Progress report
Progress in Physical Geography 2016, Vol. 40(6) 835–855 ª The Author(s) 2016 Pronival ramparts: A review Reprints and permission: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0309133316678148 ppg.sagepub.com David W. Hedding University of South Africa, South Africa
Abstract Pronival ramparts are debris ridges formed at the downslope margins of perennial or semi-permanent snowbeds beneath bedrock cliffs. These landforms, also previously known as protalus ramparts, are loca- ted in periglacial environments, but the apparent simplicity of rampart formation made these landforms far less interesting than other modified forms of talus in cold environments. As a result, limited research, use of supposed relict examples and assumed formative mechanisms led to the misidentification of ramparts, cir- cular arguments regarding genesis and inappropriate palaeo-environmental inferences. Several advances have, however, been made in the past few decades, particularly where actively-forming ramparts have been studied. Thus, this paper provides a review of research on pronival ramparts. In particular, focus is placed on the advances made in our understanding of rampart genesis, identification (diagnostic criteria) and palaeo- environmental significance. Notable advances include the development of a retrogressive model of rampart genesis to supplement the conventional downslope model of development, revised diagnostic criteria for field identification and the use of calibration equations during Schmidt-hammer exposure dating of pronival rampart. The use of pronival ramparts as palaeo-environmental indicators is also examined to determine what relict examples of these landforms may reveal about past climates.
Keywords Pronival rampart, protalus rampart, snowbed, snow, genesis, diagnostic criteria, palaeo-environmental significance
I Introduction related landform (protalus ramparts) (Scappoza, 2015) but Matthews et al. (2016) prefer the term A pronival rampart is a ridge, series of ridges or ‘embryonic rock glacier’ over protalus rampart ramp of debris formed at the downslope margins since these landforms can develop entirely by of a perennial or semi-permanent snowbed permafrost creep without the development of a overlooked by a bedrock cliff (Figure 1). These pronival rampart first. In addition, Hedding landforms were formerly referred to as protalus (2011) cautions that since the terms ‘pronival ramparts. Scappoza et al. (2011) and Scappoza rampart’ and ‘protalus rampart’ have been used (2015) have recently proposed that the term ‘protalus rampart’ be used to designate small permafrost creep phenomena in the lower part of a talus slope that can be considered as active Corresponding author: David W. Hedding, Department of Geography, University embryonic rock glaciers. This proposal makes of South Africa (Science Campus), Florida, Johannesburg, a distinction between nivo-gravitational land- Gauteng 1710, South Africa. forms (pronival ramparts) and a permafrost- Email: [email protected]
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Figure 1. Examples of actively-accumulating pronival ramparts. (a) a rampart on sub-Antarctic Marion Island. (b) a rampart at Smørbotn, Norway (Photograph: JA Matthews; used with permission). (c) a rampart at Grunehogna Peaks, Western Dronning Maud Land, Antarctica. (d) a rampart at Taskedalen, Norway (Photo- graph: R Shakesby; used with permission). interchangeably over the past two decades, it environments. Active ramparts are located in may lead to further confusion. Moreover, the periglacial environments but the apparent sim- inability to distinguish between relict pronival plicity of rampart formation made these land- ramparts and protalus ramparts, as envisioned forms far less interesting than other modified by Scappoza et al. (2011) and Scappoza forms of talus in cold environments (Shakesby, (2015), may make it difficult to adopt this sug- 1997). As a result, limited research, use of sup- gestion in practice. For instance, Colucci et al. posed relict examples and assumed formative (2016) acknowledge that, when investigating mechanisms has led to the misidentification of relict protalus ramparts and pronival ramparts ramparts, circular arguments regarding genesis using remote sensing data, both suggested forms and inappropriate palaeo-environmental infer- must be considered together owing to the diffi- ences (c.f. Shakesby, 1997; Hedding, 2014). culty in distinguishing the real origin. Several advances have, however, been made Shakesby (1997, 2004) and Hedding (2011, in the past two decades, particularly where 2016) chronicle the development of the termi- actively-forming ramparts have been studied nology used to describe pronival ramparts. (e.g. Fukui, 2003; Hall and Meiklejohn, 1997; Whalley (2015) notes that the choice of Hedding et al., 2007; Hedding et al., 2010; Mar- words and terms associated with pronival ram- gold et al., 2011; Matthews and Wilson, 2015; parts and protalus features needs particular Matthews et al., 2011; Matthews et al., 2015; attention in both terrestrial and non-terrestrial Shakesby et al., 1999; Strelin and Sone,
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1998;). Thus, this paper provides a review of 0.9 C (Hedding et al., 2007). Precipitation is research on pronival ramparts since the seminal typically above *800 mm p.a. but can vary review by Shakesby (1997). In particular, focus greatly from almost none in the Antarctic (Hed- is placed on the advances made in our under- ding et al., 2010) to above 3000 mm (water standing of rampart genesis, identification equivalent of snow) (Fukui, 2003). Shakesby (diagnostic criteria) and palaeo-environmental (1997: 410) noted that ‘fossil ramparts provide significance, but, first, an overview of the dis- little useful palaeo-environmental information tribution and characteristics of relict and other than indicating the obvious; that climatic actively-accumulating pronival ramparts is conditions were formerly cooler and/or more presented. snowy’. However, the absence or presence of relict pronival ramparts, specifically in areas which experienced marginal glaciations, may 1. Distribution and characteristics of be particularly useful in palaeo-environmental pronival ramparts reconstructions (see Hedding, 2014). Both active and relict pronival ramparts have wide geographic and altitudinal distributions. II Rampart genesis Relict ramparts have been documented primar- Relict pronival ramparts are frequently ily in Britain and Ireland, but some of these have described as comprising coarse angular rockfall been misinterpreted (see Shakesby, 1997). material derived from the bedrock cliffs (back- Examples of relict ramparts have also been wall) above the snowbed (e.g. Harris, 1986). identified in Norway (e.g. Shakesby et al., This angular material is typically attributed to 1987), Africa (e.g. Lewis and Illgner, 2001) and the supranival transport of frost-shattered debris Australia (Slee, 2015) (Table 1). The putative (Brook, 2009). One of the earliest descriptions relict pronival rampart at Guyra in mainland of frost shattering occurring at the headwall Australia identified by Slee (2015) is particu- comes from Lewis (1939) and this concept has larly interesting in terms of the uniqueness of become largely entrenched in the literature. the site. Relict examples have also been mapped Shakesby (1997: 397) noted, however, that in the Central Andes (e.g. Trombotto, 2000) and clasts of actively-accumulating ramparts are Africa (e.g. Grab, 1996) with little morphologi- ‘by no means nearly all angular, as is thought cal detail provided. Active ramparts are more typical of fossil ramparts’ and highlights the widespread (Table 2), but none have been docu- limited understanding of debris production for mented in Africa (Hedding, 2014), Australia the genesis of ramparts. (Slee, 2015) or New Zealand (Brook and Wil- liams, 2013). Given the current and former glo- bal distribution of cold climates, pronival 1. Debris production ramparts are probably underrepresented in the In general, very little research on debris produc- literature. For instance, relict pronival ramparts tion from exposed bedrock cliffs has been perched on valley sides may have been misin- undertaken in periglacial environments (see terpreted as former moraines of valley glaciers Krautblatter and Dikau, 2007; Luckman, due to a lack of understanding of rampart gen- 2013). Matsuoka and Sakai (1999) regard sea- esis and morphometrics. sonal frost weathering to be the most important Actively-accumulating pronival ramparts are process responsible for the modification of a found in a variety of environmental conditions cirque wall and show that rockfall activity (Table 3). Mean annual air temperatures at sites intensifies in spring during the seasonal thawing range from –17 C (Hedding et al., 2010) to period. Matsuoka (2001) observed frost
