Chapter 17b: Periglacial (Arctic) Landforms
Geosystems, 4CE, pp. 533-564 (Geosystems, 3CE, pp. 515-549)
**There is a video version of this lecture here: https://youtu.be/dRRd5Dn7JnM.
**The exam is based on the content in these notes, so please print them off to study from.
“Periglacial” regions are those which, although not glaciated, are or were adjacent to continental ice sheets – the dominant feature is the presence of “permafrost” (see below).
In North America this includes most regions north of approximately 56°N latitude, including Alaska, the Territories, and the northern limits of the larger provinces (see Figure 17.19; 4CE, p. 551 (Figure 17.20; 3CE, p. 532), “Permafrost distribution”)
Permafrost and periglacial are also found in Arctic regions such as Greenland, Scandinavia, and Siberia (map), as well as in Antarctica and Peru.
Periglacial environments are also found in high alpine areas, even in southerly regions (e.g. southern Rockies, Alps, and the Tibetan plateau/Himalayas) and in the Andes.
Permafrost is the key feature of periglacial environment. Permafrost is defined as a situation in which the temperature of earth materials remains at, or below 0°C for two or more years. Note it does not matter if absolutely no water is present (in other words, that nothing is “frozen”). Permafrost is defined by temperature, not by whether or not things are frozen or not-frozen (which depends on water content).
Permafrost occurs not only at high latitudes but also at high altitudes, in the high mountainous regions of western Canada.
In Canada permafrost covers approximately 50% of our total land area, as well as areas of the seabed in the western Arctic; it is also believed to exist beneath the channels of the Arctic Islands: here is a map of permafrost distribution in Canada
1. Continuous Permafrost refers to regions in which permafrost is present everywhere except the most recently deposited sediments or beneath deep lakes and rivers. (see the purple areas of Figure 17.19 and the left-hand side of Figure 17.20, 4CE, p. 551-2 (Figure 17.20 & left hand side of Figure 17.21; 3CE, pp. 532-3) “Periglacial distribution” & “Periglacial environments”).
This generally coincides with tundra areas, including the Arctic Islands and much of the Arctic continental coast
Thicknesses range from 100 m (south) to over 1000 m (north). Remember, the earth’s interior is hot, so the “cold” is coming from the surface! As you go deeper, the rock actually heats up! So … for the land up to 1000 m below the surface to be below 0°C, the air must be cold indeed!
2. Discontinuous permafrost refers to more southerly regions where permafrost is sporadic – present most often on north facing slopes, heavily shaded locations, and poorly drained sites. South-facing slopes and well-drained areas do not have permafrost (blue areas of Figure 17.19 (4CE) / 17.20 (3CE) and the right-hand side of Figure 17.20 (4CE) / 17.21 (3CE), “Periglacial environments”).
This tends to coincide with boreal forest regions.
3. Alpine permafrost occurs in many latitudes at high elevations; the elevation of permafrost rises from an altitude of 600 m (at Banff) to over 2000 m in New Mexico.
4. Sub-Sea Permafrost occurs under coastal seas at high latitudes. Here the sea bed is below 0°.
B. Zones Within Permafrost
- The “active layer” is the uppermost layer which is seasonally above 0°C/not-above 0°C; thawing in the summer to depths of 30 cm (high Arctic) to several metres (south). This layer, when thawed, is very susceptible to creep and largescale “active layer failure,” a periglacial earthflow.
- “Solifluction” also occurs: when particles freeze they are lifted at right angles to the surface; when they thaw they settle vertically. On a slope the net annual result is a small downhill movement called soil creep or solifluction. Solifluction also involves “gelifluction” – the slow flow of thawed, saturated soil downslope in summer. The result are solifluction “lobes” or “terraces.”
- Landslides are also common, as ground ice melts and the soil falls.
- The “permafrost table“ refers to the top layer of the permafrost that is perennially (always) below 0°C (no summer thawing, as in the active layer). It is the boundary between the active layer and the permanently below 0°C layer.
- Perennially non-frozen layers or regions (caused by groundwater flow or under water bodies too deep to freeze completely) are called “taliks.” **See Figure 17.20, 4CE, p. 552 (Figure 17.21; 3CE, p. 533) “Periglacial environments.”
