buttress. Jakobshavn Isbrae, Greenland: Warming 3oC over 20 years and so increased melt. Melting as trigger, results in enhanced sliding due to meltwater. Retreat of floating shelf; flow velocity increases and propagates inland. • Buttressing effect: ice shelf in front of glacier, push against each other preventing flow. If decrease size of ice shelf, then less able to stop from flowing. - Backstress: Stress induced by anything that resists forward motion of glacial ice - Loss of backstress causes acceleration and thinning of tributaries (Rignot, 2004). - Triggers: increased surface melt (poss climate); interaction of surface melt water with ice shelf surface and structure; processes on underside of ice shelf where contact with ocean water. Largely unknown. 3 case studies of various triggers. • CASE STUDY 1: Larsen ice shelf, Antarctica - Meltwater ponding prior to rapid disintegration. - Climate important: Most likely collapse mechanisms depend on atmospheric temperatures. During summer, likely to have been warmer that -5oC, resulting in surface melting. - Water in crevasses: Crevasses formed under tensile stress but also stress pushing against, holding it together (dependant on density of ice). Stress intensity at tip of crevasse depends on enhanced surface melt which increases water filling, driving enhanced crevassing and calving (water pushes open crevasse). - Whole shelf breakup: capsizing chain reaction: Crevasses join top to bottom, so pieces of ice topple (if narrower than it is deep), exert force at top/bottom of neighbouring ice: domino effect and all disintegrates. - Pre collapse: Rapid thinning of ice shelf in previous decade (Shepherd, 2003) due to enhanced basal melt, so shelf susceptible to fracture (all due to warming). - Post collapse: instantaneous speed up of glaciers inland due to disintegrated ice shelf and therefore nothing holding glacier behind (debuttressing). • CASE STUDY 2: Greenland outlet glacier change - - Rapid changes of outlet glaciers through retreat, thinning and acceleration. Flow through deep basal troughs. Not direct mass balance response as there is slight thickening inland; very small ablation area and mass flux from inland not decreasing. - Marine vrs. Land based changes: Land terminating don’t thin significantly whereas marine terminating glaciers thin increasingly quickly. Particularly quick at lower elevations. - Jakobshavn Isbrae: Seasonal fluctuations of floating terminus, coincide with velocity variations. BUT retreat starts before surface melting. Therefore, surface melt is not a trigger to retreat in the summer. Retreat begins when the sea ice front opens (Joughin et al, 2008). Possibly basal melt beneath floating tongue. Upstream ice velocity peak occurs due to coupling with surface melt? - JI Ocean Melt: Holland et al (2008): JI is a large outlet glacier which feeds a deep ocean fjord. Switch from slow thickening to rapid thinning and doubling in velocity. Suggested increase lubrication of ice bedrock interface as more meltwater drained to glacier bed during warmer summers and weakening of floating tongue that buttressed the glacier. But a sudden increase in subsurface ocean temp thought to trigger changes. Trace changes back to changes in atmospheric circulation in North Atlantic. - Straneo and Heimbach (2013): Not clear how ocean energy makes contact with ice. Fjord circulation may be key. Glacier speed up resulted from intitial retreat of the marine termini that decreased resistance to ice flow, increasing calving and thinning, leading to further retreat. • CASE STUDY 3: Antarctic ice sheet change - Joughin and Alley (2011): Much of grounded ice in West lies on a bed that deepens inland and extends below sea level. Loss of the ice shelves that provide buttress effect would accelerate the flow flow of non floating ice near the coast. Due to the sea bed slope, thinning would ultimately float much of the ice sheets interior. - Large ice shelves stable but smaller subject to rapid thinning, acceleration and grounding line retreat of marine ice streams. But small glaciers have smaller surface area, thought to melt less. Cause: enhancement of basal melt beneath ice shelves - Basal melting: Hydro static pressure at depth, lowers melting point. Denser warmer and saline water reaches grounding line. This melts freshwater which is less dense. This rises in a plume towards to end of the shelf, the pressure drops and so melting point rises so super cooled water refreezes on. - Satellite altimetry: confirms basal melt and therefore reduced buttressing as primary control of Antarctic ice sheet loss. Modelling shows firn layer thickened so mass not caused by surface ablation. Highest thinning occurs where troughs allow warm water to access deep ice shelf bases. - Wind forcing: drives ocean upwelling and atmospheric warming on Peninsula. Explains basal and surface melt patterns. - Pine Island Glacier (PIG): Rignot (2008): Contains equivalent of 1.1m sea level. Rapid thinning of main trunk of 0.5m/yr. Flow acceleration 42% 1996-2007. Grounding line retreat of 1km/yr. Ice shelf thinning and reverse sloping bed (MISI). Largest single contributor to SL rise in Antarctica. Propogates far inland by longitudinal stress transfer and diffusion (surface steepening). • Limited understanding of controls of marine ice mass dyanamics contributes t one of the biggest components of uncertainty in recent IPCC reports.

