Special issue "Advancement of our knowledge on Aso volcano: current activity and background

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Constraints on the Timing of Explosive Volcanism at Aso and Aira Calderas (Japan) Between 50 and 30 ka: New Insights From the Lake Suigetsu Sedimentary Record (SG14 Core)

Volcanoes in the East Asian/Pacific region have been the source of some of the largest magnitude eruptions during the Quaternary, and accurately evaluating their eruptive histories is essential for hazard assessments. To overcome difficulties in resolving and precisely dating eruptions in the near‐source realm, the high‐resolution (varved) sediments of Lake Suigetsu (central Honshu, Japan) were examined for the presence of non‐visible (cryptotephra) layers from 50 ka up until the 30 ka AT caldera‐forming event of Aira volcano. Cryptotephra layers are four times more frequently preserved than visible markers in the Suigetsu sediments, meaning that this archive provides a unique and unprecedented record of eruptions that were dispersed towards the densely populated regions of central Honshu. Major and trace element volcanic glass chemistry is used to fingerprint the ash layers and pinpoint their volcanic origin. Tephras are found throughout the investigated sediments, but the highest abundance of ash fall events are recorded between 39 and 30 ka, capturing a period of intense volcanism at calderas on Kyushu Island (Japan). The augmented Suigetsu tephrostratigraphy records at least seven eruption events from Aso caldera (southern Kyushu) that post‐date the widespread ACP‐4 Plinian eruption (ca. 50 ka), and four explosive events from Aira (central Kyushu) that occurred leading up to the catastrophic caldera‐forming AT eruption (ca. 30 ka)

Plant Diversity Changes during the Postglacial in East Asia: Insights from Forest Refugia on Halla Volcano, Jeju Island

Understanding how past climate changes affected biodiversity is a key issue in contemporary ecology and conservation biology. These diversity changes are, however, difficult to reconstruct from paleoecological sources alone, because macrofossil and pollen records do not provide complete information about species assemblages. Ecologists therefore use information from modern analogues of past communities in order to get a better understanding of past diversity changes. Here we compare plant diversity, species traits and environment between late-glacial Abies, early-Holocene Quercus, and mid-Holocene warm-temperate Carpinus forest refugia on Jeju Island, Korea in order to provide insights into postglacial changes associated with their replacement. Based on detailed study of relict communities, we propose that the late-glacial open-canopy conifer forests in southern part of Korean Peninsula were rich in vascular plants, in particular of heliophilous herbs, whose dramatic decline was caused by the early Holocene invasion of dwarf bamboo into the understory of Quercus forests, followed by mid-Holocene expansion of strongly shading trees such as maple and hornbeam. This diversity loss was partly compensated in the Carpinus forests by an increase in shade-tolerant evergreen trees, shrubs and lianas. However, the pool of these species is much smaller than that of light-demanding herbs, and hence the total species richness is lower, both locally and in the whole area of the Carpinus and Quercus forests. The strongly shading tree species dominating in the hornbeam forests have higher leaf tissue N and P concentrations and smaller leaf dry matter content, which enhances litter decomposition and nutrient cycling and in turn favored the selection of highly competitive species in the shrub layer. This further reduced available light and caused almost complete disappearance of understory herbs, including dwarf bamboo

Using lake sediment cores to improve records of volcanism at Aluto volcano in the main Ethiopian rift

info:eu-repo/semantics/publishe

Dispersal and grain size characteristics of the May 14, 2018 Shinmoedake eruption deposit, Kirishima Volcano, Japan, based on post-eruption field survey and meteorological datasets

Abstract This study describes the dispersal and grain size characteristics of the May 14, 2018 Shinmoedake eruption deposits of Kirishima Volcano in southern Kyushu, southwestern Japan. We discuss the eruption sequence, including the temporal variations in the behavior of the plume, by combining field and meteorological datasets. Following a magmatic activity in 2011 characterized by a substantial change in the eruption style (from subplinian eruptions to lava effusion) and subsequent vulcanian explosions, the Shinmoedake crater experienced intermittent eruptions in 2018. The May 14, 2018 eruption began at 14:44 with a vulcanian eruption, with the eruption plume rising 4500 m above the crater rim. Thereafter, it transitioned to an ash eruption; the plume height decreased gradually until the eruption ceased at 16:10. The tephra fall deposits were distributed more than 27 km to the southeast of the source crater; the mass of the tephra fall deposit was approximately 2.1 × 107 kg, calculated based on an isomass map. The deposit incidence differed between the east and west sides of the major dispersal axis. The deposits found east of the main dispersal axis were primarily composed of coarse to medium sand-sized particles with no fine fraction (fine sand to silt in size). In contrast, the deposits west of the axis were finer-grained than those east of the axis. We analyzed photographs of the eruption plume, along with the regional meteorological data and the dispersal and grain-size characteristics of the deposits, and reached the following conclusion: during the May 14, 2018 eruption, the wind directions above the Shinmoedake crater fluctuated across altitudes. The westerly winds dispersed the eruption plume that rose to a higher altitude, containing coarser tephra associated with the initial vulcanian eruption, further to the east rather than along the main axis. In contrast, a lower-altitude ash eruption plume that was rich in fine materials was dispersed westward rather than along the main axis, which was influenced by northerly winds. The findings of this study can support the analysis of similar volcanic events. Graphical Abstrac