Silicic lava dome growth in the 1934–1935 Showa Iwo-jima eruption, Kikai caldera, south of Kyushu, Japan
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Keywords:
Lava dome
Breccia
Caldera
Silicic
Stratovolcano
Dome (geology)
Effusive eruption
Dacite
Each of the three phases of the 2006 eruption at Augustine Volcano had a distinctive eruptive style and flowage deposits. From January 11 to 28, the explosive phase comprised short vulcanian eruptions that punctuated dome growth and produced volcanowide pyroclastic flows and more energetic hot currents whose mobility was influenced by efficient mixing with and vaporization of snow. Initially, hot flows moved across winter snowpack, eroding it to generate snow, water, and pyroclastic slurries that formed mixed avalanches and lahars, first eastward, then northward, and finally southward, but subsequent flows produced no lahars or mixed avalanches. During a large explosive event on January 27, disruption of a lava dome terminated the explosive phase and emplaced the largest pyroclastic flow of the 2006 eruption northward toward Rocky Point. From January 28 to February 10, activity during the continuous phase comprised rapid dome growth and frequent dome-collapse pyroclastic flows and a lava flow restricted to the north sector of the volcano. Then, after three weeks of inactivity, during the effusive phase of March 3 to 16, the volcano continued to extrude the lava flow, whose steep sides collapsed infrequently to produce block-and-ash flows. The three eruptive phases were each unique not only in terms of eruptive style, but also in terms of the types and morphologies of deposits that were produced, and, in particular, of their lithologic components. Thus, during the explosive phase, low-silica andesite scoria predominated, and intermediate- and high-silica andesite were subordinate. During the continuous phase, the eruption shifted predominantly to high-silica andesite and, during the effusive phase, shifted again to dense low-silica andesite. Each rock type is present in the deposits of each eruptive phase and each flow type, and lithologic proportions are unique and consistent within the deposits that correspond to each eruptive phase. The chief factors that influenced pyroclastic currents and the characteristics of their deposits were genesis, grain size, and flow surface. Column collapse from short-lived vulcanian blasts, dome collapses, and collapses of viscous lavas on steep slopes caused the pyroclastic currents documented in this study. Column-collapse flows during the explosive phase spread widely and probably were affected by vaporization of ingested snow where they overran snowpack. Such pyroclastic currents can erode substrates formed of snow or ice through a combination of mechanical and thermal processes at the bed, thus enhancing the spread of these flows across snowpack and generating mixed avalanches and lahars. Grain-size characteristics of these initial pyroclastic currents and overburden pressures at their bases favored thermal scour of snow and coeval fluidization. These flows scoured substrate snow and generated secondary slurry flows, whereas subsequent flows did not. Some secondary flows were wetter and more laharic than others. Where secondary flows were quite watery, recognizable mixed-avalanche deposits were small or insignificant, and lahars were predominant. Where such flows contained substantial amounts of snow, mixed-avalanche deposits blanketed medial reaches of valleys and formed extensive marginal terraces and axial islands in distal reaches. Flows that contained significant amounts of snow formed cogenetic mixed avalanches that slid across surfaces protected by snowpack, whereas water-rich axial lahars scoured channels. Correlations of planimetric area (A) versus volume (V) for pyroclastic deposits with similar origins and characteristics exhibit linear trends, such that A=cV2/3, where c is a constant for similar groups of flows. This relationship was tested and calibrated for dome-collapse, column-collapse, and surgelike flows using area-volume data from this study and examples from Montserrat, Merapi, and Mount St. Helens. The ratio A/V2/3=c gives a dimensionless measure of mobility calibrated for each of these three types of flow. Surgelike flows are highly mobile, with c≈520; column-collapse flows have c≈150; and dome-collapse flows have c≈35, about that of simple rock avalanches. Such calibrated mobility factors have a potential use in volcano-hazard assessments.
