THE PROGLACIAL AREA of MÝRDALSJӦKULL with Particular Reference to Sléttjökull and Höfdabrekkujökull
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FOLIA GEOGRAPHICA DANICA . TOM. XV. NO. 1 JOHANNES KRÜGER and OLE HUMLUM THE PROGLACIAL AREA OF MÝRDALSJӦKULL with particular reference to Sléttjökull and Höfdabrekkujökull GENERAL REPORT ON THE DANISH GEOMORPHOLOGICAL EXPEDITION TO ICELAND, 1977 WITH ONE PLATE, A MAP 1:10.000 Summary in Danish KØBENHAVN C. A. REITZELS FORLAG TH. LAURSENS BOGTRYKKERI A-S 1981 FOLIA GEOGRAPHICA DANICA . TOM. XV. NO. 1 JOHANNES KRÜGER and OLE HUMLUM THE PROGLACIAL AREA OF MÝRDALSJÖKULL with particular reference to Sléttjökull and Höfdabrekkujökull GENERAL REPORT ON THE DANISH GEOMORPHOLOGICAL EXPEDITION TO ICELAND, 1977 WITH ONE PLATE, A MAP 1:10.000 Summary in Danish KØBENHAVN C. A. REITZELS FORLAG TH. LAURSENS BOGTRYKKERI A-S 1981 ABSTRACT I nærværende afhandling redegøres for Geomorfologien langs Sléttjökulls en glacialmorfologisk ekspedition til rand fremgår af fig. 5, medens p1. 1 iskappen Myrdalsjökull, Island, i fremstiller detailmorfologien inden 1977. Det var ekspeditionens opgave for en udvalgt del (Mælifell-området) (1) at kortlægge glaciale og glacio- af dette område. Glacialmorfologien fluviale terrænformer foran en recent foran Höfdabrekkujökull er vist på gletscher med vigende isrand, (2) at fig. 26. beskrive de herskende deglaciations- Sléttjökull er et enestående eks- måder, (3) at undersøge den glaciale empel på frontal deglaciation, hvor transport såvel som de sub- og supra- grænsen mellem isfrit og isdækket om- glaciale aflejringsprocesser, samt råde er skarp; det subglacialt dan- (4) at studere sedimentære struktu- nede bundmorænelandskab frilægges i rer og teksturer i de glaciale aflej- takt med israndens tilbagesmeltning ringer foran gletscheren - alt sammen (fig. 11, 22, 24 og 25). Dele af med henblik på en sammenligning med Höfdabrekkujökulls randområde tjener det danske istidslandskab. derimod som model for areal deglacia- Undersøgelserne koncentrerede sig tion, hvor der optræder en bræmme af om to områder (fig. 1): (1) Den nord- dødis og stagneret is uden for den lige del af Myrdalsjökull - også kal- aktive del af gletscheren (fig. 27 det Sléttjökull - der ender med sin og 45). Resultatet af denne afsmelt- godt 20 km lange front på en udstrakt ningsmåde er et uregelmæssigt, små- højslette bestående af mere eller min- bakket landskab (fig. 28). De to un- dre permeable og deformerbare sedi- dersøgelsesområder ved Mýrdalsjökull menter i lighed med det nordeuropæ- supplerer således hinanden og er vel- iske isskjolds underlag i Danmark. egnede til videre undersøgelser af (2) Höfdabrekkujökull - en piedmont- henholdsvis subglaciale og supragla- gletscher, der er en udløber fra den ciale aflejringsprocesser. sydøstlige del af Myrdalsjökull. CONTENTS Abstract ............................................................................................................................ 2 Introduction ...................................................................................................................... 4 Organization of the expedition ......................................................................................... 6 Objects ...................................................................................................... 6 Personnel .................................................................................................. 7 Transport ................................................................................................... 7 Field work .................................................................................................. 8 Physiography and geology of the Mýrdalsjökull district ................................................... 9 Large-scale geomorphology in the forefield of Sléttjökull ................................................ 12 The glacier front ......................................................................................... 12 The glacier forefield ................................................................................... 12 Detailed geomorphological mapping in the Mælifell area................................................. 16 The marginal moraine system ................................................................... 17 The ground moraine and associated features ........................................... 18 The outwash fans and associated features ............................................... 24 History of glacier fluctuations in the Maelifell area............................................................ 28 The glacier advance .................................................................................. 28 The retreat between 1906 and 1945 ......................................................... 