Drone magnetic surveys for active volcanoes: a case study of Izu-Oshima volcano, Japan

SUMMARY We derive closed analytical solutions for quasi-static thermoelastic deformation in response to instantaneous point and spherical heat sources in an elastic half-space. Since we can take advantage of the solutions for an infinite medium, the derivation of solutions for a semi-infinite medium is straightforward. We examine the spatial and temporal evolution of thermoelastic deformation for point and spherical heat sources. We applied the solution to a radar interferometric observation of post-eruptive deformation associated with the 1986 fissure eruption at Izu-Oshima volcano, Japan. Assuming a spherical heat source at a depth of 240 m with a volume of 1.15 × 10 7 m 3 and a temperature step 10 3 K, the predicted rate of post-eruptive ground movement agrees with the observed rate within observational errors. Also, the same parameter values allow us to compute the co-eruptive ground displacement by the effect of mass intrusion, whose amplitude is consistent with the observed height (45 m) of the newly formed cone. The derived solutions can be applied to transient ground displacements observed at active volcanoes, and allow us to evaluate the heat amount of magma intruded at very shallow depths.

The Izu-Oshima volcano is one of the most active volcanoes in Japan, and has generated relatively large-scale eruptions every 30–40 years for the past 200 years. As more than 30 years have passed since the last eruptions in 1986–87, volcanic activity is expected to resume in the near future. To help elucidate the current and future state of the volcano’s magma system, the temporal evolution of the recent magma plumbing system was investigated through a petrological and geochemical analysis of its basaltic lavas and pyroclastics (<~53 wt.% of SiO2) that were erupted during the last ~1.5 kyrs. The basaltic products have variable phenocryst contents, ranging from ~0 to ~20 vol.%, and phenocryst-bearing samples commonly contain plagioclase, orthopyroxene, and clinopyroxene phenocrysts. The whole-rock compositions are significantly scattered in the Harker variation diagrams, suggesting that the compositional diversity was established by at least two independent magmatic processes. The application of principal component analysis on the whole-rock major element data suggests that one magmatic process was crystal fractionation of crystal-poor magmas, and the other process was either plagioclase accumulation or mixing of plagioclase-rich magmas. Based on this observation, and combined with the petrological analysis and previous geophysical studies, we propose that aphyric magmas, stored in an 8–10 km-deep magma chamber, progressively differentiated over time from the 7th to 20th century. Furthermore, the compositional variations in basalts resulted from the mixing of the differentiating aphyric magmas with variable proportions of porphyritic magmas derived from a 13–18 km-deep magma chamber. Because recent eruptions have been triggered by the ascent of porphyritic magma from the 13–18 km-deep magma chamber, and its injection into the 8–10 km-deep magma chamber, it is important to monitor the deeper magma chamber to predict future volcanic activity.

Izu-Oshima Volcano is an active insular volcano and is situated about 110 km SSW of Tokyo, Japan. It erupted in 1986, 12 years after the latest eruption. A precise aeromagnetic anomaly map in and around the volcano was compiled by the data obtained before and soon after the eruption. An interpretation of the magnetic anomalies suggested the lateral variation of magnetization intensity for volcanics which compose the edifice. Therefore, we conducted a magnetization intensity mapping in and around the volcano using the aeromagnetic anomalies, on the assumption that the magnetic anomalies are caused by the terrain magnetized in the same direction as the present Earth's magnetic field and the magnetization intensity varies only laterally

Erosion processes on active volcanoes in humid climates result in some of the highest sediment yields on Earth. Episodic sediment yields after large eruptions have been evaluated, but not the long-term and continuous patterns on persistently active volcanoes. We have used high-spatial resolution satellite imagery and DEMs/DSMs along with field-based geologic mapping to assess accurately sediment budgets for the active Semeru Volcano in Java, Indonesia. Patterns of aggradation and degradation on Semeru differ from that of other active volcanoes because (1) both episodic pyroclastic density currents (PDC) and continuous supplies of tephra generate pulses of sediment, (2) sediment is transferred via cycles of aggradation and degradation that continue for >15 years in river channels after each PDC-producing eruption, and (3) rain-triggered lahars remove much greater material than fluvial transport during long, intense rainfall events. The geomorphic response of two of Semeru’s rivers to volcanic sediment migration indicates that (1) each river experiences alternating aggradation and degradation cycles following PDC-producing eruptions and (2) spatial patterns of sediment transfer are governed by geomorphic characteristics of the river reaches. Usually high degradation in the steep source reach is followed by a long bypassing middle reach. Aggradation predominates in the depositional reaches further down valley on the ring plain. Average sediment yields (103–105 t/km2/year) at persistently active volcanoes are two to three orders of magnitude lower than sediment yields after large and infrequent eruptions, but the continuous and steady sediment transfer in rivers removes more sediment on a mid-term (10 years) to long-term (30 years) basis. In contrast to the trend observed on composite cones after large and infrequent eruptions, decay of sediment yields is not exponential and river channels do not fully recover at steadily active volcanoes as episodic inputs from BAF eruptions, superimposed on the background remobilization of daily tephra, have a greater cumulative effect.