Moraines

• Glaciers respond rapidly to climate change and so turn over mass very quickly, leaving a specific moraine signature. • Environment of deposition: terrestrial, subaqeous or supraglacial. Either linear and are parallel to ice flow; or chaotic/ not orientated. Demonstrate glacier activity e.g. advance/recession (rapid response). • ICE MARGINAL: Push/squeeze: proglacially constructed ridges, couple of metres high. Show how well drained areas are. Less than 25% glacitectonized structures. Small push moraines made up of till which is squeezed up at glacier margin. Saw tooth form: pectin (grooves) mimics snout margin where sediment is bulldozed up through crevasses. At stable glacier margins, large moraine complexes. Seasonal: deposition by active ice forms annual push moraines e.g. Iceland. 3 processes: - - 1) Deformation/bulldozing: Sharp (1984): Depends on how well drained area in front of glacier is. Bulldozing: ice moves forward, shearing (folding) the subglacial till; pressure on till causes it to be extruded; can see folding of till, over riding of pockets of pre existing sediment, debris flows on lee and stoss (from glacier margin) and ice slope colluvium on top (debris dropped from glacier). Look at orientations of till e.g. folded - 2) Squeezing: Price (1970): extrusion of saturated sub-marginal till due to weight of overlying ice, ploughs through sediment – summer process in poorly drained areas around snout. Requires a lot of meltwater. EVIDENCE: clasts vertically inclined as squeezed up at margin; saw tooth form: sediment also squeezed through crevasses due to moist environment. - 3) Slab melt out: Kruger (1993): Seasonal cycle of – a) winter freeze on; cold so margin is thin, ice base freezes onto sediment below producing frozen on till, glacier continues to advance so moves forward, breaks off ice slab; b) summer melt out of slab, thrusting forward. - Evans & Hiemstra (2005): subglacial till can be derived from range of wet based subglacial processes e.g. lodgement, deformation, ploughing and so often overprinted making impossible to classify genetically. Where meltwaters unable to flush sediment/construct thick debris rich basal ice by supercooling, submarginal processes at snouts of active temperate glaciers have cycles of refreezing and melt out of tills advected from up ice demonstrating tills that are dominated by water escape and fine grained sediment flowage NOT shearing. Glaciers with snout stabilization for several years will deposits large push/squeeze moraines composed of stacked till sequences with each wedge a product of seasonally driven submarginal processes. Due to subglacial deformation OR stacking due to influence of large pressure gradients and seasonal freezing/thawing? - GLACITECTONIC FEATURES: proglacially folded and thrust ridges in front of one another way out in front of margin, created by glacier impact. Lifted leaving hole behind. Can be composite ridges, hill hole pair, or cupola hill. Look like streamlined drumlins, need to have cross section showing tectonic structures. Sand and gravel. - Formation: low strength proglacial sediment and high glacier stresses results in compression, thrusting and folding. Gravity spreading model: glacier weight transferred into lateral stresses. Uses weight of first ice block to push second, run out of power so get smaller. Glacitectonic stress: lateral stress caused by lateral displacement of subglacial materials in response to normal and basal shear stresses; resistance causes failures (folding, thrust material). - Glacitectonic failure: total Glacitectonic stress = cohesion + (ice overburden pressure-PWP) *tan, angle of internal incidence. ANGLE: point material fails due to gravity. Failure occurs if cohesion small and PWP large (stress required to for failure reaches near 0). Thrust blocks elevated by compression. - Proglacial thrusting models: Crook (1988): Composite ridge construction from surging glacier, Iceland: Extension of material by 385% and compression of 54% shortening proglacially.; Mulugeta (1987) Squeeze box: strain partitioning in single layers by bed length balancing showed increase in layer shortening with volume loss (by crushing and folding) and decrease thrusting and ramp folding with depth. - LATERO-FRONTAL MORAINES: deposition of debris flows and glaciofluvial processes around stationary glacier margins – coalescent (coming together) debris fans which descend from the snout. - Formation: Dumping: supraglacial