THE CONTRIBUTION OF DISCONTINUOUS ROCK-MASS ......Second, melt water at the ice-rock mass contact...

Annals of Glaciology 2 1981© International Glaciological Society

THE CONTRIBUTION OF DISCONTINUOUS

ROCK-MASS FAILURE TO GLACIER EROSION

byKen Addison

(The Polytechnic, Wolverhampton WV1 1LY, and St Peter's College, Oxford OX1 2DL, England)

PRINCIPAL GEOMECHANICAL ROCK-MASS PROPERTIESA major problem in assessing the erodibility

of rock stems from the gross inequality betweenthe internal shear strength of rock and glacierice; this, is partially resolved for abrasion byregarding the glacier sole as an ice-rock-debrismix, but large-scale block removal or "quarrying"is not so effectively explained.Intact rock-mass strength (IRMS)

The failure criteria for rock is usuallydefined by a simple linear Mohr-Coulomb equation(Fig.l):

by freeze-thaw loosening (Jahns 1943, Lewis1954, Chapman and Rioux 1958, Battey 1960,Whi11ans 1978). Although the age, formation,and significance of the resultant sheetingstructures (supposedly formed irrespective ofany existing anisotropy) are sometimes qualified,preoccupation with "pressure release" demonstra-tes a simplistic and frequently inaccurate viewof rock-mass properties and response to stress,as other authors have indicated (Harland 1957,Twidale 1972, 1973, Brunner and Scheidegger 1973).Occasionally, absence of serious attention torock-mass performance under stress has led tomany omissions. The "melt-water hypothesis" ofcirque erosion (Lewis 1938, 1940) is one clearexample, where the effect of water pressure onstability is ignored, often despite substantialevidence of its abundant presence in rock mass;another is the notable avoidance of suggestedfailure mechanisms in studies which otherwisedemonstrate intimate structural control overerosion (Haynes 1968, Sugden 1974).

Bedrock performance has been examined inmore detail recently. Broster and others (1979)give qualified support to the fracture of intactrock by glacier ice; this is questioned later inthis paper. Although primarily not investigatingnor modelling rock properties, Morland andBoulton (1975), Morland and Morris (1977), andBoulton (1979) consider that a jointed bedrockmodel responding to basal ice shear would bemore appropriate. Up to now, studies of bedrockresponse to specific stress conditions inducedby glacier ice lack an understanding of theprinciples of rock mechanics and resultingfailure mechanisms. Those principles consideredby the present ai/thor to be important win nowbe outl ined.

ABSTRACTGeomechanica1 rock-mass properties control

the response of bedrock to applied stresses andcan be summarized in a linear Mohr-Coulombequation, which defines the principal parametersdetermining failure. Nevertheless, in studyingthe erosion of bedrock by glacier ice, littleattention has been paid to failure criteriaalthough a coincidence of erosional landformswith fracture systems at regional and localscales has been demonstrated. Few studies haveanalysed the precise nature of the fracturegeometry, or proposed its mechanical impact inassociation with glacier ice.

This investigation proposes that, sincealmost all bedrock possesses identifiablefracture systems, the properties of discontinuousrock mass (ORM) be regarded as defining primaryconditions of stress and stability which aresubsequently modified directly and indirectly byglacier ice. Consequent rock-mass failure modesare prescribed by discontinuity geometry andapplied stresses, and evidence from North Walesconfirms the validity of the theoretical treat-ment of rock-mass properties, and explains theaccordance of landforms with structure.INTROOUCTI ON

Glacier erosion of hard rock is a complexprocess controlled by material properties inter-'acting at what Weertman (1979) termed the bed-water-ice interface. Bedrock propertiesdetermine exclusively the first of thesecomponents and hydraulic conductivity influencesthe second. Although many ice-flow problems havebeen resolved, rock-mass performance under stressbeneath and adjacent to glaciers has receivedlittle attention, although the extent to whichthe close control on 91acier erosion exerted bygeological structure has been recognized,especially by geomorpho10gists. Randall (1961),Ho1tedahl (1967), and Nilsen (1973) consideredthat large-scale fractures or joints ofCaledonian age determined fjord and otherglacially-eroded valley ali9nment in Norway;Trainer (1973) described incipient joints openedby ice flow in a wide range of rock from Cali-fornia, Maine, and New York State, and Zumberge(1955) demonstrated structurally-aligned glacierscouring around western Lake Superior. In allcases, structural elements involved are clearlyof pre-glacial tectonic origin, whereasrelaxation of overburden-confining stresses wasbelieved by some authors to cause rock fractureimmediately preceding or during glaciation, andhence to facil itate "quarrying", often enhanced

