Lateral magma intrusion from a caldera-forming magma chamber: Constraints from geochronology and geochemistry of volcanic products from lateral cones around the Aso caldera, SW Japan
Masaya MiyoshiTaro ShinmuraHirochika SuminoTakashi SanoYasuo MiyabuchiYasushi MoriHirohito InakuraKuniyuki FurukawaKoji UnoToshiaki HasenakaKeisuke NagaoYoji ArakawaJunji Yamamoto
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Caldera
Magma chamber
Lava dome
The structures and textures preserved in lava domes reflect underlying magmatic and eruptive processes, and may provide evidence of how eruptions initiate and evolve. This study explores the remarkable cycles in lava extrusion style produced between 1922 and 2012 at the Santiaguito lava dome complex, Guatemala. By combining an examination of eruptive lava morphologies and textures with a review of historical records, we aim to constrain the processes responsible for the range of erupted lava type and morphologies. The Santiaguito lava dome complex is divided into four domes (El Caliente, La Mitad, El Monje, El Brujo), containing a range of proximal structures (e.g. spines) from which a series of structurally contrasting lava flows originate. Vesicular lava flows (with a'a like, yet non-brecciated flow top) have the highest porosity with interconnected spheroidal pores and may transition into blocky lava flows. Blocky lava flows are high volume and texturally variable with dense zones of small tubular aligned pore networks and more porous zones of spheroidal shaped pores. Spines are dense and low volume and contain small skeletal shaped pores, and subvertical zones of sigmoidal pores. We attribute the observed differences in pore shapes to reflect shallow inflation, deflation, flattening or shearing of the pore fraction. Effusion rate and duration of the eruption define the amount of time available for heating or cooling, degassing and outgassing prior to and during extrusion, driving changes in pore textures and lava type. Our new textural data when reviewed with all the other published data allows cyclic models to be developed. The cyclic eruption models are influenced by viscosity changes resulting from (1) initial magmatic composition and temperature, and (2) effusion rate which in turn affects degassing, outgassing and cooling time in the conduit. Each lava type presents a unique set of hazards and understanding the morphologies and dome progression is useful in hazard forecasting.
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Lava field
Effusive eruption
Shield volcano
Dome (geology)
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Lava flows present a recurring threat to communities on active volcanoes, and volumetric eruption rate is one of the primary factors controlling flow behavior and hazard. The time scales and driving forces of eruption rate variability, however, remain poorly understood. In 2018, a highly destructive eruption occurred on the lower flank of Kīlauea Volcano, Hawai'i, where the primary vent exhibited substantial cyclic eruption rates on both short (minutes) and long (tens of hours) time scales. We used multiparameter data to show that the short cycles were driven by shallow outgassing, whereas longer cycles were pressure-driven surges in magma supply triggered by summit caldera collapse events 40 kilometers upslope. The results provide a clear link between eruption rate fluctuations and their driving processes in the magmatic system.
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This study shows the stratigraphy, petrography, whole-rock chemistry and paleomagnetic polarity of pyroclastic flow deposits during the latest Pliocene to Middle Pleistocene in the southeastern foot area of the Hakkoda Caldera, Northeast Japan. Six pyroclastic flow deposits are identified in this area : Kumanosawa Pyroclastic Flow Deposits (Ks), Takatoge Pyroclastic Flow Deposits (Tk), Osegawa Pyroclastic Flow Deposits (Os), Hakkoda-Ose Pyroclastic Flow Deposits (Hto), Hakkoda 1st-stage Pyroclastic Flow Deposits (Ht1) and Hakkoda 2nd-stage Pyroclastic Flow Deposits (Ht2), in order of decreasing age. These pyroclastic flow deposits have dacitic to rhyolitic compositions, and show distinct modal compositions and whole-rock major element chemistry in each. Based on stratigraphy, topography and paleomagnetic polarity, eruptive ages of the pyroclastic flow deposits are estimated to be as follows : Ks, 1.95-1.77 Ma; Tk, 1.77-1.07 Ma ; Os and Hto, 0.99-0.78 Ma ; Ht1, 0.76 Ma ; Ht2, 0.40 Ma. The source calderas of the Ks, Tk, Os, and Hto can be estimated from petrological features. The source of the Ks is neither the Hakkoda Caldera nor Okiura Caldera, and is probably an unidentified caldera. The source of the Tk may be a low gravity anomaly area "Nenokuchi Caldera" located northeast of Towada Caldera. The source of the Os is not the Okiura Caldera. The source of the Hto is the Hakkoda Caldera. This study suggests that the two large-scale pyroclastic flow deposits during 1-2 Ma erupted from previously unidentified calderas (one is possibly Nenokuchi Caldera). This proposes a revised volcanic history in which the activities of caldera volcanoes overlap each other in the Hakkoda-Towada Volcanic Region.
