Pumice Formation Research Articles

Unsinkable, long-drifting, millimeter-sized pumice of the 2021 eruption of Fukutoku-Oka-no-Ba submarine volcano

Understanding the relationship between pumice formation and long-term floatability in seawater is becoming increasingly important in terms of eruption dynamics, material cycles, biological and environmental effects, and ocean hazards. Pumice rafts were produced during the 2021 eruption of the Fukutoku-Oka-no-Ba submarine volcano in the Pacific Ocean, far from the Japanese archipelago. The pumice rafts reached the Amami-Ōshima and Okinawa Islands approximately two months after the eruption and continued to cover the sea surface at several bays and ports, providing a great opportunity to study the characteristics of raft pumices. Sieve analysis of the floating pumice indicated that the pumice rafts characteristically contained several millimeter-sized particles with a peak at 2–4 mm. This evidence raises an important question why the millimeter-sized, Fukutoku-Oka-no-Ba 2021 pumice particles were able to float for over two months, which exceeds the floatation time shown in previous studies. To answer this question, a porosity measurement technique for millimeter-to-centimeter-sized pumice particles was established and applied to drifting pumice that erupted during the Fukutoku-Oka-no-Ba 2021 eruption. The total, connected, and isolated porosities (including errors) were acquired for floating and sunken pumice particles. As studied for the floating pumice from past submarine eruptions, most floating pumice particles contain a high amount of isolated porosity (> 30 vol%) and are thus unsinkable even when the pumice size is in the millimeter scale. This study emphasizes that skeletal density is a useful measure for the determination of pumice floatability (sinkable or unsinkable). As the particle size decreases, crystals are lost from the floating pumice particles, suggesting that the particle size of the floating pumice is affected by its petrological properties (crystal content and size). A comparison with natural pumices from subaerial eruptions and experimental pumices from magma decompression experiments suggests that the Fukutoku-Oka-no-Ba 2021 pumices contain abundant isolated pores due to the suppression of expansion after fragmentation by quenching in seawater, and that the relatively low to moderate crystal content in the magma (< 17 vol%) may contribute to favorable conditions to produce abundant, millimeter-sized, unsinkable pumice.Most floating pumices have lower saturation density than seawater due to abundant isolated porosity (> 30 vol%) and are thus unsinkable even when the pumice size is in the millimeter scale.

Sr–Nd–Pb isotopic geochemistry of phenocrysts in pumice from the central Okinawa Trough

AbstractPumice is the most widely distributed magmatic rock in the Okinawa Trough. Numerous scholars have conducted extensive research on the mineralogy, petrochemistry and whole‐rock isotopic characteristics of pumice. However, even with extensive research, some information about pumice is still unknown, including the initial provenance of magma, influences from subducting plates and the possibility of crustal material (including sediments) mixing in during pumice formation. As pumice is loose and porous, seawater re‐modification and injection of sediments may occur during the condensation and rock‐forming process after magma erupts from the seafloor, or in the seawater immersion process after pumice formation. In order to get a better understanding of the isotopic characteristics of magmatism phase, phenocrysts were first separated from the pumice and divided into both light and heavy minerals to analyse their Sr–Nd–Pb isotopic composition. This information was combined with existing isotopic data of volcanic rocks from the Okinawa Trough and its adjacent areas to assess the magma source composition, influence from subduction components and mantle properties in the magmatic source. The research results indicated light minerals had an average 87Sr/86Sr ratio of 0.70454, while heavy minerals averaged 0.70546. The magma, formed pumice, was a product of the crystal fractionation evolution of basic magma, with the additional injection of crustal material. The magma source in the central trough is a mixture of depleted MORB mantle (DMM) and enriched mantle (EMI‐like and EMII‐like) end members, where the EMI‐like end member is the residual subcontinental lithosphere or lower crustal material and the EMII‐like end member is subducted oceanic sediments. The Pb isotopic composition indicated that the magma source was affected by subduction components (sediments) and that pumice magma was mixed with more sediment than basalt magma material in the same area. The mantle of the magma source in the Okinawa Trough showed signatures of the Indian Ocean‐type mantle. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Effects of water depth on pumice formation in submarine domes at Sumisu, Izu-Bonin arc, western Pacific

