Geomorphic Processes and Landforms

The combination of unglaciated and periglacial environments found in Vuntut National Park and the Old Crow Flats Special Management Area result in a unique set of geomorphic processes. The most important of these processes are reviewed in the following section with reference to the landforms they have created within the land of the Vuntut Gwitchin. Several particularly significant landforms are discussed in some detail. The landform elements of unglaciated mountainous terrain are illustrated by Figure 4.9 (from Welch 1993, Fig 4.11 p 33, after Longwell, Flint and Sanders 1969).

i) Erosional Processes and Features

The mixture of loose soil and rock fragments that have moved down a slope and settled at its base due to the action of gravity is called colluvium. Colluvium is produced by the mass movement processes of weathered material by gravity, slope wash, or solifluction (defined below in periglacial environments). The most common colluvial landform is talus, the slope of rock fragments at the foot of a cliff or mountain, also known as scree. Some thick talus accumulations can have a glacier-like form and are called a rock glacier (they also include interstitial ice). In the study area, hillslopes are typically covered by colluvium (Figure 4.9b, Figure 4.14b and Soils, Figure 6.10c).

Figure 4.9b Click on the photo to enlarge and see other photos.

Slopewash is the collective term for the processes of surface wash, the downslope transport of weathered material over the ground surface by running water, and subsurface wash, the set of processes associated with water moving within the ground and sediment transport within the ground (Lewkowicz 1978, 1981). Slopewash operates on the same time scale (hours to days) as hydrological processes, rather than the decade to century time scale needed to see the effects of the slow movement of materials called solifluction (see below). In this semi arid environment slopewash may be infrequent but would be an effective erosional process in situations of heavy rain storms. Mass wasting and occasional slopewash processes in semi-arid unglaciated areas can result in features such as inselbergs (isolated hill surrounded by lowland), buttes (isolated hill with steep slopes often capped by resistant rock and bordered by talus), and mesas (similar to a butte but with a larger summit area than a butte) (Figure 4.9a). Tors, another feature of unglaciated arid terrain will be discussed in detail below)

Fluvial erosional processes are those involving the action of flowing river water. Welch (1993) concludes that even though Ivvavik National Park experiences arctic and sub-arctic climates, the landscape is dominated by fluvial features. Fluvial features dominate due to the absence of glacial processes in this unglaciated area. Some fluvial characteristics which apply to the mountainous parts of Vuntut National Park include: gravel-bed headwater streams typical of semi-arid landscapes subject to periodic runoff; interlocking spurs (Figure 4.9a, Figure 4.9b), feather drainage patterns on pediments (Figure 4.9d), and extensive fans typical of river development uninterrupted by glaciation. Gorges, bedrock terraces, and incised meanders (Figure 4.5 , Figure 4.9c and Figure 8.4 and Figure 8.7 in Hydrology) are fluvial features which reflect regional uplift during river development.

Figure 9 c. Click on photos to enlarge and see other photos.

Landslides are divided by Aylsworth et al. (in press) for the Mackenzie Valley landslide database into those in which the failure plane occurred in bedrock and those in which the failure plane occurred in unconsolidated Quaternary sediments. They are further classified as either "flows" or "slides". "Flows have a fluid character, showing evidence of mobility throughout the failure. Slides, on the other hand, show evidence of rigid movement in that components of the slide move downslope as more or less intact blocks." (Aylsworth et al. in press). Within permafrost areas, flows in unconsolidated material include shallow slope failures such as active layer detachments and the deeper more common type of flow, the retrogressive thaw flow, both of which are discussed below under periglacial processes ( Figure 4.13c, Figure 4.13d). A debris flow is a rapid flow of water saturated sediment occurring in areas of higher relief. Slides can be either rotational slides which are the downslope movement of a rigid block of sediment or bedrock "along a curving failure plane, such that the toe of the block extends well beyond the original slope" (Aylsworth et al. in press) or transitional slides which "involve rigid movement along a planar (not curved) failure plane, commonly a bedrock plane" (Aylsworth et al. in press). Duk-Rodkin (personal communication) suggests that landslides "occur extensively along the banks of the streams crossing the flats area" (Figure 4.13e). The landslides of the Mackenzie Valley have been inventoried and their mechanisms studied in detail in terms of slope stability and their relationship to climate and climate change. (Aylsworth et al. in press and Dyke in press). Slope stability and landslide frequency may be an important factor in the changes occurring within the Old Crow Flats at least along the river banks (see Figure 8.20 of slope failure draining lake in Hydrology).