debris transfer, slide, roll, flow and fall. Glacier recession: inset moraines and kame terraces; Susceptible to melt out collapse and paraglacial reworking. Boulton & Eyles (1979): supraglacial morainic till: interbedded mass flow diamictons and outwash and glacilacustrine deposits (ponding between moraine and snout) produces stratified moraines. - ICE CONTACT FANS/RAMPS: ice contact ridges marking lateral and frontal snout margins; shallow distal slope and steep proximal ice contact slope. - Processes: debris flow fans prograde out from debris charged snout onto valley floors. Sediment: debris flow diamictons and intermittent incision by meltwater streams; can see interbedding of diamictons and coarse stratified outwash. Produced in final phase of ice recessions creating a fan. - Lateral-frontal moraine & ice contact fans/ramps: relationship of debris supply and ice supply to moraines within - valley asymmetry of lateral moraines (construction of larger lateral moraines on valley sides with larger free face areas) - Benn (1989): strongly correlated with degree of asymmetry in distribution of free faces in glacierised basins due to more rapid delivery of debris from free face (steep) than from debris mantled slopes followed by immediate entrainment in glaciers or entrainment after period of storage on slopes. Primarily climatically controlled. • SUPRAGLACIAL MORAINES: - MEDIAL moraine: linear ridges at boundaries of ice masses. Eyles & Rogerson (1978) process model: a) ablation dominant, englacial melt out of debris septa in ablation zone; b) ice stream interaction, merging of lateral moraines at confluence of different glaciers; c) avalanche type, rockfall onto glacier produces discontinuous moraine e.g. beads, increasingly important if more retreat. Preservation low but can be high if debris cover high. - Deposits: thin, linear boulder; often spread associated with glaciofluvial features e.g. meltwater concentrates around - HUMMOCKY moraine: chaotic hummocks, ice overwhelmed with own debris – dirty glaciers. Process: differential ablation due to uneven sediment cover e.g. dirt cones; max ablation occurs with 0.5-1m thick debris layer so thin layer (melts faster as attracts more heat). Gravitational and meltwater reworking due to repeated topographic reversals. - Deposits: Interbedded, rubbly diamicton and distorted glaciofluvial sediment (associated with kame and kettle). Common in UK from YD. Equifinality: used for a range of glacial landforms, looks same but different processes. - CONTROLLED moraine: linear hummocks, position is controlled by the structure of ice; as glacier downwastes, concentration of debris in ice on surface (linear mounds). Common in downwasting sub polar and polar snouts and permafrost terrains (glacier not completely removed). Questionable moraines – preservation only in slow moving where less surface melt, less debris and less re working of debris on surface. - Deposits: discontinuous chains of linear hummocks; low amplitude ridges to smoothed thin layer of rubble from concentrated debris at margins. Proposed ancient moraines due to englacial thrusting better explained as push moraines – low preservation e.g. Frank Lake, Alberta (Johnson and Clayton, 2003). • SUBAQUEOUS MORAINES & DEPO CENTRES: When glacier ice reaches deep water. Ice contact accumulations of stratified sediment left by old sea levels. Moraines produced at the margin as it retreats. - Processes: Hyperconnected flows: very liquid debris flow dumped into deep water; avalanching: down the slope; debris flows. Begin as groundling line fans below water level and ice contact deltas at water level. Sediment reworked by: Glacitectonic deformation; iceberg scouring and dumping; mass movements - Deposits: ice contact depo centres: ice contact subaqueous fan created of sand and gravel, as sediment feeds into deep water, coarser is deposited near portal and finer distally. Delta continuum forms

as fan builds up, slumping occurs forming a moraine ridge if ice stable and meets water surface = delta (Cheel and Rust, 1982). - Deposits: subaqueous moraines: morainal banks formed by interlocking of subglacial till and subaqueous outwash at a stable grounding line. Can be squeezed out, creating push squeeze moraines under water. - Deposits: ice shelf moraines: freeze on and onshore pushing up of glacimarine/ glacilacustrine (deposited in lakes) sediments by floating glacier margin producing horizontal moraine (ridges) across landscape.