Domes of the Sumisu volcanic complex (western Pacific), having summits at ocean depths of 1100, 600, 245, and 95 m, are mantled with compositionally identical rhyolitic pumice that has similar vesicularity, but that varies systematically in distribution, size, and surface texture—suggesting that facies and morphology can serve as useful indicators of eruption depth. At depths >500 m, the pumice formed a thick carapace on dense rhyolite and disintegrated by quench fracture and mechanical failure into a jumble of giant (meters to tens of meters) polyhedral blocks with smooth curviplanar surfaces that display a single quenched margin. Vesiculation was arrested on eruption in seawater in all but the interior of the thickest carapace. At <500 m depths, the pumice occurs as an apron of blocky giant and smaller rough-textured clasts enclosed by quenched margins and pockmarked by coarse (cm) vesicles. No carapace pumice occurs, and the summit is composed of craggy dense dome rock. These shallower water pumice clasts resemble those spalled from historic submarine dome-forming eruptions that buoyed to the sea surface. We interpret spalling to result from vent-derived, weak volatile-driven explosions that take place at water depths <500 m. Our study shows that an increase in hydrostatic pressures over a range of 12 MPa reduces volatile-driven explosivity for subaqueous, rhyolitic, dome-forming eruptions, but does not affect vesicularity. We conclude that meter-size, highly vesicular pumice is diagnostic of subaqueous dome eruptions in water depths of at least 1300 m, and its morphology can be used to distinguish between explosive and effusive origins

Is Efate (Vanuatu, SW Pacific) a result of subaerial or submarine eruption? An alternative model for the 1 Ma Efate Pumice Formation

AbstractThe Efate Pumice Formation (EPF) is a trachydacitic volcaniclastic succession widespread in the central part of Efate Island and also present on Hat and Lelepa islands to the north. The volcanic succession has been inferred to result from a major, entirely subaqueous explosive event north of Efate Island. The accumulated pumice-rich units were previously interpreted to be subaqueous pyroclastic density current deposits on the basis of their bedding, componentry and stratigraphic characteristics. Here we suggest an alternative eruptive scenario for this widespread succession. The major part of the EPF is distributed in central Efate, where pumiceous pyroclastic rock units several hundred meters thick are found within fault scarp cliffs elevated about 800 m above sea level. The basal 200 m of the pumiceous succession is composed of massive to weakly bedded pumiceous lapilli units, each 2-3 m thick. This succession is interbedded with wavy, undulatory and dune bedded pumiceous ash and fine lapilli units with characteristics of co-ignimbrite surges and ground surges. The presence of the surge beds implies that the intervening units comprise a subaerial ignimbrite-dominated succession. There are no sedimentary indicators in the basal units examined that are consistent with water-supported transportation and/or deposition. The subaerial ignimbrite sequence of the EPF is overlain by a shallow marine volcaniclastic Rentanbau Tuffs. The EPF is topped by reef limestone, which presumably preserved the underlying EPF from erosion. We here propose that the EPF was formed by a combination of initial subaerial ignimbrite-forming eruptions, followed by caldera subsidence. The upper volcaniclastic successions in our model represent intra-caldera pumiceous volcaniclastic deposits accumulated in a shallow marine environment in the resultant caldera. The present day elevated position of the succession is a result of a combination of possible caldera resurgence and ongoing arc-related uplift in the region.

