The medial offshore record of Plinian arc volcanism in the Eastern Aegean Sea: Implications for tephrostratigraphy, correlations, ages and volumes

Abstract

<p>The Hellenic arc hosts several active volcanic centers, of which the Milos, Santorini-Kolumbo and Kos-Yali-Nisyros volcanic fields present particularly high threats due to recent unrest (2011-2012 and 1996-1997 at Santorini and Nisyros, respectively). These volcanic centers have repeatedly produced highly explosive eruptions (VEI 4 to 7) from ~360 ka into historic times. The marine tephra record provides information not only on the number of events, but also on their magnitudes and intensities inferred from tephra dispersal characteristics, and is thus essential to quantitatively assess future volcanic hazards and risks.</p><p>Here we complement earlier work on distal to ultra-distal east-Mediterranean sediment cores, which captured the largest eruptions. We present results from a grid of medial to distal sediment cores collected in 2017 during RV Poseidon cruise POS513 with core positions both comparatively close to and between the three volcanic fields, in order to record medium- to large-scale eruptions.</p><p>During this cruise, 47 gravity cores up to 7.4 m long, and 3 box cores of the uppermost 0.5 m sediment were recovered, which contain more than 220 primary ash layers. The compositions of glass shards from all layers were characterized by major (EMP) and trace-element (LA-ICPMS) analyses.</p><p>Geochemical fingerprinting supports correlations with 20 eruptions from all three volcanic fields as well as with the 39 ka Campanian ignimbrite eruption from the Campi Flegrei, Italy. Correlations with eleven eruptions from Santorini-Kolumbo (Kameni, Kolumbo 1650, Minoan, Cape Riva, Cape Tripiti, Upper Scoria 1 and 2, Middle Pumice, Cape Thera, Lower Pumice, Cape Therma 3) are established, and we newly identify two widespread tephras from eruptions on Milos (Lower and Upper Firiplaka). We have probably been able to solve some previous chronostratigraphic problems at Kos-Yali-Nisyros by correlating marine tephras with the Kos Plateau Tuff, and with the Yali 2 tephra, whereby we identify a second, less evolved facies produced by that eruption that has not yet been recognized on land. We also find tephras from four eruptions on Nisyros (Nisyros 1 to 4) including the previously established Lower (Nisyros 4) and Upper (Nisyros1) Nisyros Pumice eruptions.</p><p>These correlations also provide new age constraints for hitherto poorly or non-dated Aegean tephras based on sedimentation rates derived between multiple anchor points of dated terrestrial tephra ages. We deduce ages of ~22 ka and ~36 ka for Upper and Lower Firiplaka tephras from Milos (the latter overlying the Campanian ash) which are significantly younger than other eruption ages known from Milos, ~54 ka, ~62 ka, ~69 ka, and ~76 ka for the Nisyros 1 to 4 tephras, and ~52 ka for the Yali 1 tephra as well as a verified age of 33 ka for the Yali 2 tephra with its two contemporaneous facies.</p><p>These new tephrostratigraphic results help to improve quantifications of distribution and eruption characteristics for all these eruptions, and provide important pre-site survey data for the Santorini IODP proposal VolTecArc.</p>

Tracking timescales of magma reservoir recharge through caldera cycles at Santorini (Greece). Emphasis on an explosive eruption of Kameni Volcano

“…The total volume of the PKP is poorly constrained. Distal ash from the Kameni edifice mapped in deepsea sediments southeast of Santorini (Kutterolf et al, 2021) has a volume of 0.4 km 3 DRE; it may correlate with the PKP or with several eruptions of Kameni, but it provides a maximum volume estimate for the PKP. In this paper we take the volume of the PKP to be of the order of ~0.1 km 3 , but the exact value does not affect our conclusions.…”

“…The eruptions studied previously are the Cape Riva (22 ka; 39 km 3 DRE) and Late Bronze Age (3.6 ka, 32 km 3 DRE) caldera-forming eruptions, and three flows of the ~0.2 km 3 Therasia silicic lavas that leaked out a few thousand years prior to the Cape Riva eruption (Table 1) (Fabbro et al, 2017;Flaherty et al, 2018). The volumes for Cape Riva and LBA are estimates based on a new study of deep-sea tephra from Santorini (Kutterolf et al, 2021). In integrating the opx datasets, we have recalculated the diffusion timescales of Fabbro et al (2017) using the a-axis Dohmen et al (2016) diffusion coefficient, so as to be consistent with those of Flaherty et al (2018) and the present study.…”

“…Our study of the ~0.1 km 3 PKP allows us to compare it petrologically with the 39 km 3 Cape Riva and 32 km 3 LBA caldera-forming eruptions (Kutterolf et al, 2021), which were studied to a similar level of detail. Apart from the large volume difference, the products show several similarities (Table 3): (1) all contain 5-20 % crystals, (2) all contain plagioclase crystals with antecrystic/xenocrystic cores and distinct autocrystic rims, (3) all contain opx crystals that are sector zoned, with or without phantom skeletal morphologies, (4) all contain evidence for the mingling of compositionally variable silicic melts, (5) the mineral phases in all Frontiers in Earth Science frontiersin.org three eruptions yield crystal diffusion timescales (Mg-Fe in opx and cpx; Mg in plagioclase) that are much shorter than the duration of the preceding repose period, and (6) all contain mafic enclaves showing the involvement of mafic magma in the eruption.…”

“…Santorini is a 10 km north-south, 8 km east-west caldera with its floor 390 m below sea level (Figure 1A) (Nomikou et al, 2014). It has been active since at least 650 ka, and since 360 ka has had ~100 explosive eruptions (Figure 1B) (Druitt et al, 1999;Kutterolf et al, 2021). Twelve prominent Plinian eruptions are named, and the sequences of minor inter-Plinian tephra and lavas between them are numbered ('M' for minor; Figure 1B).…”