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 838 Table 1. Morphological and sedimentological characteristics of some relict (fossil) ramparts (adapted from Curry et al., 2001, and updated to the present). Slope angles ( ) Morphological Debris No. of Height / thickness characteristics transport Clast Location ramparts Distal Proximal (m) Length (m) (Plan form) mechanisms roundness Reference Grampians, 2 34 and 37.5 –13.5 and –12 2 and 1/4 and 6 33 and 150 Single ridge Supranival: Angular Ballantyne Scotland (arcuate – Rockfall and truncated) Kirkbride (1986) Lake District, 2 34 and 34 –11 and –21.5 2 and 3/10 and 10 225 and 300 Single ridge Supranival: Angular Ballantyne England (linear and Rockfall and Downloaded from arcuate) Kirkbride (1986) NW Highlands, 1 36 $ 4 / 34 120 Single ridge Supranival: Angular Ballantyne Scotland (arcuate) Rockfall and ppg.sagepub.com Kirkbride (1986) Rondane, 4 30* –19.5* 3–7 / 6–56 280–590 Single and Supranival: Angular Shakesby Norway double ridges Rockfall et al. atUNISA UnivofSouth Africaon November29, 2016 (ND) Subnival: Snow (1987) push and snow creep Errigal, Ireland 2 20 and 31.5 –4 and –14 5 and 13 /4 and 10 150 and 325 Single ridge Supranival: Coarse and Wilson (linear to Rockfall openwork (1990) gently arcuate) Lake District, 1 24–32 –7– –18 1–2 / ND 140 Single ridge Supranival: ND Wilson and England (linear) Rockfall Clark (1999) Macgillycuddy’s 1 35–39 –10–15 1.5 / 40–75 125 Single ridge Supranival: Angular to Anderson Reeks, south- (linear) Rockfall very et al. west Ireland angular (2001) Mount 2 37 –27 3 / ND 55 and 80 Single ridge Supranival: ND Lewis and Enterprise, (linear) Rockfall Illgner South Africa (2001) Thabana 3 45 –15 0.6–0.7 / 4–6 15–22 Single ridge Subnival: Snow Sub-angular Grab and Ntelyana, (arcuate) push and to sub- Mills Lesotho snow creep rounded (2011) Guyra, Australia 1 5 –5 2–2.5 / c. 10 c. 90 Single ridge Supranival: Openwork Slee (2015) (arcuate) Rockfall clasts
ND ¼ No data, $ ¼ No proximal slope, * denotes average. Table 2. Morphological and sedimentological characteristics of actively-accumulating ramparts (Adapted from Shakesby, 1997, and updated to the present). Slope angles ( ) Morphological No. of Height / thick- Length characteristics Debris transport Clast Location ramparts Distal Proximal ness (m) (m) (Plan form) mechanisms roundness Reference
Okskolten, 1 16–41 –44– –4 2 / 10 100 Main and Supranival: ‘mainly Harris (1986) Norway minor ridges Rockfall angular’
Downloaded from (sinuous) Kuranosake, 1 c.24 c. –17 4/52 c. 110 Ridge and Supranival: ‘angular’ Ono and Japan mound Rockfall and Watanabe complex debris flows (1986); ppg.sagepub.com (complex) Fukui (2003) Lyngen, Norway 2 34–43 –8–0 5 / 32–42 60–115 Single ridge Supranival: Sub-angular Ballantyne
atUNISA UnivofSouth Africaon November29, 2016 (arcuate) Rockfall to very (1987) angular Lassen Peak, 1 33–39 –30– –25 4 / 5–30 150 Double ridge Supranival: Rounding by Pe´rez (1988) USA (arcuate) Rockfall and particle debris flows collisions Romsdalsalpane, 10 26–37 –20–32 1-9 / 21–84 150–460 Single and Subnival: Debris Sub- Shakesby Norway multiple flows, rounded et al. ridges and meltwater, to very (1995); ramps snow push and angular Shakesby (sickle- solifluction et al. (1999) shaped) Supranival: Rockfall British 9 25–27; 25–35 –12– –6; c. –6 10 / ND ND Double ridge Supranival: ‘sharp’ and Hall and Columbia, (sinuous) Rockfall ‘highly Meiklejohn Canada angular’ (1997) James Ross 2 40–50 –40– –50 5/c. 20 150 Single ridge Supranival: ‘angular Strelin and Island, (sinuous) Rockfall, volcanic Sone Antarctic debris flows fragments’ (1998) and avalanche
839 (continued) 840
Table 2. (continued)
Downloaded from Slope angles ( ) Morphological No. of Height / thick- Length characteristics Debris transport Clast Location ramparts Distal Proximal ness (m) (m) (Plan form) mechanisms roundness Reference ppg.sagepub.com Marion Island, 1 22 –34 7–8 / 67–79 140 Single ridge Supranival: Angular Hedding et al. South Africa with step Rockfall (2007) (sinuous)
atUNISA UnivofSouth Africaon November29, 2016 Grunehogna, 1 20 14 < 1 / 5–23 85 Single ridge Supranival: ‘typically Hedding et al. Antarctica (sinuous) Rockfall angular’ (2010) Krkonosˇe 2 c. 32–48 c. –40– 18 3 / c. 10–20 40 Single ridge Supranival: Angular Margold et al. Mountains, (arcuate) Rockfall (2011) Czech Republic Smørbotn, 2 33–36 –26– –27 2.5–3 / 300–360* Single ridge Supranival: ‘very angular Matthews Norway c. 10–70 (linear to Rockfall and to angular’ et al. (2016) arcuate) snow- avalanche
* Matthews et al. (2011) note that other ramparts extend for >2 km around the cirque headwall. ND ¼ No data. Table 3. Environmental characteristics of actively-accumulating pronival ramparts. Location (Latitude; Precipitation (mm) / mean snow Longitude) Author(s) Altitude (a.s.l.) Air Temperature ( C) cover (days) Note Okskolten, Norway Harris (1986) 900 m –3 C (data cited from 1032 mm (data cited from Temperature data from (66 30’N; Worsley and Harris, Harris, 1974) / 210 (data cited Okstindsjøen (710 m a.s.l.); 14 20’E) 1974) from Harris, 1974) Precipitation data from Hattfjelldal (380 m a.s.l) Downloaded from Kuranosake, Japan Ono and Watanabe *2500 m –2.8 C (data cited from Summer precipitation > 1000 Data from Muroda (2454 m (36 36’N; (1986); Fukui (2003) Fukui and Iwata, mm; Winter precipitation > a.s.l.) 137 36’E) 2000) 3000 mm (water equivalent of ppg.sagepub.com snow) (Fukui, 2003) / ND Lyngen, Norway Ballantyne (1987) 760 m –1.8 C (Ballantyne, 600–850 mm (Ballantyne, 1987) Temperature data from (69 35’N; 1987) /ND Tromso¨ and Skibotn (700 m 20 15’E) a.s.l.); Precipitation data from atUNISA UnivofSouth Africaon November29, 2016 Jøvik and Lyngseidet (0 m a.s.l) Lassen Peak, USA Pe´rez (1988) 2615 m <0 C (winter: 1650–1700 mm (Pe´rez, 1988) / Data from Lessen Peak, (40 29’N; November to April) ND California 121 30’W) (Pe´rez, 1989) British Columbia, Hall and Meiklejohn 1850 m High summer ND / High winter snowfall (Hall Observations from Canadian Canada (1997) temperatures (> and Meiklejohn, 1997) Rockies (1850 m a.s.l.) (54 14’N; 20 C) (Hall and 120 50’W) Meiklejohn, 1997) Smørbotn and Shakesby et al. (1995); 800 m *1.5 C (Shakesby 1211 mm (Shakesby et al., 1999) Data from A˚ ndalsnes (20 m Romsdalsalpane, Shakesby et al. (1999) et al., 1999) /ND a.s.l.) Norway (62 25’N; 27 35’E) James Ross Island, Strelin and Sone (1998) 100 m *–6.5 C (Strelin and *200 mm (water equivalent) / Data from James Ross Island (0 Antarctic Sone, 1998) ND m a.s.l.) (63 52’S; 57 48’W) (continued) 841 842
Table 3. (continued) Location (Latitude; Precipitation (mm) / mean snow
Downloaded from Longitude) Author(s) Altitude (a.s.l.) Air Temperature ( C) cover (days) Note Marion Island, Hedding et al. (2007) 900 m 0.9 C (Hedding, 2008) *1000 mm (data cited from Temperature data from Delta South Africa Blake, 1996; Hedding, 2006) / Kop (1000 m a.s.l.); ppg.sagepub.com (46 54’S; snow cover from May to Precipitation data from 37 45’E) October (data cited from Katedraalkrans (750 m a.s.l.) Hedding, 2006) Grunehogna, Hedding et al. (2010) 1090 m –17 C (Hedding et al., ND / ND Temperature data from atUNISA UnivofSouth Africaon November29, 2016 Antarctica 2010) Vesleskarvet (845 m a.s.l.) (72 03’S; 2 42’E) Krkonosˇe Margold et al. (2011) 1500 m 0.3 C (data cited from > 1500 mm (data cited from Temperature data from Sneˆzˇka Mountains, Glowicki, 1997) Spusta et al., 2003) / snow (1602 m a.s.l.); Precipitation Czech Republic cover from November to data from Sneˆzˇka (1602 m (50 41’N; April (data cited from Spusta a.s.l.) 15 39’E) et al., 2003) Smørbotn, Matthews et al. (2011) 800–900 m; *1.5 C (Shakesby 1211 mm (Shakesby et al., 1999) Data from A˚ ndalsnes (20 m Nystølsnovi and 400 m; 850 et al., 1999) /ND a.s.l.) Alnesreset, m Norway (62 29’N; 7 45’E)