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Southren Kyushu has been the region of intense volcanism at least since Pliocene time. One of the most characteristic features is the prevalence of the large-scale pyroclastic flow eruptions which originated from such gigantic calderas as Aira, Ata, Kikai and Kakuto.There exist a considerable number of literature on the stratigraphic sequence and distributions of the pyroclastic flow deposits in South Kyushu. However, relatively small number of reports are available on air-fall tephra deposits, which are useful for establishing Quaternary chronology both of source volcanoes and of marine or fluvial sediments in the coastal regions such as the Miyazaki Plain. In this study, each bed of maker-tephras which erupted during the time from ca. 100, 000 to 25, 000y.B.P., is precisely discriminated and described in the northern part of the Osumi Peninsula, Kagoshima Prefecture first. And then each tephra is traced northeastward along the main axis of distributions to the Miyazaki Plain.Of many tephras, the following four well-dated tephras are used as fundamental timemakers because of their widespread occurence; Ata pyroclastic flows, originated from Ata caldera in 95, 000-90, 000y.B.P. ; Kikai-Tozurahara ash falls, originated from Kikai caldera in 75, 000y.B.P. ; Aso-4 pyroclastic flows, originated from Aso caldera in 70, 000y.B.P.; Ito pyroclastic flows and AT ash, originated from Aira caldera in 22, 000-21, 000y.B.P. Several air-fall tephras from the Aira and Kirishima volcanic centers are identified in detail and roughly dated from their stratigraphic positions between these fundamental maker-beds.About 75, 000-70, 000y.B.P., explosive activity of Aira caldera occurred resulting in the formation of plinian pumice fall deposit, Fukuyama pumice falls, which is found from the Osumi Peninsula to the Miyazaki Plain. During ca. 60, 000-25, 000y.B.P., intermittent eruptions occurred forming five sheets of tephras, of which the Iwato eruption was greatest in producing pumice falls, pyroclastic surges and pyroclastic flows. Iwato pumice falls mantle extensive area from the Osumi Peninsula to the Miyazaki Plain. Cataclysmic eruption occurred from Aira caldera, producing Osumi pumice falls, Tsurnaya and Ito pyroclastic flows and AT ash 22, 000-21, 000y.B.P. Most of these eruptions were accompanied with phreatomagmatic ones.Eruptive history of Kirishima volcano is divided into two stages deduced from the tephra sequence. At ca. 40, 000 y.B.P., older stage of activity started with ejection of relatively felsic pumice falls, Iwaokoshi pumice fall, and graded to more mafic and frequent eruptions, Awaokoshi scoria fall. Younger stage began with the plinian eruption of Kobayashi pumice fall at ca. 15, 000y.B.P.Of many terraces in Miyazaki Plain, Sanzaibaru terrace is the most extensive one and is accompanied with transgressive marine deposits. Stratigraphic relation with tephra sequence shows that Sanzaibaru terrace was emerged before the Ata pyroclastic flow eruption, ca. 95, 000y.B.P., probably indicating the Last Interglacial Stage. Most of terraces younger than Sanzaibaru are of fluvial origin, except for Nyutabaru II and probably III terraces which are partly of marine origin, and are largely devided into two groups, older and younger. Older terraces, Nyutabaru terrace group, formed during the time from the Ata eruption to the Aso-4 eruption, were chracterized by the profiles with more gentle gradient. Younger ones which were chracterized by the profiles with steeper gradient, were formed after the Aso-4 eruption and before the Kobayashi pumice fall. The difference of their profiles reflects the sea level after the maximum stage in the Last Interglacial Age.