T = c + a tan ~ ,where '[ and a are shear and normal stresses,respectively, c is the value for internal

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Addison: Contribution of rock-mass failure to glacier erosion

the failure criteria are for dry rock and afurther significant modification afforded bydiscontinuous rock mass (DRM) is high secondarypermeability (Witherspoon and Gale 1977). Aswell as contributing to shear stress, waterreduces normal stress 0 to effective normalstress On by a value u (Hoek and Bray 1974), andfor practical purposes the modified Mohr-Coulombequation may be written as

'[ = c + (0 - u) tan (~ + ~f) , (2)or, in a simplified form, as

where ~r is the effective friction angle.Roughness increases the friction angle ~ by anamount ~f, and the plane possesses, morecorrectly, bi-linear shear strength, whichassumes the lower (residual) value upon shearingof asperities (Witherspoon and Gale 1977).

In practice, all rock mass possessesinternal fractures which normally demonstrate astrongly preferred geometry, determined by geo-logical (principally tectonic) history (Attewelland Farmer 1976). Marked planar anisotropyrenders DRM liable to simple failure in a co-axial stress field and to complex failure,involving multiple planes, elsewhere. Compoundfailure along discontinuities and cracks propa-gated across rock bridges was reported in labora-tory tests (Brown 1970). Brown also suggestedthat discontinuous rock-mass failure (DRMF) only

IT

(f----

Fig.l. Linear Mohr-Coulomb relationshipsbetween shear stress and normal stress forintact rock mass (IRM); the progressivereduction in required shear stress is shownfor dry discontinuous rock mass (DRMd) whereC = 0, and wetted discontinuous rock mass(DRMw), where a given friction angle ~ isreduced to an effective friction angle ~r.

cohesion, and ~ is the angle of friction alongthe eventual failure plane (Hoek 1970). Adistinction is made between peak shear strength,beyond which the rock deforms, and the residualshear strength of the deformed mass. These maybe similar for soft rock, whereas residualstrength may be as little as half the peakstrength for hard igneous rock (Hoek and Bray1974). Typical intact rock shear strengths andother properties are shown in Table I.

'[ = c + 0- tan ~ ,n r (3)

TABLE 1. SOME TYPICAL ROCK-MASS PROPERTIES (after Hoek and Bray (1974), Kulhawy (1975), among others)Uni-axial Friction angle ~ Residual friction Cohesion C

compressive strength (tri-axial load) angle


FAILURE MODES

Plane failure (of single or multiple slabs)occurs when

Fig.2. Failure modes and their related discontin-uity stereonet (equatorial equal-area lowerhemisphere projection).

of gravity overhangs a pivot point (de Freitasand Watters 1973).

It is emphasized that, although actual slopestability may be complex, practical applicationof theoretical analysis is generally successful(Hoek 1973). Also, whilst its primary applica-tion is for gravitational loading, an extensionof principles to dynamic glacier loading may beappropriate and theoretical modifications tostress relationships induced by glacier ice arenow proposed.

o/s < o/d,i Z ~ . (9)STRESS MODIFICATIONS BY GLACIER ICE

A glacier must activate inherent rock-massinstability for erosion to occur (Terzaghi 1962);this investigation restricts itself to suggestedde-stabilizing processes and not to the necessaryresultant entrainment or incorporation with theglacier. Two quite different domains are recog-nized; (i) rock mass confined by ice and underdynamic load, and (ii) rock mass unconfined andprimarily loaded by gravity.Rock mass confined by ice

This is the more difficult to analysebecause of the relative inaccessibility of theice-rock contact, and also because DRM isinherently stable in its primary valley-floorposition. Equations (7) and (8) do not apply,and discontinuity-stress relationships show