A talik is a layer of year-round unfrozen ground that lies in permafrost areas. In regions of continuous permafrost, taliks often occur underneath shallow thermokarst lakes and rivers, where the deep water does not freeze in winter, and thus the soil underneath will not freeze either.
An open talik refers to ground above 0°C all year long, but which is surrounded by permafrost. These are often located under smaller lakes (if the lake water does not freeze all the way to the bottom, the water will be a bit above 0°C, keeping the bed just above 0°C).
A through talik is ground above 0°C that is not surrounded by permafrost. In this case, the ground is above 0°C from the upper level (usually under a large lake, where the water is above 0°C, so the bed is above 0°C) to the lowest level (kept above 0°c by heat from the earth’s interior).
Note the difference between open and through taliks on Figure 17.20 (4CE) / 17.21 (3CE).
II. Ground Ice
Permafrost simply describes a situation in which the temperature of earth materials remains at of below 0°C for two or more years. The terms frozen and unfrozen are used to refer to the state of the water content of the soil.
It is important to note that much of the Arctic is a cold desert (except for coastal areas). This is because the dominant winds, cold temperatures and frozen ocean surfaces inhibit evaporation and result in little precipitation. For instance Coppermine, NWT, receives only 231 mm mean annual precipitation, comparable to Phoenix, Arizona and Somalia, East Africa. Thus many portions of the Arctic receive little moisture input and have little moisture content. Thus, in periglacial environments, land is often below 0°C for extended periods of time, but there is no water to be frozen! Temperature is a more useful descriptor than water state (frozen/non-frozen)
“Ground ice” is the term used to described frozen moisture, when it is present, in the soil. Ground ice is a general term referring to all types of ice contained in freezing and frozen ground. Ground ice is normally concentrated near the surface and diminishes with depth because water cannot easily percolate through soil below 0°C (it freezes before it sinks down!). Ground ice usually exists at temperatures close to its melting point and so is liable to melt if the ground warms. The distribution of ground ice is influenced by soil texture; in general, fine-grained soils (rich in clay and silt) and organic soils contain more ground ice than coarse-grained soils (sand and gravels).
Some arid periglacial regions contain little or no ground ice (because they have no precipitation or water input to form it!).
Other areas, often along coastlines, may have so much ground ice that if were to melt, the soil could not possibly absorb it all. This is particularly the case in Alaska and the Mackenzie River delta.
A. Types of Ground Ice
- “Pore Ice“ – is simply frozen water which occupies pore spaces (air spaces) between soil particles in soils below 0°C.
- “Segregated Ice“ – develops as capillary action “sucks” non-frozen water toward a “freezing front”, causing a build up of layers of ice. This results in frost weathering. And this is what causes the familiar “frost heaves” on our highways!
- “Intrusive Ice“ – is formed when a body of water surrounded by sediment freezes (see pingos, below)
- “Wedge Ice“ develops when surface water penetrates cracks (that form as permafrost cools and contracts in the fall). Typically these cracks are about 1 cm wide and can extend up to 8 m down. These tend to grow annually because existing wedges represent planes of weakness along which cracks form each year; thus they “grow” over time to be more than 4 m wide and many metres deep. See Figure 17.21, 4CE, p. 553 (Figure 17.22; 3CE, p. 534) “Evolution of an ice wedge.”
- “Buried Ice” – refers to glacier, lake or sea ice, or snowbanks, which have been covered over by sediment and preserved as bodies within the permafrost (often because of mass movement).
B. Ground Ice Landforms
1. “Ice-Wedge Polygons“ are caused by thermal contraction and the development of ice wedges. As soil cools, it tends to “crack” into a network of 4-, 5-, 6-, 8- sided polygons. The cracks linking these become filled with ice wedges. This is also called patterned ground (Figure 17.22, 4CE, p. 554 (Figure 17.24, 3CE, p. 535)). See https://en.wikipedia.org/wiki/Ice_wedge
In wet areas, ice develops extensively, causing high rims and sunken cores (water expands when it freezes, becoming ice).
In well-drained areas or arid areas, ice does not build up so the polygons are high-centred with low rims.
2. “Pingos“ are small ice-cored, conical hills. They may be quite large (over 60 m high and 300 m in diameter). They are covered with soil and vegetation. The quantity of ice in the ground varies widely. At one extreme, it can exceed 90% of the volume of the ground.