ii) Aeolian Processes and Features

The erosion, transport and deposition of material due to the action of wind at or near the earth's surface is termed aeolian or eolian activity and the sediment is termed loess. French and Harry (1992) observed a thin layer of sandy silt, varying from 10 to 50 cm in thickness, capping the earth hummocks (see below) on the pediment slopes they studied in southern Ivvavik National Park. These they suggest may be partially eolian in origin since they are well sorted. Rampton (1982) speculates that some of the silt in silty colluvium throughout the northern mountains is of aeolian origin. Recently Cabana (1999) studied deposition of loess on the Porcupine river terraces. Some general observations on the importance of loess deposition follow. Winter aeolian deposition on the snow surface can speed up spring melt by insulating the snow and once melt is complete the loess is deposited on top of the vegetation. Vegetation protects the loess deposits, minimizing erosion, and these vegetation clumps can create mounds up to 1 m high. As layers of loess accumulate on the surface, permafrost grows up into the new deposits producing an increase in the total depth of permafrost. Thus the permafrost is said to be aggregating (building up) in these aeolian areas. Active ice wedges can also be present in aeolian plains. The extent and distribution of aeolian deposits in the Vuntut National Park area have not been investigated to date.

iii) Periglacial Processes and Features

The presence of permafrost dominates periglacial processes. All land surfaces in the study area are underlain by permafrost. The presence of permafrost affects the terrain and the vegetation of this periglacial environment in several ways. Within permafrost, most of the soil moisture occurs in the form of ice. This ice exists in a variety of forms, ranging from small crystals and veins with dimensions measured in millimeters to large bodies of more or less pure ice, meters to kilometers in size (see also Soils, Section 3g).

The presence of permafrost and massive ground ice results in a particular group of active geomorphic processes, with their own distinctive landforms. All are related to the action of the freeze-thaw cycle and the penetration of annual temperature cycles into the ground. The most immediately obvious are the various types of patterned ground (all terms are defined below), and the most mysterious are the conical shaped pingos. Some are slow processes such as solifluction, which result in the development of stone stripes and solifluction lobes. Others are rapid processes such as active layer detachment slides which scar the landscape in areas of massive ground ice. These features and processes have been illustrated for Ivvavik National Park by Welch (1993, Welch and Smith 1993), and qualitative descriptions for the Vuntut National Park area appear in Wiken et al. (1981) and on the Internet at the Taiga Net web site (www.taiga.net) but no systematic study of these features or quantitative evaluation of their frequency within the Park have been found to date. The occurrence and nature of many of these processes have been studied within Aulavik National Park on Banks Island (see Grayhound Information Services 1997). Specific examples integrating geology, geomorphology and soils for some of the more important features are discussed in Soils and Ecology.

In the following sections, various landscape features found in the study area, which are a result of the presence of frozen ground (permafrost), are discussed. The basic terms needed to understand these features are defined first.

a) Active layer depth is the thickness or depth to which the permafrost within the soil thaws each season (Figure 4.10a). The depth of the thawed layer varies with location due to changes in soil type, moisture content and climate. In Vuntut National Park, Wiken et al. (1981) estimate the depth of the active layer within their ecodistricts and Tarnocai (1986) provides estimates (which differ with the Wiken estimates in some areas) on a broader scale (1:1,000,000 map). There is also a variation in active layer depth from season to season linked to variations in summer warmth and the length of the thaw season (as discussed in the Climate, and Hydrology). Active layer depth is an integral part of all permafrost studies. (The active layer depths for the eco-units within Vuntut National Park and Old Crow Flats Special Management Area are discussed in Soils, Section 3f).

b) Freeze-thaw action in the active layer leads to the widespread development of distinctive landscape features in periglacial regions. It is responsible for cryoturbation, the mixing of soil layers due to the movement of moisture within the active layer and the uneven distribution of thawing and refreezing within layers. The result of this mixing is that often no horizons (distinct layers) are found in cold climate soils.