Lava dome
Stratovolcano
Peléan eruption
Lahar
Effusive eruption
Pyroclastic fall
Phreatic eruption
Phreatomagmatic eruption
Scoria
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Strombolian eruption
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Komochi volcano (1,296 m), located at the southernmost part of NE Japan arc, is a Quaternary composite volcano with a diameter of approximately 6 km and a volume of approximately 10 km3. The basement is composed of the Kirigakubo Formation, a member of the Miocene rhyolitic tuff formation, and Iwamoto volcanoes, dacite lava domes (ca. 6 Ma). The rocks of the Komochi volcano consist of low-K andesites with small amounts of basaltic andesite and dacite. All rocks of the Komochi volcano belong to the hyperthenic rock series. The volcanic activity of the Komochi volcano can be divided into following three stages: Ayado stage (c.a. 1.6 Ma), Early Komochi (0.9 Ma-) and Late Komochi (0.6-0.2 Ma) volcano stages which is subdivided into the two kinds of activities: stratovolcano-forming and lava dome-forming. At any stage, a large number of andesitic dikes intruded, which comprise radial dike swarm in the circumference of the Daikokuiwa neck. The Komochi volcano has a life span of about 1.4 m.y. and calculated production rate of 0.14-0.25 km3/104 yr., which is very small compared to lager volcanoes around Komochi volcano, for example Myoko and Hakone volcanoes, and even smaller than similar volcanoes in the Shin-etsu Highland area.
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Dome (geology)
Caldera
Effusive eruption
Chronology
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Lava dome
Effusive eruption
Dome (geology)
Strombolian eruption
Lateral eruption
Dense-rock equivalent
Phreatic eruption
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We imaged the pumice of the two explosive events using the SEM at the University of Orleans. The aim was then to be able to trace the plagioclase microlites manually , and the oxides and bubbles automatically in order to obtain the glass proportion. At the same time, we obtained the bulk water content of the pumice using an Elemental Analyzer. We then combined these results to obtain the water content of the glass. The first part of the model uses our textural analyses to obtain the initial pressures and porosi-ties of our samples. Then, the second part of the model determines the initial depths of the samples based on these parameters. 2. Eruptive Depth and Pressure Model We used the two-part eruptive depth and pressure model developed in Burgisser et al. (2010; 2011) for the 88 Vulcanian explosions that occurred at Soufriere Hills (Montserrat) in 1997. Temperature magma-chbr (°C) 950 ρ magma (kg,m-3) 2455 Pressure magma-chbr (MPa) 300 X H2O max (%wt) 7,38 Merapi volcano (Java, Indonesia) is one of the most dangerous volcanoes on Earth. It is known to produce lava domes that collapse in deadly pyroclastic flows because of gravity or auto-explosivity. Even though this volcano is mostly effusive, explosive eruptions occur in its history, most recently in 2010. Two major explosive events occurred that year, the first one on October 26, and the second one on November 05. They produced explosive columns that quickly collapsed in pumice-rich pyroclastic flows that ran up to 15.5 km from the summit. The 2010 eruption was very well observed, making this event a good candidate for investigating the effusive-explosive transition with a full suite of geochemical and geophysical data. The pumice of these two events was analyzed and the data used in a two-step computer model in order to investigate the pre-explosive conditions. The explosive-effusive transition often occurs at arc volcanoes. The parameters driving this transition (overpressure, eruptive volume,. . .) are known but the relative importance of each parameter remains unclear. This study demonstrates the primacy of overpressure in determining the eruptive mode of the volcano, with volume and other parameters contributing only to the magnitude rather than the character of the event.
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Abstract Usu volcano has erupted nine times since 1663. Most eruptive events started with an explosive eruption, which was followed by the formation of lava domes. However, the ages of several summit lava domes and craters remain uncertain. The petrological features of tephra deposits erupted from 1663 to 1853 are known to change systematically. In this study, we correlated lavas with tephras under the assumption that lava and tephra samples from the same event would have similar petrological features. Although the initial explosive eruption in 1663 was not accompanied by lava effusion, lava dome or cryptodome formation was associated with subsequent explosive eruptions. We inferred the location of the vent associated with each event from the location of the associated lava dome and the pyroclastic flow deposit distribution and found that the position of the active vent within the summit caldera differed for each eruption from the late 17th through the 19th century. Moreover, we identified a previously unrecognized lava dome produced by a late 17th century eruption; this dome was largely destroyed by an explosive eruption in 1822 and was replaced by a new lava dome during a later stage of the 1822 event at nearly the same place as the destroyed dome. This new interpretation of the sequence of events is consistent with historical sketches and documents. Our results show that petrological correlation, together with geological evidence, is useful not only for reconstructing volcanic eruption sequences but also for gaining insight into future potential disasters.
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Dense-rock equivalent
Caldera
Lateral eruption
Peléan eruption
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Peléan eruption
Strombolian eruption
Vulcanian eruption
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