Subglacial landforms

• Landforms are accumulations of sediment deposited beneath active ice, rarely in isolation. Meltwater forms: eskers; Complex forms: crevasse squeeze ridges; Elongate forms which are classified according to length, height and elongation ratio (length/width); Transverse forms: ribbed moraine. Bedform continuum (Rose, 1987) or formed by different processes? • Difficult to understand but are found everywhere. Studied for 200 years. Reveal flow patterns of paleo ice sheets, particularly important for investigating subglacial processes. 3 approaches: Morphometry: map and measure dimensions; Sedimentology: look inside them; Modelling: numerically • ESKERS: Created by meltwater. Sinuous elongate ridges of glaciofluvial sand and gravel which is sorted and non sorted (Benn and Evans, 2010). Infilling of ice walled river channels (R channels). Deposited sub, en or supraglacially. 1000sm long, 10sm high and 100sm wide (Storrar, 2014). Warren and Ashley (1994) classification: - Tunnel fill: tunnel fills englacially or subglacially - Ice channel fill: forms supraglacially - Segmented tunnel fill: tunnel fills intermittently during pulsed retreat - Beaded: subaqueous fans deposited intermittently during pulsed retreat. - Concertina: associated with surging glaciers - Formation: ground water influence on major subglacial stream and esker spacing (Boulton, 2007); consistent spacing of eskers linked to meltwater drainage evolution during deglaciation. Became more closely spaced with fewer tributaries as deglaciated – reflection of increased meltwater from surface melt? (Storrar, 2014). • Crevasse Fill Ridges: Few metres high ridges of till. Often overlie flutes. Pattern mimics radial and transverse (pulses out) crevasse structures. Low preservation. - Formation: Till squeezed up into basal crevasses where the pressure is lower. Related to glacial surges (Sharp, 1985). Bennet and Glasser (1996) use term geometric ridge due to possible role of thrusting. • FLUTES: Closely spaced, streamlined ridges and furrow. Found on till surfaces, aligned parallel to ice movement on glacier forelands (Gordon, 1992). 10sm long 10scm-m high and wide. Initiate from large boulders. Low preservation. - Formation: Several models but generally form by sediment deforming into low pressure cavity down ice from an obstacle (Boulton, 1976). - Tapering flutes: woven pattern of strain towards flute axis. Parrellel sided flutes: parallel strain patterns/slight convergence. - Erosional features suggestion: grooves formed in previously deposited till surfaces by boulders embedded in the sole of a glacier or by meltwater (Strom, 1963); or erosional remnants of till surface preserved in the lee of protective boulders (German, 1979). • DRUMLINS: Rounded hill. Blunt stoss slope and tapering lee slope (inverted spoon?). Long axes record ice flow direction. Composed of range of sediment (stratified and deformed). Can cross cut eachother (Clark, 1993). Thousands found in drumlin fields. Recently found growing under Antarctica (King, 2007). - Formation: Still searching for universal theory. Early work: sediment added (accretionary) origin but doesn’t explain stratified core. Smalley and Unwin (1968): dilantancy mechanism, expansion of sediment under stress followed by rapid deformation down ice but stratified core problem. 2 views dominate: - 1. Subglacial till deformation (Boulton, 1987). Stiffer areas with deforming layer i.e. coarse grained material act as cores around which enhanced deformation takes place. Cores may uproot and migrate. Explains stratified core with rock and till. Preservation of core controversial; even without, instabilities develop in deforming till (Hindmarsh, 1998). Links into recent ideas e.g. instability theory (instability of coupled flow of ice and sediment leading to bump growth in a deforming bed; only mechanism evolved into numerical model, can be tested) - 2. Catastrophic subglacial meltwater floods (Shaw, 1989): Suggeted subglacial landforms resemble fluvial bedforms formed by turbulent water flow. Floodwater scours the base of ice sheet which then becomes infilled with stratified sediment. Also suggests floodwaters excavate material from between resistant cores leaving behind drumlins as erosional remnants, explaining stratified cores. Theory applies to flutes and other subglacial bedforms. BUT where does water come from? Benn and Evans (2010): not testable scientific hypothesis. - OTHER: Erodent layer hypothesis (ELH): drumlins leave no substantial stratigraphic record as primarily an erosional process, cutting unconformity across pre existing bed materials (Eyles, 2016). Johnson (2010): Iceland active drumlin field on known; suggests product of depositional and erosional processes associated with surges. - Cross cutting drumlins: ice moulded landform develops from 1st ice flow; superimposition of smaller forms upon this in 2nd flow face from different direction; results in total reorganisation of sediment into new orientation (Clark, 1993). - Drumlin problem: Formation explanation must consider diverse location; differing shapes/morphology; range of internal sediment; cross cutting; trigger mechanism that operates in parts of glacier bed and not others. Equifinality? • Mega Scale Glacial Lineation’s (MSGL): Produced by ice streams; require satellite imagery to see clearly. 100km long, 1000m wide, 200-5000m apart, variance (Clark, 1993). Exceptional length related to ice velocity. Also reported from submarine settings in Antarctica. - Rutford Ice Stream, Antarctica: found beneath using radar and seismic data; indistinguishable from paleo ice stream bedforms (King, 2009). - Formation: Explanation needs to explain great length and repetitive parallel arrangement. Initially thought arises from fast ice flow assuming deforming bed to transport till (Clark, 1993) - More recent: Groove ploughing mechanism: ice base roughness elements experience transverse strain (extending across), transforming from irregular bumps into aligned keels of ice protruding down; when this slides across soft bed, ploughs through sediments carving elongate grooves, deforming material up into intervening ridges (Clark, 2003). - Meltwater origin again (Shaw, 2008): but where does meltwater come from? No observations of this under Rutford. • RIBBED MORAINE: subglacially formed transverse ridges. Cover extensive areas of Laurentide and Irish ice sheet. Found in core areas, particularly frozen core areas or slow ice velocity. 10sm high, 100sm wide, 1000sm long. Composed of various sediment, evidence of stratification and deformation. Found in association with other subglacial bedforms e.g. superimposed or underneath drumlins, eskers. - Formation: Originally thought to be produced at ice margin but falsified (Cowan, 1968). 1. Shearing and stacking of subglacial sediment; 2. Subglacial mega floods; 3. Fracturing theory based on jig saw pattern; 4. Switch from frozen to warm based ice and fractures due to extensional flow (Hattestrand and Kleman, 1997) - Rejection of fracturing theory: Moller (2006) suggests ridges are re shaped remains of pre existing moraine ridges. - Dunlop and Clarke (2006): systematically quantified 36,000 ridges and their characteristics. Morphology more complex that reported in fracturing theory, as jig saw doesn’t fit. Shear and stack, meltwater and fracturing theory questioned by new data. Till instability theory (numerical model) not falsified due to to spacing and height (Dunlop, 2008). **READ • BEDFORM CONTINUUM: Rose (1987) and others suggest this but based on limited observations and no quantitative analysis. Ely (2016) analysed 100,000 measurements (large sample) to test theory; flutes always a separate cluster. No distinction between drumlins and MSGLs suggesting a lineation continuum. Continuum of ribbed moraines; circular bedforms (do exist) link lineations and ribs = all strong evidence for. Implies common mechanism i.e. instability and commonality with Aeolian and fluvial bedforms (Shaw) • Beds of present day ice sheets difficult to observe, so subglacial landforms significant for investigating basal processes.