ND ¼ No data. Hedding 843 wedging of alpine bedrock whereby macro- assume that there is a regular decline in the cracks visible on the rock surface widened dur- gradient of the underlying slope. Based on the ing two seasonal periods; namely, during volumes of eight widely distributed Loch autumn and spring. Pancza (1998) notes that Lomond Stadial pronival ramparts, Ballantyne during spring, the surface of the snow hardens and Kirkbride (1987) suggested average stadial and acts as a slideway for the rocks detached rockwall retreat of 1.14–1.61 m (estimated aver- from the cliffs above, which can facilitate ram- age rockwall retreat rates of 1.5–4.0 mmy–1). part development. These observations support However, Hinchliffe and Ballantyne (1999) the assertion that the formation of ramparts indicate that these rates of rockwall retreat are takes place more frequently during mid to late two orders of magnitude greater than those spring and not in winter (Porter, 1987). In con- implied by recent rockfall accumulation on trast, Krautblatter and Moser (2009) have relict talus slopes. Using a relict pronival ram- reported that over 90% of the rockfall events part, Anderson et al. (2001) estimate that rock- in the German Alps were triggered by precipita- wall retreat rates during the Younger Dryas tion events. These rockfall events are ascribed Stadial varied between 13 and 195 mmy–1, but to the remobilization of stored debris on the Ballantyne and Eckford (1984) document aver- rockslope, which Krautblatter and Dikau age present-day rockwall retreat rates of 0.015 (2007) consider to be a significant link between mmy–1 (excluding infrequent large-scale falls) backwearing and rockfall deposition. and, therefore, rates of rockwall retreat (and Several studies (e.g. Anderson et al., 2001; debris production) based on relict landforms Andre´, 1997; Bower, 1998; Curry and Morris, differ greatly from rates based on active 2004; Hinchliffe and Ballantyne, 1999) assess processes. rockwall retreat under periglacial conditions A number of other slope processes (mass with retreat rates of between 10–2 and 10–1 wasting) can contribute material in the forma- mm year–1 (French, 2007). Matsuoka and Sakai tion of pronival ramparts (discussed in the next (1999) determine rockwall retreat through section). Rapid mass wasting in the form of direct observations, and other studies (e.g. snow avalanches and debris flows can deliver Andre´, 1997; Hinchliffe and Ballantyne, 1999) a wide range (in size) of material downslope, have used the volume of the sediments at the including fines. Fines are found in many base of the rockwall to infer long-term average actively-accumulating ramparts and can also rates of rockwall retreat. Although some studies result from in situ breakdown of constituent have used the volume of ramparts in relation to material, debris flows delivering fines or aeo- the source area of the backwall to infer rates of lian transport of fines. These observations show rockwall retreat (e.g. Anderson et al., 2001; Bal- that we still know relatively little in terms of the lantyne and Kirkbride, 1987), no studies have debris production linked to debris transport and specifically investigated rockwall debris pro- the genesis of pronival ramparts. Nevertheless, duction at actively-accumulating pronival ram- the volume of material deposited in relation to part sites. In addition, when determining rates of the rockwall retreat and the age of the landform rockwall retreat at pronival ramparts, a critical can be useful when identifying relict examples. factor which should be considered is how much Curry et al. (2001) noted that a pronival rampart of the rockwall is exposed. Anderson et al. origin had been valid for the Nant Ffrancon (2001) indicate that the principal source of error landform in northern Wales, assessment of the when using rampart volume to calculate rock- volume of the landform and surface area of the wall retreat is the estimation of the rampart backwall implies that the average rockwall cross-sectional area because it is necessary to retreat would have been four times greater than
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 844 Progress in Physical Geography 40(6) that indicated by pronival ramparts developed in Ballantyne, 1987; Harris, 1986, Johnson, Britain during the Loch Lomond Stade. This 1983; Shakesby et al., 1995; Shakesby et al., calculation casts doubt on the classification of 1999). This point is highlighted by Shakesby the landform as a pronival rampart and was one (1997: 414) where it is stated that ‘gravity of the aspects which prompted the reinvestiga- movement of rockfall debris across a snowbed tion of the Nant Ffrancon landform by Curry surface has been shown to be only one of several et al. (2001). Bower (1998) also noted that the possible modes of transport capable of contri- exceptionally large volume in relation to the buting debris to ramparts’. potential backwall source area of some discrete A range of supranival and/or subnival debris accumulations in Britain led to question- mechanisms of debris transport may also con- ing the landforms’ classification as pronival tribute to rampart development. Other possible ramparts. transport mechanisms include debris flows (Ono and Watanabe, 1986), snow avalanches (Ballantyne, 1987; Colucci, 2016; Matthews 2. Debris transport mechanisms et al., 2011), the reworking of till deposits from From the earliest descriptions of ramparts by upslope (Harris, 1986), solifluction and melt- Drew (1873) and Ward (1873), an overly simple water flows (Shakesby et al., 1995) and snow mode of pronival rampart genesis by supranival push (Kirkbride, 2016; Shakesby et al., 1999). processes has been assumed. Rampart develop- Recently, Matthews et al. (2011) have demon- ment was traditionally attributed to the progres- strated that rockfall is not the only primary deb- sive accumulation of clasts that fall from cliffs ris transport mechanism in the formation of upslope and roll, bounce or slide to the foot of pronival ramparts. The position of each rampart the snow (firn) (Ballantyne and Harris, 1994). studied by Matthews et al. (2011) and irregu- Pe´rez (1988) noted that ramparts formed by larly–shaped ramparts with gaps and gullies supranival debris transport mechanisms accu- (Colucci, 2016) suggests that snow avalanches mulate partly through debris cascading down can play a significant role in rampart genesis. and piling up on the distal slope, and partly by Shakesby et al. (1995) and Shakesby et al. the entrapment of moving debris against the (1999) also provide evidence for subnival pro- proximal slope. Owing to the implied simplicity cesses being at least as important as supranival of the supranival gravity fall process, this pro- debris transport processes from actively- cess was accepted by almost all subsequent accumulating ramparts in Romsdalsalpane, studies (e.g. Goudie et al., 1994) and has Norway. However, ramparts formed by subni- become a textbook paradigm (e.g. Ballantyne val processes have received very little attention, and Harris, 1994). The traditionally envisaged with only three studies having been conducted mechanism of gravity-driven supranival debris to date on actively-accumulating examples (see transport has subsequently been observed at Matthews et al., 2011; Shakesby et al., 1995, actively-accumulating ramparts (e.g. Hedding 1999). Evidence of solifluction enhanced by et al., 2007; Hedding et al., 2010; Pe´rez, 1988). wet conditions beneath and at the periphery of In general, a slope gradient of at least 20 (see snowbeds at actively-accumulating ramparts Ballantyne and Benn, 1994) is required for has been identified by Shakesby et al. (1995). gravitational transport of debris over firn sur- Shakesby et al. (1995) also found evidence of faces. The work of Ono and Watanabe (1986), what they interpreted as debris flows emerging which follows on from the initial work of Sekine from beneath a snowbed, which led them to (1973), questions the primacy of the simple deduce that debris flows could be supplying gravity-driven mode of genesis (see also debris together with meltwater action.
