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Permafrost and periglacial environments (Basics of permafrost (Permafrost…
Permafrost and periglacial environments
Basics of permafrost
Permafrost is a rock or soil the temperature of which is ≤0°C for at least two consecutive years (Dobinski, 2018)
Most of the worlds permafrost is only just slightly below 0 degrees (IPCC, 2007) meaning that it is highly susceptible to climate or surface changes.
It is formed as a result of a freezing climate. It occurs at all latitudes around the world in continuous, discontinuous, sporadic, and isolated patches and covers more than 36 × 106 km2
It is invisible and separated from the surface by an active layer from zero to several meters thick.
Mountain permafrost begins at an altitude of 500 m above sea level and reaches up to an altitude of 8848 m in the Himalayas.
Permafrost effects around 26% of the Earth (Washburn, 1979) however 35% of the Earth is affected by freeze-thaw processes (Williams and Smith, 1989).
It is believed that up to 50% of the world was periglacial during previous glaciations (French, 1996)
Basics of periglacial
Periglacial environments are defined as those that are cold but non-glacial, regardless if their spatial proximity to glaciers (Holden, 2012).
Can have periglacial environments without permafrost
Freezing and thawing are important geomorphological processes as they drive fundamental changes in the grounds mechanical and hydrological properties.
Cross section of permafrost
Active layer - freezes and unfreezes annually. It can be a few cm or many meters deep, surface temperature and snow cover are factors in its thickness
The permafrost
Subsea
Continuous
Discontinuous
alpine
Talik - geothermal heat keeps this zone from freezing
Thermokarst
It is the topographic depressions which form by thawing of ice-rich permafrost and the meltwater subsequently is released however into poorly drained lowland regions (Murton, 2009)
Thermokarst is common throughout most permafrost regions including northern Canada, Russia, Mongolia, China, Alaska and Antarctica .
While ice‐rich permafrost is sensitive to climate change and surface disturbance, there are positive and negative feedbacks involving interactions between geomorphology, hydrology, vegetation and ground thermal conditions which can exacerbate or arrest thermokarst processes (Jorgenson and Shur, 2007).
Can form lakes, gullies and slides.
Schurr et al. (2015)
permafrost carbon is the remnant of plants and animals accumulated in perennially frozen soil over thousands of years, and the permafrost region contains twice as much carbon as there is currently in the atmosphere
A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change.
Earth System models for climate change aren't taking into account permafrost gasses which are becoming a feedback system due to human activities
Abrupt permafrost thaw occurs when warming melts ground ice, causing the land surface to collapse into the volume previously occupied by ice. This process, called thermokarst, alters surface hydrology. Water is attracted towards collapse areas, and pooling or flowing water in turn causes more
Krautblatter and Leith (2015)
Risks in high mountains, as in other regions, are dynamic and not static, which poses enormous challenges to basic and applied research. It is where human and physical worlds interact.
Quincey and Carrivick (2015)
Glacier floods, also known as jökulhlaups, glacier outbursts, glacial lake outburst floods (GLOFs), aluviónes and debacles, refer to the sudden release of water from a glacier hydrological system or from glacial lakes impounded by moraine sediments and/or ice
Glacial lakes can form on top of the glacier (supraglacial), in front of the glacier (moraine-dammed), marginal to the glacier (often ice-dammed), within the glacier (englacial) or at the glacier–bedrock interface (subglacial)
Moraine-dammed lakes may fail through the gradual degradation of a permafrost core, saturation and seepage through the moraine sediments, piping and headcut retreat, or overtopping and distal scour following the influx of landslide or avalanche material into the lake.
Ice-dammed lakes occur where glaciers advance across drainage routes or where ice-avalanche deposits block river drainage, resulting in much larger lakes than their moraine-impounded counterparts and threatening populations and infrastructure for many hundreds of kilometres downstream. Ice-dammed lakes are therefore most common in areas where glaciers are in positive mass-balance, or in areas where surging glaciers cause large frontal advances.
Although glacier floods are initially 100% water by volume and are sediment supply-limited, downstream they are potent agents of rapid landscape change, causing erosion of bedrock and entrainment and redistribution of sediment.
Factors effecting GLOFS (Quincey and Carrivick, 2015)
Glacier hydrology - conduit systems lead to ponding potential
Mass balance - positive mass balance increases avalanche risk which can dam large masses of water
Geology - porosity, strength, permeability
Other hazards eg. avalanches or rockfall into lakes, tectonic activity
Seasonal variation - temperature and rainfall variation
Weather events eg. El Nino or North Atlantic Oscillation
Guglielmin, 2012
Permafrost areas of continental Antarctica with its extreme dry and cold environment similar to those on Mars
It preserves many paleoclimatic datasets which we can use
Permafrost degradation and active layer thickening is happening in Antarctica (IPCC, 2007)
This has caused methane release, changes in vegetation composition, increases in dissolved materials in river and oceans.
Future permafrost challenges
Permafrost distribution is not completely known
Ground ice distribution, its age and stability within time
are still not fully investigated
Better understanding of earth permafrost can hep our understanding of extra-terrestrial permafrost