Figure 4.10a Click photo to enlarge and see other photos.

c) Massive ice is ground ice in a relatively pure form in concentrations significantly larger than those of the permafrost which occupies the naturally occurring spaces between soil particles (Figure 4.10a). Buried massive ground ice is a term encompassing any form of surface ice which becomes buried. This includes ice-cored moraines (Ostrem 1963) and buried snow banks recently investigated by Pollard (1991) in the northern Yukon. Ice wedges are a form of massive ice in vertical or inclined sheets of wedge-shaped ground ice extending below the permafrost table (upper limit of permafrost), usually corresponding to the edges of high and low centred polygons (see below). These are a form of what is formally called in situ massive ground ice (Mackay1989, in Pollard 1991). Individual wedges are seldom more than 5 to 8 metres deep or more than 2 to 3 m across (Figure 4.10c, Figure 4.10d) .

Figure 10c. Click photo to enlarge and see other photos.

Massive ice features can be seen on exposed cliffs within Vuntut National Park and the Old Crow Flats Special Management Area. They are evident in the bluff profiles discussed above and in bluffs in Alaska and the Bluefish Basin (Figure 4.6a).

Lauriol, Duchesne and Clark (1995) studied a series of ice wedges along the Porcupine River in the Bluefish Basin. Their results show that these features are less than 4000 years old and that they are filled during the later stages of snow melt. The position of the wedges relative to stratigraphic sections discussed in the paleoclimate section are shown in Lauriol et al., 1995 ( 2 p 48 in Supplement LDC2). The ubiquitous presence of ice wedges over large parts of the study area is obvious from the air due to the patterned ground they create ( Figure 4.10f, Figure 4.10g, Figure 4.10h and see below).

d) Patterned Ground ranges from frost boils less than 1 m in diameter to ice wedge polygons 30 to 50 m across, and includes sorted and nonsorted patterns. The following five landforms are types of patterned ground.

Sorted pattern results from the movement of rocks and pebbles up toward the surface and out from a central point, as a result of frost action. Thus the fine material remains in the centre of the pattern while coarser rubble accumulates around the outside.

Ice wedge polygons form when frost cracks, produced by thermal contraction, create a pattern of polygonal fissures. These fissures fill with water which freezes into ice wedges (see above and Figure 4.10). The formation of these ice wedges and the various types of patterned ground they produce are depicted in a very informative animation found on the Arctic National Wildlife Refuge (ANWR) web site. (ANWR, web and Supplement ANWRpermcy). The two types of polygons identified by Zoltai and Tarnocai (1975) are shown in Figure 4.11 (after Zoltai and Tarnocai 1975, from Figure 5.10 Welch and Smith, 1993). When the surface next to the expanding wedge bulges up, creating furrows with peaty ridges up to 50 cm high, the resulting polygons become saucer-shaped depressions called low centered ice-wedge polygons (Figure 4.10f, Figure 4.10g). These are usually active features in that the wedges continue to crack. When the whole centre of the polygon bulges up and the furrows are depressed they are called high centered polygons (Figure 4.10h from Plate 4.39, Welch 1993). These are drier and often covered with a peat layer and vegetation and are usually older and less active. High centered peat polygons are often defined by the richer vegetation growing in the wet areas of fissures over the melting ice wedges.

Mud boils are common in loamy sand and are circular, elongated or irregular in pattern. Their formation is attributed to pressure developed by annual freezing of the active layer, forcing liquified mud to the surface. They are normally unvegetated.