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Shakesby et al. (1995) attributed rampart development to snow creep, which involves slow sliding of snow on an internal or, more likely, a basal shear plane (see Thorn, 1978). Later, Shakesby et al. (1999) revisited the ram- parts at Romsdalsalpane, Norway, and noted snow push through the basal sliding of a snowbed acting on deformable, fines-rich dia- micton as another form of subnival debris trans- port responsible for the development of small, distinct snowbed ridges. Ramparts formed by subnival debris transport mechanisms typically display ‘distinct’ rampart morphology in the form of asymmetrical ridges which take on a sickle shape in plan form (Shakesby et al., 1999). The ramparts in Romsdalsalpane, Nor- way, appear to be smaller than ramparts formed by supranival processes and, thus, subnival pro- cesses would potentially be limited to ramparts which are matrix, rather than clast-supported. Figure 2. Models for rampart genesis. (a) the down- slope model of rampart formation (adapted from Limiting factors in the genesis of ramparts Ballantyne and Kirkbride, 1986). (b) the retro- formed by subnival processes are the slope or gressive upslope model of rampart formation snowbed gradient, size of the snowbed and size (adapted from Hedding et al., 2007). Numbers in of constituent material. the figure refer to sequential stages in rampart Kirkbride (2016) provides evidence that pro- development. nival landforms (snow push ridges) can also be associated with the deformation and/or bulldoz- bulldozing of debris by snow creep may pro- ing of sediment by late-season snowbeds duce small debris ridges less than one meter through the gravitational sliding of snowbeds. high, it cannot explain the formation of large Densely packed snow, produced in maritime ramparts several meters high. periglacial climates with heavy winter snowfall and rapid snow-firn conversion, may eventually begin to slide, pushing boulders of over 50 cm in 3. Rampart development length (a-axis) in a matrix of clasts where the Although various observations were made majority are less than 20 cm in length (a-axis) regarding rampart genesis (e.g. Sissons, 1979), (Shakesby et al., 1999). Similarly, Grab and Ballantyne and Kirkbride (1986) were the first Mills (2011: 185) propose that ‘snowcreep [sic] to develop a model for rampart genesis through and snowpush [sic] may cause considerable supranival debris transport and deposition localized stresses and initiate boulder move- (Figure 2A). Their model proposed downslope ment where snow-basal frictional forces are suf- rampart extension at the foot of thickening ficiently low’, but shallow slope gradients and snowbeds, which contrasts with the previous the interlocking of large clasts may arrest the interpretation of Sissons (1979) whereby the movement of clasts downslope and is likely a snowbed (firn field) maintained fairly stable limiting factor at their site in Lesotho, southern dimensions during the period of rampart forma- Africa. Ballantyne (2002) noted that although tion. In the downslope rampart extension model,
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 846 Progress in Physical Geography 40(6) the rampart crest migrates outwards away from ramparts from cirque moraines. Harris (1986), the talus as the debris accumulates at the foot of Shakesby and Matthews (1993) and Brook et al. thickening snowbeds (Ballantyne and Harris, (2011) highlight that ramparts are notoriously 1994). A suggested morphological characteristic difficult to identify since their morphological of ramparts which extend downslope was that the characteristics and position on a slope resemble distal slope was formed at the angle of repose the characteristics of glacial moraines, rock- (34–38 ) by the accumulation of cohesionless slope failures and various other talus-derived cascading debris (Ballantyne and Kirkbride, landforms. Much of the initial research on pro- 1986; Gordon and Ballantyne, 2006). Not all nival ramparts focused on supposed exemplar (active or relict) ramparts exhibit this character- fossil (relict) features, which presented different istic (e.g. Wilson, 1990) and Hall and Meiklejohn views on their genesis and characteristic attri- (1997) noted that ramparts in the Canadian butes (see Shakesby, 1997). Shakesby (1997: Rockies have two crests with the outer one being 394) then noted that ‘only when further investi- older than the inner. Pe´rez (1988: 89) also found gations on actively-accumulating ramparts have that the outer rampart ridge on Lassen Peak, Cali- been carried out, will it be possible to compile a fornia, had a more subdued topography, is stabi- reliable list of criteria for distinguishing ram- lized by plants and is thus ‘clearly older and parts from moraines, protalus rock glaciers, and inactive’. These observations allude to the possibil- other bedrock cliff-foot depositional forms’. ity of alternative modes of rampart development. Early in the 21st century, much of the Hedding et al. (2007) proposed a retrogres- research on pronival ramparts shifted to sive (upslope) model of rampart development actively-accumulating landforms and has under fluctuating, and possibly declining, improved our understanding of rampart genesis snowbed volumes based on observations on and their site and morphological characteristics. sub-Antarctic Marion Island (Figure 2B). The When a snowbed maintains fairly stable dimen- retrogressive (upslope) model of rampart devel- sions during the period of formation (e.g. Bal- opment model opens rampart genesis to a wider lantyne, 1987; Sissons, 1979), rampart size will range of environmental conditions. Later, be conditioned only by the height of the rock- Hedding et al. (2010) used data on site charac- wall source area, rockfall rate and the period of teristics, rampart morphology and a debris snowbed survival, irrespective of extent and accumulation field test, in terms of locality of thickness of the snowbed (Ballantyne and Kirk- deposition, to evaluate rampart genesis. Thus, bride, 1986). This highlights the importance that outward (downslope) rampart extension is possi- the surrounding topography has on rampart gen- ble even when ramparts do not possess a distal esis. Cliff or backwall height has, however, slope at the angle of repose. Hedding (2014) also received little attention in studies on pronival supports the notion expressed by Howe (1909: ramparts. Hedding (2014) has proposed that, 36) over a century ago that ‘the slightly different as a function of debris production, the ratio of forms and the varying size that the snow banks backwall-to-rampart height should exceed 1: 4– would have from year to year would undoubtedly 5, but this requires further supporting evidence. cause an unequal distribution of the debris’. More detail is forthcoming for the size of snow- beds above ramparts. Ballantyne and Benn (1994) give the maximum distance of the ram- III Identification and interpretation part crest from the source of debris (backwall) at of pronival ramparts c. 30 to 70 m on slope gradients of 35 and 25 , Nearly a century ago, Marr (1916) recognized respectively. Ballantyne and Benn’s (1994) the difficulty in discriminating pronival model uses an estimated average density of
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 Hedding 847 perennial firn fields in non-polar environments (protalus ramparts) in Alpine environments, and average shear stress of 70–100 kPa at the which supports genesis by permafrost creep of base of the glacier, whereas the bases of glaciers matrix supported landforms in the lower part of in polar regions typically exhibit an average a talus slope. shear stress of 150 kPa. Therefore, the transition distance from stationary cold-based firn into a moving body of ice would be even greater in IV Palaeo-environmental polar environments (Hedding et al., 2010). Nev- significance ertheless, the model of Ballantyne and Benn Regardless of changing snowbed dimensions, (1994) to differentiate glaciers (dynamic ice) rampart genesis is dependent on the existence from snowbeds (static ice) remains a useful tool, of a long-lasting snowbed (probably several but the importance of ice characteristics, sur- months). When the snowbeds disappear season- rounding topography and area (height) of source ally or through climatic amelioration, and ram- material cannot be understated. parts become inactive, relict pronival ramparts are conspicuous landforms from which useful inferences may be drawn. Relict ramparts have 1. Diagnostic criteria been used in various palaeo-environmental A growing body of literature, based on actively- reconstructions for Great Britain (e.g. Ballan- accumulating ramparts (e.g. Fukui, 2003; Hall tyne and Harris, 1994; Ballantyne and Kirk- and Meiklejohn, 1997; Hedding et al., 2007; bride, 1986) and southern Africa (e.g. Grab Hedding et al., 2010; Margold et al., 2011; Mat- and Mills, 2011; Grab et al., 2012; Lewis, thews et al., 2011; Shakesby et al., 1999; Strelin 1994; Lewis and Illgner, 2001). However, Hed- and Sone, 1998) has provided the opportunity to ding (2014) has reinterpreted the origin of sev- develop a more robust set of diagnostic criteria eral relict pronival ramparts in southern Africa. by which pronival ramparts can be distin- Ballantyne and Kirkbride (1986) used relict guished from other discrete bedrock cliff-foot ramparts to