An isotropic source of volcanic tremor-observation with a dense seismic network at Izu-Oshima volcano, Japan

Secular variations of carbon and helium isotopes at Izu-Oshima Volcano, Japan

Volcanoes in humid tropical environments are frequently cloud covered, typically densely vegetated and rapidly eroded. These factors complicate field and laboratory studies and even the basic identification of potentially active volcanoes. Numerous previous studies have highlighted the potential value of radar remote sensing for volcanology in equatorial regions. Here, cloud- and vegetation-penetrating LHH-band (λ≈24 cm) synthetic aperture radar (SAR) data from the Japanese Earth Resources Satellite (JERS-1) are used to investigate persistently active volcanoes and prehistoric calderas in East Java, Indonesia. The LHH-band JERS-1 SAR produces high-spatial-resolution (18 m) imagery with relatively high incidence angle that highlights structures and topographic variations at or greater than the wavelength scale while minimising geometrical distortions such as layover and foreshortening. These images, along with Internet browse data derived from the Canadian RADARSAT mission, provide new evidence relating regional tectonics to volcanism throughout East Java. Volcanic events, such as caldera collapse at the Tengger caldera, appear to have been partly controlled by northwest-aligned faults related to intra-arc sedimentary basins. Similar regional controls appear important at historically active Lamongan volcano, which is encircled by numerous flank maars and cinder cones. A previously undocumented pyroclastic sheet and debris avalanche deposit from the Jambangan caldera complex is also manifested in the synoptic radar images. At the currently active Semeru volcano these data permit identification of recent pyroclastic flow and lahar deposits. Radar data therefore offer a valuable tool for mapping and hazard assessment at late Quaternary volcanoes. The criteria developed in the analysis here could be applied to other regions in the humid tropics.

Underground structure and magmatic activity of Izu-Oshima volcano, Japan as inferred from seismic reflection survey

Continuous chemical monitoring of volcanic gas in Izu-Oshima volcano, Japan

Long-distance magma transport from arc volcanoes inferred from the submarine eruptive fissures offshore Izu-Oshima volcano, Izu–Bonin arc

&amp;lt;p&amp;gt;Since 2000 an intense development of remote stations, transmission device, data processing software and tools for time series analysis aimed to high rate GNSS surveillance and monitoring of active Italian volcanoes has been realized or implemented at INGV. Since the very first case study (the 2001 Mt.Etna&amp;amp;#8217;s eruption) to the 2019 paroxysms of Stromboli, many observations and a lot of specific experience has been achieved on Italian active volcanoes (Etna, Stromboli) to track rapidly developing deformation patterns associated to different volcanic processes, as dike intrusions or explosive activity. Moreover, we here describe the hardware and software improvements for High Rate GNSS monitoring network with a specific attention to the recently realized network in the densely populated area of the Campi Flegrei caldera.&amp;lt;/p&amp;gt;

Quantitative impact assessment of the 2019 tropical cyclone Kammuri lahars: Mayon volcano, Philippines

Object-oriented classification of a high-spatial resolution SPOT5 image for mapping geology and landforms of active volcanoes: Semeru case study, Indonesia

Characteristics of the Frontier Northern Houtman Sub-Basin Formed on a Magma-Rich Segment of the Western Australian Margin

The presence of alluvial dolines in the Ebro Basin causes problems to both agricultural and urban areas. At present, new urbanization of former farming areas requires new tools to detect karst zones and so diminish the hazard linked to collapses. In the surroundings of Zaragoza, dolines (developed mainly on Quaternary alluvial terraces covering a Tertiary gypsum substratum) are commonly filled with alluvial deposits, agricultural soils, urban debris, etc. Measurements of magnetic susceptibility show a remarkable contrast between host rocks and cavity fillings, demonstrating the value of magnetic surveying. A field test was made in a recently collapsed (September 2003) doline filled currently with urban debris. A magnetic survey was carried out following a 130 m 2 grid, with 1–10 m spacing between profiles. A proton magnetometer with gradiometer was utilized, and the total field intensity and gradient measurements were taken. The magnetic survey demonstrated a strong anomaly with a dipole defined by more than 650 nT and a gradient of about 100 nT m −1 . The 2.5-dimensional (2.5D) modelling of the magnetic anomaly fits well with the known geometrical data. Two other dolines (that are not clearly defined at the surface) were also detected during the survey. These results validate the starting hypothesis and open a new research approach to the problem. The magnetic survey output allows the construction of realistic geological models.