K-Ar ages of the lavas from Goshikigahara volcano, Central Hokkaido, Japan
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Abstract:
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.Keywords:
Stratovolcano
Volcanic plateau
Lava dome
Lava field
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
Dome (geology)
Strombolian eruption
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The volcanic morphology of a number of segments of the slow spreading Mid‐Atlantic Ridge (MAR) have been reinterpreted based on our understanding of dike emplacement, dike propagation, and eruption at the East Rift Zone of Kilauea Volcano, Hawaii and its submarine extension, the Puna Ridge. The styles of volcanic eruption at the submarine Puna Ridge are remarkably similar to those of the axial volcanic ridges (AVRs) constructed on the median valley floor of the MAR. We use this observation to relate volcanic processes occurring at Kilauea Volcano to the MAR. We now consider that volcanic features (e.g., seamounts and lava terraces) built on the flanks of the AVRs are secondary features that are fed from lava tubes or channels, not primary features fed directly from an underlying dike. We examine simple models of pipe flow and conclude that lava tubes can transport lava down the flanks of submarine rifts to build all of the volcanic features observed there. In addition, deep water lava tubes are strong enough to withstand the pressures of a few megapascals that the building of a volcanic structure 150 m high at the end of the tube would generate. The volumes of individual volcanic terraces and seamounts on the Puna Ridge and at the MAR are large (0.1–1 km 3 ) and similar to the volumes of lava flows that are broadly distributed at the subaerial East Rift Zone of Kilauea. This striking difference in the volcanic morphology on a scale of 1–2 km (producing terraces and seamounts underwater and low‐relief flows on land) must be related to the enhanced cooling and to the greater mechanical stability of tubes in the submarine environment. We suggest that at the MAR a crustal magma reservoir, most likely located beneath shallow, flat sections of the segment, provides magma to the rift axis through dikes that propagate laterally tens of kilometers. The zone of dike intrusion, at least in the neighborhood of the magma body, is likely narrower than the width resurfaced by flows, yielding a crustal structure that has a rapid vertical transition from lavas to sheeted dikes. At segment ends the zone of dike intrusion is likely to be wider, giving a resulting structure with a more gradual transition from lavas to dikes.
Lava field
Shield volcano
Rift zone
Submarine volcano
Seamount
Lava dome
Subaerial
Volcanic plateau
Effusive eruption
Volcanic cone
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The Quaternary Andahua volcanic group in southern Peru has been studied by present author since 2003. The Andahua Group stretches out at intervals within an area, which is 110 km long and 110 km wide. Seven regions bearing centres of volcanic eruptions have been distinguished: the Valley of the Volcanoes, Antapuna, Rio Molloco, Laguna Parihuana, Rio Colca Valley, Jaran, and Huambo. The Valley of the Volcanoes, where the Andahua Group was identified for the first time, contains the biggest variety of volcanic landforms. The valley is covered by a nearly 60 km long, continuous cover of lava flows. 165 individual eruption centres of the Andahua Group were distinguished including apparent pyroclastic cones, 50–300 m high, and usually smaller lava domes and fissure vents. Domes, eruptive vents and lava craters greatly outnumber pyroclastic cones. Most commonly, lava flows start from lava domes or craters. Small domes are often aligned along their feeding fissures. Lava domes and pyroclastic cones of the Andahua Group are aligned mainly along N–S and WNW–ESE trending fault systems. Projection points of the analysed Andahua lavas on the TAS diagram concentrate in the lower part of the trachyandesite field, entering also the basaltic trachyandesite or trachyte/trachydacite fields.
Volcanic plateau
Lava dome
Lava field
Trachyte
Volcanic cone
Stratovolcano
Effusive eruption
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Stratovolcano
Pyroclastic fall
Massif
Peléan eruption
Chronology
Caldera
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Monogenetic volcanic fields: Origin, sedimentary record, and relationship with polygenetic volcanism
Monogenetic volcanism is commonly represented by evolution of clusters of individual volcanoes. Whereas the eruption duration of an individual volcano of a volcanic field is generally short, the life of the entire volcanic field is longer than that of a composite volcano (e.g., stratovolcano). The magmatic output of an individual center in a volcanic field is 1–3 orders of magnitude less than that of a composite volcano, although the total field may be of the same volume as a composite volcano in any composition. These features suggest that the magma source feeding both monogenetic volcanic fields and composite volcanoes are in the same range. Monogenetic volcanic fields therefore are an important and enigmatic manifestation of magmatism at the Earth's surface. The long eruption duration for an entire volcanic field makes this type of volcanism important for understanding sedimentary basin evolution. Accumulated eruptive products may not be significant from a single volcano, but the collective field may contribute significant sediment to a basin. The eruptive history of volcanic fields may span millions of years, during which dramatic climatic and paleoenvironmental changes can take place. Through systematic study of individual volcanoes in a field, detailed paleoenvironmental reconstructions can be made as well as paleogeographic evaluations and erosion-rate estimates. Monogenetic volcanoes are typically considered to erupt only once and to be short-lived; recent studies, however, demonstrate that the general architecture of a monogenetic volcano can be very complex and exhibit longer eruption durations than expected. In this way, monogenetic volcanic fields should be viewed as a complex, long-lasting volcanism that in many respects carries the basic characteristics similar to those known from composite volcanoes.
Stratovolcano
Lava field
Volcanic plateau
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Statistical relations have been determined between geometry, volume, slope, and age for 26 circum‐Pacific composite (strato) volcanoes. General trends in eruption characteristics, repose periods, flow lengths, and petrology are also documented. Few examples of the earliest stages of composite volcano activity are known, perhaps because these small volcanoes are indistinguishable from cinder cones. If cinder cones evolve into composite volcanoes a fundamental change in morphometry, eruption style, and petrology occurs at a basal diameter of 2 km. Composite volcanoes (stratovolcanoes), composed of layered deposits of pyroclastics and lavas, are the characteristic volcanic landform at sub‐ducting plate margins, and are the most abundant type of large volcano on the Earth's surface. Composite volcano morphology results from repeated eruptions of pyroclastics and relatively short lava flows from a central vent. By comparison, pyroclastics are insignificant and lava flows tend to be much longer (10‐100 km) for shield volcanoes. Most composite cones are formed of andesites or basaltic andesites, but some are composed of basalts (Fuji, Fuego, Izalco); thus petrology may be less important in determining the morphology of composite cones than eruption style, as is true for shield volcanoes ( Wood , 1977a). In this study, observations of eruption characteristics and chemical/petrological trends for a number of composite cones were synthesized with newly determined measurements of cone morphology to document statistically the evolution of composite volcanoes and to examine their relation to cinder cones. Additionally, such quantitative descriptions of terrestrial volcanoes provide basic data for comparisons with volcanic structures on Mars and the Moon.
Stratovolcano
Cinder cone
Shield volcano
Volcanic cone
Lava field
Maar
Andesites
Volcanic plateau
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At Unzen volcano, rainfall caused lava dome collapses and pyroclastic flow in some cases. Heavier precipitation increases the probability of dome collapses and pyroclastic flows, and increased pyroclastic flows are correlated with precipitation for certain periods, but not others. Dome collapses and pyroclastic flows were clearly triggered on fresh, and not yet cooled lava, and presumable originates in the instability of the lava dome cracked due to rapid cooling by rainwater.
Lava dome
Dome (geology)
Rainwater Harvesting
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