30 The retreat between 1945 and 1960 ......................................................... 30 The retreat between 1960 and 1977/78.................................................... 31 Annual rates of retreat ............................................................................... 32 The Maelifell area: a model of deglaciation by frontal retreat........................................... 34 Large-scale geomorphology in the forefield of Höfdagrekkujökull ................................... 36 Processes of glacial transportation and sedimentation ................................................... 43 Subglacial sedimentation in the Mælifell area............................................ 43 Basal and englacial transport at Höfdabrekkujökull .................................. 45 Supraglacial sedimentation on Höfdabrekkujökull .................................... 47 Höfdabrekkujökull: a model of deglaciation by areal down-wastage ............................... 52 Final remarks .................................................................................................................... 54 References ....................................................................................................................... 56 INTRODUCTION The last decades have seen a great activity in areas of existing gla- increase in number of publications ciers, have presented valuable con- on glaciations and deglaciation pro- tributions to the understanding of blems within the Danish area. The till formation. The present authors main focus of attention has been the are of the opinion that also among regional glacial geology, especially the Danish glacial geologists and characterized by the contributions glacial geomorphologists there ex- of workers studying the geomorpho- ists a need for making comparative logy, stratigraphy, and chronology. studies at the margin of present-day (Smed 1962; Krüger 1969; Berthelsen glaciers with the express purpose of 1973; Sjørring 1973; 1977; Bahnsen attaining more reliable ideas on the et al. 1974; Rasmussen 1975; Larsen past glacier behaviour within the et al. 1977). Danish area. In recent years, however, there During the last 5 years the Geo- have also been considerable advances morphological Department of the Geo- in the characterisation of glacial graphical Institute of the Univer- sediments, especially glacial tills sity of Copenhagen has organized (Krüger 1970; 1979; Marcussen 1973; scientific expeditions, as well as 1975; Humlum 1978; 1979). This is a field courses and excursions for very important development as advan- students of physical geography, to ces in the understanding of the en- the margin of existing glaciers in vironmental conditions prevailing at the Austrian Alps, Norway, and Green- the time of formation of the glacial land; the expedition to Mẙrdalsjö- landforms depend on a reliable inter- kull in Iceland in the summer of 1977 pretation of the Pleistocene sedi- forms part of these current activi- ments. However, in some cases the ties in present glaciated areas. studies of specific occurrences of The object of the present paper is tills have led to controversial ideas to give a general report on the gla- on the mode of deposition and this in cial geomorphological expedition to turn has recently started another ma- Myrdalsjökull in 1977, while details jor controversy on the behaviour of of the work will be published in se- the Pleistocene glaciers in Denmark parate papers (Krüger 1979; Humlum (Humlum et al. 1978). This confu- in prep.). Furthermore, this paper sion largely stems from the fact that is intended to lead up to more de- in Denmark the greatest attention tailed investigations of the glacial has hitherto been given to a charac- geomorphology and sedimentology in terisation of the end-products of the the promising research areas at Mẙr- work by the Pleistocene glaciers, dals jökull. and only in a minor degree to the mechanisms involved in till forma- tion and the processes responsible For financial support the authors for the glacial landforms. wish to express their warm thanks to It is conspicuous that many coun- the Danish Natural Science Research tries, e.g. the U.S.A., Canada, Brit- Council. For most valuable assist- ain, Sweden, and Poland, where stu- ance during the preparatory stage of dents of Pleistocene landscapes have the expedition thanks are due to Pro- an almost traditional interest and fessor S. Thorarinsson, Reykjavik. XV, 1 THE PROGLACIAL AREA OF MÝRDALSJӦKULL 5 Students of physical geography at the spondent Kirsten Winther kindly im- University of Copenhagen, Niels Gyl- proved the English of the manuscript ling Mortensen, Lisbeth Pedersen, Physician Hannah Wulffsberg acted as and Henrik Højmark Thomsen assisted medical adviser. The report was typed in the field and in the photogram- by Annie Witte. To all these indi- metric laboratory. The laboratory