A shift in eruption mode of Hekla volcano, Iceland, 3000 years ago: two‐coloured Hekla tephra series, characteristics, dispersal and age. (25th November 2019)

• Record Type: Journal Article
• Authors: LARSEN, GUDRÚN; Róbertsdóttir, Bryndís G.; Óladóttir, Bergrún A.; EIRÍKSSON, JÓN
• Other Names: Abbott Peter M. guestEditor.; Jensen Britta J.L. guestEditor.; Lowe David J. guestEditor.; Suzuki Takehiko guestEditor.; Veres Daniel guestEditor.
• Is Part Of: Journal of quaternary science. Volume 35:Number 1/2(2020)
• Page Start: 143
• Page End: 154
• Publication Date: 2019-11-25
• Subjects: age -- Hekla -- tephra dispersal -- tephrochronology -- two‐coloured tephra; Geology, Stratigraphic -- Quaternary -- Periodicals; Paleontology -- Quaternary -- Periodicals; 551.79
• DOI: 10.1002/jqs.3164
• Languages: English
• ISSNs: 0267-8179

Abstract

ABSTRACT: 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% SiO2 ), while the upper unit is basaltic andesite (53–57% SiO2 ). 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 SiO2 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.