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COMMUNICATION / COMMUNICATION
An unusual stone circle, Chilcotin Range, British
Columbia, Canada
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Michael Czajkowski and Andrew V. Okulitch
Abstract: A unique circular feature of uncertain origin lies above the tree line on the eastern flanks of the Coast Range of
British Columbia, Canada. It is composed of white, fractured, angular cobbles to boulders predominantly under 1 m across,
arrayed in a slightly flattened circle nearly 50 m in diameter with the ring mostly about 4 m in width. The felsic granitoid
lithology of the circle is unlike any in the immediate region, and no clasts of this composition occur within the circle. The
debris rests on soliflucted soil containing rounded pebbles to cobbles of granodiorite that forms the regional lithology. The
age of the circle is deglacial with post-glacial modification. Given the absence of similar lithologic units in the region and
no obvious symbolic purpose for such a feature, an anthropogenic origin for the circle is improbable. Mechanisms for transporting the foreign rock unit to its final location, distributing fragments into a circle, and preserving it include flow of alpine
and fringing continental ice masses, deglaciation, freeze–thaw cycles, and post-glacial solifluction and erosion. One large
slab was either entrained within or fell onto a flowing glacier from some unknown outcrop at least 2 km from the site of
the circle. During deglaciation, the insulating cap preserved the ice beneath it forming an isolated stagnant mass of ice.
Freeze–thaw cycles likely affected the slab when it was on the surface of the ice, but it remained coherent, otherwise glacial
flow or meltwater streams might have scattered loose clasts. Once the ice became stagnant, continued freeze–thaw cycles
eventually created a rubble pile, which slid off the presumably symmetrical mass of ice to become arranged in a roughly circular ring. Having lost its protective cover, the ice melted and subsequent solifluction slightly modified the ring.
Résumé : Un cercle particulier d’origine incertaine est situé au-dessus de la ligne des arbres sur les flancs est de la Chaîne
côtière de la Colombie-Britannique, Canada. Il est composé de pierres blanches, fracturées et angulaires, dont les tailles varient de galets à blocs de moins de 1 m de diamètre, placées selon un cercle légèrement aplati d’un diamètre de 50 m alors
que la bordure a une largeur de 4 m. La lithologie granitoïde felsique du cercle ne ressemble à rien dans la région immédiate et aucune claste de cette composition ne se trouve à l’intérieur du cercle. Les débris reposent sur un sol qui a subi de
la solifluxion; il contient des pierres arrondies, de la taille de cailloux à galets, de granodiorite, laquelle forme la lithologie
régionale. Le cercle date de la déglaciation et il a été modifié après la glaciation. En raison de l’absence d’unités de lithologie semblable dans la région et du fait qu’il n’y a aucun symbolisme évident pour une telle caractéristique, il est peu probable que le cercle soit d’origine anthropique. Les mécanismes pour le transport de la roche étrangère à son emplacement
final, la distribution des fragments en un cercle et sa préservation comprennent l’écoulement de masses glaciaires alpines et
de bordure continentale, la déglaciation, les cycles de gel–dégel ainsi que de la solifluxion et de l’érosion postglaciaires.
Une grande dalle aurait été entraînée à l’intérieur d’un glacier ou serait tombée sur un glacier en écoulement depuis un affleurement inconnu situé à au moins 2 km du site du cercle. Durant la déglaciation, la dalle isolante a préservé la glace qui
était sous elles, formant une masse de glace stagnante et isolée. Les cycles de gel–dégel ont probablement eu un effet sur la
dalle alors qu’elle était à la surface de la glace mais elle est restée cohérente, sinon l’écoulement glaciaire ou des ruisseaux
d’eau de fonte auraient pu disperser les clastes détachées. Une fois la glace devenue stagnante, les cycles continuels de gel–
dégel ont fini par créer un talus de pierres cassées, lequel a glissé de la masse de glace probablement symétrique pour se
placer dans un anneau plus ou moins circulaire. La glace n’ayant plus sa couverture protectrice, elle a fondu et la solifluxion
a par la suite légèrement modifié l’anneau.
[Traduit par la Rédaction]
Received 19 February 2011. Accepted 17 September 2011. Published at www.nrcresearchpress.com/cjes on 08 November 2011.
Paper handled by Associate Editor Timothy G. Fisher.
M. Czajkowski. The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK.
A.V. Okulitch. Geological Survey of Canada, 625 Robson Street, Vancouver, BC V6B 5J3, Canada; 195 Little Mountain Road, Salt
Spring Island, BC V8K 2L4, Canada.
Corresponding author: Andrew V. Okulitch (e-mail: aokulitc@nrcan.gc.ca).