“Closed-system pingos“ form as taliks close over. In the Mackenzie Delta (where these are most common), they normally form when a river channel migrates or a lake is drained by erosion. Left behind is water-saturated soil, below 0°C. As the pore water in the talik freezes, it expands. Trapped by the surrounding permafrost, it bulges upward to form a hill.
Pingos then grow as surrounding water is attracted by capillary action (segregated ice), resulting in a relatively pure ice core.
If the pingo “grows” to the extent that the ice core is exposed – it stretches the soil layer covering it too thinly – it may melt and “collapse, leaving a donut shaped landform behind.
“Open system pingos” are formed at the base of slopes in which groundwater movement occurs (often in more southerly regions of discontinuous permafrost). Groundwater flows downhill toward a freezing surface, where it freezes, building an ice core, which causes the overlying sediments to bulge upwards.
For a reasonable video of pingo formation click here.
Thermokarst refers to the thaw of ground ice in a permafrost area and the irregular, hummocky topography that results.
The upper layers of permafrost tend to have a high ground ice content that, if disturbed on a large scale, can dramatically alter the landscape.
For instance, the exposure of ice layers by erosion may cause large scale melting. Or, forest fires may melt vast areas. Human activity, from pipelines to settlements, may also melt ground ice.
The result may be large scale subsidence (settling down) into valleys and hollows. Or localized hummocky terrain due to variations in the ice content. In general, when permafrost which a high water (H2O) content is thawed, the ground will subside to a low level (the volume of water leaves). When permafrost with a low water content is thawed, it will subside less, because the majority of the volume is occupied by soil particles. So … even ground can thaw to a very uneven surface.
Or, “Thermokarst lakes” may develop where the water resulting from ground ice is more than the soil can absorb. These lakes tend to grow over time as they melt the ground ice in surrounding sediments.
IV. Periglacial Fluvial Processes
The major feature of periglacial rivers is that almost all their discharge is related to runoff – which occurs over only two or three months in the spring/summer.. Therefore, even though precipitation is often low, Arctic rivers can have high discharges for short periods, resulting in substantial erosion and sediment transport. For most of the year, Arctic rivers may be completely dry. Seasonally, they are intermittent rivers. Most small Arctic rivers are braided because they are seasonal, there is little vegetation, much sediment and shallow slopes.
The exceptions are the major Arctic rivers, like the MacKenzie River. These flow all year. However their discharge is still much higher in spring/summer (because of runoff) than other times of the year.
Arctic rivers freeze in winter, providing major transportation arteries, ice roads, vital lifelines to northern communities with no permanent road access. This is the major way many large supplies reach communities up the Mackenzie River in the NWT and in Nunavut. As climates change, however, there are potential serious challenges for getting goods and services in and out of Arctic communities.
V. Periglacial Environments and Humans
Human activity in periglacial environments is problematic. Not only are they COLD, but the presence of permafrost creates challenges …
A. The Problem
The crucial issue is soil temperature.
Almost every human activity involves the generation of heat, which, if its transferred to the soil, may result in large-scale subsidence or the development of uneven ground (thermokarst). So, if you build a nice new home on level ground, as soon as you turn on the furnace, heat from your floor may melt the underlying permafrost, causing your house to settle very unevenly.
See Figure 17.23, 4CE, p. 555 (Figure 17.25, 3CE, p. 536) “Permafrost melting and structure collapse.”
For a good introduction see: People and Frozen Ground | National Snow and Ice Data Center
Human activity, for instance compacting the soil by driving over it or removing an upper layer of sediment, may also change the thermal balance of the permafrost enough to result in melting. Constructing a road will create a darker, denser surface that will absorb more solar energy, resulting in heating, melting, and uneven subsidence.
Global warming and climate change is a significant concern in periglacial environments. Even a small change in global temperatures could destabilize much of the permafrost environment. The effects of climate change are more extreme in polar regions than other parts of the globe. As you know, form all the recent discussions about global warming, this is a “hot” topic these days! Check out:
- Climate Change and Ice Roads (CBC)
- Thawing permafrost could cost $43 trillion by end of century: new study – North – CBC News
- Permafrost and climate change – interactive | Environment | theguardian.com
- Climate and Frozen Ground | National Snow and Ice Data Center
- Climate Change in Nunavut | Nunavut Climate Change Centre
- Climate Change Impact | Nunavut Climate Change Centre
- Climate Change Mitigation | Nunavut Climate Change Centre
- Climate Change Adaptation | Nunavut Climate Change Centre
- Thawing permafrost sinks buildings, hikes costs in North – North – CBC News
For the current status of permafrost in Canada, click here.