Subglacial processes and deforming beds

• Glacier movement & ice bed relationships: Glacier beds are mosaics characterised by frozen, thawed, sliding and deforming zones. Unfrozen substrate/till forms a layer below the ice bed interface where deformation can occur throughout. Usually component of ice movement in addition to sliding and creep. Effective transport critical: amount of water at bed critical for deformation/ de coupling and also grain size (how soft and erodible). Pervasive till shearing: increases exponentially towards ice bed interface, so lower deformation layer protected; 20-30cm thick, thin. • Subglacial and Englacial debris production: Combo of erosion, transport, deformation and deposition produce. How does sediment get between bedrock and ice? - Bedrock comminution: crushing and grinding down of material to finer till through abrasion, plucking as dragged under ice. Produces very dense till from soft bedrock (Elson, 1988). - Bulk freeze on: from regelation and supercooling. - Apron entrainment: glacier runs over something in front e.g. debris or pre existing landform, trapping the material. Entrains through deformation – folding and stretching of ice occurs, changing structure laterally, causes material to break off. - Advection: moves material from up ice to down ice, resulting in net advection of debris to sub marginal zones. Thickest deposits of subglacial material. • Plucking and bedrock comminution: release of blocks by bedrock plucking; ice injection plucking; and deforming bed cannibalisations - Deposits RM in cavity after plucking the bedrock before (Evans, 1998). - Glacitectonite to Communition till: stages of till evolution. Continuum from fractured to pulverised (reduced to fine particles) bedrock to mono lithological diamictons (sourced from a distinct source). GT: material picked up, plucked and ground down but can still see source material. • Bulk freeze on: net adfreezing/regelation. Polythermal glaciers: can be warm and cold based e.g. Svalbard maritime (moist) Artic climate. Entrain debris by freezing on at margin of cold to warm ice. Occurs at the pressure melting point, providing basal water source, results in thicker basal debris (Evans, 1989) - Freeze on: occurs at thawed/cold bed boundary. Thickening of debris rich basal ice towards the snout (originally thin) due to slowing of ice, resulting in net compression and so ice folds and thickens. - Frozen toe zone: penetration of winter cold wave of ice at temperate margins; produces freeze on subglacial till layer. - Regelation and glaciohydraulic cooling: certain types can produce debris rich ice i.e. water moving at base re freezes back on. Landforms interpreted by looking at sedimentary signals from when formed. • Apron entrainment: sub polar and polar snouts override and entrain, most effective process of entrainment. Little research of understanding debris entrainment in these areas where arid conditions. Results in high debris concentrations in basal ice layers (Shaw, 1977). Contain variety of material dependant on predominant ice marginal process. - Dry calved apron: pile of ice formed in front of a glacier, ice runs over it and so sediment and stagnant ice gets incorporated into ice - Glacitectonic forms: sediment from the base of bed - Ice cored moraine and outwash: glacier ice buried in the landscape which is incorporated into a glacier. - Debris rich basal ice • Deformation thickening/stacking: Regional architecture of tills and associated sediment results in thickening sub marginal wedge. - Boulton (1996): Where dominant mode of transport in ice sheet is by subglacial sediment deformation, flux of glacially transported sediment is related to ice flux: increases in the accumulation area and decreases in the ablation area. So inner zone of ice sheet is dominated by erosion and outer zone is deposition. - Advance and retreat: fixed ice divide zone with little erosion and thin till; intermediate zone of increasing erosion depth and till thickness. Inner/intermediate zone: till is deposited during the retreat; outer zone (margin), till from advance survives beneath retreat phase till as its • EVIDENCE: Local scale sub marginal stacking of subglacial till/push moraines suggest temperate active glaciers that just have seasonal freeze of snout e.g. Iceland, Svalbard; due to water at base, sliding allowing deformation of bed, advecting material to margins where it thickens. • Deforming bed theory: Boulton and Hindmarch (1987) tunnel experiment: Wanted to prove link that sediment deformed at rate of ice movement. Not clear whether happened. - Observed layer of saturated till which had a high pore water pressure. This broke down into A Horizon upper layer and B Horizon lower layer - Upper: 80-95% glacier motion through ductile deformation (less consolidated material, WP able to push particles apart and tried to rotate past eachother). Lower: brittle deformation (shearing of material; base dry and unsaturated). Suggests partitioning of layer.

