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Izu-Oshima volcano is an active basaltic stratovolcano in the Izu-Mariana arc, and its last major eruption occurred in 1986. This field guide includes descriptions about the 1986 products, the Miharayama Central Cone, the 1421? product at the southern coast, the 1.7-ka caldera-forming products, the pre-caldera tephra formation and the 2013 lahar.
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Context 1
... volcano is composed of lava flows and volcaniclastic rocks of low-K, arc-type tholeiitic olivine basalt and pyroxene-olivine basalt (Kawanabe, 1991). The older edifice of the volcano is called the Senzu Group (Nakamura, 1964) and is made up of phreatomagmatic coarse ejecta and lahar deposits with a small amount of lava flows (Fig. 2). Volcanic activity started at about 40 to 50 ka, and represents the stage of emergence of an island. The younger edifice of the volcano consists of normal subaerial alternations of lava flows and scoria and ash falls. This activity began about 20 ka and marks the stage of continuous growth of a stratovolcano above sea level. The upper ...
Context 2
... of the summit caldera is thought to be formed in this syncaldera stage (Sashikiji Formation;Nakamura, 1964). The post-caldera products are composed of 10 large eruptions and several minor ones (Koyama and Hayakawa, 1996;Kawanabe, 2012). Nakamura (1964) has divided into the Nomashi and Yuba Formations across an erosional contact (1998; 2012). (Fig. 2). The eruptive volume of these large eruptions is up to a cubic kilometer and the average recurrent interval of the large ones is 100 to 150 years (Fig. 3). The most recent large eruption occurred in 1777-78 (Y 1 ). Largescale eruptions usually began with scoria fall deposition followed by effusion of lava flows. In some events, flank ...
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Citations
... St. Helens in USA, Pallister et al. 2017; Vesuvius in Italy, Cioni et al. 2008;Cotopaxi in Ecuador, Pistolesi et al. 2011; Editorial responsibility: L. Pioli * Arianna Beatrice Malaguti a.malaguti2@campus.uniurb.it Izu-Oshima in Japan, Yamamoto 2017). Accurate investigations of volcanic history and assessment of eruptive parameters have provided the background for model-based hazard assessments of tephra fallout, vent opening and pyroclastic density flows at Vesuvius and Phlegrean Fields in Italy (Macedonio et al. 2008;Bevilacqua et al. 2015;Neri et al. 2015). ...
During the past millennia, several eruptions have occurred within the La Fossa caldera on the island of Vulcano (Aeolian Islands, Italy), some being also described in historical documents dating back to Republican Roman times (first to second century BC). The absolute and relative timing of such activity, however, has remained poorly defined and controversial, due to contrasting ages provided by radiometric and unconventional palaeomagnetic methods. Here, we present a detailed reconstruction of the eruptive history focused on the ninth to fifteenth century AD period that occurred at both La Fossa cone and Vulcanello. This integrated approach involves tephrostratigraphy, standard palaeomagnetic methodology and radiocarbon dating. The new dataset confirms that the lavas exposed above sea level at Vulcanello were erupted between the tenth and eleventh century AD, and not between the first and second century BC as previously suggested. In this same time interval, La Fossa cone was characterized by long-lasting, shoshonitic, explosive activity followed by a discrete, sustained, rhyolitic explosive eruption. Between AD 1050 and 1300, activity was focused only on La Fossa cone, with alternating explosive and effusive eruptions that emplaced four rhyolitic and trachytic lava flows, resulting in significant growth of the cone. After the violent, phreatic event of the Breccia di Commenda (thirteenth century), the eruption continued with a substantial, long-lasting emission of fine ash until activity ceased. Magmatic explosive activity resumed at La Fossa cone at the beginning of the fifteenth century marking the onset of the Gran Cratere cycle. This phase lasted until the mid-sixteenth century and produced at least seven explosive eruptions of intermediate magma composition and a couple of lateral explosions (Forgia Vecchia I and II). During this time interval, a third cinder cone was emplaced at Vulcanello, and the activity produced the lava flows of Punta del Roveto and Valle dei Mostri. From the seventeenth to twentieth centuries, volcanic activity was concentrated at La Fossa cone, where it ended in 1890. This work confirms that Vulcanello island formed in Medieval times between the tenth and eleventh centuries. Moreover, between the tenth and mid-sixteenth centuries, La Fossa caldera was the site of at least 19 eruptions with an average eruption rate of one event every 34 years. This rate makes volcanic hazard at Vulcano higher than that suggested to date.
