A preface from the Governor of Yogyakarta Special Province SULTAN HAMENGKU BUWONO X on the occasion of the publication of the special issue on Merapi Volcano
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Stratovolcano
Volcanic hazards
Shield volcano
Phreatomagmatic eruption
Volcanic cone
Phreatic
Caldera
Volcanic cone
Shield volcano
Lineament
Submarine volcano
Dike
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The most active voJcano in Central Volcanic Zone (CVZ) is Lascar Volcano (230:22'S-67°44'W) (Francis & Rothery, 1987), a composite voJcano formed by andesitic and dacitic lava and pyroclastic flows, and occasional basaltic andesites lava flows (Gardeweg et al., 1998). Its historie activity have been explosive principally (vulcanian and subplinian eruptions) and is related to viscous lava dome growth and collapse cycles (Matthews et al., 1997). The largest historical eruption took place in April 1993 (subplinian eruption), which produced eruptive column that extended up to 20 km and pyroclastic flows that extended up to 7.5 km of the summit (Gardeweg & Medina, 1994). The more active voJcanoes in Southern VoJcanic Zone (SVZ) are Villarrica and L1aima voJcanoes (Moreno & Fuentealba, 1994). ViUarrica Volcano (390:25'S-71 °57'W) is a stratocone built over two calderas, with more than 30 adventitious eruptive centers (Moreno, 1998), formed by basaltic and andesitic lava and pyroclastic flows (Gonzalez-Ferran, 1995). In its summit crater there is a small and continuously active lava lake (Ortiz et al., 2003; Calder et al, 2004). Since 1558,59 important eruptions have been reported (Petit-Breuilh, 1994), with hawaiian, phreatomagmatic, vuJcanian and strombolian eruptions (Moreno, 1998). ViUarrica VoJcano eruptions have emitted lava flows as long as 18 km (Ortiz et al., 2003) and important lahars (» 20 km) have been formed by glaciers melting (Gonzalez-Ferran. 1995). One of most important historical eruptions occurred in 1971 (Gonzalez-Ferran, 1995). L1aima Volcano (38°42'S-71 °44'W) is a complex composite-shield volcano, with a buried caldera and 40 parasitic scoria cones, formed by basaltic and andesitic lava flows, andesitic pyroclastic flows and, dacitic surge and pumice fall deposits (Naranjo & Moreno, J991). Since 1640, about 47 eruptions have been reported, with phreatornagmatic, strombolian and subplinian eruptions (N aranjo & Moreno, 1991; Gonzalez-Ferran, 1995). At least, 10 eruptions have emitted voluminous lava flows and pyroclasts, also lahars have been formed by glaciers melting (Moreno & Fuentealba, 1994), being the 1957 eruption the biggest historie eruption (Naranjo & Moreno, 1991). In this work, are characterized the contrasting styles of voJcanic activity of these three volcanoes, correlated the voJcanic activity with satellite responses and determined the causes of thermal anornaly for each one, using radiance data from Landsat TM and ETM+ images, between December 1984 and December 2001.
Phreatomagmatic eruption
Stratovolcano
Strombolian eruption
Lava dome
Lahar
Effusive eruption
Phreatic eruption
Volcanic hazards
Peléan eruption
Basaltic andesite
Lapilli
Lava field
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Volcanic cone
Scoria
Cinder cone
Stratovolcano
Volcanic plateau
Lava dome
Lava field
Shield volcano
Landform
Caldera
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우리나라에서 가장 큰 화산섬인 제주도에는 약 360여 개의 단성화산체가 분포되어 있다고 알려져 있으나, 본 연구를 통해 기존에 일려진 것보다 100여 개가 더 많은 총 455개의 단성화산체가 분포하고 있음을 확인하였다. 총 455개의 단성화산체를 형태학적으로 분석해 본 결과, 분석구가 373개로 전체의 82.0%를 차지하여 가장 높은 비율로 나타나며, 분석구 외에도 정상부가 뾰족한 형태이면서 용암으로 구성된 것이 9개(2.0%), 순상화산체가 27개(5.9%), 응회환이 17개(3.7%), 응회구가 3개(0.7%), 마르가 1개(0.2%), 용암돔이 25개(5.5%)가 분포하고 있다. 또한 이들 중 알오름의 형태로 나타나는 것이 15개가 있다. 단성화산체의 지역별 분포를 살펴보면 전체적으로 제주도의 서쪽에 비해 동쪽에 더 우세하게 분포하고 있음을 알 수 있다. 또한 강수량과 같은 풍화 요인에 의해 분석구의 형태가 영향을 받는다면, 강수량이 월등히 더 많은 남부 지역에 한 방향으로 터진 말발굽형 화구를 가진 분석구나 초승달형 분석구, 불규칙한 형태의 분석구 등이 더 많이 분포해야 할 것이다. 그러나 실제 제주도에서는 오히려 강수량이 더 적은 북부 지역에 이러한 분석구들이 더 많이 분포하는 것으로 나타나, 제주도의 남북 간의 기후적인 요소의 차이가 분석구의 형태나 분포에 크게 영향을 끼친 것은 아니라고 생각된다. 단성화산체 중 응회환, 응회구와 마르는 주로 제주화산섬의 지하 또는 해안가의 저지대에 위치하며, 분석구는 대부분이 해안에서 떨어진 섬의 내륙부에 위치한다. 