Can. J. Earth Sci. 48: 1523–1529 (2011)
doi:10.1139/E11-063
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Description
Situated near the top of a ridge between Whitton and
Stuart valleys, south of Mount Ada on the eastern flank of
the Coast Range, British Columbia, Canada, is an unusual
near-circular ring of stones. This feature is located at 52°04′
13.49″N and 125°33′52.37″W (Fig. 1). It can be readily seen
from the air (Fig. 2) and even on Google Earth, lying above
the present tree line at an elevation of approximately 1980 m.
In the summer of 2009, one day was spent hiking up northwards from Nuk Tessli lodge on an unnamed lake along
Whitton Creek, mapping the circle, excavating underlying
soil, collecting samples, and examining bedrock within a
2 km radius of it. Subsequently, an area of over 400 km2 approximately centred on the stone circle was examined using
high-resolution Google Earth images. Over two dozen indistinct, vaguely circular features were observed ranging from 7
to 102 m in diameter. Some may be patterned ground, many
may be visual artefacts, but none have the distinct colour
contrast or show the distinct clast outlines of the stone circle
under investigation. Vague, semi-circular structures on the
ridge near the stone circle were examined briefly in passing
and seem to be formed of the same coarse-grained granodiorite that forms most of the local diamictite. These may be solifluction lobes. The white stone circle is, therefore, the only
one of its kind known in this region, and understanding of
its formation may not only be valuable in its own right but
may also shed light on the glacial history of this area.
Ice flow directions over the region examined are mainly to
the northeast and east (Slotnick 2004, fig. 8; Stumpf et al.
2000), but late glacial flow was controlled by local topography.
The circle, (Figs. 3, 4), which is slightly flattened on its
western side, lies on a gently undulating, south to southeasterly 5° slope along a southern ridge flank, and is about
47 m (north–south) by 39 m (east–west). It comprises a
nearly continuous ring of loose stones, 0.2 to 0.9 m high,
the ring being thicker on its western and eastern sides. The
width varies from 1.5 to 10 m but is predominantly about
4 m. On the northern side, the ring is thin, with small clasts
(<30 cm across) spread inwards into the circle forming a
patch and a slight gap in the ring. On the south and southeast
sides are clasts up to 1 m across, with one 3.5 m long. The
stones forming the ring are generally angular, blocky, commonly with well-preserved planar facets, edges, and corners.
No glacially striated surfaces were observed. The volume of
clasts was estimated at about 1000 m3 from measurements of
the length, width, and depth of 11 segments of the ring.
The area within and outside the circle is blanketed by a residuum of weathered bedrock and till whose clasts are
rounded to subrounded. Their weathered surfaces do not preserve glacial striae.
Bedrock is observed in places within 0.5 km of the site,
but most of the area is blanketed with a sandy, clast-rich till.
Bedrock, where visible, is composed of sheared to gneissic
granitoids interspersed with veins of massive granodiorite,
both significantly more mafic than the ring rubble, and thin
veins of felsite (map units 5 and 7, Tipper 1968). The surface
around the ring and upon which it is draped shows evidence
of solifluction with apparent flow of lobes downslope to the
south and southeast. Two major lobes are shown in Fig. 4.
Can. J. Earth Sci., Vol. 48, 2011
Lobe (a) is elevated about 20 to 30 cm above the lower part
of the inside of the ring, while lobe (b) is flatter and lower.
Clast analysis
No felsite clasts in the size range of those making up the
ring were found inside or outside the circle. All the clasts
outside and inside the ring are composed of granitoid gneiss
and granodiorite with varying amounts of biotite. No clasts
of these rocks were seen within the ring of stones forming
the circle itself. Those clasts are all felsite, and although thin
felsite veins occur within the foliated granitoids, no felsite
outcrop of the size required to be a source for the clasts making up the ring was found within about 2 km of the circle.
Felsite clast shapes are mainly blades, discs, and rods,
whereas granitoid clasts within and outside the ring are more
heterogeneous with spherical shapes predominating (Zing
classification, Briggs 1977).
Sections
Small pits (Fig. 5) were dug outside and inside the western
edge of the ring (see Fig. 4 for location). Pit A penetrated the
angular blocks of felsite making up the ring and bottomed
about 0.5 m down in soil and parent material consisting of a
sandy clay (60%/40%) matrix containing rounded pebbles to
cobbles of granitoid gneiss and granodiorite. The sand appeared to be mainly derived from the breakdown of the granitoids, and the matrix was slightly sandier near the surface.
Pits B and C, dug inside and outside the circle, exposed
only soil and parent material. No clasts of felsite were found
beneath the surface.