Explosive silicic volcanism in Iceland and the Jan Mayen area during the last 6 Ma: sources and timing of major eruptions

Fifty-three major explosive eruptions on Iceland and Jan Mayen island were identified in 0–6-Ma-old sediments of the North Atlantic and Arctic oceans by the age and the chemical composition of silicic tephra. The depositional age of the tephra was estimated using the continuous record in sediment of paleomagnetic reversals for the last 6Ma and paleoclimatic proxies (δ18O, ice-rafted debris) for the last 1Ma. Major element and normative compositions of glasses were used to assign the sources of the tephra to the rift and off-rift volcanic zones in Iceland, and to the Jan Mayen volcanic system. The tholeiitic central volcanoes along the Iceland rift zones were steadily active with the longest interruption in activity recorded between 4 and 4.9Ma. They were the source of at least 26 eruptions of dominant rhyolitic magma composition, including the late Pleistocene explosive eruption of Krafla volcano of the Eastern Rift Zone at about 201ka. The central volcanoes along the off-rift volcanic zones in Iceland were the source of at least 19 eruptions of dominant alkali rhyolitic composition, with three distinct episodes recorded at 4.6–5.3, 3.5–3.6, and 0–1.8Ma. The longest and last episode recorded 11 Pleistocene major events including the two explosive eruptions of Tindfjallajökull volcano (Thórsmörk, ca. 54.5ka) and Katla volcano (Sólheimar, ca. 11.9ka) of the Southeastern Transgressive Zone. Eight major explosive eruptions from the Jan Mayen volcanic system are recorded in terms of the distinctive grain-size, mineralogy and chemistry of the tephra. The tephra contain K-rich glasses (K2O/SiO2>0.06) ranging from trachytic to alkali rhyolitic composition. Their normative trends (Ab–Q–Or) and their depleted concentrations of Ba, Eu and heavy-REE reflect fractional crystallisation of K-feldspar, biotite and hornblende. In contrast, their enrichment in highly incompatible and water-mobile trace elements such as Rb, Th, Nb and Ta most likely reflect crustal contamination. One late Pleistocene tephra from Jan Mayen was recorded in the marine sequence. Its age, estimated between 617 and 620ka, and its composition support a common source with the Borga pumice formation at Sør Jan in the south of the island.

Volcanic-fan Formation in the Northern Foot of Mt. Iwaki, Northeast Japan

The ages and formation processes of volcanic-fans in the foot of Mt. fwaki in the Aomori prefecture, Northeast Japan, were discussed.The author recognized seven periods of volcanic-fans formation based on the stratigraphy of fan deposits and the six key tephra layers.The key tephras are the Hachinohe Pumice (ca. 13ka.), the Ofudo Pumice (ca. 26ka.), the Upper brown loam, the Toya Ash (ca. 100ka.), the Lower brown loam and the Shinboshi Pumice formation (probably during the Riss Glacial Age).From the examination of facies of the fan deposit and the comparison between the volume of debris and the volume of dissecting valleys in the side slope of the volcano, the most of the fan deposits may not be the normal sediments derived from the dissecting valleys but the volcanic debris flow, lahar or other kinds of debris flow caused by volcanic activities.The history of the volcanic-fans formation in the northern foot of Mt. Iwaki are supposed as follows;Period I (before the fall of Shinboshi Pumice formation): The deposit during the Period I might be provided as debris avalanche. The deposits of terrace I were composed of angular gravels, fractured huge blocks and many flow mounds.Period III (after the formation of the Lower brown loam and before the fall of Toya Ash): The deposit during the Period III might be provided as debris flow. The sand and gravel deposits of terrace III show the facies of poor sorting, sub-round to round gravel shape. Partly the terrace III deposits are composed of coarse sand layers.Period V (after the formation of the Upper loam and before the flow of Ofudo Pumice): The deposit during Period V might be provided as lahar. The deposits of terrace V were composed of tuffacious sandy gravel beds, including burned woods. Its facies is similar to the facies of deposits of period III.Period VI (after the flow of Ofudo Pumice and before the flow of Hachinohe Pumice): The deposit during Period VI might be provided as pyroclastic flow. The deposits were composed of poorly sorted sub-angular gravels and the alternation of volcanic sand and fine sand layers. Terrace VI develops in the dissecting valleys.Period VII (after the flow of Hachinohe Pumice): The most of the deposits were the normal fluvial deposits provided by stream flow through the dissecting valleys.It is newly revealed that the most of deposits of volcanic-fans in the northern foot of Mt. Iwaki are the sediments occured by the volcanic activities.