Earth hummocks are formed from fine and medium textured materials (Tarnocai and Zoltai 1978). Welch (1993) says they are common on well-drained sites. Tarnocai and Zoltai (1978) measured moisture content to be from 17 to 39% on a volume basis. Hummocks generally appear as circular as seen from above (Figure 4.12a). Shaped like a half sphere (Figure 4.12b), they are separated by deep troughs and are typically 1 to 2 m across. Welch (1993) gives heights of 5 cm to 10 cm for Ivvavik National Park, while Tarnocai and Zoltai (1978) in their study of 173 arctic and subarctic hummocks suggests and average heights of 40 cm to 60 cm.

Figure 12a Click photo to enlarge and see other photos.

Earth hummocks develop by cryoturbation, or frost churning, within the active layer (Welch 1993). The internal and external characteristics of the earth hummocks indicate that, during the lifetime of an earth hummock, a great deal of activity takes place (Tarnocai and Zoltai 1978). Externally this is indicated by the domed shape and by rupturing of the apex of the hummock. Internally, the most striking feature is the presence of organic or mineral intrusions throughout the active layer of the hummock (Figure 4.12b). Vertically aligned elongated stones are also very characteristic features. Vegetation tends to be most dense towards the outside of the hummocks, creating the patterns which are seen from the air. On slopes the hummocks become elongated due to downslope motion.

It is very difficult to determine the age of hummocks as they are periodically if not constantly active. Tarnocai and Zoltai (1978) found that hummocks they investigated were as old as 5500 years. No detailed study of hummocks within Vuntut National Park or the Old Crow Flats Special Management Area were found but they are very common in the area, especially on pediment surfaces (French and Harry, 1992). Hummocky terrain is often found in the middle of ice wedge polygons.

Striped pattern is the result of a combination of heaving which creates mounds and downslope movement due to gravity which elongates these into separated by depressions. They develop in a number of ways on slopes, sometimes as the result of solifluction (see below) and other times as a result of the sorting of materials, such that the larger materials accumulate in the depressions and form lines parallel to the slope. The colonization of the slight depressions by vegetation which is denser and therefore a darker green than the sparser vegetation on the ridges also makes a pattern which also runs parallel to the slope.

The large cone-shaped ice mounds called pingos are thought to form from the freezing of a layer of unfrozen ground occurring between the permafrost and the seasonally frozen ground.

French (1987) suggests that these unfrozen layers might exist beneath lakes and deeper sections of stream channels. If the channel is abandoned, thus exposing the bed to the full force of winter cold, or the overall climate becomes colder and drier, pingos grow, typically into conical shaped mounds. The actual mechanism of growth is complex and is still being studied. A simplified formation sequence is shown in the ANWR animation of the ice wedge cycle (ANWR, web and Supplement ANWRpermcy).

Excavation of four mounds in river channels in Aulavik National Park showed massive ice cores in each. Freezing of localized sub-channel taliks (unfrozen ground within the permafrost) was probably related to a change in the river's course which exposed the deep subchannel bed to permafrost formation. Radiocarbon dates of willow fragments recovered from beneath the level of these pingos suggest formation between 3500 and 5000 years before present. This time period coincides with the beginning of a colder-drier cycle indicated by the onset of aeolian activity (Pissart et al. 1977) and the cessation of peat development (Zoltai et al. 1980).

A few small pingos have been found in Ivvavik National Park to the north and pingos are common in the Mackenzie delta area. No observations of pingos have been found to date for Vuntut National Park or the Old Crow Flats Special Management Area but they would be expected in areas of changing river course or recently drained lakes.