B. The Solutions
Constructing lasting buildings on frozen ground is difficult. Huge layers of ice can grow underground and thicken over time. When ice forms underground, it expands. This can make the ground move, causing frost heave. Frost heave lifts up the ground, as well as everything on top of it. Building on permafrost is also challenging. Buildings that are heated from the inside give off heat. The heat can thaw the permafrost underneath the building. Once the permafrost thaws, it sinks, damaging the building it supports
Engineers sometimes solve this problem by preventing the ground under the building from getting warm. They put the building on top of a steel frame, a few feet above the ground, so cold air can flow under the house. The cold air stops the permafrost from thawing. Another way to stop damage from thawing permafrost is to thaw the ground first. This method makes the ground more stable to build on. Then there is no danger of the ground beneath the new structure refreezing, because the structure keeps the ground from freezing.
All buildings are raised on wooden piles to avoid heating the ground. Water, sewer and other services are distributed through elevated, insulated tunnels called “utilidors” (right).
Roads, bridges, railroads, and other types of transportation infrastructure sometimes cross frozen ground and permafrost. If the ground thaws unevenly, it can cause damage. Some roads might need constant repairs to keep them safe. Sometimes the effects of frozen ground can be unexpected. For example, during the winter of 1950 near Fairbanks, Alaska, the active layer of ground froze under a bridge. Frost heave caused the ground to expand around the footings of the bridge. Part of the bridge was lifted up, creating a sharp bump in the tracks. A train passed over the uplifted bridge, and the train’s cars came disconnected from the engine. The engine kept going because the conductor was unaware of what had happened until he came to the next town, 60 miles away. The people on the train also didn’t know what had happened, and they wondered why the train had stopped so long. They were getting cold because the engine was providing heat to the car they were riding in. Finally, the engine came back to get them, and they then realized what had happened.
Engineers have several ways to stop road damage. Engineers sometimes replace soil under roads with gravel so that water drains better and there is less frost heave. Experts recommend painting roads white to reflect more heat and keep them cooler. A cooler road surface helps prevent frozen ground from thawing underneath.
Pipelines are raised on steel stilts over ice rich terrain, because a buried pipeline can not be insulted adequately (oil requires a temperature of 18°C to flow sufficiently). Even when raise on stilts, heat was being transferred down the steel stilts to the permafrost. Consequently an elaborate system of radiator fins and sealed tubes containing anhydrous ammonia had to be installed on each vertical support to diffuse the heat in winter (essentially refrigerating each support). The cost for the Trans Alaska pipeline skyrocketed from an estimated $900 million to over $8 billion actual cost.
Proposals to build a Mackenzie Valley Gas Pipeline will have significant environmental impacts. In this case, the proposal is to bury the pipeline to mitigate its environmental footprint and cool the gas so it doesn’t melt the permafrost. More recently, a proposal has been suggested to export bitumen (from the Alberta oil sands) up the Mackenzie Valley: Pipeline from oilsands to Arctic is feasible: Alberta study – North – CBC News
See Figure 17.24, 4CE, p. 555 (Figure 17.26, 3CE, p. 536) “Special structures for permafrost.”
Worth reflecting on …
Alister McGrath is a an Oxford theologian who has written a lot in the area of science and theology (including a monumental 3 volume tome, A Scientific Theology).
Watch this video:
- Why do some people find that science leads them to God, but others do not: http://www.youtube.com/watch?v=j5odDhSE00A&feature=c4-overview-vl&list=PLF4C6C2C69DA9BCD3
- What is the role of science? http://www.youtube.com/watch?v=teYEHefyJCA&list=PLF4C6C2C69DA9BCD3
“One of the core arguments of Richard Dawkins’ book The God Delusion is that religious faith is irrational. “Dyed-in-the-wool faith-heads are immune to argument,” he opines. Faith is a “process of non-thinking”, which is “evil precisely because it requires no justification, and brooks no argument”. This is typical of Dawkins’ swashbuckling style, which mingles overheated rhetoric with a scant regard for evidence and accuracy. So let’s look at things in a little more detail.