Although gravitational load does not meet limit-ing equilibrium requirements, two factorsincrease shear stress. First, ice flow generatesa low-magnitude shear stress of about 0.1 MN m-2(Weertman 1979) enhanced for an ice-rock mix.Second, melt water at the ice-rock mass contactpenetrates discontinuities, contributing a forceV and reducing normal stress by a value u(Equation 6). However, it is recognized that acomplex feedback relationship exists here,whereby secondary penneability afforded by DRMmay alter critically the basal pressure-meltingbalance. Two further qualifications are made tothis domain. Once begun, block removal permitt-ing low-angled planes to "daylight", and alsoremoving the restraining presence of the block,may reduce sliding resistance sufficiently underdynamic load, where o/d j


*To be published as "The instability of chalkslopes".

fracture geometry (Fig.4). In both cases,structurally controlled DRMF beneath and adjacentto the glacier bed is believed to have been theprincipal mechanism of excavation.

Fig.3. Frequency orientation diagrams of regionalfracture systems for each of the six mountaingroups of Snowdonia, mapped from stereographicair photograph cover. Circular scale shows 5 km.Inset outline shows location of Figure 4.

REGIONAL STRUCTURALDISCONTINUITIES

5'

? ~ ~ 'kmIT""TI mileso 1 2 3

FIELD EVIDENCE OF GLACIER-INDUCED DISCONTINUOUSROCK-MASS FAILURE

A combination of inferred and calculatedconditions identifies failure in a previously-glaciated environment. The difficulties ofobserving rock-mass failure and erosion aroundexisting glacie~s, especially under the ice,justify the study of failure at previouslyglaciated sites (where a comprehensive survey ofthe fracture systems is possible), provided thatthe evidence for a glacial origin of failure isconvincing. Location and mode of failure iseasily recognized by residual rock-wall elementsrepresenting the release surfaces, block debriswhere present, and visual comparisons of theslope and discontinuity geometries (de Freitasand Watters 1973, Addison, unpublished, Causayand Farrar, in preparation*). Detailed confir-mation may be calculated from measurement of thediscontinuity geometry (Silveira and others 1966,Young and Fowell 1978) with typical values .ofgeomechanical properties, or specific valuesobtained from in situ and laboratory tests, and

the back-wall zone of cirque glaciers must beconsidered to make a major contribution to DRMFwithout recourse to freeze-thaw mechanisms.

Again, further qualifications may be madewith respect to the destabilizing mechanism.(i) Unconfined failure can only apply toglaciers confined within bedrock channels,limiting the mechanism almost entirely to valleyand cirque glaciers, and thus accounting in partfor their significantly greater erosive power.(ii) Once initiated, progressive failure iscontrolled primarily by the DRM geometry; unlikeengineering applications, where the requiredslope and discontinuity geometries mayor maynot coincide favourably, it is suggested thatglacier erosion will always show close conforma-tion. Principal applied stress will seek outthe most closely related potential failure planes,and hence structure controls glacier erosion.

Geomechanical principles, modified for theglacier environment, are now investigated forapplication to glacier-eroded rock mass in Snow-donia, North Wales, after reviewing the generalstructural geology of the region.

STRUCTURAL GEOLOGY OF SNOWDONIA, NORTH WALESClastic marine sediments, progressively

interstratified with ignimbrites and laterintruded by dolerites, rhyolites, and microgran-ites, form a lmost all of the 1 200 km2 study area,and represent a complex Lower Palaeozoic (lateCambrian to late Ordovician) synclinal accumula-tion whose axis forms the mountain core above1 000 m.

The pile was subjected to pronounced poly-phase deformation of Caledonian tectonic origin(late Silurian-early Devonian (Shackleton 1954)),and four distinct structural components arerecognized, represented by four fold axes( Fl - If) and associated syngenetic axial-planarcleavage (Sl _If) (Helm and others 1963, Lynas1970). The regional structure is dominated byF2' S2, with their typical Caledonoid NNE-SSW

strike, mainly dipping steeply north-west.A primary fracture geometry of steep-

vertical discontinuities, which confirms theCaledonoid tectonic stress field, has beendescribed (Addison, unpublished). Over 2 900 kmof principal fractures were recorded. Thesystematic regional ("master") fracture pattern(Fig.3) corresponds to expected tectonic config-uration (Badgley 1965, Fookes and Wilson 1966,Price 1966, Causay 1977); in the field, thethree-dimensional discontinuity geometry measuredin bedrock outcrops replicates the establishedregional pattern, and continues within rock slabswith close facsimile planar anistropy. Strengthand spacing depend on lithology at the smallerscales, but otherwise the fracture network dis-regards lithological boundaries.

