Rock Glaciers, Protalus Ramparts and Related Phenomena, Rondane, Norway: a Continuum of Large- Scale Talus-Derived Landforms
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Rock glaciers, protalus ramparts and related phenomena, Rondane, Norway: a continuum of large- scale talus-derived landforms RICHARD A. SHAKESBY, ALASTAIR G. DAWSON AND JOHN A. MATTHEWS Shakesby, Richard A,, Dawson, Alastair G. & Matthews. John A. 1987 09 01: Rock glaciers. protalus BOB ramparts and related phenomena, Rondane, Norway: a continuum of large-scale talus-dcrivcd landforms. Boreas. Vol. 16, pp. 305-317. Oslo. ISSN0300-9483. Talus-derived landforms from Rondanc National Park, southern Norway, arc described and classified as protalus ramparts, valley-floor and valley-side talus-foot rock glaciers. and a ‘push-deformation’ mor;uiic A morphological and developmental continuum of talus and derivative large-scale landforms is proposed. with simple talus slopes at one end and more complex ridge, lobe and hcnch forms at the other. The various types of feature probably develop from simple talus slopes via separate dcvclopmentel route$, rather than as a linear sequence. Lichen size and Schmidt hammer R-values were used to indicatc thc relative ages of the features. Although all are thought to have originated during the early Holocene. thcy differ in the presence or extent of recent activity. Hence an age and activity continuum is also suggested. the recency of activity increasing in the direction protalus rampart + rock glacier + ‘push-deformation’ morainc. Richard A. Shakesby. Department of Geography, Unioersity College of Swunseu. Singleton Purk. Swunsrci SA2 8PP, U.K.; Alastair G. Duwson, Departmentof Geography. Lanchester (Coventry) Po/vlechnic, Priory Street, Cooeiitry CVl 5FB, U.K.; John A. Matthews, Sub-Department of Geogruphy. Lkpartrnent of Geology. Uniuersity College Cardiff, P.O. Box 78, Cardiff CFI IXL, U.K.; 27th January, 1987. During the last two decades, interest in rock lack of vegetation on the front slope (Wahrhaftig & glaciers, protalus ramparts and related landforms Cox 1959; Barsch 1977), and fresh breaks in the has increased markedly, but our understanding surface (Foster & Holmes 1965). Supposed indi- remains limited. Rock glaciers in particular have cators of inactivity have ranged from low-angle attracted increased attention but disagreement boundary slopes, presence of collapse structures continues about their definition and classification (Barsch & Treter 1976; Sissons 1976), large lichens (cf. 0strem 1971; Johnson 1973; Barsch 1971, (Luckman & Crockett 1978), continuity of lichen 1977; Whalley 1979) and about their origin and cover (Wahrhaftig & Cox 1959) to a well-estab- sensitivity to environmental change (e.g. Swett et lished soil and vegetation cover (Barsch & Treter al. 1980; Humlum 1982; Giardino 1983). For the 1976). purposes of this study talus-foot or lobate rock gla- Protalus ramparts also present problems of ciers are defined as being broader than they are definition and origin. They are generally assumed long and composed of deformed talus developed to form by debris sliding over the snow and along valley walls below cliffs. Various theories accumulating at the foot of a perennial snowbank have been proposed to explain their movement (Richmond 1962), but this remains unsubstanti- down valley sides and onto valley floors, including ated by field observation (Johnson 1983) and simi- creep of an ice core or of interstitial ice, or basal larities or connections have been proposed in the shearing which may be aided by hydrostatic pres- development of protalus ramparts and rock gla- sure or by pore water trapped beneath a frozen ciers (Grotzbach 1965; CortC 1976; Sissons 1976; veneer (Giardino 1983; Giardino & Vick 1985). A Ballantyne & Kirkbride 1987). range of indicators of activity and inactivity of rock With a few exceptions (e.g. Griffey & Whalley glaciers has been proposed. Indicators of activity 1979; Matthews & Petch 1982; Lindner & Marks have included the presence of an ice core (CortC 1985;Vere & Matthews 1985), little is known about 1976), the considerable thickness of a feature, the rock glaciers and related forms in Scandinavia. presence of steep boundary slopes with sharp This was emphasized by the debate on ice-cored breaks of slope, the existence of fine material or the moraines between astrem (1971) and Barsch 306 Richurd A. Shmkesby ef UI BOKEAS 16 (1987) 11971). in Rondane, StrOm (1945) described sheet, giving rise on deglaciation to extensive 'debris ledges' formed in a similar manner to that fluvioglacial deposits in the valley bottoms ofDor%- assumed for protalus ramparts while Barsch & Tre- len and its tributaries. ter (1976) used mainlv aerial photographs to iden- The area comprises mainly an arkosic sandstone tify fourteen rock glaciers. We present here the known as sparagmite. The combination of steep results of a more detailed investigation carried out vallev sides. well-jointed