A comprehensive study of pumice formation and dispersal: the Cretaio Tephra of Ischia (Italy)

The Cretaio Tephra is a small-volume (<0.02 km3) pumice deposit on the island of Ischia in Italy. It was erupted during historical time and is associated with a tuff ring-dome complex extruded along a N-S-trending normal fault system bordering the east side of the Mt. Epomeo resurgent block. 14C ages of the deposit average 1860 a B.P., which is in agreement with the potsherds found in paleosols underlying and overlying the deposit. The eruption sequence consists of 7 members; most of these members are pumice fall deposits, one is an ash and pumice fallout and another is a surge bed. The tephra have a trachytic-phonolitic composition. All chemical characteristics, including major and trace elements, and Sr-isotope composition are homogeneous throughout the sequence. The vesicularity of pumice clasts does not show any systematic change; the erupted magma had the same amount of volatiles, the same flux and vesicle growth behavior throughout the eruption sequence. Grain-size analyses of 90 tephra samples, representative of all the members at variable distance from the supposed vent, have been processed using the Sequential Fragmentation/Transport theory in order to define the effects of eruptive fragmentation and subsequent transport on the particle sizes distribution. Four significant subpopulations have been identified and related to transport mechanisms.

Stratigraphy and nature of Taupo Pumice Formation

Abstract Tephras erupted from Taupo Volcanic Centre, North Island, New Zealand, during the most recent eruptive event (c. 1820 years ago) are defined as 4 members of Taupo Pumice Formation. From youngest to oldest these are Taupo Ignimbrite, Taupo Lapilli, Rotongaio Ash, and Hatepe Tephra. All are airfall in origin except Taupo Ignimbrite which is the product of pyroclastic flows. Three stratigraphic units are here recognised within Taupo Ignimbrite. The Lower unit, restricted in occurrence mostly between Taupo and Turangi, is predominantly reddish brown in colour and has previously been included within Waitahanui Breccia. It is here recommended that use of the name Waitahanui Breccia be discontinued. The Middle unit is the most extensive and is discontinuously underlain by a “lithic lag layer”, rich in accessory lithics and crystals. The Upper unit is widely distributed and noted for the large pumice blocks found at the top of the ignimbrite, as well as interbedded fine ash airfall layers containing chal...

Lake Taupo—probable source of Taupo Pumice Formation (Note)

Abstract New evidence for the source of Taupo Pumice Formation includes orientation of charred logs, distribution of pumice and lithic material, absence of ballstic lithics, and bathymetry of Lake Taupo. All these clearly suggest an origin within eastern Lake Taupo, most probably at Horomatangi Reefs. No new evidence was found to substantiate sources beyond Lake Taupo.

A Mössbauer spectroscopic study of the cooling history of hypersthene from selected members of the Taupo Pumice formation, New Zealand

Summary57Fe Mössbauer spectroscopy has been used to determine the Mg2+-Fe2+ distribution between the two crystallographically inequivalent cation sites in hypersthenes from a stratigraphic tephra sequence of the Taupo Pumice formation, North Island, New Zealand. From these distributions and X-ray fluorescence analytical data, cooling histories were constructed using previously determined Mg2+-Fe2+ equilibrium isotherms for orthopyroxenes. The results showed that this cooling history geothermometer could be used to enable airfall and airflow tephra to be distinguished. In addition, they showed that the cooling rate of the above deposits correlated better with the deposit thickness, than with the distance of the deposit from the source.

Some tephra deposits in the South-West Waikato area, North Island, New Zealand

Abstract The distribution of tephras in the south-west Waikato area is mapped using sections and correlation lines. A new member of the Kauroa Ash Formation, the Oparau Tephra, is defined. Within the Hamilton Ash Formation, the Huntly and Te Uku Variants of the Ohinewai Ash Member are regarded as two separate tephras. Part of the late Quaternary tephra sequence from the Okataina and Taupo Volcanic Centres, including the Taupo Pumice Formation, Oruanui Formation, and Rotoehu Ash, is traced to the west coast of the North Island.

Mechanism of Pumice Formation

Mechanism of Pumice Formation