Radiocarbon dating of mid-Holocene megaflood deposits in the Jokulsa a Fjollum,north Iceland

Abstract

Two megafloods in the canyon of the Jokulsi i Fjóllum, the major northern routeway for glaciovolcanic floods from Vatnajókull, have been closely dated by 14C AMS dates from Betula macrofossils within peat immediately below beds of flood-deposited sand. Ages of c. 4415 and c. 4065 yr BP (5020 and 4610 cal. yr BP) are consistent with the presence of the Hekla 4 tephra (c. 3830 yr BP) resting on the upper surface of the younger flood sand. These sediments are correlated across the Jókulsa a Fjollum canyon with the upper flood sands in a stack recording around 16 flood events. Deposits on both sides of the canyon were trimmed by the last megaflood after the Hekla 3 tephra fall at c. 2900 yr BP, and the highest Holocene flood stages were at the culmination of a series peaking at c. 3500 yr BP. These floods have wider palaeoclimatic significance because they require the formation of large subglacial reservoirs below Vatnajókull. Therefore, the dated floods indicate that a large composite ice cap covered volcanoes in the southeastern highlands through the early and middle Holocene, and that flood routeways largely switched to the south after c. 3500 yr BP.

Keywords

Jokulhlaups radiocarbon dating slackwater sediment megafloods mid-Holocene Iceland

Get full access to this article

View all access options for this article.

References

Dugmore, A.J. , Shore, J.S. , Cook, G.T. , Newton, A.J. , Edwards, K.J. and Larsen, G. 1995: The radiocarbon dating of tephra layers in Britain and Iceland . Radiocarbon 37, 286-295 .

Dugmore, A.J. , Newton, A.J. , Larsen, G. and Cook, G.T. 2000: Tephrochronology, environmental change and the Norse settlement of Iceland . Environmental Archaeology 5, 21-34 .

Einarsson, D. 1961: Pollenanalyische untersuchung zur spatund postglazialen klimageschichte Islands. Sonderveroffentischungen des Geologischen Institutes der Universitat Koln 6.

Einarsson, D. 1963: Pollen analytical studies on the vegetation and climate history of Iceland in Late and Postglacial times. In Love, A. and Love, D. , editors, North Atlantic biota and their history. Pergamon Press , 355-365.

Eliasson, S. 1977: Molar um Jokulsarhlaup og Asbyrgi . NattturufreOingurinn 47, 160-179 .

Guómundsson, M.T. , Sigmundsson, F. and Bjornsson, H. 1997: Icevolcano interaction of the 1996 Gjalp subglacial eruption, Vatnajokull, Iceland . Nature 389, 954-957 .

Knudsen, O. and Russell, A.J. 2002: Jokulhlaup deposits at the Asbyrgi Canyon, northern Iceland: sedimentology and implications for flow type . International Association of Scientific Hydrologists Publication 271, 107-112 .

Reimer, P.J. , Baillie, M.G.L. , Bard, E. , Bayliss, A. , Beck, J.W. , Bertrand, C. , Blackwell, P.G. , Buck, C.E. , Cutler, K.B. , Damon, P.E. , Edwards, R.L. , Fairbanks, R.G. , Freidrich, M. , Guilderson, T.P. , Hughen, K.A. , Kromer, B. , McCormac, F.G. , Manning, S. , Bronk Ramsey, C. , Reimer, R.W. , Remmele, S. , Southon, J.R. , Stuiver, M. , Talamo, S. , Taylor, F.W. , van der Plicht, J. and Weyhenmeyer, C.E. 2004: IntCalO4 terrestrial radiocarbon age calibration, 26-0 ka BP . Radiocarbon 46, 1029-1058 .

Stuiver, M. and Reimer, P.J. 1993: Extended 14C database and revised CALIB 3.0 14C age calibration program . Radiocarbon 35, 215-230 .

10.

Thórarinsson, S. 1960: Der Jokulsa-Canyon und Asbyrgi . Petermanns Geographische Mitteilungen 104, 154-162 .

11.

Tómasson, H. 1973: Hamfarahlaup i Jokulsai a Fjollum . Nóttturufretingurinn 43, 12-34 .

12.

Tómasson, H. 2002: Catastrophic floods in Iceland . International Association of Scientific Hydrologists Publication 271, 121-126 .

13.

Waitt, R.B. 2002: Great Holocene floods along Jokulsa a Fjollum, north Iceland . Special Publication of the International Association of Sedimentologists 32, 37-51 .