The multi‐component Hekla Ö Tephra, Iceland: a complex widespread mid‐Holocene tephra layer

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We present a tephra stratigraphical and tephrochronological record from eight lakes in Vestfirðir, NW Iceland. About 50 tephra units have been identified, representing nearly 30 eruptive events originating from five volcanic systems: Hekla, Katla, Snæfellsjökull, Grímsvötn and Veiðivötn‐Bárðarbunga. Most of the tephra layers originate from Grímsvötn, although there is a prominent presence of andesitic to basaltic tephra layers from Hekla in the record. We propose that the previously described Brattihjalli tephra is actually the 6060‐year‐old Hekla Ö tephra marker layer, recording a more north‐westerly dispersal than before and providing new correlation possibilities across Iceland. Thus, the Hekla Ö tephra covers as large an area in Iceland as the Hekla 5, Hekla 4, Hekla 3 and Hekla 1104 tephra layers, emphasizing its importance as a chronological marker. The tephra markers Hekla 1693, V877/Settlement layer, Sn‐1, Hekla 3 and Hekla 4 have been found and, additionally, our study identifies four potential tephra markers, the Katla D1 ∼2750 cal a BP, Katla D2 ∼3700 cal a BP, Reykjarfjörður tephra ∼8800 cal a BP and Dagverðardalur tephra ∼9300–9500 cal a BP. Our data reveal several new tephra layers in Vestfirðir, including chronological markers important for dating and correlation.

Section: Resultsmentioning

confidence: 99%

“…; Table ). Here we propose that the Brattihjalli tephra is in fact the 6060‐year‐old Hekla Ö tephra marker layer (Gudmundsdóttir et al ., ; Jónsson, ) based on stratigraphical position, age and geochemistry (Fig. ).…”

Section: Resultsmentioning

confidence: 99%

Holocene tephrostratigraphy in Vestfirðir, NW Iceland

Guðmundsdóttir

Schomacker

Brynjólfsson

et al. 2018

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“…The fine ash fraction contains a range of grains that are not present in the coarser grade pumices that represent the bulk of the material erupted (e.g. Jónsson, ).…”

Section: Discussionmentioning

confidence: 99%

“…The fine ash fraction contains a range of grains that are not present in the coarser grade pumices that represent the bulk of the material erupted (e.g. Jónsson, ). Detailed electron probe micro‐analysis (EPMA) geochemistry of the TC‐tephra layers has already been carried out by Meara ().…”

Section: Methodsmentioning

confidence: 99%

“…Its eruption history is fairly well known, in particular the historical activity from the 12th century onwards, and the large prehistoric explosive events of 3000–7100 years ago producing the Hekla‐3, ‐S, ‐4, ‐Ö, ‐5 tephra deposits (e.g. Kjartansson, ; Thorarinsson, ; Sigvaldason, ; Larsen and Thorarinsson, ; Grönvold et al ., ; Gudmundsson et al ., ; Lacasse et al ., ; Gudmundsdóttir et al ., ; Stevenson et al ., ; Jónsson, ). However, the two millennia following the Hekla‐3 eruption have not received comparable attention.…”

Section: Introductionmentioning

confidence: 99%

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A shift in eruption mode of Hekla volcano, Iceland, 3000 years ago: two‐coloured Hekla tephra series, characteristics, dispersal and age

Larsen

Róbertsdóttir

Óladóttir

et al. 2019

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Hekla volcano is a major producer of large, widespread silicic tephras. About 3000 years ago, the dominant eruption mode shifted from infrequent large (>1 km 3 ) to more frequent moderate (<1 km 3 ) eruptions. In the following two millennia ≥20 explosive silicic-to-intermediate eruptions occurred, and six or more basaltic. Three categories can be identified with dacite/andesite to basaltic andesite in the oldest eruptions through basaltic andesite to basalt in the youngest eruptions. Ten tephra layers of the first category have distinct field characteristics: a pale lower unit and a dark upper unit (two coloured or TC-layers). Colour separation is sharp indicating a stratified magma chamber origin. The lower unit is dominantly andesitic (61-63% SiO 2 ), while the upper unit is basaltic andesite (53-57% SiO 2 ). Volumes of the eight largest TC-layers range from 0.2 to 0.7 km 3 as freshly fallen. Radiocarbon and soil accumulation rate dates constrain the TC-layers to between 3000 and 2200 years ago. Two of these (~2890 and~2920 b2k) are likely to occur overseas. Low SiO 2 in the last erupted tephra of the TC-layers is comparable to that of historical Hekla lavas, implying a final effusive phase. The Hekla edifice may, consequently, be younger than 3000 years.

Hekla 1947, 1845, 1510 and 1158 tephra in Finland: challenges of tracing tephra from moderate eruptions

Kalliokoski

Guðmundsdóttir

Wastegård

2020

Several cryptotephra layers that originate from Icelandic volcanic eruptions with a volcanic explosivity index (VEI) of ≤ 4 and tephra volumes of < 1 km3 have previously been identified in Northern Europe, albeit within a restricted geographical area. One of these is the Hekla 1947 tephra that formed a visible fall‐out in southern Finland. We searched for the Hekla 1947 tephra from peat archives within the previously inferred fall‐out zone but found no evidence of its presence. Instead, we report the first identification of Hekla 1845 and Hekla 1510 cryptotephra layers outside of Iceland, the Faroe Islands, Ireland and the UK. Additionally, Hekla 1158 tephra was found in Finland for the first time. Our results confirm that Icelandic eruptions of moderate size can form cryptotephra deposits that are extensive enough to be used in inter‐regional correlations of environmental archives and carry a great potential for refining regional tephrochronological frameworks. Our results also reveal that Icelandic tephra has been dispersed into Finnish airspace at least seven times during the past millennium and in addition to a direct eastward route the ash clouds can travel either via a northerly or a southerly transport pathway.