Monogenetic Volcano Group Research Articles

The effect of fault systems on volcanic activity: Insights from the subduction-related, Quaternary Villamaría-Termales monogenetic volcanic field in Colombia

Structural control of volcanic activity is a topic of great significance around volcanic fields, mostly associated with risk management near cities. Structural geology provides valuable information for understanding the magmatic processes associated with the rise of magma and the presence of volcanoes. The Villamaría-Termales Monogenetic Volcanic Field (VTMVF) is a group of Quaternary monogenetic volcanoes settled in an active fault system, which allows us to propose the role that these faults play in the volcanic activity. The field is located near the city of Manizales (∼475.000 inhabitants), Colombia, on an active fault system at the western flank of the Cordillera Central in the northern Andes. The VTMVF is characterized by andesitic lava domes and flows, which individually reach volumes of up to 2.5 km3. This work uses 1) geometry and kinematics of the faults that affect the VTMVF to define the structural features associated with the emplacement of the volcanoes, and 2) new and published ages to evaluate periods of volcanic activity. Three trends of fault systems associated with the location of the volcanoes were identified: 1) NW-SE (Villamaría-Termales), 2) NE-SW (Sancancio, El Perrillo, Santa Rosa and Palestina), and 3) N-S to NNE-SSW (San Jerónimo and Samaná-sur). The fault kinematics are dominantly normal, with dextral (NE) and sinistral (NW) movements. Analysis of ages shows that the field has temporally evolved since 2 Ma in different time intervals (2.0–1.2 Ma, 0.18–0.045 Ma, and 0.045 Ma – Present). This supports the presence of different emplacement mechanisms related to both the movement in the strike of some faults and the intersection between faults. The pauses of volcanic activity could coincide with the absence of structural conditions (interseismic cycles for faults, where the sealing of the faults is generated) to facilitate the rise of magma; this is related to temporary compressive conditions. Despite the apparent structural controls, there is no clear spatial or temporal pattern of volcano distribution within the field. There is evidence of seismic activity in the area. Thus, the future formation of dilatating zones that allow the magma to rise and the emplacement of new monogenetic volcanoes is feasible not only in the area defined for the volcanic field but also in the continuation of the fault lines around it.

Case study and event analysis for mitigation of unpredictable volcanic hazard

Volcanology is an extremely important scientific discipline. Shedding light on how and why volcanoes erupt, how eruptions can be predicted and their impact on humans and the environment is crucial to public safety, economies and businesses. Understanding volcanoes means eruptions can be anticipated and at-risk communities can be forewarned, enabling them to implement mitigation measures. Professor Tsukasa Ohba is a scientist based at the Graduate School of International Resource Studies, Akita University, Japan, and specialises in volcanology and petrology. Ohba and his team are focusing on volcanic phenomena including: phreatic eruptions (a steam-driven eruption driven by the heat from magma interacting with water); lahar (volcanic mudflow); and monogenetic basalt eruptions (which consist of a group of small monogenetic volcanoes, each of which erupts only once). The researchers are working to understand the mechanisms of these phenomena using Petrology. Petrology is one of the traditional methods in volcanology but has not been applied to disastrous eruptions before. The teams research will contribute to volcanic hazard mitigation.

西南日本,阿武単成火山群中のアルカリ玄武岩のK-Ar年代

西南日本,阿武単成火山群中のアルカリ玄武岩のK-Ar年代

近畿北部,神鍋単成火山群に「太田火山」の発見

近畿北部,神鍋単成火山群に「太田火山」の発見

A41 東伊豆単成火山群における 3 火山列の噴出物の全岩化学組成

A41 東伊豆単成火山群における 3 火山列の噴出物の全岩化学組成

A19 東伊豆単成火山群のデイサイト類と安山岩類の成因 : そのマグマ混合と同化作用

A19 東伊豆単成火山群のデイサイト類と安山岩類の成因 : そのマグマ混合と同化作用

E21-08 神津島単成火山群の噴火史

E21-08 神津島単成火山群の噴火史

Application of Modern Technologies in Popularization of the Czech Volcanic Geoheritage

Four volcanic geoheritage sites in the Czech Republic were selected to showcase new technologies for communicating the recent results of scientific research to a wider nonprofessional public. The selected volcanic sites are scoria cones with late intrusive plugs, phonolite lava-dome erupted within a maar crater, phonolite laccolith, and a nested group of monogenetic volcanoes of Oligocene to Miocene age. The available scientific results from each volcanic site were summarized and transformed into images (playscreen) used for the 3D animation. The identical sources used for 3D animations were also used for generation of virtual models of augmented reality. The outcomes were tested on school children, and the results indicate that the modern methods applied in popularization of volcanic geoheritage are highly attractive for the youngest generation and have a potential to bring more interest in Earth Sciences. Using such techniques makes the communication of geoheritage to the public more effective.