... Focal mechanism analysis also shows compression in the same direction (Ichikawa 1971). The last major activity in 1986-1987 started as strombolian eruption localized at Miharayama, and then fissure eruption occurred at the northwestern caldera floor and the northern flank of the caldera, forcing the evacuation of the largest town of Motomachi (Yamamoto 2017). The spatio-temporal distribution of volcanic tremor observed in the 1986 activity gave insights of eruption type changes and magma injection processes (Kurokawa et al. 2016). ...
SUMMARY - Source location determination of volcanic tremor has been a challenge in seismology due to the waveform complexity and difficulties in reading P-and S-wave arrival times. We present a method for locating volcanic tremor recorded at a seismic network distributed around a volcano. The method combines the source-scanning algorithm and cross-correlation analysis. Tremor records are processed using a technique adopted from ambient seismic interferometry to obtain stacked cross-correlation functions (CCFs) for all station pairs, which are expected to show high amplitudes at the lag time that corresponds to the traveltime difference between the stations. The best seismic source location is determined from the maximum of the sum of envelope amplitudes of CCFs at predicted traveltime differences between all pairs of stations. This method does not compute theoretical amplitudes, assume an initial hypocentre location or measure the arrival times. To quantitatively evaluate the accuracy of the location determination, we examine the method by using the vertical component seismic data of volcano-tectonic (VT) earthquakes recorded at six seismic stations at Izu-Oshima volcano. The VTs have been previously located by using arrival times of P and S waves, and the hypocentres are used as the reference for evaluation and error estimation of the method. The results show that the misfit, which is the distance between our estimated sources and the references, is about 2 km or less when using CCFs at the frequency band of 4-16 Hz which contains the dominant frequencies of direct S waves. To test whether the method can be used for volcanic tremor, we simulate the tremors by combining the observed VTs that occurred randomly in time in a localized region. The simulated tremors are determined with location errors of approximately 1 km or less, when the sources of VTs are located within a distance of 1 km and CCFs are calculated for a minimum data length of about 2 min. The volcanic tremor location method we present here can be used as an alternative tool for volcano monitoring, especially to locate tremors and seismic events with no clear phase arrival.
... The most recent large eruption occurred in 1777-1778 (Y1.0). Before the Y1.0 layered, the large eruption also occurred around 1421 (Y4.0) (Yamamoto, 2017). ...
On October 16th, 2013, numerous landslides occurred at Izu Oshima Volcano triggered by heavy rainfall associated with the typhoon T1326 (Wipha). The most landslide debris rapidly transformed into lahars, cascading downwards and flooding inhabited areas. Soil plasticity is one of parameter for an indicator at slope stability. Plastic properties of soils are directly related with the interaction of the soils particles. Density of soil particle has a high correlated with the organic carbon content. Furthermore, organic carbon content have a relation with the clay minerals. Clay minerals form through the weathering of rock fragments, especially those containing a large proportion of silicate minerals.
We conducted a high-resolution aeromagnetic survey using an autonomously driven uncrewed helicopter that flew as low as several tens of meters above the ground along precise flight tracks with 1 m accuracy. The geomagnetic total intensity was measured by a total intensity magnetometer suspended beneath the helicopter at a ~ 50 m or less flight spacing over the entire caldera of Mt. Mihara, located on Izu-Oshima Island, Japan. From the observed geomagnetic data, we estimated high-resolution subsurface magnetization intensity. A high average magnetization intensity of 13.5 A/m was obtained for the entire caldera. The distribution of the magnetization intensity was not only consistent with the results of conventional airborne surveys, but it also had a high spatial resolution of less than 100 m. Highly magnetized areas were observed along the NW–SE lines that intersected the summit pit crater, Crater A, which is consistent with the principal stress direction of Izu-Oshima Island. These highly magnetized areas might be solidified magma that did not reach the surface during past eruptions. A large and deep-rooted weakly magnetized area was found just outside of the NE side of the central cone, which corresponds to the location of Fissure B, and the conduit must have been demagnetized at the previous event. Other weakly magnetized areas were also observed at the N, E, and SW sides around the pit crater. These regions correspond to the location of fumaroles in the crater. The high-resolution subsurface magnetization imaged by the autonomous uncrewed helicopter will be helpful for the mitigation of future eruption damage by enabling the assessment of potential fissure eruption areas.