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Abstract Merapi volcano has a well-known eruption type, namely Merapi type, in which an extruded lava dome collapses and is accompanied by pyroclastic density current (PDC). This type of eruption makes morphological monitoring of the lava dome crucial in the hazard mitigation process. After the VEI 4 eruption in 2010, a new lava dome of Merapi appeared on top of the 2010 lava dome in August 2018 and continuously grew. In November 2019, the lava dome started to collapse outward the crater area. We reported the lava dome morphological monitoring using a UAV (Unmanned Aerial Vehicle) photogrammetry conducted from August 2018 to February 2019. This UAV monitoring provides processed aerial photo data in Digital Terrain Model (DTM) and orthophoto with low operating costs and short data acquisition time. The lava domes erupted from the same eruptive canter within this period and grew evenly in all directions. The 2018-2019 Merapi lava dome has basal ratio of 0.183 to 0.290 with height of 11 to 41 m, respectively. Volume changed from 33,623 m 3 in August 2018 to 658,075 m 3 in February 2019, suggesting growth rate at ~3,500 m 3 /day. The lava base filled the crater base area (0.21 km 2 ) and started to collapse outward in November 2019.
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Volcanic hazards
Volcanology
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: Lava flow and lava dome growth are two main manifestations of effusive volcanic eruptions. Less-viscous lava tends to flow long distances depending on slope topography, heat exchange with the surroundings, eruption rate, and the erupted magma rheology. When magma is highly viscous, its eruption on the surface results in a lava dome formation, and an occasional collapse of the dome may lead to a pyroclastic flow. In this chapter, we consider two models of lava dynamics: a lava flow model to determine the internal thermal state of the flow from its surface thermal observations, and a lava dome growth model to determine magma viscosity from the observed lava dome morphological shape. Both models belong to a set of inverse problems. In the first model, the lava thermal conditions at the surface (at the interface between lava and the air) are known from observations, but its internal thermal state is unknown. A variational (adjoint) assimilation method is used to propagate the temperature and heat flow inferred from surface measurements into the interior of the lava flow. In the second model, the lava dome viscosity is estimated based on a comparison between the observed and simulated morphological shapes of lava dome shapes using computer vision techniques.
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This chapter contains sections titled: Introduction Precaldera Events The Osumi Pumice Fall Tsumaya Pyroclastic Flow Kamewarizaka Breccia Ito Pyroclastic Flow Nature of the Magma Formation of the Aira Caldera Post-Aira Caldera Activity Funnel-Shaped Underground Structure of the Aira Caldera and Other Japanese Calderas Conclusion
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Imaging growing lava domes has remained a great challenge in volcanology due to their inaccessibility and the severe hazard of collapse or explosion. Changes in surface movement, temperature, or lava viscosity are considered crucial data for hazard assessments at active lava domes and thus valuable study targets. Here, we present results from a series of repeated survey flights with both optical and thermal cameras at the Caliente lava dome, part of the Santiaguito complex at Santa Maria volcano, Guatemala, using an Unoccupied Aircraft System (UAS) to create topography data and orthophotos of the lava dome. This enabled us to track pixel-offsets and delineate the 2D displacement field, strain components, extrusion rate, and apparent lava viscosity. We find that the lava dome displays motions on two separate timescales, (i) slow radial expansion and growth of the dome and (ii) a narrow and fast-moving lava extrusion. Both processes also produced distinctive fracture sets detectable with surface motion, and high strain zones associated with thermal anomalies. Our results highlight that motion patterns at lava domes control the structural and thermal architecture, and different timescales should be considered to better characterize surface motions during dome growth to improve the assessment of volcanic hazards.
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Lava dome
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