K-Ar ages for lava samples of Koganegahara volcano, Central Hokkaido, Japan
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Abstract:
Koganegahara volcano is a large Quaternary composite volcano situated in the southwest of the Tomuraushi volcano group in Central Hokkaido, Japan. The lowermost eruptive units of the Koganegahara volcano have previously been dated at about 1.1 Ma. In this study, two lava samples from the uppermost eruptive units of the eastern and central parts of the volcano are dated, giving K-Ar ages of 0.70±0.02 Ma and 0.70±0.01 Ma. This indicates that the Koganegahara volcano was active for 400000 years from 1.1 to 0.7 Ma. Furthermore, based on previously reported and new age data, the K-Ar ages appear to be concentrated around 1.1-1.0 Ma and 0.75-0.7 Ma, suggesting that volcanic activity peaked in these periods.Keywords:
Stratovolcano
Lava dome
The Goshikigahara volcano, situated at the northern part of the Tomuraushi volcano group in Central Hokkaido, Japan, is a large Quaternary composite volcano consisting of a basal volcanic edifice (Kaundake volcano) and three overlying volcanic edifices (Ponkaundake, Chubetsudake, and Goshikidake volcanoes). Based on the K-Ar ages determined previously for the Kaundake volcano (NEDO, 1990) and the K-Ar ages determined in this study for three volcanic rocks collected from the uppermost (or near uppermost) lavas of the Ponkaundake, Chubetsudake and Goshikidake volcanoes, the formation history of the Goshikigahara volcano can be summarized as follows: (1) ca. 1.0 Ma-0.95 Ma, voluminous lava and pyroclastic eruptions to form the Kaundake stratovolcano, (2) <0.95 Ma-0.8 Ma, volcanic activity on the western flank of the Kaundake volcano to build the main part of the Ponkaundake stratovolcano, and (3) ca. 0.75 Ma, volcanic activity on the eastern flank of Kaundake, forming the two lava plateaus of Chubetudake and Goshikidake.
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Abstract The level of lava within a volcanic conduit reflects the overpressure within a connected magma reservoir. Continuous monitoring of lava level can therefore provide critical insights into volcanic processes and aid hazard assessment. However, accurate measurements of lava level are not easy to make, partly owing to the often dense fumes that hinder optical techniques. Here we present the first radar instrument designed for the purpose of monitoring lava level and report on its successful operation at Erebus volcano, Antarctica. We describe the hardware and data‐processing steps followed to extract a time series of lava lake level, demonstrating that we can readily resolve ∼1 m cyclic variations in lake level that have previously been recognized at Erebus volcano. The performance of the radar (continuous, automated data collection in temperatures of around −30 °C) indicates the suitability of this approach for sustained automated measurements at Erebus and other volcanoes with lava lakes.
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Modern volcanoes can be classified as three main forms in shape (Shield-shape,cone-shape and dome-shape) and seven different types.In surrounding sections and northern faulted depression in the Songliao Basin,there are mainly four types of volcanoes such as shield volcano,composite volcano,pyroclastic cone and lava dome.Shield volcanoes are built almost entirely of fluid lava flows,with little explosive pyroclastics.Composite volcanoes are built of flow layers alternating with pyroclas-tics,thus the alternate sequence of effusive and explosive facies is well developed.Pyroclastic cones,the simplest type of volcano,consist of particles and blobs of congealed lava from a single vent,mainly of explosive facies.Lava domes are formed by relatively small,bulbous masses of the lava which is too viscous to flow long distance,therefore,the lava piles over and around its vent by extrusion.Eruption patterns here mainly include effusive,extrusive and volcanic vent facies.In the Songliao Basin the buried volcanic edifices is characterized by slope angle ranging from minimum 3° to maximal 25°,bottom diameter from 2 to 14 kilometers and volcanic rock thickness from 100 to 600 meters.The buried volcanic edifices may cover an area of 4 to 50 sq.kilometers for each.As a whole,buried volcanoes of the northern Songliao Basin appear numerous,individually small and are controlled by regional faults.They are normally featured with crack and multi-central type eruptions,volcanic products of different vents commonly pile up each other.Volcanic lithology and lithofacies are the main factors that control the types and forms of the volcanic apparatus in the Songliao Basin.
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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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Electrical conduit
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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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Caldera
Silicic
Stratovolcano
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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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Lava field
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Volcanology
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