• Subglacial shear zone concept: Fault gouge analogy: shear zone acts as a fault boundary; fault boundary is glacier sole and shearing occurs between this and the glacier bed. - Sole either sliding or frozen to bed. - Strain elipse (black circles) show nature of deformation across shear zone. This depends on the sediment type and the amount of water e.g. clay, low porosity and high cohesion - Strain vertically: as glacier flows across the bed, strain stretched across the ice bed interface; moves continuously up the layer once deformed at shear. Folding and stretching of substrate. - Shear zones characterised by: Isoclinal folds: overturned folds; augens: bits of material that are stretched and dragged along, rotate; laminations/stringers: discontinuous, broken up pieces of stretched material. Often in upper layer of deforming bed.

- Advecting till: not just one till unit, advance and retreat seasonally forming layers of till. • Effective pressure and PWP: If pore pressure us increased through reduction of effective stress, deformation through creep can occur. BUT if PWP reach overburden pressure, effective stress with be 0 and sediment may liquefy and deform at high strain rates in a ductile manner. - Soft bed: low basal shear stresses, flow at higher rates, developing lower profile and grow/decay rapidly. Different if hard bed. • SECOND EXPERIMENT: Boulton (2001): Excavation of trenches and burying of pressure transducers in front of mini surge snout. - Found: rates of deformation and strain don’t increase until threshold basal water pressure is reached – water drains, decreasing porosity and ice flow velocities and stick/slip processes occur. - Stick: water pressure falls below threshold for deformation, stress builds within sediment and glacier sticks to bed; Slip: rising water pressure, stress builds and particles begin to become forced apart causing rotation and sliding and deformation increases - Deformation: water pressure falls, glacier starts to re couple to bed, ductile behaviour as particle far apart and rotate, drives lateral shear stress. Ice fully re couples to bed, but saturated layer moves down through deforming bed – complex. • Deforming bed structure: upper dilated active zone (high PWP, less cohesion, more volume, less grain connectivity); transition zone; then non dilated solid state (low PWP, high cohesion etc.) - Upper A Horizon: dilation allows free rotation of clasts; zone of maximum displacement/deformation allowing movement of ice across bed. • Deforming bed pressure variation: Fluctuations between basal sliding and deformation due to water pressure cycles. Therefore, stick/slip motion related to water on the bed (Boulton and Dobbie, 1998). - Till forms if ice still coupled to the bed. If theres water in the till, deformation will occur. Too much water, sliding occurs and completely de-couples. - Importance of drainage networks: critical to how till behaves. During melt season, switches to drainage system, starts with thin water film, aiding sliding, more water in system produces braided and channelized system, allowing evacuation through efficient system; bed then recouples – governs stick/slip • Subglacial drainage: different types of water movement e.g. Darcian flow; pipe flow (earlier lecture); where there is till (therefore deforming bed layer), there is potential for different systems governed by the amount of water, porosity of sediment • Deformation style: viscous/ plastic: a) Perfectly plastic: material that deforms instantly with yield stress of 100kPa; b) Newtonian viscous: ductile, strain rate linearly proportional to shear stress; c) Non linearly viscous: strain rate is proportional to the cube of shear stress e.g. ice. - Boulton and Hindmarsh (1987): Found strain till pattern were non linearly viscous material - Lab experiments (Iverson, 1997): found on reproduce perfect plastic (Coulomb) rheology. Subglacial process measurements found plastic failure at vertically migrating levels (Truffer, 1999). - Second Boulton experiment (2001): temporal variations in water pressure and therefore vertical variations in the locus of plastic failure • Deformation partitioning: deforming till layer is not homogenous. Complex as made up of different stratified sediments that have been picked up by glacier e.g. sand pools and diamictons layers causes peaks of localised deformation in A and B Horizons. Can see strain signals in tills. • Subglacial mosaic: demonstrates variation in deformation (Piotrowski, 2004). - Spots of deforming areas and ice bed coupling where there is no deformation. Depends on EP, melting, sediment - Temporal evolution of till: evolves through time and so overprinted signatures of bed deformation, lodgement and basal decoupling. • Sedimentary evidence: net advection of debris to sub marginal zone theory, supported by thick sequences of glacitectonite and subglacial traction till demonstrate former glacier limits - Alley (1997): Most glacial sediment transport occurs subglacially. Glaciers function to collect precipitation and concentrate runoff if melt occurs. Sediment transport increases more rapidly than runoff, glacial streams most efficient transport mechanisms. Subglacial till deformation also efficient: operates with or without debris in ice; increasing the basal velocity of ice, bed deformation increases transport of debris in ice.

