The Kverkfj?ll fissure swarm and the eastern boundary of the Northern Volcanic Rift Zone, Iceland |
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Authors: | ásta Rut Hjartardóttir Páll Einarsson |
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Institution: | (1) Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, 101 Reykjav?k, Iceland |
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Abstract: | Rift zones at the divergent plate boundary in Iceland consist of central volcanoes with swarms of fractures and fissures extending
away from them. Fissure swarms can display different characteristics, in accordance with their locations within the ∼50-km-wide
rift zones. To better discern the characteristics of fissure swarms, we mapped tectonic fractures and volcanic fissures within
the Kverkfj?ll volcanic system, which is located in the easternmost part of the Northern Volcanic Rift Zone (NVZ). To do this,
we used aerial photographs and satellite images. We find that rifting structures such as tectonic fractures, Holocene volcanic
fissures, and hyaloclastite ridges are unevenly distributed in the easternmost part of the NVZ. The Kverkfj?ll fissure swarm
extends 60 km north of the Kverkfj?ll central volcano. Holocene volcanic fissures are only found within 20 km from the volcano.
The Fjallgarear area, extending north of the Kverkfj?ll fissure swarm, is characterized by narrow hyaloclastite ridges indicating
subglacial volcanism. We suggest that the lack of fractures and Holocene volcanic fissures there indicates decreasing activity
towards the north in the easternmost part of the NVZ, due to increasing distance from the long-term spreading axis. We argue
that arcuate hyaloclastite ridges at the eastern boundary of the Northern Volcanic Rift Zone are mainly formed during deglaciations,
when three conditions may occur; firstly, eruption rate increases due to decompression of the mantle. Secondly, the high tensile
stresses accumulated during glaciations due to lack of magma supply may be relieved as magma supply increases during deglaciations.
Thirdly, faulting may occur during unloading due to differential movements between the thinner and younger Northern Volcanic
Rift Zone crust and the thicker and older crust to the east of it. |
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