PERIGLACIATION
Updated October 2004
Most important feature is development of permanently frozen ground: permafrost, containing masses of ice: ground ice.
Great deal of variability in periglacial climates.
PERMAFROST
A layer of frozen ground that doesn’t completely thaw in summer. Surface of permanently frozen layer is called the permafrost table. Annual summer thawing produces a layer of material called the active layer. There may be unfrozen areas within the permafrost: called taliks.
Permafrost varies in thickness: greatest in continental interiors, but declines towards southern margins of periglacial zone and towards the coast.
Continuous permafrost is formed under most extreme temperatures (below -6 degrees Celsius)
Discontinuous permafrost: temperatures between -1 and -6. Becomes sporadic as temperature increases. Permafrost is often product of past climatic conditions: a relict feature (often left over from Pleistocene)
Slope angle and orientation strongly influence the amount of solar radiation and snow accumulation. Occurrence of permafrost is affected by the character of the ground surface and vegetation cover.
Depth of active layer is increased around deep lakes.
Interestingly PERMAFROST despite the name may not be permanently frozen, or frozen in the first place. Oh well...
Evidence points to deep permafrost in East Anglia during the last glaciation.
Frost action is the most important form of weathering, with freeze-thaw cycles either side of freezing point.
Vary from diurnal cycle (day-night) to annual or seasonal changes.
Action of frost on the ground can produce a number of processes and features,
Frost cracking: temperature below freezing causes ground surface to contract and crack open.
Frost heave: freezing of moisture into ice crystals within the ground creates pressure: upward pressure
Frost thrust: as above but horizontal pressure.
Frost wedging: breaking open of rocks by water freezing in cracks.
Ice can also create a whole range of other features.
Human actions can affect the permafrost: removal of surface layers expose permafrost table to rapid summer melting. This creates a landscape of mounds and small ponds called human induced thermokarst.
Depth of melting is affected by a number of factors:
- air temperature
- particle size: coarse gravels thaw rapidly due to high conductivity
- vegetation cover
Ground ice occurs in many forms and on a series of scales, from small ice needles called pipkrake, to large sills or domes of almost pure ice.
There are three main types recognised:
- ice wedges (or veins)
- segregated ice
- intrusive ice
LIFE IN PERIGLACIAL AREAS
Read David Waugh: pp. 123 - an example of why you need to read more! - one book with a few pages is not enough...
Why are these areas now being used ?
Permafrost underlies 20% of ground surface, including under surface ice.
Growing demand for minerals and fossil fuels led to development. Were always of strategic importance: DEW systems. Most of examples used here are from Arctic N.America [ See OHT ]
Problems caused by climate ? (Cont.)
Low temperatures
Storms: blizzards - snowfall
High Winds (Wind Chill)
Surface Processes
Permafrost is a very fragile environment: tracks from a vehicle tear up the tundra, scarring the ground. If water runs into the tracks, they are enlarged, and the scars may never heal. Known as thermal erosion.
Active Layer thaws out in the summer, or wherever the thermal condition of the ground is changed. [ See OHT ]
As ground thaws it subsides, and thermokarst develops. Also makes material more prone to solifluction: surface slow on any slights slope.
Permafrost causes problems for economic development of these areas, which contain coal and mineral reserves.
Also have problem of remoteness of the area: have to bring machinery etc. in and get the ores etc. out.
Construction.
3 ways of dealing with permafrost:
1. Keep it frozen
2. Thaw it out
3. Let the building move
Have to be careful to avoid a ‘sinking feeling’, as the construction alters the natural re-freezing process.
Large scale concrete coverage is a problem. Runways, roads etc. are all difficult and expensive to build. Frost heaving occurs so quickly that buildings and roads will be ruined within one year unless built correctly. Dark surfaces alter the albedo.
Often gravel is used as a buffer layer, or backfill. Houses are said to be ‘floated’ on the ‘rafts’ of gravel: which has to be extracted from river beds, where it is important as a spawning ground for salmon etc. Also interferes with usual flow of river.