e) Solifluction describes both gelifluction, the downhill flow of soil saturated by water in permafrost regions, and frost creep, a rachet-like downslope movement in which particles are lifted in a direction perpendicular to the slope by freezing and then redeposited slightly downslope during thaw (Egginton and French 1985). Solifluction and soil creep activity was investigated in the adjacent Richardson Mountains, where average movement of 2.5 cm/year was been measured on vegetation-bare slopes (Rampton and Dugal 1974; Rampton 1982). Large solifluction lobes are present in the Barn Mountains, but no quantitative monitoring of mass wasting processes has been undertaken there (French and Harry 1992). Welch (1993) treats solifluction as distinct from frost creep and points out that frost creep dominates over solifluction on steep slopes. Welch suggests that on steep unvegetated slopes, material moves at an average of 2.5 cm per year and that vegetated slopes slow the movement. These significant mass wasting processes were monitored in the hummocky morainal terrain at the south-eastern tip of the Aulavik National Park area, over an eleven year period (from 1972 to 1983). Eight low- to moderate- angle (3-8E) slopes showed displacements ranging from 0.3 to 1.3 cm/year. Three styles of motion were observed. In mud burst and mud flow, which can be rapid and may occur at the base of melting snow banks, surface materials appear to liquify and flow for some distance downhill before consolidating once again. Pluglike flow involves the downslope motion of whole sections of hummocky ground. (Solifluction and solifluction lobes are illustrated in Plates 4.14 from Welch (1993) in Supplement W4.14).

f) Thermokarst refers to any process of thermal degradation (reduction in the amount of permafrost through melting) or landscape change due to the melt of permafrost or massive ground ice.

Thermokarst lakes can form when massive ice melts under the surface or becomes exposed to the surface and begins to melt. This forms a thermokarst depression or basin (see ANWR animation figure, ANWR, web - U.S. Fish and Wildlife Services 2000, and in Supplement ANWRpermcy. Water accumulates in the depression and the warm water deepens the active layer under the pond or lake. Eventually these lakes fill in by peat accumulation (Welch 1993). Peat is a good thermal insulator, and so permafrost can once again build in the soil. Expansion of water upon freezing in turn raises the soil surface so that ponds and small lakes are drained. Frost features such as ice wedges may again reach the soil surface, beginning again the so-called tundra-pond cycle.

Many of the lakes in the Old Crow Flats are described as both thermokarst lakes and oriented lakes. Oriented lakes are usually rectangular in shape with the long axis oriented parallel to each other (Figure 4.13a, Figure 4.13b and Plate II). There appears to be some disagreement as to the origin of the Old Crow Flats oriented lakes. Welch (1993), discussing the lakes on the arctic coastal plain, states that the lakes are oriented perpendicular to the wind direction. The explanation for this is that maximum shore drift, and therefore erosion, takes place where the shore is at 50 degrees to the wind direction, hence extending the lake at the downwind corners. A similar process has been suggested for the lakes of the Old Crow Flats. The lakes are oriented northwest-southeast which is perpendicular to the prevailing wind at Old Crow. However, it should be noted that this wind direction is produced by the direction of the valley in which the town of Old Crow sits and may not be the prevailing wind at Old Crow Flats. Allenby (1989) examined satellite photos and the geological literature for the area and argued that "The data suggests that the Old Crow / Bluefish lakes, while thermokarst in origin, are shaped and oriented by a nearly orthogonal [square or rectangular] fracture pattern in bedrock and / or crystalline basement underlying the recent, thick lake sediments." (Allenby 1989, page 50).

Figure 13 a and b. Click photos to enlarge and see other photos.

Recently Hamilton (1999) discussed another version of this bedrock explanation on for the orientation of the Old Crow Flats lakes. The Old Crow Basin is an elliptical depression with its long axis oriented northwest southeast (see Geology). The oriented thaw lakes of the Flats are elongated parallel to the basin’s long axis. These rectangular lakes differ in both form and setting from the elliptical thaw lakes on the windswept Alaskan Arctic Coastal Plain, which are shaped by the prevailing wind. Hamilton (1999) suggests that the orientation of the lakes could also be due to modern warping of the basin floor as indicated by the tilting of the lakes, which typically have elongated shorelines along the margins towards the basin centre. The rectangular form of the lakes might reflect fracture patterns created by deformation of permanently frozen sediments that underlie the basin floor.