mark the positions of former snow- debris accumulations (Hedding and Sumner, beds that accumulated under colder (more 2013; Table 4). Hedding and Sumner (2013), snowy) conditions and then inferred palaeo- and later Hedding (2014), adopt a multiple- environmental (temperature and precipitation) working hypothesis when investigating the ori- estimates for the Late Quaternary. However, gins of landforms (Curry et al., 2001; Harris some of the previously identified relict ramparts et al., 2004) and incorporate characteristics are now considered to represent dubious exam- which are not limited to ridge morphology but ples (see Hedding, 2014; Shakesby, 1997) and, also focus on sedimentology and topographic therefore, the palaeo-environmental inferences setting of actively-accumulating features. The drawn must be viewed with caution. diagnostic criteria presented in Table 4, in con- Lukas (2006) uses relict pronival ramparts, in junction with the assessment of morphometrics conjunction with laterally terminating thick in relation to the surrounding topography (back- talus sheets along slopes, to reconstruct a dis- wall), are not regarded as definitive (see Matthews tinct glacial limit. Similarly, the presence of et al., 2016) but are rather proposed as the numerous rock glaciers and pronival ramparts starting point for the identification of pronival in valley head areas have been used to indicate ramparts in the field, which may also facilitate that the climatic conditions and the steep relief the reappraisal of some relict examples. that is unsuitable for widespread glaciation Scappoza (2015) proposes ‘diagnostic’ criteria favour the development and preservation of to define active embryonic rock glaciers Alpine permafrost (Sattler et al., 2011).
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Table 4. Proposed diagnostic criteria for the differentiation of pronival ramparts from moraines, protalus rock glaciers and rockslope failure deposits. Criterion Reference Pronival (Protalus) Rampart Ridge crest to cliff-foot distance
Recently, Colucci et al. (2016) have used high laser scanning (LiDAR), to differentiate proni- resolution orthophotos and a high resolution val ramparts and protalus ramparts. Using the digital terrain model, interpolated from airborne ‘steepness of the front’ and the contingent
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 Hedding 849 presence or absence of a perennial or semi- scree deposits. This transformation may occur permanent snow/firn field, Colucci et al. as the snowbed disappears and rockfall debris (2016: 116) suggest that the contingent presence fills the proximal trough to create a continuous or absence of a perennial or semi-permanent apron of debris from the foot of the rockwall. snow/firn field could be considered as indica- Thus, the difficulty of positively identifying tors of activity in the case of pronival ramparts, relict pronival ramparts and a poor understand- while the presence of long-lasting summer snow ing of the topographic and climatic thresholds fields associated with a protalus rampart governing rampart genesis can limit the poten- (embryonic rock glacier) could be an indicator tial for specific palaeo-environmental infer- of permafrost presence. However, Shakesby ences. The wide range of temperature and (1997: 413) stresses that ‘permafrost is not nor- precipitation characteristics at actively- mally viewed as a requirement of rampart for- accumulating pronival ramparts (Table 3) sub- mation’ and this is supported by the absence of stantiates this view. In contrast, White (1981: permafrost at several active sites (e.g. Hedding 135) indicates that the study of pronival ram- et al., 2007; Table 3). In addition, Matthews parts enables ‘a series of past episodes of refrig- et al. (2016) note that embryonic rock glaciers eration to be determined in a detail that cannot can develop entirely by permafrost creep be obtained from larger and more bulky mor- without the prior development of a pronival aines’. The existence of relict ramparts is usu- rampart. ally used in conjunction with independent Matthews and Wilson (2015) highlight that information such as glacier reconstructions to the legacy of glaciers, glacier–permafrost inter- infer palaeo-environmental conditions (e.g. action and the specific type of periglacial envi- Grab, 1996). Palaeo-environmental informa- ronment must all be considered when assessing tion can also be derived from estimating ram- the palaeo-environmental and palaeo-climatic part volumes (e.g. Bower, 1998), but the significance of pronival ramparts. For example, growth rate during the formation of a rampart Colucci (2016) notes the importance of the dam- should be considered to be variable in response ming effect of pronival ramparts and moraine to changes in climate and debris supply (Hedding ridges at the snout of small ice bodies, as the et al., 2007). damming effect represents a geomorphological Rampart ridge morphology in the context of control on the evolution (and persistence) of site characteristics (topography) and sedimen- such ice masses in relation to climatic warming. tology may also be of value. Ridge morphology Therefore, in some instances, pronival ramparts coupled with relative-age dating or calibrated- may occur at lower altitudes than might be age dating (see Matthews and Wilson, 2015) of expected and may remain active for longer dur- the constituent material of the rampart can be ing periods of climatic warming. used to infer up- or downslope rampart genesis Pronival ramparts can, under certain climatic and the associated snowbed conditions during conditions, transform into protalus rock glaciers rampart genesis (e.g. Hedding et al., 2007; Hed- (e.g. Corte 1976; Ballantyne and Kirkbride, ding et al., 2010). Several studies (e.g. Mat- 1986) and even moraines (Ballantyne and Benn, thews and Wilson, 2015; Matthews et al., 1994; Van Tatenhove and Dikau, 1990), but this 2011; Matthews et al., 2015; Shakesby et al., is not a ubiquitous occurrence. Hedding et al. 2006) adopt calibrated-age dating techniques (2007) show that pronival ramparts can also to provide a developmental history of ramparts develop under fluctuating, possibly declining, in relation to their surroundings, while other snow falls, while climatic amelioration can also studies use relative-age dating techniques to lead to the incorporation of the ridges within assess rampart genesis (Hedding et al., 2007;
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Hedding et al., 2010). The use of calibration debris production and debris transport affect equations in Schmidt-hammer exposure dating rampart genesis. Advances in the understanding of pronival ramparts, described by Matthews of rampart genesis include the addition of the and Wilson (2015), is an important advance in retrogressive model of rampart genesis (see determining the timing of their development Hedding et al., 2007), which supplements the and use as palaeo-environmental indicators. The conventional downslope model of rampart establishment of a calibration equation quanti- development and the observation that the crests tatively describes the relationship between a of pronival ramparts can migrate downslope mean Schmidt-hammer R-value and rock- under stable snowbed conditions (Hedding surface age (see Matthews and Wilson, 2015). et al., 2010). It requires at least two surfaces of known age Another recent advance is the proposal of a (control points) which are comparable in respect set of diagnostic criteria by Hedding and Sum- of lithology of the rock surfaces being dated ner (2013) and Hedding (2014), which focus on (Matthews and Wilson, 2015). As such, its the characteristics of actively-accumulating application should be considered when studying ramparts and provide the basis to differentiate supposed examples of relict ramparts. Determi- ramparts from other discrete debris accumula- nation of the absolute age of pronival ramparts tions. The set of ‘diagnostic’ criteria proposed is complicated by the absence of datable com- by Hedding and Sumner (2013) place more ponent material within the landform (Anderson emphasis on site and sedimentological rather et al., 2001), but most ramparts are thought to than morphological characteristics and should post-date the Last Glacial Maximum. Grab and be tested on supposed active and relict ramparts. Mills (2011) use radiocarbon dating to deter- In addition, the importance of using a multiple- mine the age of a palaeosol beneath a rampart working hypothesis (see Curry et al., 2001) in Lesotho. They date the palaeosol to AD when distinguishing active (and relict) ramparts 300–1000, which would imply very recent is highlighted. Scappoza (2015) proposes diag- rampart development. However, the pronival nostic criteria to define protalus ramparts ramparts identified by Grab and Mills (2011) (active embryonic protalus rock glaciers), but have been reinterpreted as solifluction lobes the use of the term ‘protalus rampart’ to refer (see Hedding, 2014). to permafrost-related phenomena may be pro- blematic (see Hedding, 2011). The value of ramparts as palaeo-environmen- V Summary and future research tal indicators has, in some instances, been seen Pronival ramparts were initially considered to to be limited (Shakesby, 1997), but the absence represent simple, easily understood landforms or presence of relict pronival ramparts, specifi- (Thorn, 1988), but they are now considered to cally in areas which experienced marginal gla- be more complex landforms (see Hedding, ciations, may be particularly useful in palaeo- 2014). Research shows a variety of debris trans- environmental reconstructions (see Hedding, port mechanisms exist and that the environmen- 2014). Relative-age dating techniques have tal controls under which ramparts develop may been used successfully in research on pronival be more varied than previously thought. Unfor- ramparts (see Hedding et al., 2007; Matthews tunately, this review shows that we still know et al., 2011; Shakesby et al., 2006). The use of relatively little in terms of the debris production relative-age dating techniques will be particu- linked to debris transport and the genesis of larly important for research on rampart genesis; pronival ramparts. This aspect should receive as is demonstrated by Matthews et al. (2011). more attention, particularly in terms of how Also, the use of calibration equations in
