Jökull - 01.01.2005, Blaðsíða 56

Bergrún Arna Óladóttir et al.
Table 1. a) Key marker tephra layers in the study area. Also shown are published 14C-ages, calibrated years,
and source volcanic system for each tephra layer (Larsen et al., 2001; Dugmore et al., 1995b; Grönvold et al.,
1995). b) Estimated 14C age of key tephra layers and Hólmsár Fires from their relative position compared to
dated tephra layers (Larsen et al., 2001), calibrated after Stuiver et al., (1998) assuming a standard deviation
of 100 years. An eruption age based on the SAR-method (see discussion in text) is also given for those tephra
layers that have not been dated by the radiocarbon method. – a) Tímasett lykilgjóskulög á rannsóknasvæðinu,
aldur þeirra og uppruni (Guðrún Larsen og fl., 2001; Andrew Dugmore og fl., 1995; Karl Grönvold og fl.,
1995). Taflan sýnir geislakolsaldur og leiðréttan aldur samkvæmt trjáhringjatali (Stuiver og fl., 1998). Í næst-
síðasta dálki er aldur miðaður við árið 2005 (ekki 1950). b) Lykillög af áætluðum aldri miðað við tímasett
gjóskulög og áætlaður aldur Hólmsárelda (Guðrún Larsen og fl., 2001). Taflan sýnir geislakolsaldur (gert er
ráð fyrir ±100 ára staðalfráviki) og leiðréttan aldur fjögurra lykillaga á sama hátt og í 1a), aldur í árum fæst
með að bæta 2005 árum við tölur í fjórða dálki. Reiknaður aldur, byggður á jarðvegsþykknun (SAR) milli
tímasettra lykillaga, er hins vegar 90–195 árum hærri, eins og sýnt er í fimmta dálki.
Tephra layer Log number Publ. 14C age1 Calibr./calend. year2 Cal. age bf 2005 AD Volcanic system
Settlement AT-2 ∼870 AD 1135 years Veiðivötn
SILK-UN AT-49 2660±50 BP 850±70 BC ∼2855 years Katla (SILK)
SILK-MN AT-65 2975±12 BP 1230±30 BC ∼3235 years Katla (SILK)
SILK-LN AT-70 3139±40 BP 1440±75 BC ∼3445 years Katla (SILK)
HS AT-80 3515±55 BP 1855±125 BC ∼3860 years Hekla
H4 HA-1 3826±12 BP 2255±55 BC ∼4260 years Hekla
Katla RF-5 6400±80 BP 5360±130 BC ∼7365 years Katla
A13 RF-44 7505±42 BP 6380±55 BC ∼8385 years Torfajökull?
1Age values are given relative to the calendar year 1950.
2Calibrated after Stuiver et al., (1998).
Tephra layer Log number Estim. 14C age1 Estim. calibr. year2 SAR age bf 2005 AD3) Volcanic system
SILK-N2 HA-11 ∼4200 BP ∼2790 BC ∼4960 years Katla (SILK)
SILK-N1 HA-27 ∼4900 BP ∼3730 BC ∼5830 years Katla (SILK)
SILK-A1 HA-30 ∼5000 BP ∼3810 BC ∼6010 years Katla (SILK)
A6 RF–1 ∼7130 years Torfajökull
Hólmsár Fire RF-14? ∼6800 BP ∼5680 BC ∼7560 years Katla
1Larsen et al., (2001).
2Estimated 14C age calibrated by the method of Stuiver et al., (1998)
3Calculated age with the SAR method (see text for further details)
pears to be similar to that observed in historical times.
The number of Holocene subglacial explosive erup-
tions at the Katla volcano was previously estimated
to have exceeded 180 eruptions, of which > 170 are
basaltic, and 12 are felsic (Larsen, 2000). In contrast,
the ice-free part of the system, or the fissure swarm
outside the central volcano, has had a much lower
eruption frequency, or only 8–12 effusive basalt erup-
tions during the Holocene. Nonetheless, the activity
on the fissure swarm includes the two largest events in
the Katla system; the Hólmsá Fires ∼7700 years ago
(≥5 km3) in addition to the above mentioned Eldgjá
Fires (Larsen, 2000).
56 JÖKULL No. 55