The life cycle of these lakes and the polygonal peat bogs associated with them on the Old Crow Flats is discussed in Hydrology, Section 3C, in connection with the topic of whether the lakes of the Flats are drying out. The thermokarst lakes in the Old Crow Flats are called perched lakes because the rivers have cut down into the old glacial lake sediments leaving the lakes perched on the plateau above the river bed. Sometimes the rivers "cut" into the embankment of the thermokarst lake resulting in a catastrophic draining of the lake (see Figure 8.2, Hydrology).

Ground ice slumps (sometimes referred to as retrogressive thaw slumps or flows) and headwall retreat occur in ice-rich areas where massive ice bodies become exposed. These can be sea coasts where cliffs are created by coastal erosion processes such as wave action as in Ivvavik National Park (Figure 4.13d) or on the banks of modern or ancient lakes and rivers, and would be expected to occur in the Old Crow Basin. Once the ice is exposed, it is subject to melting by the sun (solar radiation) and warm air (turbulent heat fluxes).	Figure 4.13d. Click to enlarge.
As the ice melts, the cliff is under-cut and the soil and organic material overlying the massive ice body falls to the bottom of the slump. When sufficient material has accumulated to cover the once exposed ice, the retreat stops (or slows greatly) and the slump is said to be stabilized. A very warm summer or other disturbance such as the removal of the debris at the bottom of the slope can reactivate the slump.
Active layer detachments result from slipping of the melted, saturated, active layer along the surface of the frozen permafrost. This happens when water accumulates at the surface of the frozen permafrost due either to heavy rainfall or particularly long periods of unusually warm summer temperatures. They are sometimes aided by the build up of ice lenses, due to the refreezing of melt water from past summers, at the bottom of the active layer. These features, sometimes called skin flows, can occur on slopes as gentle as 5E and can change the face of the land in less than a day (Figure 4.13c, from Welch 1993, Plate 4.38).	Figure 4.13c Click to enlarge.

They can be responsible for the initiation of ground ice slumps by exposing buried massive ice bodies. They are common features in the upper levels of river bluffs in the Old Crow Basin due to the thick layer of ice-rich glacial lake sediments which occur under the recent (Holocene) sediments and organic mat (Matthews et al. 1987).

iv) Landforms of an Unglaciated, Periglacial Basin

The landforms of the Northern Mountains are well described in the Ivvavik National Park Resource Description and Analysis (Welch 1993). The major focus here will be on discussions of features found in Vuntut National Park which are not common in Ivvavik National Park, but it should be remembered that at least a third of Vuntut National Park is mountainous and thus displays many of the montane features discussed by Welch (1993). Further illustrations and discussions of landform features are given in Soils (fluvial features) and in Hydrology (aufeis or river icings, oriented lakes, river meanders and oxbow lakes).

a) Tors are bedrock crags and pinnacles which protrude through surrounding colluvium. They are of two main types, summit and sideslope tors (Figure 4.14). There are several theories as to their origin, involving long-term weathering under periglacial and/or subtropical climates (French 1976). Tors are considered to be diagnostic of non-glaciated terrain. On summits this may imply that local glaciers or tongues of continental ice simply did not pass over divides, but that glacier ice existed in valleys. Sideslope tors (Figure 4.14a) rule out this possibility. The British Mountains and Old Crow Range abound with both types.

Figure 4.14a. Click photo to enlarge and see other photos.

b) Cryoplanation Terraces are described by Lauriol (1990) as large benches carved in hillslopes in the tundra zone of unglaciated areas. These often occur with as many as 25 terraces in sequence, transforming slopes into a series of giant steps, ranging in length from 100 m to 1000 m across the slope, and from 10 m to 300 m up and down the slope. The steps between them are from 1m to 10 m high. They typically occur at elevations between 700 m and 800 m above sea level, often facing northeast or southwest (Lauriol and Godbout 1988). Cryoplanation terraces are absent from the sides of V-shaped valleys, and on mountains where tors are found. For instance, in the Old Crow Range, the slopes of the granitic batholith do not have terraces, but are dominated by remarkable tors. On the other hand, the quartzite and argillite mountains near the northern and eastern borders of the batholith contain abundant terraces but no tors. Cryoplanation terraces are cut into argillite, quartzite, limestone, dolomite, and sandstone, but are absent on granite and shale. Most occur on the upper slopes of pediments.