Scoria cone formation through a violent Strombolian eruption: Irao Volcano, SW Japan

Scoria cones are common volcanic features and are thought to most commonly develop through the deposition of ballistics produced by gentle Strombolian eruptions and the outward sliding of talus. However, some historic scoria cones have been observed to form with phases of more energetic violent Strombolian eruptions (e.g., the 1943–1952 eruption of Paricutin, central Mexico; the 1975 eruption of Tolbachik, Kamchatka), maintaining volcanic plumes several kilometers in height, sometimes simultaneous with active effusive lava flows. Geologic evidence shows that violent Strombolian eruptions during cone formation may be more common than is generally perceived, and therefore it is important to obtain additional insights about such eruptions to better assess volcanic hazards. We studied Irao Volcano, the largest basaltic monogenetic volcano in the Abu Monogenetic Volcano Group, SW Japan. The geologic features of this volcano are consistent with a violent Strombolian eruption, including voluminous ash and fine lapilli beds (on order of 10−1 km3 DRE) with simultaneous scoria cone formation and lava effusion from the base of the cone. The characteristics of the volcanic products suggest that the rate of magma ascent decreased gradually throughout the eruption and that less explosive Strombolian eruptions increased in frequency during the later stages of activity. During the eruption sequence, the chemical composition of the magma became more differentiated. A new K–Ar age determination for phlogopite crystallized within basalt dates the formation of Irao Volcano at 0.4 ± 0.05 Ma.

Relationships between volcano distribution, crustal structure, and P-wave tomography: an example from the Abu Monogenetic Volcano Group, SW Japan

Achieving an understanding of the nature of monogenetic volcanic fields depends on identification of the spatial and temporal patterns of volcanism in these fields, and their relationships to structures mapped in the shallow crust and inferred in the deep crust and mantle through interpretation of geophysical data. We investigate the spatial and temporal distributions of volcanism in the Abu Monogenetic Volcano Group, Southwest Japan, and compare these distributions to fault and seismic data in the brittle crust, and P-wave tomography of the crust and upper mantle. Essential characteristics of the volcano distribution are extracted by a nonparametric kernel method using an algorithm to estimate anisotropic bandwidth. Overall, E-W elongate smooth modes in spatial density are identified that are consistent with the spatial extent of P-wave velocity anomalies in the lower crust and upper mantle, supporting the idea that the spatial density map of volcanic vents reflects the geometry of a mantle diapir. While the number of basalt eruptions decreased after 0.2 Ma, andesite eruptions increased and overall volume eruption rate is approximately steady-state. Estimated basalt supply to the lower crust is also constant. This observation and the spatial distribution of volcanic vents suggest stability of magma productivity and essentially constant two-dimensional size of the source mantle diapir since 0.46 Ma.

A quaternary monogenetic volcanic field in the Xalapa region, eastern Trans-Mexican volcanic belt: Geology, distribution and morphology of the volcanic vents