Need to do careful preliminary investigations. River silts are prone to formation of small ice lenses, and are more frost sensitive. They possess great ‘wicking’ capacities: enabling water to migrate into them and accumulate. Melting of this material produces the consistency of soup.
Posts put into the surface are heaved, or ‘jacked’ upwards e.g gate or fence posts can rise at different rates.
Where land has been cleared for building, palsas develop. Houses are built in the summer season.
Heat escaping from a building is a major problem. The heat doesn’t dissipate evenly, and buildings will tend to be distorted. Shown by buildings put up by gold prospectors in Dawson City in Yukon.
Best foundation is to go down to bedrock, or coarse soils. [ See OHT ]
Houses can also be placed on stilts raised above the ground, so that cold air circulates beneath. Piles are driven into the ground: entire Siberian cities are built using this method. Rule of thumb is to sink them to twice the depth of the active layer, and surround them with silt-water slurry which then freezes and ‘cements’ the piles in place.
A settlement in Fairbanks was affected by subsidence despite being built on 9m of gravel, because of summer warming of paved areas.
Problem of how to get water etc. pipes to the buildings is solved by using a ‘UTILIDOR’ (short for Utility Corridor), which is heated but kept off the ground. This is also important for disposal of sewage.
Forced air ventilation through pipes can help to keep the ground frozen.
Transport
Vehicles have a mains electricity supply plugged into a heater in the cylinder block which prevents the engine freezing overnight. Chemicals can also be used.
In spring, a problem found on roads are icings (also called nalyedi or aufeis).
Culverts take small streams below the roads. A culvert filled with meltwater and ice blocks will flood as the ice dams the water. As it spreads over a flat surface the water freezes, building up to a layer several metres thick. Sometimes use solar powered heaters to keep culverts clear.
Also form where cuttings meet groundwater table, and where water under pressure it can break through the thin frozn crust, and burst out under pressure. Where this occurs under buildings it has been known to fill the building with ice, causing it to collapse. As the frozen soil ruptures it can produce a sound like a cannon shot. (Also a potential risk when drilling down into the permafrost)
Where routes pass through taiga, trees are felled. This inevitably leads to soil erosion, and ground subsidence [ See OHT ]
Roads can be stabilised using VSMs (see pipeline) e.g Dalton Highway, the main route into Alaska., or on wide gravel pads. Dalton Highway was built to serve Alyeska pipeline. Carries tourists to Arctic Circle. Runs for 660km, and only 2 places to get petrol. Pipeline lorries are under instructions not to assist travellers.
Maintenance costs are high, particularly on railway lines.
Strong winds make it impossible for helicopters to operate. Frozen rivers and sea ice hinder sea traffic. Difficult to maintain airstrips, and the best orientation for local winds may not be the best orientation with respect to surface drainage.
As with the tropical rainforests, once communications are built, people tend to move into an area and develop it further: hunters, and tourists. The tourists are seeking a ‘wilderness’ experience, but these landforms and areas have a low carrying capacity. The Tuktoyaktuk pingos of the Mackenzie Delta were protected by being given ‘Landmark’ status.
There are 2 theories of PINGO formation, which create 'OPEN SYSTEM' or 'CLOSED SYSTEM' types features.
For more on the landscape of these areas, try the weblinks below:
Mineral Extraction
Where reserves lie beneath the surface, roads, railways, pipelines and buildings need to be constructed to allow their extraction. [ See OHT ]
e.g The Baikal-Amur Mainline is mostly constructed over permafrost.
Drilling is often carried out in a single winter to reduce damage to tundra. If deeper than around 3000m, then may have to carry on into summer. These need gravel drill pads, to spread load and insulate ground.