Lauriol and Godbout (1988) describe a cryoplanation terrace at 800 m near the summit of the mountain overlooking Old Crow Village. The terrace is 200 m long by 100 m wide and and is separated from the flat summit of felsenmeer (shattered rock debris) by 110 m-high talus inclined at 18E.

Terrace material is formed exclusively of angular blocks covered with lichens (Figure 4.15a). At this talus foot the terrace slopes at 1E and contains blocks set in a silty matrix. In middle zone the terrace slopes at 3E and contains inactive sorted circles 3 m to 4 m in diameter. The distal (outer) part slopes at 5E and contains sorted stripes. Pebbles and blocks are free of lichens and stand vertically. Gelifluction appears to be very active here. The terrace is bordered distally by another talus, similar to the proximal one (Lauriol 1990, p347-349).

Figure 4.15b Click photo to enlarge.

The mechanism of formation is still poorly understood though Lauriol (1990) suggests the following possibilities. Accumulation of snow against the proximal part of a terrace surface (Figure 4.15b, from Lauriol 1990) and its subsequent melt bring about processes of frost shattering, mass movement, rill wash, and slope wash. These processes have previously been identified as responsible for the formation of cryoplanation terraces (Peltier 1950, Tricart and Cailleux 1962, St-Onge 1969, Washburn 1979). The date of formation of cryoplanation terraces is also uncertain. Recent studies on Ptarmigan terrace located on Old Crow Mountain (Lauriol et al., 1997) suggest that the oldest part of the terrace may be mid-Pleistocene. Some terraces are still active, but the great majority are inactive (Welch 1993, Lauriol 1990, Lamirande et al., 1999).

c) Pediment slopes are one of the most distinctive features of the unglaciated landscape of Vuntut National Park and the Old Crow Flats Special Management Area. In the Wiken et al. (1981) ecosystem classification, they comprise a whole ecodistrict which makes up almost a third of the Park and a major portion of the Old Crow Flats Special Management Area. This is in contrast to Ivvavik National Park where pediments are greater than 10 % of the terrain in only a few limited ecosections such as the Tulugaq Pediment ecodistrict and Timber Creek ecodistrict.

There is some uncertainty as to the mechanisms and timing of the formation of the Old Crow pediments. Welch (1993) says "pediments are erosional surfaces believed to be formed by water flow over slopes under semi-arid climate conditions." Hughes (1972) first mentions them as low-

angled surfaces in the unglaciated northern Yukon. Hughes et al. (1974) were successful in drilling a core in the 1 to 2 m of permanently frozen silt that typically mantles the Old Crow pediments but unsuccessful in the lag gravel (residual cover of coarse gravel that prevents further wind erosion of fine-grained particles beneath) or bedrock detritus below the silt. They found the pediments remarkably uniform, despite the fact that they are developed on a wide range of bedrock types (carbonates, sandstones, shale, quartzite, and granite). "Typically, 1 to 3 m of ice-silt and organic silt overlies 1 to 3 m of silty lag gravel that in turn lies on bedrock. Particularly in the case of granite, the bedrock may be so deeply weathered that there is no sharp demarcation between lag gravel and weathered bedrock." (Hughes et al. 1972, p 276). The YEWG (1999) suggest that the pediments in the Old Crow Basin Ecoregion are covered by colluvium (see below). On the other hand, Welch (1993) describes the pediments in Ivvavik National Park as covered by alluvial gravels capped by ice-rich silty loams (Figure 4.16a). Hughes (1972) and Tarnocai (1987) point out that the pediments are at least older than the Wisconsinan glacial deposits such as the moraines of the Buckland Glaciation which have formed on top of the pediments in places.