Previous research on glacier erosion inSnowdonia concentrated on the significance of theorientation and elevation of nearly 50 cirques inreconstructing Pleistocene glacio-climatology(Seddon 1957, Unwin, unpublished), and, whilstdistribution conforms to a north-west Europeanpattern, it also corresponds intimately to thefracture geometry (Addison 1977). Moreover, arecently reconstructed Pleistocene "Merioneth"ice cap, centred to the south-east of Snowdonia(Addison, unpublished, Foster, unpublished,Rowlands, unpublished), was shown to have beenthe source of radial outlet glaciers whichbreached the mountain axis with transfluenttroughs up to 600 m deep. As with the cirques,they too show a marked conformity to the regional

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REGIONAL STRUCTU-RAl DISCONTINUITY CONTROL

Fig.4. Primary fractures in the Snowdon (SW) andGlyder (NE) groups and principal glacier-erodedcirques and troughs. Fractures are shown bybroken lines, cliffs by toothed shading, andlakes by stippling.

expressed as a factor of safety F where F =represents limiting equilibrium (Hoek 1970,1973) .

A glacial origin for DRMF is inferred fromthe glacial history of the site, contemporarystability in the absence of glacier-relateddisturbing forces, and, in particular, absenceof the failed mass at the toe of the slope.Site examples from Snowdonia are now presented.Confi ned failure

Slope-failure criteria do not apply soreadily here as stated earlier. At the threechosen sites, DRMF was compound, being induceddynamically in otherwise stable rock mass bybasal shear, and then, once block separationbegan, local small-scale slab, wedge, andtoppling failures occurred along destabilizeddiscontinuities.( i) Culm Stwlan

Excavation for the upper dam foundations ofthe Ffestiniog pumped-storage hydro-electricscheme, constructed on the bedrock threshold ofa glacial cirque, revealed considerably disturbed,hard, unweathered rhyolite dislocated along pre-existing discontinuities to a depth of 13 macross a front 150 m wide, which necessitateddesign modifications. Anderson (1969:193) con-sidered the dislocation to have been caused byglacier drag across the threshold: " ...facili-tated by the presence of five faults in the partmost affected and by joints almost at rightangles to the rock-lip ... The affected zone doesnot tail off but ends abruptly on both sides.

The limits may be partly related to the faults.but they may also mark the width within whichthe glacier was thick enough to exert drag".(ii) Ogwen

Bedrock floor in a major glacier-breachedwatershed is shown in Figure 5. Ice flowing fromleft to right first abraded the rock, followedby "quarrying" (displaced blocks show striationson one surface only) which removed some blocksaltogether and displaced others; thereafter,gravitationally loaded secondary failure furtherdislocated the rock mass, at least in part sub-

Fig.5. Ogwen valley floor. Sub-glacier confinedDRMF, with secondary failure evident in excava-ted sections. Slab failure occurred along twoplanar sets (a, b) and toppling failure awayfrom (c).

Fig.6. Toppling failure in Nant Peris; de-stabilization caused the parting of blocksalong arrowed discontinuities.

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glacially since many blocks are missing. Failuresurfaces were entirely controlled by the discon-tinuity geometry, and primary and modified con-fined failure is indicated by the displacement ofdebris down-glacier and down-slope.(iii) Nant Peris

Figure 6 shows an example of topplingfailure towards the valley floor generated bythe removal of adjacent rock mass under glacierconfinement close to the valley floor. Cliffelements such as these are common, with at leastthe greater part of the failed rock mass absentfrom the toe; by comparison, the few remaininginstable blocks which have recently toppled fromthe now unconfined face are all present at thetoe, and exhibit less-weathered contact planes.Unconfined failureCWm Graianog

This cirque basin affords one of the finestsite concentrations of all modes of rock-massfailure in Snowdonia. It is excavated inFfestiniog grit, and failure modes are discussedwith reference to a standard structural presenta-tion (Hoek and Bray 1974) shown in Figure 7.