The most abundant volcanic manifestations along the east–west trending Trans-Mexican Volcanic Belt (TMVB) are the scoria cones. These have been grouped by other authors in extended monogenetic volcanic fields such as Michoacán-Guanajuato, Chichinautzin, Apan and Los Tuxtlas. Here we present geological and morphological data of a relatively unknown group of monogenetic volcanoes located on the east flank of the Cofre de Perote volcano (CP), around the city of Xalapa in the state of Veracruz, Mexico. Within an area of about 2400 km 2, the “Xalapa Monogenetic Volcanic Field” (XMVF) contains over 50 late Quaternary volcanoes. Most of them are scoria cones, but small shield volcanoes and tuff rings also occur. The lava flows produced by these volcanoes are constrained by an abrupt topography and cover a great percentage of the surface on the eastern and northeastern flanks of CP, between 3000 and 500 m a.s.l. The representative rocks of the different volcanic centers include olivine basalt, basaltic andesite with phenocrysts of plagioclase, pyroxene and minor olivine, and andesite with phenocrysts of plagioclase and pyroxene. SiO 2 and Al 2O 3 contents of the rocks vary between 45 and 62 wt% and 15 to 18 wt%, respectively. Most of the basaltic rocks have MgO contents between 4.2 and 9 wt%, Ni and Cr concentrations between 23 and 180 and 10 to 380 ppm, respectively, with a typical calc-alkaline behavior. Trace elements suggest two types of magmas; the most abundant are characterized by an enrichment of LILE and LREE with negative anomalies of Nb and Ti, which denote a calc-alkaline affinity. Others are LILE depleted and show high concentrations of MgO, Cr, and Ni, which is typical of primary calc-alkaline magmas. The mean scoria cone morphological values are: cone height (Hco) = 90.8 m, cone diameter (Wco) = 686.38 m, crater diameter (Wcr) = 208.49 m and 0.12 km 3 for the cone volume. We dated twelve different scoria cones using the 40Ar/ 39Ar method; for the other cones we used morphologic indicators such as the ratio of the scoria cone height to basal diameter (Hco/Wco) and maximum slope angle. Additionally, vegetation type, and cone and lava flow morphologies were also considered in order to determine rough relative ages. In general, the ages fall into three groups, those older than 2.0 Ma, those between 0.25–0.40 Ma and those less than approximately 0.1 Ma.

Dependence of volcanic systems on tectonic stress conditions as revealed by features of volcanoes near Izu peninsula, Japan

Five volcanoes, Asama, Fuji, Izu-Tobu, Izu-Oshima and Miyakejima, which are aligned along the same volcanic chain in central Japan, are subjected to different degrees to the stress conditions associated with the continental collision and subduction along wedge shaped trenches near Izu peninsula. At a great distance from the collision boundary, Asama is characterized by an axially symmetric edifice with a unique summit crater for magma effusion and Miyakejima has a similar symmetric structure accompanied by radial eruptive fissures. At the opposite extreme Izu-Tobu, which is the closest to the collision boundary, consists of many small monogenetic volcanoes that lack a central vent. In intermediate locations, Fuji and Izu-Oshima exhibit elongated volcanic edifices with both summit vents and parallel fissures on their flanks for magma effusion. To understand this systematic trend of volcanic features, growth of volcanic systems is analyzed based on magma transport in cylindrical conduits and planar fissures available in individual stress conditions. It is assumed in this analysis that fissures are produced with extensional stresses or high magma pressures enough to overcome compressive stresses and that cylindrical conduits that have arisen from localization of fissures can be persistently used for repeated magma supply. The analysis predicts that volcanoes are classified into the following three types that represent their growth processes in different stress conditions. (1) A polygenetic volcano having an axially symmetric edifice grows with unique magma supply through the central conduit under compressive or neutral stresses, (2) a polygenetic volcano having an elongated edifice grows with a summit crater and eruptive fissures parallel to the elongation under weak extensions, and (3) a group of small monogenetic volcanoes is constructed along many parallel fissures under strong extensions. This classification is examined for the five volcanoes and some other volcanoes in the world. The alternate occurrences of summit and flank eruptions observed at some polygenetic volcanoes are interpreted to be controlled by the summit height, magma densities and stress conditions that influence the pressure of a common magma source.

230Th/238U and 226Ra/230Th Activity Ratios in Rhyolite from Izu Arc Volcanoes

Observation was made with rhyolitic volcanic rocks erupted from Kozu-shima, Niijima and Higashi-Izu monogenetic volcano group for activity ratios of 230Th/238U and 226Ra/230Th. While the activity ratios of basaltic products from Izu arc volcanoes showed disequilibria of 230Th/238U<1 and 226Ra/230Th>1, the majority of rhyolitic products was considered to be almost in equilibrium of 238U=230Th=226Ra. The observation that 238U-230Th and 230Th-226Ra for the rhyolite are in radioactive equilibrium is consistent with the recent petrological suggestions that the rhyolitic magma from Izu arc was generated in the partial melting of the crust, where 238U-230Th and 230Th-226Ra are in equilibrium, by the basaltic magma of high temperature. Some of the rhyolite samples showed the enrichment of 230Th over 238U, indicating that the young marine sediments with 230Th>238U may possibly take part in the generation of the rhyolitic magmas.