Water in Glaciers

• MELTWATER = due to surface ablation and basal melting. Can be water source (central Asia, Andes); hydro-electric (Iceland); a hazard; can disrupt ocean circulation (THC during YD cold reversal); and contributes to sediment erosion, transport and deposition. Make ice wetter = flows faster. • SOURCES OF MELT - Surface melt: depends on surface energy balance, changes daily/seasonally - Frcitional/pressure melting – subglacial – hotter rocks - Rainfall and dew: melts snow due to heat transfer from atmosphere - Runoff: from adjacent land and groundwater - Release: of stored water from lakes • Primary permeability: Tiny interconnected air spaces, thin lenses between ice crystals. Snow and firn. Possible in ice under high pressure gradients. • Secondary permeability: Large channels and tunnels (m). Most of meltwater drainage. Supraglacial (rivers over ice), Englacial or subglacial (river under) channels. All systems become interconnected: combined effect on glacier. • TEMPERATE GLACIERS = daily and seasonal meltwater discharges: - DAILY = Peaks = day; troughs = night. - SEASONAL = Base discharge increases gradually throughout melt season: drainage system evolves, draining more water with time = improves efficiency; Daily amplitudes increase and peak daily discharge arrives earlier in the day through melt season - Summer snow storms reduce discharge due to increased albedo and decreased melt. • SUPRAGLACIAL MELTWATER DRAINAGE: - Surface melt may percolate through snowpack and re-freeze as surface is too dense. - If melting greater than refreezing: water accumulates (ponds/channels), developing in the ablation zone, mm-m in depth, smooth channels. Meander but ice structures (cracks, crevasses) control. In large ablation areas, extensive networks can form (Greenland). • ENGLACIAL MELTWATER DRAINAGE: - Most water is from the surface via moulins (circular, vertical shafts formed by surface melt) which develop from structural weakness. - Dynamic as water pressures can fluctuate rapidly with moulins being abandoned quickly (Holmlund & Hooke, 1983). Vertical profile develops, leading water to passageways and moves via pressure gradients, exploiting weaknesses. - Investigate: through moulin at surface in cold ice where there is slow closure, to the Englacial conduit bed. Create larger plunge pools from caverns and tunnels (Gulley and Benn, 2009). - Hydraulic potential: water flow governed by this. Dependant on elevation and water pressure (supra glacial, just elevation). HP = constant dependant on pressure, shape, size of conduit + elevation potential (weight of water and elevation) + water pressure (atmospheric or cryostatic) - Conduit open = water pressure will be atmospheric; Closed = it can equal the cryostatic pressure and support the whole weight of the ice. - EFFECTIVE PRESSURE: Difference between water (Pw) and cryostatic pressure (Pi). If water pressure 0, EP is same as cryostatic and EP is at its maximum. Conversely, ice is supported by water pressure. EP very important in influencing Englacial and subglacial motion (Benn and Evans). - Size of conduit: Balance between = water flow, produces frictional heat melting and enlarging; deformation due to pressure gradient, i.e. EP, if CP is greater than WP the conduit walls deform and narrow. - THUS: if WP increase, EP decreases reducing conduit closure; larger conduits have lower pressure and so water flows this way; melt rates increase with conduit radius (due to increased surface area to melt = more water). • SUBGLACIAL MELTWATER DRAINAGE: Englacial water penetrates to the bed through moulins. Most comes from surface but some generated by basal melting from geothermal and frictional heat from sliding (Paterson, 1994). If in polar ice sheet e.g. Antarctica more comes from base. Influences ice velocity, glacier stability, sediment erosion, transport and deposition (Benn and Evans, 1999). - 7 types of drainage system dependant on discharge, temp distribution of the ice- bed interface, permeability, topography and rigidity of the bed. - Distributed systems: Inefficient drainage. Lots of extensive, smaller conduits. Generates high water pressures and slippery bed and so greater chance of becoming de-coupled from the bed. - Discrete systems: Efficient. Fewer, but larger channels. Generate low pressure and sticky bed and so doesn’t flow as much. Channels flat bottomed, steep sided and cut into rock creating R and N channels - 1. Bulk movement with deforming till (distributed): Sediment at base has pore spaces and so water flows with this. - 2. Darcian porewater flow (distributed): Flows relative to mineral skeleton under a hydraulic gradient. Pore water discharge is proportional to hydraulic potential gradient and permeability and thickness of the aquifer. For