Jökull

Ataaseq assigiiaat ilaat

Jökull - 01.01.2014, Qupperneq 54

Jökull - 01.01.2014, Qupperneq 54
J. Helgason and R. Duncan Table 3. Main stages in the landscape evolution of Hafrafell. – Helstu stig í landslagsþróun Hafrafells. Land- Erosion Period / Age Group For- Thickness of Dominating Relief1 (m) scape surface Chron (Ma) mation volcanic activity stage strata (m) 1st HR1 Neogene Gilbert 4.187–3.596 H1 HF1–HF5 161 SAV2 + 50? 2nd HR2 Neogene Gauss 2.581–3.596 H2 + H3 HF6–HF9 234 SGV3 + 100? 3rd HR3–HR6 Quaternary Lower Matuyama 2.581–1.945 H4 + H5 HF10–HF19 829 SAV >-829 4th HR7 Quaternary Lower Matuyama – – – Erosion – Hafrafell + 260 2.581–1.945 – – – valley formation 5th HR8– Quaternary Upper Matuyama 1.945– H6 HF20– 448 Hafrafell valley -448? HR10 –0.781 HF31 filled up, SAV + SGV 6th HR11– Quaternary Brunhes < 0.781 H7 +H8 HF32– 1100 SGV +1000 HR12 HF39 Explanations: 1Relief: positive values indicate relief generation while negative values indicate landscape evening out due to accumulation. 2SAV: Subaerial volcanism – lavas. 3SGV: Subglacial volcanism – subglacially formed lithologies. Stage 2. Subglacially erupted volcanics in Hafrafell date at least from the Gauss chron (ca. 2.6–3.6 Ma). Relief in Hafrafell during stage 2 is controlled by the sub-ice environment. Stage 3. Volcanism during lower Matuyama (2.581– 1.945 Ma) produced a ≥800-m-thick sequence of lavas, intercalated with a few erosion surfaces. This extensive volcanic activity in the Hafrafell area filled negative relief and smoothed landscape in relatively short time, ≤0.64 Myr. Stage 4. During Upper Matuyama time, or from about the Olduvai subchron to almost the onset of Brunhes (ca. 1.945–0.781 Ma), older lava flow bedrock was carved by glacial erosion forming the >260-m-deep Hafrafell valley. Stage 5. The Hafrafell valley was filled during Upper Matuyama time (ca. 1.945–0.781 Ma) with lava flows that contain the Olduvai subchron. The filling during this stage was a minimum of 260 m and may have been as much as 448 m. Stage 6. During Brunhes time, volcanism was exten- sive from the Hrútfjallstindar and Öræfajökull vol- canic centers (Helgason and Duncan, 2013; Steven- son et al., 2006). Simultaneously, erosion continued and valleys deepened by at least 1000 m. Topographic evolution When considering the topographic evolution of east- ern Iceland Walker (1982) stated: "the contrast be- tween the Austfirðir and inland plateau is attributed to a departure about 5 m.y. ago from steady state con- ditions, caused by a significant southward migration of the locus of volcanism". This view does not con- sider the influence of glaciers on the landscape. We demonstrate that glaciers have generated over 2-km- deep valleys that formed roughly during the last 3.5 Myr at Hafrafell. We conclude that until about 3 Ma, glaciers had not set their mark on the region, either in the form of a valley network or formed the deep de- pression now present below the Vatnajökull ice sheet. Keeping in mind that SE Iceland is regarded a rift flank volcanic regime (Einarsson, 2008) it follows that subsidence of the volcanic products there should be much less than in the active accreting rift zones to the west and north. We speculate that the major