Náttúrufræðingurinn - 2013, Side 17

125
Tímarit Hins íslenska náttúrufræðifélags
eruption frequency of each volcanic sys-
tem was estimated; Grímsvötn has been
the most active with an average of ~7
eruptions/100 years (range 4–14) during
prehistoric time (before ~870 AD);
Bárdarbunga has been the second most
active with ~5 eruptions/100 years
(range 1–8); and Kverkfjöll has remained
essentially calm with 0–3 eruptions/100
years but showing periodic activity with
repose times of >1000 years. A lull in ac-
tivity from 5 ka to 2 ka, referred to as the
“Mid-Holocene low,” is observed in all
three volcanic systems. It appears to
have resulted from a decrease in magma
generation and delivery from the mantle
plume rather than from changes in ice-
load/glacier thickness. In prehistoric
time, there was a time lag of 1000–3000
years between a peak of activity at vol-
canoes directly above the mantle plume
versus volcanoes located in the non-rift-
ing part of the Eastern Volcanic Zone,
closer to the periphery of the island.
This time-space relationship suggests
that a significant future increase in vol-
canism can be expected there, following
increased levels of volcanism above the
plume.48
Þakkir
Grein þessi er byggð á doktorsverkefni unnu á árunum 2005–2009 við Há-
skóla Íslands og Université Blaise Pascal í Clermont-Ferrand í Frakklandi
og grein sem birtist í tímaritinu Bulletin of Volcanology árið 2011. Verkið
var fjármagnað af Rannís, Landsvirkjun, Háskólasjóði Eimskipafélagsins,
Rannsóknarsjóði Háskólans, Franska sendiráðinu og fransk-íslenska sam-
starfssjóðnum Jules Vernes. Jean-Luc Devidal fær sérstakar þakkir fyrir að-
stoð við efnagreiningar og hjálplegar umræður þeim tengdar, eins þökkum
við Þorvaldi Þórðarsyni yfirlestur frumhandrits, Magnúsi Tuma Guð-
mundssyni og ónafngreindum yfirlesara fyrir góðar ábendingar. Einnig
þökkum við öllum þeim sem aðstoðuðu á einn eða annan hátt við feltvinnu
eða veittu aðgang að feltgögnum og sýnum, Elsu G. Vilmundardóttur, Jóni
Eiríkssyni, Óskari Knudsen, Aðalsteini Eiríkssyni og síðast en ekki síst Guð-
mundi Óla Sigurgeirssyni og Ester Önnu Ingólfsdóttur.
Heimildir
1. Sigrún Hreinsdóttir, Páll Einarsson & Freysteinn Sigmundsson 2001.
Crustal deformation at the oblique spreading Reykjanes Peninsula, SW
Iceland: GPS measurements from 1993 to 1998. Journal of Geophysical
Research 106(B7). 13803–13816.
2. Bryndís Brandsdóttir & Menke, W.H. 2008. The seismic structure of
Iceland. Jökull 58. 17–34.
3. Freysteinn Sigmundsson 2006. Iceland geodynamics: crustal deforma-
tion and divergent plate tectonics. Springer, Praxis, Berlin. 209 bls.
4. Axel Björnsson 1985. Dynamics of crustal rifting in NE Iceland. Journal of
Geophysical Research 90. 10151–10162.
5. Simkin, T. & Siebert, L. 2000. Earth’s volcanoes and eruptions: an
Overview. Í: Encyclopedia of Volcanoes (ritstj. Haraldur Sigurðsson).
Academic press, San Diego. Bls. 249–261.
6. LaFemina, P.C., Dixon, T.H., Malservisi, R., Þóra Árnadóttir, Sturkell, E.,
Freysteinn Sigmundsson & Páll Einarsson 2005. Geodetic GPS meas-
urements in south Iceland: Strain accumulation and partitioning in a
propagating ridge system. Journal of Geophysical Research 110(B11405).