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Schmidt-hammer exposure dating, described by and sedimentological characteristics of push Matthews and Wilson (2015), is a significant moraines (see Shakesby et al., 1999). In some step forward for dating landforms, including instances, there is a lack of appreciation in liter- pronival ramparts. Its application when study- ature of just how large the source area (backwall) ing supposed relict examples of pronival ram- must be to facilitate the development of fairly parts may be extremely useful in resolving the small pronival ramparts. Hedding (2014) pro- timing of rampart development and its palaeo- poses that, as a function of debris production, the environmental significance. Anderson et al. ratio of backwall-to-rampart height should (2001) noted that the absence of datable com- exceed 1: 4–5, but this requires further research. ponent material complicates absolute age deter- Rampart morphology should also receive fur- mination of relict ramparts, but it is hoped that ther attention since differing modes of rampart improvements in cosmogenic dating will genesis can result in various rampart morphol- improve to the stage where inheritance (pre- ogies. Therefore, it is worth investigating if exposure) can be eliminated in the dating pro- rampart morphology may represent an expres- cess of depositional landforms (Anderson et al., sion of the environmental conditions under 1996). This is yet another exciting avenue for which they form. However, rampart morphol- research on pronival ramparts. ogy is dependent on the mechanism of debris Use of a combination of techniques such as transport, topographic setting (e.g. underlying ground radar, climate modelling and sedimen- slope gradient), the nature and size of constitu- tology (see Slee, 2015) coupled with relative- ent material and the rate of debris production, age dating or calibrated-age dating could be par- which may explain why rampart morphology ticularly useful when analysing the probable varies so greatly. Superimposition of ramparts mode of origin for pronival ramparts. Several on other talus landforms and post-depositional other techniques adapted from engineering change of relict ramparts also needs to be taken geology could also be particularly useful when into account when assessing the morphology of assessing the genesis of actively-accumulating relict fossil features. Also the possibility of ramparts. For instance, kinematic analyses and ‘form-convergence’ for discrete debris accumu- micro-seismicity could be used to investigate lations, as suggested by Whalley (2009) should debris supply and debris transport, respectively. be considered. Ramparts can accumulate down- Finite elements modelling of the slopes, or use slope of snowbeds which are increasing, stable of terrestrial laser scanning or structure from or decreasing in volume. Ramparts may also motion (SfM) from drones, or satellite imagery develop downslope of snowbeds which fluctu- could be used to map the extent of ramparts and ate in volume throughout the period of debris associated snowbeds (Martin S. Brook, 2016, accumulation. Based on these recent findings, personal communication). questionable examples of ramparts should be Research should focus on mechanisms of reinvestigated and further detailed studies of debris transport and the scale of ramparts in actively-accumulating ramparts may construct relation to the backwall and on the potential of the body of knowledge needed to resolve dis- snow avalanching in the formation of ramparts agreements over the interpretation of land- (see Matthews et al., 2011). Ballantyne (2002) forms; particularly in light of post-depositional doubts the efficacy of snow push as a mechan- changes in morphology. ism for the development of large ramparts, sev- eral metres high, but it is necessary to establish Acknowledgements whether active snowbeds can produce (snow The author wishes to thank Professors Ian Meikle- push) large ramparts or landforms with the scale john, Werner Nel, Kevin Hall and Paul Sumner, in
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 852 Progress in Physical Geography 40(6) particular, for enlightening discussions on the topic. Ballantyne CK and Kirkbride MP (1986) The character- Dr Alastair Curry is also thanked for making some of istics and significance of some late glacial protalus his literature available. Professor John Matthews and ramparts in Upland Britain. Earth Surface Processes Dr Richard Shakesby are thanked for supplying the and Landforms 11: 659–671. photographs of the actively-accumulating ramparts Ballantyne CK and Kirkbride MP (1987) Rockfall activity at Smørbotn and Taskedalen, Norway. The in upland Britain during the Lock Lomond Stadial. reviewers are thanked for greatly improving the Geographical Journal 153: 86–92. quality of the manuscript. Benn DI and Evans DJA (2007) Glaciers and Glaciation. London: Hodder Arnold. Declaration of conflicting interests Bower TM (1998) Fossil pronival (protalus) ramparts on The author(s) declared no potential conflicts of interest Cadair Idris, mid-Wales: a reassessment. MPhil Dis- with respect to the research, authorship and/or publi- sertation, University of Wales Swansea, UK. cation of this article. Brook MS (2009) Glaciation of Mt Allen, Stewart Island (Rakiura): the southern margin of LGM in New Funding Zealand. Geografiska Annaler: Series A, Physical Geography 91: 71–81. The author(s) disclosed receipt of the following Brook MS and Williams J (2013) A relict pronival (protalus) financial support for the research, authorship, and/ rampart in the Tararua Range, North Island, New Zeal- or publication of this article: This work is published and. Permafrost and Periglacial Processes 24: 67–74. under the NRF/SANAP project: Landscape and cli- Brook MS, Neall VE, Stewart RB, et al. (2011) Recogni- mate interactions in a changing sub-Antarctic envi- tion and paleoclimatic implications of late Holocene ronment (grant number 93075). glaciation on Mt Taranaki, North Island, New Zealand. The Holocene 21: 1151–1158. References Colucci RR (2016) Geomorphic influence on small glacier Anderson E, Harrison S and Passmore D (2001) A late- response to post-Little Ice Age climate warming: Julian glacial protalus rampart in MacGillycuddy’s Reeks, Alps, Europe. Earth Surface Processes and Landforms south-west Ireland. Irish Journal of Earth Sciences 19: 41: 1227–1240. 43–50. Colucci RR, Boccali C, Zˇ ebre M, et al. (2016) Rock gla- Anderson RS, Repka JL and Dick GS (1996) Explicit ciers, protalus ramparts and pronival ramparts in the treatment of inheritance in dating depositional surfaces south-eastern Alps. Geomorphology 269: 112–121. 10 26 using in situ Be and Al. Geology 24: 47–51. Corte AE (1976) Rock glaciers. Biuletyn Peryglacjalny 26: Andre´M-F (1997) Holocene rockwall retreat in Svalbard: 175–195. a triple-rate evaluation. Earth Surface Processes and Curry AM and Morris CJ (2004) Lateglacial and Holocene Landforms 22: 423–440. talus slope development and rockwall retreat on Ballantyne CK (1987) Some observations on the mor- Mynydd Du, UK. Geomorphology 58: 85–106. phology and sedimentology of two active protalus Curry AM, Walden J and Cheshire A (2001) The Nant ramparts, Lyngen, northern Norway. Arctic and Alpine Ffrancon ‘protalus rampart’: evidence for Late Pleis- Research 19: 167–174. tocene paraglacial landsliding in Snowdonia, Wales. Ballantyne CK (2002) The Conachair Protalus Rampart, St Proceedings of the Geologists’ Association 112: Kilda. Scottish Geographical Journal 118: 343–350. 317–330. Ballantyne CK and Benn DI (1994) Glaciological con- Drew F (1873) Alluvial and lacustrine deposits and glacial straints on protalus rampart development. Permafrost records of the Upper-Indus Basin. Quarterly Journal of and Periglacial Processes 5: 145–153. the Geological Society of London 29: 441–471. Ballantyne CK and Eckford JD (1984) Characteristics and French HM (2007) The Periglacial Environment. 3rd ed. evolution of two relict talus slopes in Scotland. Scottish Chichester: John Wiley & Sons. Geographical Magazine 100: 20–33. Fukui K (2003) Permafrost and surface movement of an Ballantyne CK and Harris C (1994) The Periglaciation active protalus rampart in Kuranosuke Cirque, the of Great Britain. Cambridge: Cambridge University northern Japanese Alps. In: Phillips M, Springman S Press.
