Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice C-Change in GEES Changing Permafrost Environments Session Four Session Four: Ground Ice

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Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Lecture Topics The freezing process. “Ground ice”: –Types of ground ice. –Processes of ground ice formation. Ground ice and the formation of distinctive landforms (unique features). Provides a foundation for lectures on permafrost degradation (5) and engineering problems (lectures 6-7). Ground ice within a permafrost tunnel in Alaska (R I Waller)

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice The Freezing Process OºC isotherm progressively moves downwards into the substrate. T1 T2 T3 Negative surface energy balance and surface cooling causes 0°C isotherm to descend into the substrate...

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Table of average thermal conductivities for a variety of materials. High thermal conductivity promotes more rapid changes in temperature... BUT – still missing an important factor... Table From: French, H.M The Periglacial Environment (3 rd ed.). Wiley & Sons, Chichester(p.87). © Wiley and Sons

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Freezing of 1 kg of water at 0°C produces 334 kJ of heat energy (latent heat of fusion). This heat energy needs to be removed before temperature can drop below 0°C. Water Content R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice A. Temperature initially drops below 0°C (supercooling). B. Start of ice crystallisation C. Production of latent heat counterbalances the negative heat flow. Temperature remains at 0°C (“zero curtain”). D. All water has frozen. Cooling continues. Figure From: Harris, S.A The Permafrost Environment. Croom Helm, Beckenham (p.35). © Croom Helm Publishers

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Freezing point depression Can be depressed by: High pressures (  depth): e.g. at a pressure of 100 atmospheres water freezes at -0.9ºC. Impurities: e.g. dissolved salts (why they grit roads…) Grain-size: will look at in a moment...  Freezing front  O°C isotherm KEY POINT - Freezing doesn’t necessarily occur at 0°C (273K). Graph showing the pressure-dependence of the freezing point of water

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Freezing in granular materials In a granular material, water is held: Within pores (“free water”) Adsorbed onto the surface of the grains. “Free water” freezes first… Adsorbed water doesn’t freeze until temperatures drop well below 0°C. Fine-grained materials often contain liquid water at temperatures well below 0°C.

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Variations in Liquid Water Content Has major implications for construction projects in permafrost regions (fine-grained sediments are more easily deformable)… Figure From: Harris, S.A The Permafrost Environment. Croom Helm, Beckenham (p.35). © Croom Helm Publishers

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Ground Ice Deformed “massive ice” at Mason Bay, western Canadian Arctic R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Two important concepts… Ice content Ice contents commonly calculated by weight (weight of ice/dry sample weight x 100%).  Ice contents can exceed 100%. (Referred to as gravimetric ice content) Excess ice If upon thawing, the volume of water exceeds the sample’s porosity, excess ice is said to be present.

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice 1. Wedge Ice Common in continuous permafrost zones Associated with drainage of water into thermal contraction cracks. Size depends on water availability and age. Can reach 4 m in thickness and 10 m in depth. Not always composed of ice: can be composed of sand (sand wedges) or a combination of the two (composite wedges). Key Features Vertically-orientated ice crystals, tubular bubbles, horizontal sheets of spherical bubbles.

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Wedge ice in the Mackenzie Delta, Canadian Northwest Territories Note: abrupt upper surface small veinlets in the surrounding sands characteristic vertical foliation. Vertical foliation Abrupt upper surface (=AL) Veinlets R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Ice-wedge formation 1. Crack initiation: thermal contraction causes a crack to form; usually between mid-January and mid- March. 2. Crack infill: Water (or sediment) fills the crack in the spring and freezes to form a new veinlet. Repetition of this process causes the wedge ice to propagate downwards and outwards.

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Ice-wedge polygons Intersecting ice wedges produce distinctive polygonal patterns at the ground surface. Common in relict channels or lake basins - characterise up to 25% of tundra regions. Two main types of polygons: –Low-centred –High-centred Climatic significance: active ice wedges found in continuous permafrost where MAAT < -6ºC. Polygon wedge ice near Tuktoyaktuk, Northwest Territories, Canada.

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Ice-wedge polygons near Barrow, Alaska Coastal Plain R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice 2. Segregated Ice Occurs as discrete layers or lenses of excess ice. Associated with migration of porewater to the freezing front – occur in “frost- susceptible” materials. Few millimetres to tens of metres in thickness. Sediments containing segregated ice are always supersaturated, i.e. excess water will be released on thawing. Key Features Vertically-orientated ice crystals, tubular bubbles radiating from a debris- rich central section. Segregated ice lens within surface peats near Nuiqsut, Alaska. R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Ice segregation within jointed bedrock is considered one of most effective processes of weathering in permafrost environments. R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Frost “Susceptibility” Determines the likelihood of segregated ice lenses forming. Fine-grained soils are frost susceptible (more likely to produce ice lenses): –High water contents. –Small pore spaces allow generation of capillary forces and cryosuction. –Water is “sucked” to a stationary freezing front to produce an ice lens. Coarse-grained soils are non-susceptible: –Pores are too wide to generate capillary forces and water cannot be “sucked” to the freezing front. –Freezing results in formation of pore ice.