DOI:10.1029/2005JB003675.
7. Guðmundur E. Sigvaldason, Annertz, K. & Nilsson, M. 1992. Effect of
glacier loading/deloading on volcanism: Postglacial volcanic produc-
tion rate of the Dyngjufjöll area, central Iceland. Bulletin of Volcanology
54. 385–392.
8. Guðrún Larsen, Magnús T. Guðmundsson & Helgi Björnsson 1998. Eight
centuries of periodic volcanism at the centre of the Icelandic hotspot
revealed by glacier tephrostratigraphy. Geology 26. 943–946.
9. Maclennan, J., Jull, M., McKenzie, D., Slater, L., & Karl Grönvold 2002.
The link between volcanism and deglaciation in Iceland. Geochemistry,
Geophysics, Geosystems 3(11). 1062–1087. DOI 10.1029/2001GC000282.
10. Bergrún Arna Óladóttir, Guðrún Larsen, Þorvaldur Þórðarson & Olgeir
Sigmarsson 2005. The Katla volcano S-Iceland: Holocene tephra stratig-
raphy and eruption frequency. Jökull 55. 53–74.
11. Sigurður Þórarinsson & Kristján Sæmundsson 1979. Volcanic activity in
historical times. Jökull 29. 29–32.
12. Þorvaldur Þórðarson & Ármann Höskuldsson 2008. Postglacial volcan-
ism in Iceland. Jökull 58. 197–228.
13. Sveinn P. Jakobsson 1979. Petrology of Recent basalts of the Eastern
Volcanic zone, Iceland. Acta Naturalia Islandica 26. 1–103.
14. Bergrún Arna Óladóttir, Olgeir Sigmarsson, Guðrún Larsen & Þorvaldur
Þórðarson 2008. Katla volcano, Iceland: magma composition, dynamics
and eruption frequency as recorded by Holocene tephra layers. Bulletin
of Volcanology 70(4). 475–493.
15. Guðrún Larsen & Jón Eiríksson 2008. Late Quaternary terrestrial tephro-
chronology of Iceland – frequency of explosive eruptions, type and
volume of tephra deposits. Journal of Quaternary Science 23(2). 109–120.
16. Guðrún Larsen & Jón Eiríksson 2008. Holocene tephra archives and
tephrochronology in Iceland – a brief overview. Jökull 58. 229–250.
17. Esther Ruth Guðmundsdóttir, Guðrún Larsen & Jón Eiríksson 2012.
Tephra statigraphy on the North Icelandic shelf: extending tephrochro-
nology into marine sediments off North Iceland. Boreas 41(4). 719–734.
DOI 10.1111/j.1502-3885.2012.00258.x.
18. Þorvaldur Þórðarson & Guðrún Larsen 2007. Volcanism in Iceland in
historical time: Volcano types, eruption styles and eruptive history.
Journal of Geodynamics 43(1). 118–152.
19. Meyer, P.S., Haraldur Sigurðsson & Schilling, J.G. 1985. Petrological and
geochemical variations along Iceland’s Neovolcanic zones. Journal of
Geophysical Research 90. 10043–10072.
20. Kristján Sæmundsson 1979. Outline of the geology of Iceland. Jökull
29. 7–29.
21. Wolfe, C.J., Ingi Þ. Bjarnason, VanDecar, J.C. & Solomon, S.C. 1997. Seis-
mic structure of the Iceland mantle plume. Nature 385(6613). 245–247.
22. Sigurður Þórarinsson 1950. Jökulhlaup og eldgos á jökulvatnasvæði
Jökulsár á Fjöllum. Náttúrufræðingurinn 20. 113–133.
23. Sigurður Þórarinsson 1974. Vötnin stríð. Bókaútgáfa Menningarsjóðs,
Reykjavík.
24. Magnús T. Guðmundsson & Helgi Björnsson 1991. Eruptions in Gríms-
vötn, Vatnajökull, Iceland, 1934–1991. Jökull 41. 21–45.