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 Hedding 853
and Arenson LU (eds) Permafrost. Lisse: Swets & Hedding DW (2016) Pronival ramparts: origin and Zeitlinger, 265–270. development of terminology. Erdkunde 70: 141–151. Fukui K and Iwata S (2000) Result of permafrost investi- Hedding DW and Sumner PD (2013) Diagnostic criteria gation in Kuranosuke cirque, Tateyama, the Japanese for pronival ramparts: site, morphological and sedi- Alps. Seppyo 62: 23–28. mentological characteristics. Geografiska Annaler: Glowicki B (1997) Wieloletnia seria pomiaro´w tempera- Series A, Physical Geography 95: 315–322. tury powietrza na S´niezˇke. In Sarosiek J and Sˇtursa J Hedding DW, Meiklejohn KI, Le Roux JJ, et al. (2010) (eds) Geoekologiczne problemy Karkonoszy. Wroclaw: Some observations on the formation of an active pro- KRNAP and KPN, 117–125. nival rampart at Grunehogna Peaks, Western Dronning Gordon LS and Ballantyne CK (2006) ‘Protalus Ramparts’ Maud Land, Antarctica. Permafrost and Periglacial on Navajo Mountain, Utah, USA: reinterpretation as Processes 21: 355–361. blockslope-sourced rock glaciers. Permafrost and Hedding DW, Sumner PD, Holness SD, et al. (2007) Periglacial Processes 17: 179–187. Formation of a pronival rampart on sub-Antarctic Goudie A, Atkinson BW, Gregory KJ, et al. (1994) The Marion Island. Antarctic Science 19: 443–450. Encyclopaedic Dictionary of Physical Geography. 2nd Hinchliffe S and Ballantyne CK (1999) Talus accu- ed. Oxford: Blackwell. mulation and rockwall retreat, Trotternish, Isle of Grab S (1996) The occurrence of a Holocene rock glacier Skye, Scotland. Scottish Geographical Journal 115: on Mount Kenya: some observations and comments. 53–70. Permafrost and Periglacial Processes 7: 381–389. Howe E (1909) Landslides in the San Juan Mountains, Grab S and Mills S (2011) Quaternary slope processes and Colorado. US Geological Survey Professional Paper morphologies in the upper Sehonghong Valley, eastern 67. Washington DC: US Government Printing Office. Lesotho. Proceedings of the Geologists’ Association Jarman D, Wilson P and Harrison S (2013) Are there any 122: 179–186. relict rock glaciers in the British mountains? Journal of Grab S, Mills SC and Carr SJ (2012) Periglacial and Quaternary Science 28: 131–143. glacial geomorphology. In: Holmes P and Meadows Johnson PG (1983) Rock glaciers: a case for change in M(eds)Southern African Geomorphology: Recent nomenclature. Geografiska Annaler: Series A, Physical Trends and New Direction. Bloemfontein: Sun Press, Geography 65: 27–34. 233–265. Kirkbride MP (2016) A snow-push mechanism for ridge Hall K and Meiklejohn KI (1997) Some observations formation in the Cairngorm Mountains, Scotland. regarding protalus ramparts. Permafrost and Perigla- Scottish Geographical Journal 132: 66–73. cial Processes 8: 245–249. Krautblatter M and Dikau R (2007) Towards a uniform Harris C (1974) Autumn, winter and spring soil tempera- concept for the comparison and extrapolation of rock- tures in Okstindan, Norway. Journal of Glaciology 13: wall retreat and rockfall supply. Geografiska Annaler: 521–533. Series A, Physical Geography 89: 21–40. Harris C (1986) Some observations concerning the mor- Krautblatter M and Moser M (2009) A nonlinear model phology and sedimentology of a protalus rampart, coupling rockfall and rainfall intensity based on a four Okstindan, Norway. Earth Surface Processes and year measurement in a high Alpine rock wall (Reintal, Landforms 11: 673–676. German Alps). Natural Hazards and Earth System Harris T, Tweed FS and Knudsen O´ (2004) A polygenetic Sciences 9: 1425–1432. landform at Stı´ga´O¨ ræfajo¨kull, southern Iceland. Geo- Lewis CA (1994) Protalus ramparts and the altitudinal line grafiska Annaler: Series A, Physical Geography 86: during the last glacial stage in Bokspruit, East Cape 143–154. Drakensberg, South Africa. Geografiska Annaler: Hedding DW (2011) Pronival rampart and protalus ram- Series A, Physical Geography 76: 37–48. part: a review of terminology. Journal of Glaciology Lewis CA and Illgner PM (2001) Late Quaternary gla- 57: 1179–1180. ciation in southern Africa: moraine ridges and glacial Hedding DW (2014) On the identification, genesis and deposits at Mount Enterprise in the Drakensberg of the palaeo-environmental significance of pronival ram- Eastern Cape Province, South Africa. Journal of Qua- parts. PhD Thesis, University of Pretoria, South Africa. ternary Science 16: 365–374.