Except for the shallow pits, no systematic observations of
the glacial deposits forming the regional surface on which the
stone circle rests were made during the brief field investigations reported here. The surface may be relict (Fjellanger and
Sorbel 2007; Clarhall and Kleman 1999), having been overridden by the last, cold-based ice sheet and not significantly
modified, but no data are available to support this supposition.
Analysis
Clearly, the ring is late deglacial with some post-glacial
modification, since the glacial deposits lie entirely beneath
it. It is purely a surface feature. The circle may have been
modified after its deposition by solifluction, suggested by
the apparent re-distribution of felsite clasts into a patch and
gap array on the west flanks of the two lobes (Fig. 4). The
fact that the larger ring clasts lie within depressions suggests
that mobility during frost heave may have caused some settling.
The marked angularity of the felsite clasts testifies to its
siliceous composition and a feldspar and mica content lower
than that of adjacent granitoids. Feldspars and micas are subject to disintegration by frost shattering along cleavage
planes. An example of differential weathering between the
granitoids and the felsite was observed in a boulder where
the finer grained felsite protruded significantly. The coarsegrained granitoids weather to produce the coarse sand grains
and fine micaceous debris. Different lichen growths on the
two lithologies also testify to the differing composition, availability of nutrients, and local thermal regimes.
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Czajkowski and Okulitch
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Fig. 1. Southwestern British Columbia and stone circle location. Glacial features predominantly derived from examination of Google Earth
images. Contours sketched from topographic maps NTS (National Topographic System) 93 C/3 and 93 C/4, North American Datum (NAD)
27, published 1984. Contour values are approximate conversions from values in feet above sea level at 500′ intervals (1 ft = 0.3048 m) and
differ from elevations in Google Earth by about +90 m.
The absence of felsite clasts beyond the circle suggests that
they may have a common origin as a single slab either
plucked from an outcrop under the ice or as a rockfall from
a felsite outcrop onto the ice. The source is unknown. Volume estimates suggest a maximum initial slab size of 30 m
× 30 m × 1 m. Such a tabular shape might be likely if the
primary regional occurrence of felsite is in late dykes intruding the granitoids, as has been observed on a small scale in
cobble found about 3 km south of the circle on the trail
from Nuk Tessli.
Formation hypotheses
Circular features are quite common in nature but frequently spark much discussion as to whether they are natural
or anthropogenic. In this case, an anthropogenic origin was
dismissed since there is no evidence of stacking of the clasts
and large clasts seem to overly smaller stones. The largest
clast (3.5 m long) would probably weigh 10 tonnes or more
and would be unlikely to have been moved into its present
location from a distant outcrop if smaller clasts were available. The harsh climate and absence of sustenance at
2000 m elevation in post-glacial times likely discouraged occupation or even travel in the region, and no obvious astronomic or spiritual reason for such a structure can be
imagined, even if a supply of unique stones was available in
the immediate area. However, smaller stone rings and human
artifacts have been reported to the west at undisclosed locations (G. Woodsworth, personal communication, 2010).
Frost heave in periglacial conditions can produce patterned
ground with well-defined, near-circular polygons but does
not produce single circles or raised accumulations of boulder
material. Development of polygons on slopes can lead to
stone stripes and elongate polygons, but again these are not
observed as single features.
Circular moraine features (CMFs) that resemble this stone
circle (Ebert and Kleman 2004) are postulated to have formed
from discrete accumulations of debris, 10–20 m in diameter,
entrained near the base of ice sheets in transition zones between cold- and warm-based sheets. During deglaciation,
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Fig. 2. Aerial view of the stone circle looking north.
Fig. 3. Stone circle looking south-southwest. Note the snow lying in the gully on the north-northeast side of the circle. (Photo Chris Czajkowski, Nuk Tessli Alpine Experience, 2007). Human (∼1.7 m tall) on far side of circle.
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Fig. 4. Map of stone circle deposits and associated features. The
stone fields show areas of major clast accumulation. Finer clast
scatter is not shown. The positions of the largest clasts are indicated
as are the two major solifluction lobes.
these accumulations insulated underlying stagnant ice remnants. Debris slid off the shrinking remnants to create circular features. These occur in large numbers on high ground
between major ice streams. A significant feature of many of
the CMFs is an asymmetry, indicating the direction of ice
flow; thicker debris upstream and a thinner tail downstream.