이는 제주도 단성화산체를 형성한 화산활동이 물(지하수 또는 얕은 바닷물)과의 접촉 유무에 따라 수성화산활동(수증기마그마분화)을 하거나, 마그마성화산활동(스트롬볼리안분화 혹은 하와이안분화)을 한 것임을 알 수 있다. 또한 이들 단성화산체의 고도별 분포를 살펴보면 고도 300 m 이하의 해안저지대에 253개(55.6%), 고도 300~600 m의 중산간지대에 110개(24.2%), 600 m 이상의 산악지대에 92개(20.2%)가 분포하고 있어 과반수 이상이 해안저지대에 분포하고 있음을 알 수 있다. 제주화산섬에 분포하는 단성화산체들은 응력장 안에서 생긴 단층이나 틈을 따라서 틈새 분출을 통해 선상으로 배열되어 나타나는 것과 이러한 틈새와는 무관하게 독립된 단일 화구를 통한 중심 분출을 통해 생성된 것이 함께 나타남을 알 수 있다. Jeju island is the biggest volcanic island in Korea and there are over 455 Quaternary monogenetic volcanoes, of which approximately 373 volcanoes(82.0%) are cinder cones. Other volcanic forms in the island include sharp-pointed lava cone without crater(9 volcanoes; 2.0%), shield volcanoes(27 volcanoes; 5.9%), tuff rings(17 volcanoes; 3.7%), tuff cones(3 volcanoes; 0.7%), a maar(1 volcano; 0.2%) and lava domes(25 volcanoes; 5.5%). The monogenetic volcanoes include 15 small nested cinder cones(aloreum). The monogenetic volcanoes are more abundant in the eastern part of the island than in the western part. If the main cause of the weathering such as precipitation affected the shape of the monogenetic volcanoes, more monogenetic volcanoes(BC, CC, DC, etc.) are supposed to be present in the southern part that have more precipitation than in the northern part. But the distribution of the monogenetic volcanoes shows no difference between the southern and the northern parts. So we suggest that the difference of the climatic conditions did not affect the distribution or the shape of cinder cones. Tuff rings, tuff cones and a maar are distributed beneath the island or in the low-altitude areas along the shore although cinder cones are distributed in the interior of the island. This means that the volcanic activity which formed the monogenetic volcanoes resulted from either phreatomagmatic eruption or magmatic (hawaiian or strombolian) eruptions depending on the reaction with water (underground water or shallow waters). The distribution of the monogenetic volcanoes according to the altitude shows that 253(55.6%) volcanoes occur in low-lying coastal areas at an altitude below 300 m, 110(24.2%) in a middle mountainous area at an altitude between 300~600 m and 92(20.2%) in a high mountainous area at an altitude above 600 m. So more than half of monogenetic volcanoes are distributed in low-lying coastal areas.
Cinder cone
Maar
Shield volcano
Lava field
Volcanic cone
Volcanic plateau
Stratovolcano
Submarine volcano
Cinder
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Modern volcanoes can be classified as three main forms in shape (Shield-shape,cone-shape and dome-shape) and seven different types.In surrounding sections and northern faulted depression in the Songliao Basin,there are mainly four types of volcanoes such as shield volcano,composite volcano,pyroclastic cone and lava dome.Shield volcanoes are built almost entirely of fluid lava flows,with little explosive pyroclastics.Composite volcanoes are built of flow layers alternating with pyroclas-tics,thus the alternate sequence of effusive and explosive facies is well developed.Pyroclastic cones,the simplest type of volcano,consist of particles and blobs of congealed lava from a single vent,mainly of explosive facies.Lava domes are formed by relatively small,bulbous masses of the lava which is too viscous to flow long distance,therefore,the lava piles over and around its vent by extrusion.Eruption patterns here mainly include effusive,extrusive and volcanic vent facies.In the Songliao Basin the buried volcanic edifices is characterized by slope angle ranging from minimum 3° to maximal 25°,bottom diameter from 2 to 14 kilometers and volcanic rock thickness from 100 to 600 meters.The buried volcanic edifices may cover an area of 4 to 50 sq.kilometers for each.As a whole,buried volcanoes of the northern Songliao Basin appear numerous,individually small and are controlled by regional faults.They are normally featured with crack and multi-central type eruptions,volcanic products of different vents commonly pile up each other.Volcanic lithology and lithofacies are the main factors that control the types and forms of the volcanic apparatus in the Songliao Basin.