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 854 Progress in Physical Geography 40(6)
Lewis WV (1939) Snowpatch erosion in Iceland. Geo- Pancza A (1998) Les Bourrelets-Protalus: Liens entre les graphical Journal 94: 151–161. Eboulis et les Glaciers Rocheux. Permafrost and Luckman BH (2013) Processes, transport, deposition and Periglacial Processes 9: 167–175. landforms: rockfall. In: Shroder J, Marston RA and Pe´rez FL (1988) Debris transport over snow surfaces: a Stoffel M (eds) Treatise on Geomorphology. San field experiment. Revue de Ge´omorphologie Dynami- Diego, CA: Academic Press, 174–182. que 37: 81–101. Lukas S (2006) Morphostratigraphic principles in gla- Porter SC (1987) Early descriptions of pro-talus ramparts. cier reconstruction: a perspective from the British Journal of Glaciology 33: 247–248. Younger Dryas. Progress in Physical Geography 30: Rapp A (1984) Nivation hollows and glacial cirques in 719–736. Soderasen, Scania, South Sweden. Geografiska Margold M, Treml V, Petr L, et al. (2011) Snowpatch Annaler: Series A, Physical Geography 66: 11–28. hollows and pronival ramparts in the Krkonosˇe Sattler K, Keiler M, Zischg A, et al. (2011) On the con- Mountains, Czech Republic: distribution, morphology nection between debris flow activity and permafrost and chronology of formation. Geografiska Annaler: degradation: a case study from the Schnalstal, South Series A, Physical Geography 93: 137–150. Tyrolean Alps, Italy. Permafrost and Periglacial Pro- Marr JE (1916) The Geology of the Lake District. Cam- cesses 22: 254–265. bridge: Cambridge University Press. Scappoza C (2015) Investigation on protalus ramparts Matsuoka N (2001) Direct observation of frost wedging in in the Swiss Alps. Geographica Helvetica 70: alpine bedrock. Earth Surface Processes and Land- 135–139. forms 26: 601–614. Scappoza C, Lambiel C, Baron L, et al. (2011) Internal Matsuoka N and Sakai H (1999) Rockfall activity from an structure and permafrost distribution in two alpine alpine cliff during thawing periods. Geomorphology periglacial talus slopes, Valais, Swiss Alps. Geomor- 28: 309–328. phology 132: 208–221. Matthews JA and Wilson P (2015) Improved Schmidt- Sekine K (1973) Mechanism of the formation if a protalus hammer exposure ages for active and relict pronival rampart at the bottom of the so-called Kuranosuke ramparts in southern Norway, and their palaeoenvir- Glacial Cirque, Japanese Alps. Geographical Review of onmental implications. Geomorphology 246: 7–21. Japan 46: 264–274. Matthews JA, McEwen LJ and Owen G (2015) Schmidt- Shakesby RA (1997) Pronival (protalus) ramparts: a hammer exposure-age dating (SHD) of snow- review of forms, processes, diagnostic criteria and avalanche impact ramparts in southern Norway: palaeo-environmental implications. Progress in Phys- approaches, results and implications for landform age, ical Geography 21: 394–418. dynamics and development. Earth Surface Processes Shakesby RA (2004) Protalus ramparts. In: Goudie A (ed.) and Landforms 40: 1705–1718. Encyclopedia of Geomorphology. London: Routledge, Matthews JA, Wilson P and Mourne RW (2016) Landform 813–814. transitions from pronival ramparts to moraines and rock Shakesby RA, Dawson AG and Matthews JA (1987) Rock glaciers: a case study from the Smørbotn cirque, glaciers, protalus ramparts and related phenomena, Romsdalsalpene, southern Norway. Geografiska Rondane, Norway: a continuum of large-scale talus- Annaler: Series A, Physical Geography. doi: 10.1080/ derived landforms. Boreas 16: 305–317. 04353676.2016.1256582. Shakesby RA and Matthews JA (1993) Loch Lomond Matthews JA, Shakesby R, Owen G, et al. (2011) Pronival Stadial glacier at Fan Hir, Mynydd Du (Brecon rampartformationinrelationtosnow-avalanche Beacons), south Wales: critical evidence and activity and Schmidt-hammer exposure-age dating palaeoclimatic implications. Geological Journal 28: (SHD): three case studies from southern Norway. 69–79. Geomorphology 130: 280–288. Shakesby RA, Matthews JA and McCarroll D (1995) Ono Y and Watanabe T (1986) A protalus rampart related Pronival (‘protalus’) ramparts in the Romsdalsalpane, to alpine debris flows in the Kuranosuke Cirque, southern Norway: forms, terms, subnival processes and northern Japanese Alps. Geografiska Annaler: Series alternative mechanisms of formation. Arctic and Alpine A, Physical Geography 86: 213–223. Research 27: 271–282.
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016 Hedding 855
Shakesby RA, Matthews JA, McEwen LJ, et al. (1999) Van Tatenhove F and Dikau R (1990) Past and Snow-push processes in pronival (protalus) rampart present permafrost distribution in the Turtmanntal, formation: geomorphological evidence from Smør- Wallis, Swiss Alps. Arctic and Alpine Research 22: botn, Romsdalsalpane, southern Norway. Geografiska 302–316. Annaler: Series A, Physical Geography 81: 31–45. Ward C (1873) The glaciations of the northern part of the Shakesby RA, Matthews JA and Owen G (2006) The Lake District. Quarterly Journal of the Geological Schmidt hammer as a relative-age dating tool and its Society London 29: 422–441. potential for calibrated-age dating in Holocene gla- Watson E (1966) Two nivation cirques near Aberystwyth, ciated environments. Quaternary Science Reviews 25: Wales. Biuletyn Peryglacjalny 15: 79–101. 2846–2867. Whalley WB (2009) On the interpretation of discrete Slee AJ (2015) The distribution and paleoclimate debris accumulations associated with glaciers with implications of periglacial landforms in eastern special reference to the British Isles. In: Knight J and Australia. PhD thesis, University of Queensland, Harrison S (eds) Periglacial and Paraglacial Processes Australia. and Environments. Special Publications 320. London: Sissons JB (1979) The Loch Lomond Advance in the The Geological Society, 85–102. Cairngorm Mountains. Scottish Geographical Maga- Whalley WB (2015) Protalus features. In: Hargitai H and zine 95: 66–82. Kereszturi A´ (eds) Encyclopedia of Planetary Forms. Spusta V, Spusta V Jr, and Kocia´nova´M (2003) Ukla´da´nı´ London: Springer, pp. 1653–1657. sneˆhuna za´veˆtrny´ch svazı´ch cˇeske´ strany Krkonosˇ White SE (1981) Alpine mass-movement forms (non- (tundrova´cˇa´st). Opera Corcontica 40: 87–104. catastrophic): classification, description and sig- Strelin JA and Sone T (1998) Rock glaciers on James Ross nificance. Arctic and Alpine Research 13: 127–137. Island, Antarctica. In: Lewkowicz AG and Allard M White SE (1987) Differential movement across trans- (eds) Permafrost: Seventh international conference verse ridges on Arapaho rock glacier, Colorado Front proceedings. Yellowknife: Collection Nordicana, Range, USA. In: Giardino JR, Shroder JF and Vitek 1027–1033. JD (eds) Rock Glaciers. Boston, MA: Allen and Thorn CE (1978) The geomorphic role of snow. Annals Unwin, 145–149. of the Association of American Geographers 68: Wilson P (1990) Characteristics and significance of pro- 414–425. talus ramparts and fossil rock glaciers on Errigal Thorn CE (1988) Nivation: a geomorphic chimera. In: Mountain, County Donegal. Proceedings of the Royal Clark MJ (ed.) Advances in Periglacial Geomorphol- Irish Academy 90B: 1–21. ogy. New York: John Wiley & Sons, 3–31. Wilson P and Clark R (1999) Further glacier and snowbed Trombotto D (2000) Survey of cryogenic processes, sites of inferred Lock Lomond Stadial age in the periglacial forms and permafrost conditions in northern Lake District, England. Proceedings of the South America. Revista do Instituto Geolo´gico 21: Geologists’ Association 110: 321–331. 33–55. Worsley P and Harris C (1974) Evidence for neoglacial Unwin DJ (1975) The nature and origin of the corrie solifluction at Okstindan, North Norway. Arctic 27: moraines of Snowdonia. Cambria 2: 20–33. 128–144.
Downloaded from ppg.sagepub.com at UNISA Univ of South Africa on November 29, 2016