rock. freeze-thaw con- in Rondane of five landforms identified as active ditions and low stream activity in the upper valleys rock glaciers and one as inactive according to these has led to talus-covered lower slopes and block- authors. together with an additional three land- field-covered floors. The features on which this forms. Emphasis is given to the morphology. age study focuses are located in the valleys of Lang- and activity of these features with special ref- holet, Smedbotn and Bergedalen at altitudes of erence to their classification, development and c. [email protected] m (Fig. 1). interrelationships. Morphology Background Selected long profiles for the features were deter- The central massif of Rondane National Park is a mined using an Abney level and 30 ni tape. Read- mountain range of some 200 km- with a number of ings were recorded to marked breaks of slope or peaks exceeding 2.000m and a highest point of to 30 111 ground lengths (Fig. 2). All features are 2.178 m (Rondslottet) (Fig. 1). The mean annual characterized by angular blocks up to about 6 m temperature is(. -5°C at 1.500 m and mean annual in size. Morphological details of each feature are precipitation amounts to about 460 mm (Dahl given in Table I, 1956). Glacier ice is absent except for a possible residual patch in Smedbotn. According to Sollid s( Lairgltolr,f.-Four landforms along the W slope of Reite (1983:50). the last ice sheet covered Ron- Langholet valley were studied (Fig. 1; Table 1). ciane up to c. I .XU0 m in the Preboreal Chrono- Langholet I has a crtnulate plan form partly Lone. At that time local cirque glaciers occupying obscured by snow when measured. Langholet 11, the higher i,allrys converged with the main ice I11 and IV have not been previously referred to in big. 1. Location of talus-dcrivcd A ROCK glocierorreioted landform Londrltde Loke 8 rlvei landtotin5 in Rondane. central southern Norway. Table 1. Characteristics and classificatioii of talus-derived landforms, Rondanc. Distal slope Max. Max. Altitude length Breadth talus slopt Overall angle Max. angle Morphological Feature Aspect (m) (n1) (m) angle (“) (“1 (“1 characteristics CI a s si fi c a tion Langholet I ENE 1,580 230 550 31 29 36 2 ridges Talus-foot rock glacier Langholct 11 E I .52(J 6 280 35 33 34 1 ridge Piotalus rampart Langholet 111 E 1,480 56 590 34 25 35 2 ridges Protalus rampart Langholet 1V NE 1,480 23 305 31 31 31 1 ridge Protalus rampart Smedbotn I N 1,600 350 580 34 25 41 Multiple ridges Push-deformation moraine Smedbotn I1 W 1.580 180 420 33 41 54 Bench + Talus-foot surface ridges rock glacier Rondslottet N 1,520 230 750 34 31 50 Bench + lobes Talus-foot rock glacier Midtrondcn SW 1,540 190 i,m 38 34 43 Bench, lobes Talus-foot + surface ridges rock glacier Vcrkilsdalcn NW 1.30(1 1,600 750 ~ - - Lohate ridge Landslide complex Note: Altitude = aititudc of toe. Maximum length = niax. length trom the talus foot mcasurcd to the outer ridge/bench crcst. Full details on the Verkiladalen feature are given in Dawaon ef a[. 1986. 308 Richard A. Shukesby et al. BOREAS 16 (1987) 100 No exaggeratlon lk ........ 50 1. ..........................................* .......................:.:.: .:_: ....... ..... -LET .:_ ........ I Snow........... .....:.:.: .... I Talus ’ LANGHOLET I1 0 I I I I 0 100 200 300 In metres :100 +.a +.a al E 1 50 Degraded ridges 0 0 100 200 300 metre8 250 200 R - Ridge feature 150 Vertlcal exaggeration :v) - 100 E 50 I-- Distal slope ---; 0 I 1 I 0 200 400 600 metres BOREAS 16 (1987) Talus-derived landforms 309 Table2. Lichen size data for the talus-derived landforms in Ron- the literature. They consist of well-defined single dane. Result,aregivenforthediameter(mm) ofthesinglelargest or double ridges (Fig. 3). (1.1) and the mean diameter of the five largest (5.1) lichens in 250 m2search areas Smedbotn. - Two landforms were investigated in Location 1.1 5.1 Smedbotn (Fig. 1).Smedbotn Iforms alarge, high, arcuate, multiple-ridged structure enclosing a Smedboin I deep hollow near the valley headwall (Fig. SC). Outside 270 25 1 Proximal slope angles range from 8" to 48" with an Ridge 1 235 206 Ridge 2 225 212 overallangleof24". SmedbotnII, locatedc. 0.5 km Ridge 5 260 222 downvalley from Smedbotn I (Fig. l), comprises a Ridge 6 235 220 broad, undulating bench at its Send from where it Ridge 7 180 158 narrows northwards to form two ridges (Fig. 2). Ridge 8 115 100 Ridge 9 95 95 Proximal slope Bergedaien. - Two Iandforms were analysed in (top) 93 79 Bergedalen (Fig. 1). The Rondslottet feature is an Proximal slope 65 55 arcuate bench, ridge and lobe complex below the Smedbotn I1 N-facing spur of Rondslottet peak (Fig. 4). At its Outside 265 232 S end, it forms a narrow bench emanating from an Outer ridge 370 280 area of two small, ill-defined lobes (Fig. 2). Below Inner ridge 325 274 the bench, the valley floor comprises up to three Langholet I low, ill-defined ridges (<3 m high) paralleling the Outside 285 216 Outcr ridge 250 226 bench.