deforming tills, permeability can increase through time in response to dilation or decrease due to compaction (Benn and Evans, 1998). - 3. Pipe flow (discrete): Conduits that form large channels like a subglacial river - 4. Dendritic channel network * (discrete): R channels: Incise upwards into ice. Low pressure, water flows through small pathways from high pressure (dictated by hydraulic pressure); kept open by melting of tunnel walls and frictional heat; bumps in glacier bed can cause flow back uphill due to high pressure at bed; sedimentation can create eskers, blocking the channel and creating sinuous flow. N channels: Bedrock incision if prolonged meltwater erosion (a lot of water) Either single channels or become braided and interconnected. Suggests stabilisation of glacier. - 5. Linked cavity systems *(distributed): Passages where the diameter fluctuates (Paterson, 1994) due to bumpy bed topography which creates high and low pressures. Unstable systems and so inefficient – rapidly switch to larger R channel during melt season (more water), maybe linked to surging (Kamb, 1985). Nienow (1998): dye tracing showed increased drainage efficiency through melt season = switch distributed to discrete. - 6. Braided canal system: flow together then apart into multiple channels. Shallow and wide - 7. Water films * (distributed): Regelation sliding – Glacier flows over a bump, high pressure on the stoss (upglacier) side and so melting occurs; water passes through thin film (mm deep (Walder, 1982)); re-freezes on the lee side where there is low pressure. This smoothes irregularities in the bed and helps the glacier move more efficiently as reduces resistance. Very theoretical. • Glacial lakes: - 1. Supraglacial/Englacial: Small. Temperate glaciers: supra form early in ablation season and later drain into englacial system. Cold polar glaciers: supraglacial lakes. Debris covered glaciers help collect water as drainage inefficient. Form in Englacial conditions when crevasses/conduits close off. Large supra can form on GrIS (10km2) and increasingly in Antarctica - Drainage: drain via moulin or river. Most form below the ELA. The amount of water determines whether it drains all the way to the bed, but a lot can cause sudden acceleration in ice flow, due to lubrication in the base, causing the glacier to move (Zwally, 2002). - 2. Subglacial lakes: Vary in size, mm-1000skm. Accumulate in areas of low hydraulic potential (no exit so accumulates) from basal melting from high geothermal heat fluxes e.g. volcanics in Iceland. 140 lakes identified beneath Antarctica which may influence ice velocity (Bell, 2007). Identified using radars waves from planes as can see the different densities between air and ice, within ice and within the ice bed interface. Some large lakes have only recently been suggested due to radio echo sounding data (Jamieson, 2015). - Lake Ellsworth (Antarctica): Drilled through ice into lake to investigate if there was any life forms and for Paleoclimate change evidence. But the drilling mechanism didn’t have enough hot water to move the whole way through ice. - Lake Whillians (Antarctica): successful, took samples of sediment and found signs of life. - Lake Vostok (Antarctica): Russians claimed to find bacterium but was controversially found to be contamination. - Subglacial drainage: very dynamic beneath Antrarctica (Fricker, 2007). Satellite altimetry showed short term uplift (filling) and lowering (drainage) of ice surface. Measure height of lake surface monthly. - 3. Ice dammed lakes: Develop where glaciers block drainage routes, often form at cold glacial margins where en/subglacial drainage prevented. Variable size but ancient lakes were large e.g Lake Agassiz 2million km2. - 4. Proglacial lakes: Form in front of glacier margins and blocked by topography not ice such as old moraines. Can drain catastrophically if breached. E.g. Caucasus Mt. • Glacial floods: Called jokulhlaups. Triggered by sudden drainage of ice dammed lake; lake water overflow and incision of dam; growth and collapse of subglacial reservoirs. Can be periodic and predictable e.g. Grimsvotn, Iceland drains every 6 years. Mostly during ablation season. Most common in Iceland. - Volcanic activity: mostly catastrophic jokulhlaups. Although ancient Lake Missoula 3 million m3s-1. - Grimsvotn 1996 eruption: initially supraglacial depression. Eruption caused crater to be visible after 9 days; discharge of up to 5,000m3s-1 creating major sediment plume and destroying Gygja. - Feedback mechanism: positive. Once barrier broken the drainage route progressively enlarges through frictional heating and mechanical energy = increase discharge = increased frictional heating and mech energy etc. Hydrographs rise steeply, peak and end abruptly as lake empties.