Everyone agrees that science is one of the most secure forms of knowledge we possess. How do we know that the chemical formula for water is H2O? How do we know the structure of DNA? The answer is simple: because that’s what the scientific evidence tells us. I don’t think anyone will quibble with this.
Dawkins is right to praise the sciences for their ability to give clear, reliable answers to some important questions, such as “how is genetic information transmitted?” So far, so good. But look at another question: “What is the meaning of life?” This is clearly an important question. But can science answer it? Dawkins’ answer is that science discloses no meaning to life – and therefore that there is no meaning to life. But is he right?
Let’s look at some wise words written by Peter Medawar, one of Oxford’s most brilliant scientists, who won the Nobel Prize in Medicine for his work on immunology. In a book titled, Medawar reflects on the question of how the scope of science was limited by the nature of reality. Emphasising that “science is incomparably the most successful enterprise human beings have ever engaged upon”, he distinguishes between what he calls “transcendent” questions, which have to be answered by religion and metaphysics, and questions about the organisation and structure of the material universe.
With regard to the latter, he argues, there are no limits to the possibilities of scientific achievement. He thus agrees with Dawkins – but only by defining and limiting the domain within which the sciences possess such competency.
The limits of science
So what of other questions? What about the question of God? Or of whether there is purpose within the universe? As if pre-empting Dawkins’ brash and simplistic take on the sciences, Medawar suggests that scientists need to be cautious about their pronouncements on these matters, lest they lose the trust of the public by confident and dogmatic overstatements.
Though a self-confessed rationalist, Medawar is clear on this matter: “That there is indeed a limit upon science is made very likely by the existence of questions that science cannot answer, and that no conceivable advance of science would empower it to answer…. I have in mind such questions as: How did everything begin? What are we all here for? What is the point of living? “Doctrinaire positivism – now something of a period piece – dismissed all such questions as nonquestions or pseudoquestions such as only simpletons ask and only charlatans profess to be able to answer.”
Perhaps The God Delusion might have taken Sir Peter by surprise, on account of its late flowering of precisely that doctrinaire positivism which he had happily, yet apparently prematurely, believed to be dead. The point is obvious and important: Science cannot tell us whether there is a God. It cannot tell us why we are here (although it may have some very interesting insights in how that happened). When it comes to questions of meaning, purpose and value, science is blind. And that is no criticism of science – it is simply about recognizing and respecting its limits.
Dawkins is not typical of science at this point, as most scientists are aware of the limits of their discipline, and see no problems in seeking answers elsewhere when it comes to the really big issues of life.
The God Delusion was published in 2006. In that same year, some other notable books were published by leading research scientists. Owen Gingerich, professor of astronomy at Harvard, published his God’s Universe; Francis Collins, director of the famous Human Genome Project, came out with The Language of God. Both of these top scientists argued passionately and persuasively that their
Christian faith gave them a way of making sense of the world, which resonated strongly with their scientific careers and research. It was, they argued, deeply satisfying intellectually.
Now this doesn’t resonate with Dawkins’ somewhat simplistic take on things at all. But it does make the fundamental point that thinking people can be outstanding research scientists, enjoying the respect and admiration of their peers, while believing in God.
Belief in God is not irrational, but possesses its own distinct and robust rationality. It represents a superb way of making sense of things. “I believe in Christianity as I believe that the sun has risen – not only because I see it, but because by it, I see everything else,” said CS Lewis.
To use the language of philosophy, God is the “best explanation” of the way things are. We can’t prove that God is there, any more than an atheist can prove that there is no God. But all of us, whether Christians or atheists, base our lives on at least some fundamental beliefs that we know we cannot prove. That’s just the way things are.”
For more information, read Alister McGrath’s books The Dawkins Delusion? (SPCK, 2007) or Dawkins’ God (Blackwell, 2004).
How do you feel about the authors’ comments? Do you agree? Feel free to discuss this quote on the course discussion site (see the syllabus for details …)
To review …
Check out the resources at www.masteringgeography.com
This page is the intellectual property of the author, Bruce Martin, and is copyrighted © by Bruce Martin. This page may be copied or printed only for educational purposes by students registered in courses taught by Dr. Bruce Martin. Any other use constitutes a criminal offence.
Scripture quotations marked (NLT) are taken from the Holy Bible, New Living Translation, copyright © 1996. Used by permission of Tyndale House Publishers, Inc., Wheaton, Illinois 60189. All rights reserved