Minturn circles (Appel 1996a, 1996b) are also similar to
the stone circle in size and are similarly composed of syenite
rubble different from the underlying granitic bedrock. They
occur in large numbers in a regional fan-shaped array, are
clearly derived from a syenite intrusion by sub-glacial erosion at the apex of the array and were transported within and
on top of the ice. The size range of the rubble was not provided but can be crudely estimated to be 10 to 50 cm and
finer on photographs. Rounding of clasts increases with distance from the source. It was hypothesized that debris was
concentrated in potholes and meanders of meltwater streams
on the ice surface and gently deposited during deglaciation.
The circles are enhanced by preferential lichen growth on
the syenite.
Circular rubble rings and piles also form as ablation moraines on blockfields (Fjellanger et al. 2006) and from debrisrich blocks of ice carried by jokulhlaup flows that settle on
outwash plains (Maizels 1992). Differential ablation of debriscovered ice is the common process in the formation of all circular features, such as domes and rings (Swithinbank 1950).
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Fig. 5. Stone ring and underlying soil. Metre stick for scale.
Our hypothesis, developed independently (before we were
directed to the literature by our reviewers), is constrained by
the unique occurrence of the circle, its isolation, shape, size,
and nature of its clasts. The felsic material fell onto the surface of the ice sheet as one fractured slab probably derived
from an outcrop of a large felsic dyke exposed in a nunataq.
Basal or sub-glacial entrainment is not favoured because of
the fresh surfaces of the clasts and the absence of glacial
striae. Jagged, angular forms typically form on nunataqs during freeze–thaw cycles. Although such evidence is not conclusive, the distinction is moot; the circle does not begin to
form until it lies on the surface of the ice. A small rubble
pile is considered unlikely because of its probable dispersal
during transportation whether within or on top of the ice.
One weakness of the hypothesis for formation of CMFs is
the lack of a mechanism to concentrate and preserve entrained debris during flow. The remarkable circularity of the
Minturn circles and their common occurence in pairs seems
at odds with the irregular shapes of potholes and most meltwater meanders; however, the rounding of the clasts testifies
to some transportation, and meltwater would appear to be the
only likely medium that could form the many small accumulations of rubble required to produce hundreds of circles.
Meltwater streams do not seem to be a sufficiently energetic
agent to move angular, sharply faceted rubble ranging in size
from 0.1 to 3.5 m across, and would seem more likely to disperse rather than concentrate such a diverse collection of
clasts.
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Upon stagnation of the glacier and its subsequent melting,
the slab, which might have begun to fracture, would have
shaded the ice beneath it. A single slab, however, would
have preserved an ice stalk supporting the erratic (Fig. 6)
and would not by itself result in a circle. A mechanism is
needed to produce a circular structure with the largest clasts
on the down slope side. To ensure that no felsic rubble remains within the ring, it is necessary for all the rubble to
slide off the mound. An erratic, if gradually broken up by
numerous freeze–thaw cycles in situ, might be expected to
slide off the mound in all directions prior to the ice stalk
stage, thereby forming a rough circle. Once the rubble “blanket” is gone, the mound melts.
The presence of larger clasts on the south side may be
merely a random variation related to pre-existing fractures.
Alternatively, slightly warmer conditions on the south side
of the mound may have influenced freeze–thaw cycles to
produce more small rubble on the cooler north side. The
largest fragments may then have slid off to the south, possibly assisted by softer, wetter ice and solifluction on the
sunny side.
A potential problem is the time needed for freeze–thaw
cycles to break up a single fractured slab. One study (Lautridou and Seppala 1986) suggested that granitoid rocks are
very resistant to reduction to sand-sized grains. That study
did not consider the effect of fractures. Simple energy and
strength of materials considerations (Gordon 1968), wherein
the energy required to break a material is proportionate to
the surface area created, indicate that creation of sand-sized
grains (1 mm cubes) requires three orders of magnitude
more energy than the creation of a 1 m cube. Moreover, a
fractured, water-soaked felsic slab could, in theory, be shattered into large angular cobbles and boulders in one cycle.
This stone circle seems to resemble CMFs in one aspect
only: it is thinner on the north than the south side, consistent
with regional, northeasterly, ice flow directions, although as
noted earlier in the text this might be related to warm conditions on its sunny side. However, clast sizes are significantly
greater than those of CMFs and the basal ice source postulated for CMFs seems unlikely. The stone circle is similar to
Minturn circles: the presence of contrasting lithologies and
the differential ablation of accumulated debris. However,
there is no evidence of the influence of meltwater streams,
and only one circle was formed rather than a broad field of
them. No blockfields or jokulhlaup flow deposits are evident
in this area, the latter usually taking the form of high-energy
braided stream outwash, as observed on the south coast of
Iceland.
