Jökull


Jökull - 01.12.1984, Page 53

Jökull - 01.12.1984, Page 53
Traces of Icelandic Eruptions in the Greenland Ice Sheet C.U. HAMMER Geophysical Isotope Laboratory, Haraldsgade 6 University of Copenhagen, 2200 Copenhagen N, Denmark. ABSTRACT The information in polar ice sheets on long range transported volcanic debris is discussed. Acidity data from the Greenland Ice Sheet are presented, which indicate a possible relation between the volcanic fall-out pattern on Greenland from a past eruption and the latitude zone of the eruption site. A special presentation of the Icelandic eruptions Lakagígar, 1783 A.D., Katla 1179 A.D., Eldgjá 934 A.D., Hekla I, III, IV and V is given. Finally the potential of future volcanological research “via" the polar ice sheets is discussed. INTRODUCTION The importance of the polar ice sheets in research on past atmospheric composition stems from the fact that they consist of well layered frozen past precipitations. These individual pre- cipitations are generally formed between the ice sheet surface and 1—2 km above it, which for the more central parts of the Greenland Ice Sheet corresponds to some 2.5—5.5 km above sea level. The special importance of the two major ice sheets — the Greenland Ice Sheet and the Antarctic Ice Sheet - relates to their vast extent, high surface elevations and remoteness from most aerosol sources. Not only does this secure a certain uniform mixing ratio of atmospheric trace substances, at levels where the precipitation forms, but it also keeps the impurity concentra- tion in the snow very low. The polar ice sheets are therefore unique “lib- raries” of past mid-tropospheric aerosol loads over a very broad latitudinal zone. The stratos- pheric and upper tropospheric impurities will add to the mid-tropospheric impurity load and in this way part of the upper atmospheric impurities is deposited on the ice sheets. As volcanic eruptions inject substantial amounts of trace substances and gases into the troposphere and in many cases also into the stratosphere, it is not surprising that the ice sheets have proven to offer information on the amount and nature of long-range atmospherical transported volcanic products. There are of course differences in this kind of information, which will depend on the site of information i. e. usually from a drill site on the ice sheet. The major differences between the Greenland Ice Sheet and Antarctica are for inst- ance: 1) Antarctica reveals mainly eruptions in the southern hemisphere, while Greenland offers information on northern hemisphere erup- tions. 2) Due to a greater precipitation in Greenland, as compared to Antarctica, the Greenland Ice Sheet can be dated to a higher accuracy by various stratigraphical methods; at least for the past 10,000 years. 3) During the Ice Age the aerosol load increased over both ice sheets, but while the Antarctic snow remained fairly clean and slightly acidic, the Greenland snow became alkaline and showed rather high impurity concentrations, as compared to present values. Loess and dust from the continental shelves added strongly to the mid-tropospheric aerosol load in the northern hemisphere. Such large differences are not encountered, if we confine us to e. g. the Greenland Ice Sheet and the Holocene period: Then only moderate differences exist from site to site, but as will be seen later such differences offer additional information on the volcanic eruptions. The possibility of extending tephra-chronology to the large ice sheets or ice caps remote from JÖKULL 34. ÁR 51
Page 1
Page 2
Page 3
Page 4
Page 5
Page 6
Page 7
Page 8
Page 9
Page 10
Page 11
Page 12
Page 13
Page 14
Page 15
Page 16
Page 17
Page 18
Page 19
Page 20
Page 21
Page 22
Page 23
Page 24
Page 25
Page 26
Page 27
Page 28
Page 29
Page 30
Page 31
Page 32
Page 33
Page 34
Page 35
Page 36
Page 37
Page 38
Page 39
Page 40
Page 41
Page 42
Page 43
Page 44
Page 45
Page 46
Page 47
Page 48
Page 49
Page 50
Page 51
Page 52
Page 53
Page 54
Page 55
Page 56
Page 57
Page 58
Page 59
Page 60
Page 61
Page 62
Page 63
Page 64
Page 65
Page 66
Page 67
Page 68
Page 69
Page 70
Page 71
Page 72
Page 73
Page 74
Page 75
Page 76
Page 77
Page 78
Page 79
Page 80
Page 81
Page 82
Page 83
Page 84
Page 85
Page 86
Page 87
Page 88
Page 89
Page 90
Page 91
Page 92
Page 93
Page 94
Page 95
Page 96
Page 97
Page 98
Page 99
Page 100
Page 101
Page 102
Page 103
Page 104
Page 105
Page 106
Page 107
Page 108
Page 109
Page 110
Page 111
Page 112
Page 113
Page 114
Page 115
Page 116
Page 117
Page 118
Page 119
Page 120
Page 121
Page 122
Page 123
Page 124
Page 125
Page 126
Page 127
Page 128
Page 129
Page 130
Page 131
Page 132
Page 133
Page 134
Page 135
Page 136
Page 137
Page 138
Page 139
Page 140
Page 141
Page 142
Page 143
Page 144
Page 145
Page 146
Page 147
Page 148
Page 149
Page 150
Page 151
Page 152
Page 153
Page 154
Page 155
Page 156
Page 157
Page 158
Page 159
Page 160
Page 161
Page 162
Page 163
Page 164
Page 165
Page 166
Page 167
Page 168
Page 169
Page 170
Page 171
Page 172
Page 173
Page 174
Page 175
Page 176
Page 177
Page 178
Page 179
Page 180
Page 181
Page 182
Page 183
Page 184
Page 185
Page 186
Page 187
Page 188
Page 189
Page 190
Page 191
Page 192
Page 193
Page 194
Page 195
Page 196

x

Jökull

Direct Links

If you want to link to this newspaper/magazine, please use these links:

Link to this newspaper/magazine: Jökull
https://timarit.is/publication/1155

Link to this issue:

Link to this page:

Link to this article:

Please do not link directly to images or PDFs on Timarit.is as such URLs may change without warning. Please use the URLs provided above for linking to the website.