intru- sive process and lack of crustal subsidence is likely to generate local volcanoes that may reach high ele- vation above the surrounding area and actually higher elevation than comparable volcanic centers of the ac- tive rift zones. Also, the formation of inclined sheet swarms and major magma intrusion in SE Iceland has added to the crustal build-up (Walker, 1975). There, sheet intrusions commonly amount to over 50% of the stratigraphic sequence. Referring to the net move- ment caused by inclined sheets, Torfason (1979, p. 324) states: "the sheets and the major intrusions are the major cause of the extensive uplift of south-eastern Iceland, which is more than anywhere in Iceland." These factors likely maintained the landscape in SE Iceland at relatively high elevation above sea level. Glacial erosion, on the other hand, may first have counteracted the positive build-up caused by rift flank volcanism and intrusions. Later, a deeply eroded val- ley system with high peaks in between would have 54 JÖKULL No. 64, 2014
Qupperneq 1
Qupperneq 2
Qupperneq 3
Qupperneq 4
Qupperneq 5
Qupperneq 6
Qupperneq 7
Qupperneq 8
Qupperneq 9
Qupperneq 10
Qupperneq 11
Qupperneq 12
Qupperneq 13
Qupperneq 14
Qupperneq 15
Qupperneq 16
Qupperneq 17
Qupperneq 18
Qupperneq 19
Qupperneq 20
Qupperneq 21
Qupperneq 22
Qupperneq 23
Qupperneq 24
Qupperneq 25
Qupperneq 26
Qupperneq 27
Qupperneq 28
Qupperneq 29
Qupperneq 30
Qupperneq 31
Qupperneq 32
Qupperneq 33
Qupperneq 34
Qupperneq 35
Qupperneq 36
Qupperneq 37
Qupperneq 38
Qupperneq 39
Qupperneq 40
Qupperneq 41
Qupperneq 42
Qupperneq 43
Qupperneq 44
Qupperneq 45
Qupperneq 46
Qupperneq 47
Qupperneq 48
Qupperneq 49
Qupperneq 50
Qupperneq 51
Qupperneq 52
Qupperneq 53
Qupperneq 54
Qupperneq 55
Qupperneq 56
Qupperneq 57
Qupperneq 58
Qupperneq 59
Qupperneq 60
Qupperneq 61
Qupperneq 62
Qupperneq 63
Qupperneq 64
Qupperneq 65
Qupperneq 66
Qupperneq 67
Qupperneq 68
Qupperneq 69
Qupperneq 70
Qupperneq 71
Qupperneq 72
Qupperneq 73
Qupperneq 74
Qupperneq 75
Qupperneq 76
Qupperneq 77
Qupperneq 78
Qupperneq 79
Qupperneq 80
Qupperneq 81
Qupperneq 82
Qupperneq 83
Qupperneq 84
Qupperneq 85
Qupperneq 86
Qupperneq 87
Qupperneq 88
Qupperneq 89
Qupperneq 90
Qupperneq 91
Qupperneq 92
Qupperneq 93
Qupperneq 94
Qupperneq 95
Qupperneq 96
Qupperneq 97
Qupperneq 98
Qupperneq 99
Qupperneq 100
Qupperneq 101
Qupperneq 102
Qupperneq 103
Qupperneq 104
Qupperneq 105
Qupperneq 106
Qupperneq 107
Qupperneq 108
Qupperneq 109
Qupperneq 110
Qupperneq 111
Qupperneq 112
Qupperneq 113
Qupperneq 114
Qupperneq 115
Qupperneq 116
Qupperneq 117
Qupperneq 118
Qupperneq 119
Qupperneq 120
Qupperneq 121
Qupperneq 122
Qupperneq 123
Qupperneq 124
Qupperneq 125
Qupperneq 126
Qupperneq 127
Qupperneq 128
Qupperneq 129
Qupperneq 130
Qupperneq 131
Qupperneq 132
Qupperneq 133
Qupperneq 134
Qupperneq 135
Qupperneq 136
Qupperneq 137
Qupperneq 138
Qupperneq 139
Qupperneq 140
Qupperneq 141
Qupperneq 142
Qupperneq 143
Qupperneq 144
Qupperneq 145
Qupperneq 146
Qupperneq 147
Qupperneq 148
Qupperneq 149
Qupperneq 150
Qupperneq 151
Qupperneq 152
Qupperneq 153
Qupperneq 154
Qupperneq 155
Qupperneq 156
Qupperneq 157
Qupperneq 158
Qupperneq 159
Qupperneq 160

x

Jökull

Direct Links

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.