Volcano-air-sea interactions in a coastal tuff ring, Jeju Island, Korea

The Holocene tuff ring of Songaksan, Jeju Island, Korea, is intercalated with wave-worked deposits at the base and in the middle parts of the tuff sequence, which are interpreted to have resulted from fair-weather wave action at the beginning of the eruption and storm wave action during a storm surge event in the middle of the eruption, respectively. The tuff ring is overlain by another marine volcaniclastic formation, suggesting erosion and reworking by marine processes because of post-eruption changes of the sea level. Dramatic changes of the chemistry, accidental componentry, and ash-accretion texture of the pyroclasts are also observed between the tuff beds deposited before and after the storm invasion. The ascent of a new magma batch, related to the chemical change, could not be linked with either the Earth and ocean tides or the meteorological event. However, the changes of the pyroclasts texture suggest a sudden change of the diatreme fill from water-undersaturated to supersaturated because of an increased supply of external water into the diatreme. Heavy rainfall associated with the storm is inferred to have changed the water saturation in the diatreme. Songaksan demonstrates that there was intimate interaction between the volcano and the environment.

Composite development and stratigraphy of the Onepoto maar lake sediment sequence (Auckland Volcanic Field, New Zealand)

The accurate and precise reconstruction of Quaternary climate as well as the events that punctuate it is an important driver of the study of lake sediment archives. However, until recently lake sediment-based palaeoclimate reconstructions have largely concentrated on Northern Hemisphere lake sequences due to a scarcity of continuous and high-resolution lake sediment sequences from the Southern Hemisphere, especially from the southern mid-latitudes. In this context, the deep maar lakes of the Auckland Volcanic Field of northern New Zealand are significant as several contain continuous and well-laminated sediment sequences. Onepoto Basin potentially contains the longest temporal lake sediment record from the Auckland Volcanic Field (AVF), spanning from Marine Isotope Stage 6e (MIS 6e) to the early Holocene when lacustrine sedimentation was terminated by marine breach of the south-western crater tuff ring associated with post-glacial sea-level rise. The Onepoto record consists of two new, overlapping cores spanning ca. 73 m combined with archive material in a complete composite stratigraphy. Tephrochronology and 14C dating provide the fundamental chronological framework for the core, with magnetic relative palaeo-intensity variability downcore, and meteoric 10Be influx into the palaeolake to refine the chronology. The µ-XRF (micro X-ray fluorescence) downcore variability for the entirety of the lake sediment sequence has been established with measurement of a range of proxies for climate currently underway. This work will produce the first continuous record of the last 200 kyr of palaeoclimate from northern New Zealand to date.

Magma fragmentation and timing of water-magma interaction of La Joya de Yuriria maar volcano and La Sanabria-San Roque tuff ring complex, Mexico

<p>La Joya de Yuriria maar volcano and La Sanabria-San Roque tuff ring complex manifests at the southern and northern extreme of the NNW-SSE trending clusters of phreatomagmatic vents of Valle de Santiago volcanic field, which forms the NE part of the famous Michoacan-Guanajuato Volcanic Field ( (MGVF), central Mexico. La Sanabria-San Roque complex is located in the south of the town of Irapuato and is composed of three tuff rings namely San Joaquin (SJ), La Sanabria (LS) and San Roque (SR). Their tephra deposits were studied at 7 different active quarries, which suggests that the San Joaquin tuff ring was formed before La Sanabria-San Roque tuff ring complex. San Joaquin is composed of medium-size lapilli flow (Mdphi=-2.05 to -3.90, σphi=2.00 to 2.58) and fine ash surge units and contains different types of lithics and juvenile fragments (50-68 vol.%.). About four types of lithics were identified namely: grey-colored vesicular basaltic andesites (9-27 vol.%), grey-colored non-vesicular basaltic andesites (17-19 vol.%), white lithics (sediments 0-1 vol.%), red-colored lithics (volcanic breccias 1-3 wt.%) along with few plagioclase crystals (0.54-0.66 vol.%) that are exposed at quarries 1, 3. La Sanabria-San Roque tuff ring complex tephra deposits are exposed at quarries 2, 5 and 8 and are composed of intercalated flow (Mdphi=-1.65 to -2.15, σphi=1.00-1.83) and fallout (Mdphi=-2.00 to -6.10, σphi=2.00) units with juvenile content from 41-87 vol.% and four different types of lithic fragments: grey-colored vesicular lithics (1- 20 vol.%), grey-colored compact lithics (2-6 vol.%), which is considerably lower than the amount encountered within SJ deposits. Further-more, white-colored lithics, mostly sediments (0-10 vol.%) and red-colored lithics (rhyolites and/or volcanic breccias) around 0-3 vol.%.</p><p>La Joya de Yuriria is currently located on the southern margin of the artificial lake of Yuriria and its tephra sequence is composed of mostly fallout units (Mdφ=-4.45 to -4.60, σφ=1.88 to 2.55), followed by flow units (Mdφ=-2.95 to -3.800, σφ=1.93 to 2.05) that are separated with both indurated, fine-ash wet and dry surge units of which a very particular fine-ash dry surge unit ( Mdφ=-0.95, σφ=2.03), yellowish in color (due to oxidation?), may represent a short-term break within the phreatomagmatic activity. It is also composed of flow units (Mdφ=-1.50 to -2.95, σφ=1.40 to 3.43) that are clast supported, friable and contains medium to coarse lapilli size fragments that are rich in accidental lithics with very juvenile clasts (<33 vol.%) of basaltic andesite (SiO<sub>2</sub>= 54.4 wt%, Na<sub>2</sub>O+K<sub>2</sub>O= 5.21 wt%) with very few juvenile content (5-37 wt.%), except at VS-1741-P7 (85 vol.%) and abundance of light grey colored angular lithics that were classified as vesicular (4.51 vol.%) and non-vesicular (1-66 vol.%) with few reworked lithics (1-5 vol.%) and altered lithics (1-5 vol.%).</p><p>Vesicularity index on 2741 juvenile clasts from these vents was utilized to determine the magma fragmentation and the timing of magma-water interactions (especially exsolution of volatiles before or during mag-water interaction). To corroborate this, Bubble Nucleation Density and crystal texture of primary vesicles within glass shards were also performed to validate the interpretations made.</p>