From sink to volcanic source: Unravelling missing terrestrial eruption records by characterization and high‐resolution chronology of lacustrine volcanic density flow deposits, Lake Inawashiro‐ko, Fukushima, Japan

Abstract

Eruption records in the terrestrial stratigraphy are often incomplete due to erosion after tephra deposition, limited exposure and lack of precise dating owing to discontinuity of strata. A lake system and sequence adjacent to active volcanoes can record various volcanic events such as explosive eruptions and subaqueous density flows being extensions of eruption triggered and secondary triggered lahars. A lacustrine environment can constrain precise ages of such events because of constant and continuous background sedimentation. A total of 71 subaqueous density flow deposits in a 28 m long core from Lake Inawashiro-ko reveals missing terrestrial volcanic activity at Adatara and Bandai volcanoes during the past 50 kyr. Sedimentary facies, colour, grain size, petrography, clay mineralogy, micro X-ray fluorescence analysis and chemistry of included glass shards characterize the flow event deposits and clarify their origin: (i) clay-rich grey hyperpycnites, extended from subaerial cohesive lahars at Adatara volcano, with sulphide/sulphate minerals and high sulphur content which point to a source from hydrothermally altered material ejected by phreatic eruptions; and (ii) clay-rich brown density flow deposits, induced by magmatic hydrothermal eruptions and associated edifice collapse at Bandai volcano, with the common presence of fresh juvenile glass shards and low-grade hydrothermally altered minerals; whereas (iii) non-volcanic turbidites are limited to the oldest large slope failure and the 2011 Tohoku-oki earthquake events. The high-resolution chronology of volcanic activity during the last 50 kyr expressed by lacustrine event deposits shows that phreatic eruption frequency at Adatara has roughly tripled and explosive eruptions at Bandai have increased by ca 50%. These results challenge hikers, ski-fields and downstream communities to re-evaluate the increased volcanic risks from more frequent eruptions and far-reaching lahars, and demonstrate the utility of lahar and lacustrine volcanic density flow deposits to unravel missing terrestrial eruption records, otherwise the recurrence rate may be underestimated at many volcanoes.

Major fluvial erosion and a 500‐Mt sediment pulse triggered by lava‐dam failure, Río Coca, Ecuador

“…Sedimentologists interpreting stratigraphy in lacustrine or marine cores offshore of volcanic terrain would likely interpret a thick ‘event’ deposit as representing some tectonic or climatic disturbance, i.e., a major earthquake (Hill et al, 2022) or storm rainfall and flooding associated with a strong El Niño episode (Covault et al, 2010). Even if enough sediment cores were available to reveal that the deposit was spatially localized rather than extending along a continental margin (as expected from a megathrust earthquake or climatic disturbance), it would seem reasonable to attribute a thick volcaniclastic deposit to a large volcanic eruption (Kataoka & Nagahashi, 2019; Manville et al, 2009). It is unlikely that scientists interpreting the downstream sedimentary record would arrive at the interpretation of a rare, autogenic, stochastic watershed process involving a collapse of grade control and major regressive erosion.…”

Crisis hazard assessment for snow-related lahars from an unforeseen new vent eruption: the 2018 eruption of Kusatsu-Shirane volcano, Japan

“…Lahar deposits associated with magmatic pyroclastic eruptions include gravel and sand-sized particles (e.g., Pierson et al 1996) and can vary from matrix-rich (not clay-rich but silt-and sand-rich) to clast-rich, depending on the eruption style, size, and explosiveness (e.g., Mothes and Vallance 2015). In contrast, phreatic and magmatic hydrothermal activity through extant hydrothermal systems can produce clay-rich ejecta and hence clay-rich, syn-and post-eruptive lahars (Kataoka et al 2018;Kataoka and Nagahashi 2019). Also, gravitational collapse of hydrothermally altered parts of the volcanic edifice can produce clay-rich lahars (Vallance and Scott 1997;Vallance 2005).…”

Volcanism‐induced sedimentation and model: A case study of the Upper Jurassic‐Lower Cretaceous sediments in the Liuhe‐Tonghua Basin, NE China

“…Mixed sediments vary in lithology, lithofacies and vertical succession, related to the varied transportation distances and environments. Kataoka and Nagahashi (2019) reconstructed the missing terrestrial eruption from the modern lacustrine records of volcanic flow deposits of Lake Inawashiro‐ko in Fukushima, Japan, manifesting a dispersal path from volcanic source to sink. Cas et al (2001) provided a case study of the Upper Devonian, Australia, demonstrating that the deposits in lakes are distinctive and useful for a systematic understanding of the behaviour of volcanic clasts and dispersal processes.…”