Fig.8. Cwm Graianog (Ffestiniog grit). Northside wall (right) with D1 planar surfaces;head wall (1eft) wi th D1- D2 wedgi ng and D2planar surfaces.

CWM GRAIANOG

Fig.9. Cwm Graianog. Single D1 major planar-slide release surface, (showing ripple marks).

slab towards the western end of the basin mayhave failed to the full height of the rock wall(200 01) and across a width averaging 60 m. Theremaining rock wall is clean, being devoid ofresidual blocks, overhanging elements below whichrock mass have been released, and stable laterally-confining units. With a principal D1 spacing of3 01, this would have yielded a single failure of36 000 m3 of the side wall, all of which wasremoved by the glacier. D1 planes in the wallat this point are marked uniquely by large-scalebedding-plane ripples (Fig.9), and the only debris

-4-Plane

DEGRADED

ROCKWALL/MORAINE

BOUNDARY

LOWER ROCKWALL

LIM ITUPPER ROCKWA\..\..liMITr7l. :.> Moel PerfeddU Granophyre

1II11anVirn Slate

@ Ffest ini ogl2:;l Grit --

f........ -~~----~~~--~------~--O-----125--250m

I I I

04~

Sl!a£i.!!g01 3m02 2m03 2m04 I-3m05 ~5m

(b) Discontinuity Slereollel

Fig.7. Bedrock map and discontinuity stereonetfor Cwm Graianog.

The north sidewall consists almost entirelyof a spectacular series of D1 surfaces (Fig.B)and the slope angle is effectively the same as thediscontinuity dip of 38-40° to the south-east.Slab failure down D1 was released along D2'which frequently possesses an injected quartzfill, and D3' and the vertical extent ofindividual slabs is limited by D" with the samestrike, but opposite dip, as D1. One entire

blocks so marked are found several hundred metresaway in, and resting upon, cirque moraines inpositions where they could have been depositedonly by glacier ice.

The irregular strength and spacing of D5renders it 1ess apparent as a control, but D 2and D" become more important as the back wall isapproached. The "curved" transition is effectedby D1- D2 wedge failure (1/Ji=39°, orientated at130°) producing a series of buttresses, and theextent to which the geometry predeterminedfailure on excavated slopes is completed by thesuperi mpos it ion of topp 1ing fa ilure releasedfrom D1 and low-angled D" (itself below tileassumed friction angle) on more complex slab and

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wedge failure in the south wall. A rapid assess-ment of current stability (after Hoek 1970)suggests that 01 has a factor of safety F >- 1for typical assumed mechanical values, which hastwo important implications. (i) Excavation atthe toe would rapidly cause 01 to "dayl ight" andgenerate further slab failure; this is consideredto be typical of the effect of 91acier erosion.(ii) Other modifications to Mohr-Coulomb para-meters would result in failure; locally smallcontemporary slides are evident, considered to bethe smoothing effect of weathering on roughnessesalong the 01 planes.There is a dramatic decline in side-wallheight at the Llanvirn slates-granophyre contact;it is suggested that the lower ORMS of slatespermitted greater excavation of the side wall,and it is further noted here and elsewhere thatcleavage planes do not appear to have providedsignificant failure surfaces during glaciererosion.