Oil extraction on the N.Shore of Alaska produced oil, which was then carried to the ice-free port of Valdez. [ See OHT ]
The solution was the Alyeska pipeline: 1300km long, and completed in 1977 at a cost of £8 billion. 12,000 holes were drilled to test the permafrost conditions
Pipeline carries hot crude oil under pressure. Is heavily insulated, particularly where it had to be buried to allow caribou migration.
Difficult to spot breaks when buried, and Alaska is an earthquake zone: one of largest earthquakes ever recorded was in Anchorage in 1964: 8.4 on Richter Scale.
Vertical supports (VSMs) are kept frozen in the permafrost. Over 123,00 piles used. Pipe is supported on a cradle, for 615km and coated in Teflon so that sideways movement can take place. Some of VSMs contain liquid ammonia, which cools the base of the support.
Important to reduce spillages to a minimum as oil pollution is worse in the tundra environment. There is little evaporation, and frozen ground prevents it seeping in. Lichens, the main food of reindeer are easily polluted, or damaged.
Problem with extracting ores due to frozen ground. Explosives don’t work very well. Prospectors removed overburden and waited for summer thaw. Ore freezes to metal wagons
Groundwater
Supply and availability of groundwater is controlled by presence of permafrost which affects recharge of aquifers (which take the form of taliks) and discharge to surface water systems. Within NW territories, over half of water supply comes from groundwater, despite the numerous surface lakes and ponds. Difficult to establish a stable supply for industrial purposes.
At Inuvik, NWT, population of over 5000 supplied by water pumped from Mackenzie River during clear water conditions into nearby lake. In smaller communities, water is supplied by truck and personal water tanks are refilled due to cost of piping water. Reservoirs have to be deep enough not to freeze to the bottom during winter.
Communications
Weather poses problems for radio communications due to disturbance caused by electro-magnetic radiation (linked to aurora). Snow blowing across aerials produces static electrivcity which creates problems.
Also get ‘white out’ conditions, where all contrast provided by light and shade is lost. Difficult to judge height for landings.
River Crossings
Problem of nival flood swelling discharge considerably. Bridges can become dams if ice blocks get trapped.
If pipelines are placed under the river, need considerable backfill surrounding them to prevent them being uncovered by scour.
Machinery
Construction machinery used in TAPS had to be left switched on permanently to prevent oil and fuel freezing in the engine.
Agriculture
These areas generally have very low agricultural potential: ‘marginal’.
Glacial deposits in Siberia can be farmed. Can cultivate sunny slopes.
NEW STUFF (January 2004)
GeographyPages is now referenced in a German seminar on Periglacial processes and landforms which goes by the name of:
"Prozesse und Erscheinungen des Periglazialraumes" by Constanze Tschritter
Some useful links came out of the above SEMINAR which can be downloaded in PDF format if you speak German.
Go HERE for an excellent map showing the distribution of PERMAFROST, and links to other related maps, such as the presence of groundwater in Permafrost areas. This is very useful to illustrate the huge areas underlain by frozen ground which may or may not be permanently frozen.
This link also gave me an insight into a FAB resource with loads of great maps!!
Don't forget the FETTES COLLEGE website for more on this from a UK angle...
If you want to get some fantastic photos showing the scraped KNOCK and LOCHAN topography of Harris and Lewis and the MACHAIR coastal vegetation, check out Ian Murray's GEOGRAPHY PHOTOS Gallery - click to go to the NEW Gallery.
Russia has just finished the final section of a road which links St. Petersburg with Vladivostok: the longest road inside a single country: it's 10 000 km long. This is an important stage in the development of infrastructure in Siberia. The road was first planned in 1966, but the construction had to cross inhospitable terrain, taiga forests, mountains and up to 50 different types of soil, including PERMAFROST. More than 250 bridges are required. Temperatures range from 40 degrees in the summer to minus 50 in the winter. One stretch of the nearby 2000 mile Baikal-Amur railway line collapsed into a swamp when the permafrost melted after forest clearances. Much of the road surface is still gravel, but the surface will eventually be smoother. (The Times, 28/02/04)