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Schematic diagram illustrating the difference between frost susceptible and non-susceptible soils Non-susceptible (b) - coarse grained materials cannot generate high capillary forces, so ice advances through pores producing pore ice. Susceptible (c) - capillary forces draw water towards the freezing front leading to creation of a segregated ice lens. Figure From: French, H.M The Periglacial Environment (3 rd ed.). Wiley & Sons, Chichester (p.53). © Wiley and Sons

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Palsas Small ice-cored hummocks, up to 1- 2 m in height. Characteristic feature of discontinuous permafrost, usually found in peatland areas. Associated with ice segregation between peat and underlying sediments. Initiation associated with permafrost aggradation below areas with limited snow cover. Ice core forms and domes the surface upwards. Insulating qualities of peat help preserve the resulting ice core. Palsas in a peat bog in Northern Finland R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice 3. Pore Ice Ground ice that occurs within the pores of unconsolidated materials. Acts to cement the particles together. No excess ice present. i.e. if material was thawed, volume of water  porosity. Occurs in non-susceptible materials: –Created by freezing of pre- existing porewater. –Some water is also expelled by the advancing freezing front, leading to the generation of increasing porewater pressures. –Can lead to the formation of intrusive ice… N.B. No associated landform expression. Pore ice and segregated ice within organic-rich sediments in Alaska. R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice 4. Intrusive Ice Often associated with the generation of high porewater pressures and hydrofracturing. Water is injected into the frozen zone where it freezes rapidly. Conceptually similar to igneous intrusions (sills, dykes, laccoliths etc). Key structures Generally bubble-poor, chilled margins (small ice crystals at the margin of the intrusion due to rapid freezing).

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Intrusive ice dykes penetrating a frozen till layer overlying massive ice in the western Canadian Arctic Massive ice Ice dyke R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Pingos Best known of all permafrost landforms. Inuvialuit word used to describe conical hills in the Mackenzie Delta. Largest and most stable of all ice-cored permafrost features. e.g. Ibuyuk pingo near Tuktoyaktuk is 40 m high. Two main types: –Closed-system pingos (Mackenzie type). –Open-system pingos (East Greenland type). Pingos near Tuktoyaktuk, Northwest Territories, Canada

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice Lecture Summary Ground ice occurs in numerous different forms. Main types include: pore ice, wedge ice, segregated ice and intrusive ice. Formation of ground ice associated with two main processes: segregation and intrusion. Aggradation of subsurface ground ice associated with distinctive geomorphological features including ice-wedge polygons, palsas and pingos. Presence of ground ice can have significant geotechnical implications.

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Ground Ice References French, H.M The Periglacial Environment (3 rd ed.). Wiley & Sons, Chichester. Harris, S.A The Permafrost Environment. Croom Helm, Beckenham. Williams, P.J. & Smith, M.W The Frozen Earth. Studies in Polar Research. CUP, Cambridge.

This resource was created by the University of Keele and released as an open educational resource through the 'C-change in GEES' project exploring the open licensing of climate change and sustainability resources in the Geography, Earth and Environmental Sciences. The C-change in GEES project was funded by HEFCE as part of the JISC/HE Academy UKOER programme and coordinated by the GEES Subject Centre. This resource is licensed under the terms of the Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales license ( However the resource, where specified below, contains other 3rd party materials under their own licenses. The licenses and attributions are outlined below: 1.Slide 6 – Table of thermal conductivities from: French, H.M The Periglacial Environment (3 rd ed.). Wiley & Sons, Chichester, is the copyright of Wiley and Sons. Permission should be sought from the copyright holders prior to re-use 2.Slide 8 – Graph showing ice formation from: Harris, S.A The Permafrost Environment. Croom Helm, Beckenham, is the copyright of Croom Helm Publishers. Permission should be sought from the copyright holders prior to re-use 3.Slide 11 – Graph of variations in liquid water content from: Harris, S.A The Permafrost Environment. Croom Helm, Beckenham, is the copyright of Croom Helm Publishers. Permission should be sought from the copyright holders prior to re-use 4.Slide 22– Figure showing frost susceptible/non-susceptible soils from: French, H.M The Periglacial Environment (3 rd ed.). Wiley & Sons, Chichester, is the copyright of Wiley and Sons. Permission should be sought from the copyright holders prior to re-use 5.The name of Keele University and its logos are unregistered trade marks of the University. The University reserves all rights to these items beyond their inclusion in these CC resources. 6.The JISC logo, the C-change logo and the logo of the Higher Education Academy Subject Centre for the Geography, Earth and Environmental Sciences are licensed under the terms of the Creative Commons Attribution -non-commercial-No Derivative Works 2.0 UK England & Wales license. All reproductions must comply with the terms of that license

AuthorDr Richard Waller Stephen Whitfield Institute – OwnerKeele University, School of Physical and Geographical Sciences TitleGround Ice PowerPoint Presentation Date CreatedMarch 2010 DescriptionPart Four of Changing Permafrost Environments Educational Level3 Keywords (Primary keywords – UKOER & GEESOER) UKOER, GEESOER, soil, climate, landforms, ice wedge, polygons, palsas, pingo, pore ice Creative Commons LicenseAttribution-Non-Commercial-Share Alike 2.0 UK: England & Wales Item Metadata