Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation C-Change in GEES Changing Permafrost Environments Session Five Session Five: Permafrost Degradation – Active Layers and Thermokarst

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Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Session Outline Examine processes and products associated with thawing: –Seasonal (active layer). –Longer term (thermokarst). Focus on key processes: –frost heave –thaw settlement / consolidation –frost sorting / cryoturbation … and their geomorphological expression. Patterned ground developed on an old river bed in northern Finland (R I Waller)

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation The “Active Layer” R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Active Layer Surface layer exposed to seasonal freezing and thawing. Variable thickness and duration, affected by: –Latitude –Local factors Change in active layer thickness with latitude. Williams, P.J. & Smith, M.W The Frozen Earth. Studies in Polar Research. CUP, Cambridge. Fig 1.8 p.14 Reproduced with the permission of Cambridge University Press

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Thermal Regime of the Active Layer Freezing and thawing of the active layer occurs in response to diurnal and seasonal temperature changes. Seasonal changes involve: –spring thaw –autumn freeze-back Spring thaw occurs rapidly from the surface downwards once air temperatures rise > 0°C. Autumn freeze-back more complicated: takes longer and can occur from the surface downwards and the permafrost table upwards.

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Complicating factors... Subsequent distinction between: Active layer: seasonally-thawed layer. Seasonally-active permafrost: seasonally-thawed permafrost that remains < 0 ° C....and... Cryofront: O ° C isotherm. Freezing front: boundary between frozen and unfrozen material (e.g. usually < O ° C ). Remember: 0°C  freezing (or thawing) point

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Active Layer Processes: 1. Frost Heave Associated with autumn freeze-back. Occurs when moisture is present and substrate is “frost-susceptible”. Results from the formation of ice lenses (excess ice). Can result in displacements of several centimetres. Geomorphologically important: production of distinctive landforms. Important for engineers: can damage built structures (e.g. roads). Needle ice associated with the freezing of surface sediments (R.I. Waller)

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Active Layer Processes 2. Thaw Consolidation Opposite process to frost heave - associated with thawing, drainage of porewater, consolidation, and subsidence. If drainage is impeded, porewater pressures rise and shear strength drops. Promoted by: Rapid rates of thaw. Fine-grained particle sizes (low permeability). Can result in slope failure even on very shallow slopes with the permafrost table acting as a perfect slip plane. Differential thaw subsidence can lead to structural damage or collapse

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Active Layer Processes 3. Seasonal Freezing & Thawing Seasonal repetition of freezing and thawing within the active layer is associated with a series of distinctive processes and products: Physical weathering: blockfields (felsenmeer) and talus (scree) slopes. Mass movement: e.g. solifluction Frost sorting and cryoturbation: formation of “patterned ground”, one of the most distinctive and enigmatic periglacial geomorphic features. R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Frost Sorting Result of a series of processes which sort material into zones of uniform grain size: –Sorting by uplift (frost heaving): when freezing occurs from the surface, large clasts tend to migrate upwards. –Sorting by migration in front of the freezing front: fine-grained material tends to migrate away from a moving freezing front. –Gravitational sorting: coarser particles will tend to roll to the edges of uplifted zones of fine-grained sediment (frost-susceptible). Boundary between coarse-grained and fine-grained sediments in an area of patterned ground (R I Waller)

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Frost Sorting Patterned ground near the Norway/ Finland border. R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Patterned Ground Attracted attention of early explorers; yet despite over a century of work, origin remains uncertain! Huge range of suggested modes of formation, e.g. Washburn (1956) reviews 19 different hypotheses! Probably “polygenetic” – product of a variety of different mechanisms. Mechanisms can be subdivided into those that involve cracking, and those that do not. R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Long-Term Thaw: Thermokarst Retrogressive thaw slump on Summer Island, Mackenzie Delta Refers to the semi-permanent thaw of excess ice and associated subsidence and landscape instability. Usually associated with a disruption in the surface energy balance and permafrost degradation. Major problem for engineers. Increased awareness of thermokarst over the last 30 years associated with development of permafrost regions. BUT not always caused by human activity. Can be caused by natural processes and environmental change. R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Left: Retrogressive thaw slump and thermokarst associated with fluvial erosion in the Mackenzie Delta. “Natural thermokarst” Right: Building subsidence associated with the thaw of ice-rich permafrost beneath a heated building in Fairbanks, Alaska. “Human-induced thermokarst” R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Illustration of the volumetric loss and thaw subsidence associated with terrain disturbance and the melting of excess ice. After: MacKay, J.R. (1970) ‘Disturbances to the tundra and forest tundra environment of the western Arctic’ Canadian Geotechnical Journal

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Causes of Thermokarst Primary cause is the disruption of the pre-existing ground thermal regime. Initially small disturbance can spread rapidly as ground ice melts. Specific causes include (induced either naturally or anthropogenically)... –Geomorphic: e.g. coastal recession. –Vegetational: e.g. deforestation due to fire. –Climatic: e.g. Future global warming?

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Flow chart illustrating the varied causes of thermokarst. Figure From: French, H.M The Periglacial Environment (3 rd ed.). Wiley & Sons, Chichester(p.188). © Wiley and Sons

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Thermal erosion and bank collapse along a river in the Alaskan Coastal Plain R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Thaw lakes in the western Canadian Arctic associated with climatic warming during the Holocene (“hypsithermal”). R.I. Waller

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Methane release (ebullition) from thaw lakes may represent a positive feedback of recent climate warming... Walter, K.M. et al Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming. Nature, 443, Thaw lakes on the Arctic Coastal Plain, northern Alaska (R I Waller)

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation Lecture Summary Seasonal thawing of the ground surface in permafrost regions results in the formation of an active layer. Seasonal freezing and thawing associated with two key processes: frost heave and thaw consolidation. Continued repetition of frost heave and thaw consolidation can result in cryoturbation and the creation of features such as patterned ground. Longer-term thaw of permafrost, usually associated with disturbance of the ground thermal regime, results in thermokarst development. Causes landscape disturbance and major headaches for engineers!

Dr Richard Waller, Keele University, C-Change in GEES: Changing Permafrost Environments – Permafrost Degradation References Davis, N Permafrost: a guide to frozen ground in transition. Univ. of Alaska Press. French, H.M The Periglacial Environment (3 rd ed.). Wiley & Sons, Chichester. Williams, P.J. and 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 19 – Flow chart showing the causes of thermokarst 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.The name of the 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. 3.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 TitlePermafrost Degradation PowerPoint Presentation Date CreatedMarch 2010 DescriptionPart Five of Changing Permafrost Environments Educational Level3 Keywords (Primary keywords – UKOER & GEESOER) UKOER, GEESOER, thermokarst, thawing, seasonal, active layer, process, frost heave, thaw settlement, consolidation, frost sorting, cryoturbation. Geomorphology, landforms Creative Commons LicenseAttribution-Non-Commercial-Share Alike 2.0 UK: England & Wales Item Metadata