Jökull


Jökull - 01.12.1985, Side 24

Jökull - 01.12.1985, Side 24
Fig. 12. Detail from section 3 at Haelavík (Fig. 7 and 10), showing the very sharp lower contact betveen the Haelavík tephra and the lacustrine/fluvial silt. 12. mynd. Hér sést hve skörp neðri mörk Hœlavíkur-gjósk- unnar eru við árlvatnasetið í sniði 3 í Hælavík. identify any active glaciers at such low elevations. He estimated the altitude of the „snow line“ on eastern Drangajökull to 400 m. This can be compared with the more recent estimate of 700—800 m for the equilibrium line altitude (ELA) there (Th. Einarsson 1968). Old local names for cirques on Hornstrandir suggest at least perennial firns, or glaciers (e.g. Jökladalir: Glacier val- leys, Fannarlág: Site of snow fields). John (1977b) found that most of the cirque glaciers in the uplands of northern Vestfirdir have prominent moraines. He sug- gested that these moraines often mark the maximum advance of the Little Ice Age glaciers, but where multi- ple moraine sequences occur, some may date from an earlier Neoglacial advance. The present study Most of the cirques on Hornstrandir, some of which have floors as low as 150 m above present sea level, show no sign of having been glaciated since the end of the Weichselian. The moraines in front of them are well weathered, the vegetation cover within them is more or less complete, and peat formation has often taken place in their basins. However, there are a few exceptions. In Hlöduvík, Haelavík and Hornvík there are 7 cirques which show clear signs of having been glaciated recently. The cir- ques inside Hornvík, Haelavík and Hlöduvík (shown without question marks in Fig. 13) have one to several fresh looking moraines in front of them. The areas behind these moraines also look very fresh and the vegetation cover there is sparse. This is not an effect of altitude, as extensive vegetation cover often occurs at higher altitudes near the cirques, and at similar exposi- tions. Inside Hlöduvík and Haelavík the floors of these cirques lie around 300—350 m above sea level, but they lie as high as 500 m inside Hornvík (Fig. 13). The Hornvík cirques are surrounded by the highest moun- tains on Hornstrandir, which probably causes some precipitation shadow. This is also suggested by our conclusions, that during the Little Ice Age the glaciers in the more exposed cirques in Hlöduvík and Haelavík reached 150 m below the altitude of their floors (Fig. 13), whereas those inside Hornvík only reached some 50 m below their floors. Thus during the Little Ice Age (for dating, see below) the ELA in the cirques was down at, or somewhat below, 300-350 m in the Haelavík/Hlödu- vík area, but not much below 500 m at Hornvík. This can be compared with Thoroddsen’s (1906, 1911) approximation of 400 m for the eastern part of Dranga- jökull. The total glaciated area on northern and western Hornstrandir during the Little Ice Age was 8-10 km2. Lichenometry of the Fannarlág cirque. A reconnaissance scudy of lichen growth was carried out on fresh moraines and other surfaces which were covered by the Little Ice Age glacier in the Fannarlág cirque, at the head of the valley inside Haelavík. Today there is no glacier in this cirque (Figs. 7 and 14). Lichens used were of Rhizocarpon alpicola and Rhizocarpon geographicum agg. type, and thalli of the different species are used together in the calculations. Thalli diameters were measured using the diameter of the largest inscribed circle (Lock et al. 1979, p. 8). Dist- ances between moraines and other surfaces on which thalli were studied were measured by counting steps during walking. Innes (1982) showed that R. alpicola and R. geo- graphicum agg. have somewhat different growth rates, but in a preliminary study like ours that difference should not matter too much. Gordon and Sharp (1983), in a study on southern Iceland, found that for R. geographicum agg. the growth rate since the late 19th century was approximately linear, and Caseldine (1983) came to the same conclusion as regards central North Iceland. Our results are presented in Fig. 15, where the mean values for the five largest thalli (M5) on each surface (numbered as in Fig. 7) are shown together with the size interval covered by them. In two cases (points 5 and 7) single unexpectedly large and perhaps coalescent thalli 22 JÖKULL 35. ÁR
Side 1
Side 2
Side 3
Side 4
Side 5
Side 6
Side 7
Side 8
Side 9
Side 10
Side 11
Side 12
Side 13
Side 14
Side 15
Side 16
Side 17
Side 18
Side 19
Side 20
Side 21
Side 22
Side 23
Side 24
Side 25
Side 26
Side 27
Side 28
Side 29
Side 30
Side 31
Side 32
Side 33
Side 34
Side 35
Side 36
Side 37
Side 38
Side 39
Side 40
Side 41
Side 42
Side 43
Side 44
Side 45
Side 46
Side 47
Side 48
Side 49
Side 50
Side 51
Side 52
Side 53
Side 54
Side 55
Side 56
Side 57
Side 58
Side 59
Side 60
Side 61
Side 62
Side 63
Side 64
Side 65
Side 66
Side 67
Side 68
Side 69
Side 70
Side 71
Side 72
Side 73
Side 74
Side 75
Side 76
Side 77
Side 78
Side 79
Side 80
Side 81
Side 82
Side 83
Side 84
Side 85
Side 86
Side 87
Side 88
Side 89
Side 90
Side 91
Side 92
Side 93
Side 94
Side 95
Side 96
Side 97
Side 98
Side 99
Side 100
Side 101
Side 102
Side 103
Side 104
Side 105
Side 106
Side 107
Side 108
Side 109
Side 110
Side 111
Side 112
Side 113
Side 114
Side 115
Side 116
Side 117
Side 118
Side 119
Side 120
Side 121
Side 122
Side 123
Side 124
Side 125
Side 126
Side 127
Side 128
Side 129
Side 130
Side 131
Side 132
Side 133
Side 134
Side 135
Side 136
Side 137
Side 138
Side 139
Side 140
Side 141
Side 142
Side 143
Side 144
Side 145
Side 146
Side 147
Side 148
Side 149
Side 150
Side 151
Side 152
Side 153
Side 154
Side 155
Side 156
Side 157
Side 158
Side 159
Side 160
Side 161
Side 162
Side 163
Side 164

x

Jökull

Direkte link

Hvis du vil linke til denne avis/magasin, skal du bruge disse links:

Link til denne avis/magasin: Jökull
https://timarit.is/publication/1155

Link til dette eksemplar:

Link til denne side:

Link til denne artikel:

Venligst ikke link direkte til billeder eller PDfs på Timarit.is, da sådanne webadresser kan ændres uden advarsel. Brug venligst de angivne webadresser for at linke til sitet.