The later history of formation of the circle includes postglacial erosion and solifluction. A small gully on the northeast side appears to be a consequence of water being deflected by an obstruction, in this case remnants of the ice
mound and the ring rubble. Solifluction may have slightly
displaced material down slope to the south and east making
the structure larger and less regular. Mapped lobes within
the ring may be re-mobilized debris from the ice mound, but
the spatial relationship between the mapped solifluction lobes
and the gap in the circle (Fig. 3) suggests that flow from outside the circle breached the ring and redistributed some of its
clasts.
Can. J. Earth Sci., Vol. 48, 2011
Fig. 6. Old photograph of a Glacier Table supported by an ice pillar.
Talafre Glacier Mt. Blanc, European Alps. Courtesy of The National
Snow and Ice Data Center, 449 UCB University of Colorado,
Boulder, Colorado (nsidc.org/cgi-bin/words/topic.pl?glaciers)
Acknowledgements
The careful and informative preliminary review by Dr. R.
Smith, Geological Survey of Canada, Calgary, Alberta,
greatly improved this paper and refined our hypothesis of
formation of the stone circle. Thorough reviews by critical
readers J. Kleman and P.W.U. Appel broadened our understanding of glacial processes and further improved the paper,
as did careful work by the Associate Editor. The generosity
and hospitality of C. Czajkowski, discoverer of the circle
and owner of Nuk Tessli Lodge, is greatly appreciated. The
Geological Survey of Canada generously provided office facilities where some of the manuscript preparation was done
and published a condensed popular version in an internal
newsletter.
References
Appel, P.W.U. 1996a. A new type of glacial deposit. Nature, 379(6566):
590–591. doi:10.1038/379590b0. PMID:11536728.
Appel, P.W.U. 1996b. Minturn circles: a new glacial feature.
Canadian Journal of Earth Sciences, 33(10): 1457–1461.
Briggs, D.J. 1977. Sources and methods in geography: sediments. In
Shape analysis, Ch. 4. Butterworth, London. pp. 113–114.
Clarhall, A., and Kleman, J. 1999. Distribution and glaciological
implications of relict surfaces on the Ultevis Plateau, northwestern
Sweden. Annals of Glaciology, 28(1): 202–208. doi:10.3189/
172756499781821599.
Ebert, K., and Kleman, J. 2004. Circular moraine features on the
Varanger Peninsula, northern Norway, and their possible relation
to polythermal ice sheet coverage. Geomorphology, 62(3–4): 159–
168. doi:10.1016/j.geomorph.2004.02.009.
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Can. J. Earth Sci. Downloaded from www.nrcresearchpress.com by 79.68.121.65 on 05/06/12
For personal use only.
Czajkowski and Okulitch
Fjellanger, J., and Sorbel, L. 2007. Origin of the palaeic landforms
and glacial impact on the Varanger Peninsula, northern Norway.
Norwegian Journal of Geology (Norsk Geologisk Tidsskrift),
87: 223–238.
Fjellanger, J., Sorbel, L., Linge, H., Brook, E., Raisbeck, G., and
Yiou, F. 2006. Glacial survival of blockfields on the Varanger
Peninsula, northern Norway. Geomorphology, 82(3–4): 255–272.
doi:10.1016/j.geomorph.2006.05.007.
Gordon, J.E. 1968. The new science of strong materials: or why you
don’t fall through the floor. Penguin Pocket Book, ISBN
0140209204.
Lautridou, J.-P., and Seppala, M. 1986. Experimental frost shattering of
some Precambrian rocks, Finland. Geografiska Annaler, 68A(1–2):
89–100. doi:10.2307/521179.
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Maizels, J. 1992. Boulder ring structures produced during Jokulhlaup
flows. Geografiska Annaler, 74A(1): 21–33. doi:10.2307/521467.
Slotnick, B.S. 2004. Glaciation and glacial history of British Columbia
during Fraser Glaciation. University of California Davis: Centre for
Watershed Sciences. http://watershed.ucdavi.edu/skeena_river/documents/initial_reports/BSSlotnick.pdf. [accessed 15 September 2010].
Stumpf, A.J., Broster, B.E., and Levson, V.M. 2000. Multiphase flow
of the Late Wisconsin Cordilleran ice sheet in western Canada.
Geological Society of America Bulletin, 112(12): 1850–1863.
doi:10.1130/0016-7606(2000)112<1850:MFOTLW>2.0.CO;2.
Swithinbank, C. 1950. The origin of dirt cones on glaciers. Journal of
Glaciology, 1: 461–465.
Tipper, H.W. 1968. Geology, Anahim Lake, British Columbia.
Geological Survey of Canada, Map 1202A, scale 1 : 250 000.
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