25. Kristján Sæmundsson 1978. Fissure swarms and central volcanoes of the
neovolcanic zones of Iceland. Geological Journal Special Issue 10. 451–432.
26. Guðrún Larsen 1984. Recent volcanic history of the Veidivötn fissure
swarm, Southern Iceland. An approach to volcanic risk assessment.
Journal of Volcanology and Geothermal Research 22. 33–58.
27. Olgeir Sigmarsson, Haraldur Karlsson & Guðrún Larsen 2000. The
1996 and 1998 subglacial eruptions beneath the Vatnajökull ice sheet in
Iceland: contrasting geochemical and geophysical inferences on magma
migration. Bulletin of Volcanology 61(7). 468–476.
28. Guðrún Larsen 1982. Gjóskutímatal Jökuldals og nágrennis. Bls. 51–65
í: Eldur er í norðri: afmælisrit helgað Sigurði Þórarinssyni sjötugum 8.
janúar 1982 (ritstj. Helga Þórarinsdóttir). Sögufélag, Reykjavík.
29. Þorvaldur Þórðarson & Ármann Höskuldsson 2002. Iceland. Terra Pub-
lishing, Harpenden, Bretland. 200 bls.
30. Friedman, J.D., Williams, R.S., Sigurður Þórarinsson & Guðmundur
Pálmason 1972. Infrared emission from Kverkfjöll subglacial volcanic
and geothermal area, Iceland. Jökull 22. 27–43.
31. Helgi Björnsson & Páll Einarsson 1990. Volcanoes beneath Vatnajökull,
Iceland: Evidence from radio echo-sounding, earthquakes and jökul-
hlaups. Jökull 40. 147–168.
32. Guðrún Larsen & Sigurður Þórarinsson 1977. H-4 and other acid Hekla
tephra layers. Jökull 27. 28–46.
33. Guðrún Larsen & Elsa G. Vilmundardóttir 1985. Gjóskurannsóknir
á Þjórsársvæði 1983–1984: áfangaskýrsla. Orkustofnun OS-85037/
VOD-16B, Reykjavík. 20 bls.
34. Snorri P. Snorrason, Ingibjörg Kaldal, Skúli Víkingsson & Guðrún Larsen
2006. Hálsslón, setlög og rofhjallar. Áfangaskýrsla. Landsvirkjun
2006/047. 27 bls.
35. Sigurður Þórarinsson 1961. Uppblástur á Íslandi í ljósi öskulagarann-
sókna. Ársrit Skógræktarfélags Íslands 1960–1961. 17–54
36. Ólafur Arnalds 2004. Volcanic soils of Iceland. Catena 56(1–3). 3–20.
37. Esther Ruth Guðmundsdóttir, Guðrún Larsen & Jón Eiríksson 2011.
Two new Icelandic tephra markers: The Hekla Ö tephra layer, ~6060 cal.
yr BP, and Hekla DH tephra layer, ~ 6650 cal. yr BP. Land-sea correla-
tion of mid-Holocene tephra markers. Holocene 21(4). 629–639. DOI:
10.1177/0959683610391313.
38. Karl Grönvold, Níels Óskarsson, Johnsen, S.J., Clausen, H.B., Hammer,
C.U., Bond, G. & Bard, E. 1995. Ash Layers from Iceland in the Greenland
Grip Ice Core Correlated with Oceanic and Land Sediments. Earth and
Planetary Science Letters 135(1–4). 149–155.
39. Zielinski, G.A., Mayewski, P.A., Meeker, L.D., Karl Grönvold, Germani,
M.S., Whitlow, S., Twickler, M.S. & Taylor, K. 1997. Volcanic aerosol
records and tephrochronology of the Summit, Greenland, ice cores. Jour-
nal of Geophysical Research 102(C12). 26625–26640.