CONCLUSIONGeomechanical rock-mass' properties have

been neglected in examining processes of glaciererosion, and it is proposed that alteration ofstress relationships in discontinuous rock massdirectly or indirectly by glacier ice provides arealistic principal mechanism for the study ofbedrock excavation by glaciers. Theoreticalfailure criteria applied to specific rock-massproperties are sustained by field evidence, andsupport the following conclusions.1. Failure of rock slabs occurs along pre-existing discontinuities, and the relative dis-position and strength of the discontinuitygeometry provides an exclusive framework forexcavation and is manifest in structurally-controlled erosional landforms at all scales.2. Failure in confined rock is due primarily tothe dynamic loading potential of the conditionsat the ice-rock mass contact, and in unconfinedrock to the activation of gravitational loadingon otherwise stable slopes.3. ORMF re-defines in more appropriate mechanicalterms conditions which in certain circumstanceshave been identified as erosion processes involv-ing "pressure release" and "melt-water sapping".It is contended that many quoted instances ofpressure release in fact describe parallel slopefacets determined by pre-existing discontinuitygeometry, where forms of glacial erosion havebeen controlled by structure rather than viceversa.4. Stress conditions in discontinuous rock masscan be incorporated usefully into theoretical andpractical examination of ice flow patterns andbehaviour at the rock-ice interface.

ACKNOWLEOGEI4ENTSThe author wishes to thank M.V. Barr,

British Petroleum Research Centre, Sunbury, forcommenting on the draft; Peter Masters and JackLandon, School of Geography, University of Oxford,for photographic work; Brenda Cartwright, ThePolytechnic, WOlverhampton, for typing the manu-script; and The Polytechnic, Wolverhampton, forfinancial support in presenting the paper.

REFERENCESAddison K 1977 The influence of structural

geology on glacial erosion in Snowdonia,North Wa 1es. x INQUA Congress, Birmingham,1977. Abstracts: 5

Addison K Unpublished Aspects of the glacia-tion of Snowdonia, North Wales. (OPhilthesis, UniverSity of Oxford, 1975)

Anderson J G C 1969 Geological factors in thedesign and construction of the Ffestiniogpumped storage scheme, Merioneth, Wales.Quarterly Journal of Engineering Geology2 (3) : 183-194

Attewell P B, Farmer I W 1976 Principles ofengineering geology. London, Chapman andHall

Badgley P C 1965 Structural and tectonicprinciples. New York, Harper and Row

Barton N 1973 Review of a new shear-strengthcriterion for rock joints. EngineeringGeology 7(4): 287-332

Battey M H 1960 Geological factors in thedevelopment of Veslgjuv-botn and Vesl-Skautbotn. In Lewis W V (ed) Investigationson Norwegian cirque glaciers. London,Royal Geographical Society: 5-10 (RGSResearch Seri es 4)

Boulton G S 1979 Processes of glacier erosionon different substrata. Journal ofGlaciology 23(89): 15-38

Broster B E, Oreimanis A, White J C 1979 Asequence of glacial deformation, erosion,and deposition at the ice-rock interfaceduring the last glaciation: Cranbrook,British Columbia, Canada. Journal ofGlaciology 23(89): 283-295

Brown E T 1970 Modes of failure in jointedrock mass. In: Proceedings of the secondCongress of the International Society ofRock Mechanics, Belgrade, [1970?} 2: 293-298

Brunner F K, Scheidegger A E 1973 Exfoliation.Rock Mechanics 5: 43-62

Causay 0 1977 The measurement of fracturepatterns in the chalk of southern England.Engineering Geology 11: 201-215

Chapman C A, Rioux R L 1958 Statistical studyof topography, sheeting and jointing ingranite, Acadia National Park, Maine.American Journal of Science 256(2): 111-127

Fookes P G, Wilson 0 0 1966 The geometry ofdiscontinuities and slope failures inSiwalik clay. Geotechnique 16(4):305-320

Foster H 0 Unpublished. The glaciation of theHarlech Dome. (PhD thesis, University ofLondon, 1968)

Freitas M H de, Watters R J 1973 Some fieldexamples of toppling failure. Geotechnique23(4): 495-514

Harland W B 1957 Exfoliation joints and iceaction. Journal of Glaciology 3(21):8-10

Haynes V M 1968 The influence of glacialerosion and rock structure on corries inScotland. Geografiska Annaler 50A(4):221-234

Helm 0 G, Roberts B, Simpson A 1963 Polyphasefolding in the Caledonides south of theScottish Highlands. Nature 200 (4911):1060-1062

Hoek E 1964 Fracture of anisotropic rock.Journal of South African Institute ofMining and Metallurgy 64: 501-518

Hoek E 1970 Estimating the stability ofexcavated slopes in opencast mines.Transactions of the Institution ofMining and Metallurgy 79 (A): 109-132

