Jökull


Jökull - 01.12.1984, Page 145

Jökull - 01.12.1984, Page 145
period M>3.5 M>3.0 1925-1931 (0) 9 • 1932-1941 (6) ? 1942-1951 (1-10) ? # 1952-1961 46 88 1962-1971 20 61 1972-1981 38 97 Table 1. Frequency of Vatnajökull earthquakes in the magnitude range 3.5 > M ^ 3.0 and M ^ 3.5. The seismicity can be divided into two peri- ods. A low seismicity period 1925—1953 and higher seismicity period since 1954. The higher seismicity period coincides with increased geo- thermal activity in the cauldron area northwest of Grímsvötn. (Fig. 1). Tafla 1. Taflan sýnir fjölda Vatnajökulsskjálfta á stœrðarbilinu 3.5 > M > 3.0 og M g- 3.5 á árunum 1925—1981. Skjálftavirknin eykst til muna 1954, um leið og vart verður aukningar í jarðhita á sigkatlasvœðinu norðvestan Grímsvatna (Mynd 1). recorded. All these large earthquakes originated in the Bárðarbunga area ( Páll Einarsson , pers. comm.). SKEIÐARÁRHLAUPS AND ERUPTIONS IN WESTERN VATNAJÖKULL THIS CENTURY. 1903 On the 25th of May 1903 local farmers at Skaftafell noticed that a jökulhlaup was begin- ning in Skeiðará. During the following days the flow rate of Skeiðará steadily increased to reach a maximum on the 28 and 29 of May. Uncertain reports from people in Öræfi tell of earthquakes felt on two nights (no dates) during the jökul- hlaup along with heavy rumble and crashing noises from the jökulhlaup which in a western breeze could be heard in Hornafjörður 100 km east of Skeiðará. The quakes and noises reached their maximum in the afternoon of May 28th and the following night. A great steam and ash coluntn indicating eruption was first noticed Thursday afternoon the 28th of May coinciding within few hours of the jökulhlaup maximum. The eruption originated in the vicinity of Thórðarhyrna 20 km SSW of Grímsvötn (Thórarinsson 1974). On the other hand, (Haukur Jóhannesson 1983) has sug- gested that unusual water bursts in glacier rivers north of Vatnajökull in December 1902 and May 1903 were caused by an eruption in the Gríms- vötn area that continued in 1903, at the same time as the Thórðarhyrna eruption. He considers the Grímsvötn eruption to be the largest during this century. The tephra fall during this eruption was greater than in most Grímsvötn eruptions but the composition of the tephra was the same as that of Grímsvötn tephra (Thórarinsson 1974), suggesting a relationship of the Thórðarhyrna eruption with the Grímsvötn volcano. The erup- tion was visible on and off until January 1904. No reports are of felt earthquakes during the erup- tion. In 1903 seismometers had not been installed in Iceland. 1910 An eruption believed to originate in western Vatnajökull, close to Hamarinn, was first noticed on the 18th of June 1910. Tephra fall from this eruption was frequent in August and lasted until October same year ( Tltórarinsson 1974). There are no reports of felt earthquakes or jökulhlaups related to this eruption. No earthquakes were recorded on the Reykjavík seismometer, indicat- ing that if there were earthquakes associated with this eruption, they were all smalier than magni- tude 3.5—4.0. 1913 A large jökulhlaup discharged to Skeiðará in April 1913 but no visible eruption or tephra fall reported (Thórarinsson 1974). Askelsson (1936, p. 12) claimed that „in all probability” there was an eruption in Grímsvötn accompanying the jökulhlaup. Jóhannesson (1983) pointed out, that an eruption in Hekla coinciding with the jökul- hlaup might have drawn attention from a possible Grímsvötn eruption at the same time. According to a diary of Ari Hálfdánarson froni Kvísker an earthquake was felt on the 25th of April 1913, but he does not comment on the intensity of the quake (Thórarinsson 1975). No earthquakes that could possibly originate in Vatnajökull were recorded in Reykjavík during that time. There- fore the earthquake on April 25th was probably a local quake in Öræfi. JÖKULL 34. ÁR 143
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.