230Th/238U Activity Ratios in Rhyolite from Izu Arc Volcanoes

Observation was made with rhyolitic volcanic rocks erupted from Kozu-shima, Niijima and Higashi-Izu monogenetic volcano group for activity ratios of 230Th/238U. While the activity ratios of basaltic products from Izu arc showed 230Th/238U<1, the majority of rhyolitic products was in radioactive equilibrium, suggesting that the addition of fluid for rhyolitic magma from subducting slab was less significant than for basaltic magma at the magma genesis. Separate distribution of(230Th/232Th)-(238U/232Th)activity ratios of the rhyolite group from those of the basalt group indicated that the rhyolite of Izu arc might not have genetic relation to the basaltic magma from Izu arc volcanoes.

High- and lower-alumina basaltic melt inclusions from the Higashi-Izu Monogenetic Volcano Group, Japan

High- and lower-alumina basaltic melt inclusions from the Higashi-Izu Monogenetic Volcano Group, Japan

PB07 小値賀島単成火山群における噴石丘の形成にともなうマグマ組成の時間変化 : 斑晶サイズ・モード, フッ素, HFS 元素の時間変化に注目して

PB07 小値賀島単成火山群における噴石丘の形成にともなうマグマ組成の時間変化 : 斑晶サイズ・モード, フッ素, HFS 元素の時間変化に注目して

The Mode of Lava Outflow from Cinder Cones in the Ojika-Jima Monogenetic Volcano Group

The Mode of Lava Outflow from Cinder Cones in the Ojika-Jima Monogenetic Volcano Group

Formation Process of Cinder Cones in the Ojika-Jima Monogenetic Volcano Group

Formation Process of Cinder Cones in the Ojika-Jima Monogenetic Volcano Group

阿武単成火山群のＫ‐Ａｒ年代とマグマ活動史

More than 40 monogenetic volcanoes are distributed over an area of 400 km2 in the Abu Monogenetic Volcanic Field, southwest Japan. The eruptive products consist of alkaline basalt and calc-alkaline andesite to dacite lavas and pyroclastics, which are collectively known as the Abu Monogenetic Volcano Group. We have examined the eruption history of the Abu Monogenetic Volcano Group based on 33 new K-Ar ages. Most samples were dated by normal K-Ar method, and yielded ages between 1.9 and 0.1 Ma. The ages of two very young samples were determined using an unspiked method incorporating a mass-fractionation correction procedure. This gave an averaged age of about 40 ka. K-Ar ages from the Abu Monogenetic Volcano Group are concentrated at around 1.7 Ma and 0.2 Ma, and the activity is therefore classified into early and late periods, respectively. The early activity had a duration of about 0.4 mys, during which time 0.3 km3 of alkaline basalt alone was erupted. The late activity produced 0.8 km3 of alkaline basalt and 2.1 km3 calc-alkaline andesite to dacite, and lasted about 0.8 mys. Alkaline basalt was mostly produced in the first half of the late period, with maximum eruption rate at about 0.4 Ma. This activity was followed by more voluminous calc-alkaline andesite-dacite eruptions which climaxed at 0.2 Ma. Although associated alkaline basalt activity continued in this period, eruption volumes steadily decreased. Periodic alkaline basalt activity in southwest Japan is thought to have originated from small mantle diapirs, with intermediate calc-alkaline magmas being produced by mixing between alkaline basalt and felsic crustal melts. Coincidence of alkalic and calc-alkaline magmas and the eruption history in the later period in the Abu Monogenetic Volcano Group suggest that heating induced by repeated intrusion of alkaline basalt resulted in partial melting of the lower crust, thus producing intermediate to felsic calc-alkaline magmas. These crustal melts may then have mixed with alkaline basalt and produced the relatively voluminous intermediate calc-alkaline magmas erupted in the latest stage.

K-Ar geochronology of a Quaternary monogenetic volcano group in Ojika Jima District, Southwest Japan

An unspiked K–Ar dating method using a mass-fractionation correction procedure was applied to a Quaternary independent group of monogenetic volcanoes, Ojikajima Volcano Group, located in northwestern Kyushu in Southwest Japan, in order to clarify in detail secular variations in eruptive volume, locations of eruptive vents, and magma compositions in a single monogenetic volcano group. The major results were as follows: (a) K–Ar ages of monogenetic volcanoes distribute from 1.08 to 0.30 Ma, with voluminous peaks at approximately 1.0 and 0.6 Ma. (b) The volcanic activity commenced in the central part of the field, expanded to the whole field at approximately 0.6 Ma, and then shrank to the central area. (3) Concentrations of incompatible elements, such as Ba, K, and Nb, increase with decreasing age, whereas P, Y, and Zr concentrations remain constant. These concentrations suggest gradual decrease in the degree of partial melting from an identical mantle source with residual garnet.