French and Harry (1992) studied the formation mechanisms and timing of the Barn Mountains pediments just north of Vuntut National Park. Their works appears to be the most recent and most extensive study of pediments relevant to the Park area. The Barn Mountain pediments are nearly flat or gently concave surfaces and not as extensive as the Old Crow pediments to the south. Typically, the pediments are most extensive upon the soft shale and siltstone of the Kingak Formation (Norris 1977). The pediment slopes are separated from steep upper bedrock slopes by a relatively sharp pediment junction. Immediately below the junction, the pediments are covered by a layer of angular, lichen-covered sandstone rubble ( French and Harry 1992, Figure 4, page 150, Supplement F&H4). Lower down, however, the pediments are mostly vegetated with tussock tundra (Zoltai and Pettapiece 1973) and characterized by earth hummocks which often extends into linear ridges about 20 to 30 m long, up to 1 m wide, and about 30 cm high. This formation suggests downslope movement.

The pediment surfaces may be distinguished from fluvial terraces by the general absence of ice wedge polygons on the pediments, and by the absence of terrace bluffs parallel to the valley side. Shallow seepage lines visible from the air and outlined by willow-birch shrub are typical of many of the pediments. The late July frost table occurs at depths of between 30 and 40 cm, indicating that the maximum thickness of the active layer beneath vegetated pediment surfaces probably does not exceed 60 to 80 cm. From the lack of stratification, fluvial sediments or organic or faunal remains, French and Harry (1992) deduce that the sediments must have been deposited in a cold barren environment. They also conclude that the current geomorphic activity on the pediments is mainly limited to cryoturbation and earth hummock formation. Duk-Rodkin (personal communication) however finds soil development on pediments in the Mackenzie Mountains.

French and Harry (1992) also examined a rare fluvially dissected pediment in the upper Canoe Creek drainage just north of Vuntut National Park, where the underlying bedrock consists of black shale interbedded with thin mudstone units. At higher elevations along the valley, quartzitic sandstone outcrops often form localized blockfields and small tors. The black shale is seen to be both deformed (i.e., steeply dipping) and faulted, and occupies all but the upper 2-5 m of the section (Figure 4.16b, from Figure 5, French and Harry, 1992, p. 5).

Figure 4.16b Click photo to enlarge.

Priesnitz (1981, Priesnitz and Schuke 1983) attribute the formation of the pediments to cryogenic (formed through freezing) processes that are occurring today. Rampton (1982, p 7-8), on the other hand is of the opinion that pediments "were formed under different conditions than prevail today."

Pediments in hot arid regions have long been the subject of considerable controversy. They are generally believed to be rock-cut transportation surfaces which may truncate (cut off) geologic boundaries. Most workers in this field believe that hot semi-arid pediments are developed by rills, gullying, rainwash and sheetflooding coupled with backwearing of the steep upper slopes.

French and Harry (1992) point out that the region has experienced cold non-glacial (periglacial) conditions for much, if not all, of the last 2 to 3 million years and that the landscape may be in a state of near equilibrium with respect to present geomorphic processes. The present climate is extremely cold and dry. They believe that pediments in cold, semi-arid regions are effective slopes of transportation of waste rock materials only under certain conditions. They are active only during periods of intense frost wedging and high sediment, and are inactive whenever moisture levels fall below a critical level.

French and Harry agree with Rampton (1982, p 8) and Budel (1982, p 78) that current sheetwash activity is an inadequate mechanism to explain the formation of the pediments. They further state that the deposits overlaying the bedrock are related to a different climate than today. They suggest that enhanced transport across the pediments probably occurred during the Pleistocene at the beginning and end of each cold period. Thus the existence of pediments in unglaciated Vuntut National Park and the Old Crow Flats Special Management Area implies the great antiquity of the landscape and argues against a highly dynamic concept of Pleistocene periglacial landscape evolution

GEOMORPHIC PROCESSES AND LANDFORMS

i) Erosional Processes and Features

ii) Aeolian Processes and Features

iii) Periglacial Processes and Features

iv) Landforms of an Unglaciated, Periglacial Basin