Hoek E 1973 Methods for the rapid assessmentof the stability of three-dimensional rockslopes. Quarterly Journal of EngineeringGeology 6(3-4): 243-255

Hoek E, Bray J W 1974 Rock slope engineering.London, Institution of Mining and Metallurgy

Holtedahl H 1967 Notes on the formation offjords and fjord-valleys. GeografiskaAnnaler 49A(2-4): 188-203

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Jahns R M 1943 Sheet structures in granites:its origin and use as a measure of glacialerosion in New England. Journal of Geology51 (2): 71-98

Kulhawy F H 1975 Stress deformation propertiesof rock and rock discontinuities.Engineering Geology 9: 327-350

Lewis W V 1938 A melt-water hypothesis ofcirque formation. Geological Magazine75(888): 249-265

Lewis W V 1940 The function of meltwater incirque formation. Geographical Review30 (1) : 64-83

Lewis W V 1954 Pressure release and glacialerosion. Journal of Glaciology 2(16):417-422

Lynas B D T 1970 Clarification of the polyphasedeformation of North Wales Palaeozoic rocks.Geological Magazine 107(6): 505-510

Morland L W, Boulton G S 1975 Stress in anelastic hump: the effects of glacier flowover elastic bedrock. Proceedings of theRoyal Society of London A 344(1637):157-173

Morland L W, Morris E M 1977 Stress in anelastic bedrock hump due to glacier flow.Journal of Glaciology 18(78): 67-75

Nilsen T H 1973 The relation of jointpatterns to the formation of fjords in

. western Norway. Norsk GeologiskTidsskrift 53(2): 183-194

Price N J 1966 Fault and joint development inbrittle and semi-brittle rock. Oxford,Pergamon

Randall BAD 1961 On the relationship ofvalley and fjord directions to thefracture pattern of Lyngen, Troms,N Norway. Geografiska Annaler 43(3-4):336-338

Rowlands B M Unpublished. The glaciation ofthe Arenig region. (PhD thesis, Univer-sity of Liverpool, 1970)

Seddon B 1957 Late-glacial cwm glaciers inWales. Journal of Glaciology 3(22):94-99

Shackleton R M 1954 The structural evolutionof North Wales. Liverpool and ManchesterGeological Journal 1(3): 261-297

Silveira A Fda, ROdrigues F P, Grossmann N F,Mendes F de M 1966 Quantitative charac-terization of the geometric parameters ofjointing in rock masses. In: Proceedingsof the first Congress of the InternationalSociety of Rock Mechanics, Lisbon, 1966.Lisboa, Laborat6rio Nacional de EngenhariaCivil 1: 225-233

Sugden D E 1974 Landscapes of glacial erosionin Greenland and their relationship toice, topographic and bedrock conditions.In ·Waters.R $, Brown E H (eds) Progressin geomorphology. London, Institute ofBritish Geographers: 177-195 (SpecialPublication 7)

Terzaghi K 1962 Stability of steep slopes onhard unweathered rock. Geotechnique12(4): 251-263,269-270

Trainer F W 1973 Formation of joints in bed-rock by moving glacial ice. us GeologicalSurvey. Journal of Research 1(2): 229-235

Twidale C R 1972 The neglected third dimen~sion. Zeitschrift fur Geomorphologie NF6(3): 283-300

Twidale C R 1973 On the origin of sheet joint-ing. Rock Mechanics 5: 163-187

Unwi~ D J Unpublished. Some aspects of theglacial geomorphology of Snowdonia, NorthWales. (MPhil thesis, University ofLondon, 1970)

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Weertman J 1979 The unsolved general glaCiersliding problem. Journal of Glaciology23(89): 97-115

Whillans I M 1978 Erosion by continental icesheets. Journal of Geology 86(4): 516-524

Witherspoon P A, Gale J E 1977 Mechanical andhydra.ulic properties of rocks related toinduced seismicity. Engineering Geology11: 23-55

Young R P, Fowell R J 1978 Assessing rockdiscontinuities. Tunnels and Tunnelling10(5): 45-48

Zumberge J M 1955 Glacial erosion in tiltedrock layers. Journal of Geology 63(2):149-158



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