Jökull - 01.01.2012, Blaðsíða 23

Reviewed research article
Deciphering eruption history and magmatic processes from
tephra in Iceland
Bergrún Arna Óladóttir1,2, Guðrún Larsen1 and Olgeir Sigmarsson1,3
1Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, IS-101 Reykjavík, Iceland
2The Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland
3LMV, CNRS - Université Blaise Pascal, Clermont-Ferrand, France
Corresponding author: bergrun@hi.is
Abstract – Tephra is the ideal volcanic product for the study of eruption history of Icelandic volcanoes and
the underlying magmatic processes. In the last 11 centuries, 2/3 of all eruptions have been explosive, leaving
tephra as their only product. Including eruptions of both lava and tephra increases the ratio of tephra pro-
ducing eruptions to 3/4. Tephra conservation depends on several factors such as eruption intensity, weather
conditions and volume of tephra produced as well as the surface on which the tephra is deposited. Vegetation
improves conditions for in situ preservation of tephra layers, and once embedded in soil they can be preserved
for long periods of time. Holocene eruption history can be reconstructed over the last 6–8 millennia from soil
section and further back in time from lacustrine and marine sediment records. Tephra can be used to under-
stand volcanic behaviour over long or short periods, a single eruption mechanism or individual production
phases of an eruption. Examples of combined application of chemical analyses and tephra mapping show how
(1) tephra layers from the Katla volcano unravel most of its Holocene eruption history and suggest likely in-
creased eruption frequency in the future, (2) a fundamental link between repose time and eruption magnitude is
manifested by Hekla tephra, (3) tephra from the Eyjafjallajökull 2010 eruption gives insight into rapidly chang-
ing magmatic processes taking place during a single eruption, and (4) variability within tephra grains from
the Grímsvötn 2011 eruption reflect different depth of magma storage. These examples illustrate how tephra
studies, sensu lato, can reveal magmatic and eruption processes at different temporal and spatial scales that
are of relevance for assessment of future eruptive scenarios.
INTRODUCTION
The past activity at a given volcano may be the best in-
dicator of future eruptive scenarios. Detailed knowl-
edge of eruption history and associated magmatic pro-
cesses is therefore essential for hazard prediction.
The erupted products form an invaluable archive of
magma sources, effective magmatic processes and
corresponding eruptive styles as well as the relevant
time scales and both time-limited and overall magma
productivity. To fully characterize the eruption histo-
ries, timescales and dynamics of eruption processes
at a given volcano, a high-temporal resolution time-
series must be generated on erupted products, such as
detailed tephrostratigraphy.
Today single eruptions can be effectively mon-
itored, providing information such as movement of
magma in the crust (e.g. Sigmundsson et al., 2010),
eruption plume height (e.g. Oddsson et al., 2012) and
particle content in the plume (e.g. Gouhier and Don-
nadieu, 2008). Reaching further back in time the in-
formation on single eruptions becomes scarcer, fewer
observations are available and written documents be-
JÖKULL No. 62, 2012 21