Shield volcano
Lava dome
Volcanic cone
Volcanic plateau
Stratovolcano
Diatreme
Lava field
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Volcanic eruptions represent hazards for local communities and infrastructure. Monogenetic volcanoes (usually) erupt only once, and then volcanic activity moves to another location, making quantitative assessment of eruptive hazards challenging. Spatio-temporal patterns in the occurrence of these eruptions may provide valuable information on locations more likely to host future eruptions within monogenetic volcanic fields. While the eruption histories of many stratovolcanoes along the Cameroon Volcanic Line (CVL) are relatively well studied, only fragmentary data exist on the distribution and timing of this region's extensive monogenetic volcanism (scoria cones, tuff rings, maars). Here, we present for the first time a catalog of monogenetic vents on the CVL. These were identified by their characteristic morphologies using field knowledge, the global SRTM Digital Elevation Model (30 m resolution), and satellite imagery. More than ~1100 scoria cones and 50 maars/tuff rings were identified and divided into eight monogenetic volcanic fields based on the visual assessment of clustering and geological information. Spatial analyses show a large range of areal densities between the volcanic fields from >0.2 km−2 to 0.02 km−2 from the southwest towards the northeast. This finding is in general agreement with previous observations, indicating closely spaced and smaller edifices typical of fissure-fed eruptions on the flanks of Bioko and Mt. Cameroon in the southwest, and a more focused plumbing system resulting in larger edifices of lower spatial density towards the northeast. Spatial patterns were smoothed via kernel density estimates (KDE) using the Summed Asymptotic Mean Squared Error (SAMSE) bandwidth estimator, the results of which may provide an uncertainty range for a first-order hazard assessment of vent opening probability along the CVL. Due to the scarce chronological data and the complex structural controls across the region, it was not possible to estimate the number of vents formed during the same eruptive events. Similarly, the percentage of hidden (buried, eroded) vents could not be assessed with any acceptable statistical certainty. Furthermore, the impact of different approaches (convex hull, minimum area rectangle and ellipse, KDE isopaches) to define volcanic field boundaries on the spatial distribution of vents was tested. While the KDE boundary definition appears to reflect the structure of a monogenetic volcanic field better than other approaches, no ideal boundary definition was found. Finally, the dimension of scoria cones (approximated by their basal diameters) across the CVL was contrasted to the specific geodynamic setting. This region presents a complex problem for volcanic hazard analysis that cannot be solved through basic statistical methods and, thus, provides a potential testbed for novel, multi-disciplinary approaches.
Cinder cone
Scoria
Stratovolcano
Lava field
Volcanic hazards
Volcanic cone
Shield volcano
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28 Quaternary volcanoes,which scattered along a Quaternary NE strike fault,are found in the area of Halaha River and Chaoer River,middle of Daxing'an Mountain Range.Quaternary volcanic rocks in this area,mainly alkaline basalt,cover an area of ca.1000 km~2.These volcanoes can be divided into two stages:Holocene volcanoes and Pliocene volcanoes.Both magmatic eruptions and phreatomagmatic eruptions are found in this area.The magmatic eruptions form a series of products,including scoria cones,tephra fallout deposits,and many kinds of lava(e.g.aa lava,pahoehoe lava and block lava).Typical fumarolic cones and lava hillocks are found in the lava.The phreatomagmatic eruptions have typical base surge deposits,which are characterized by parallel bedding and staggered bedding.Volcanic activity in this area form many volcanogenic lakes.According to the difference of lake forming,they are divided into four types:Crater lake,maar lake,volcanic dammed lake,collapse lava lake.Two conflict factors,water and fire, coexists harmoniously in the volcanic area,adding a splendid landscape to the Aershan Volcano and Warm Spring National Geopark.
Phreatomagmatic eruption
Scoria
Lava field
Volcanic plateau
Maar
Lava dome
Cinder cone
Shield volcano
Volcanic cone
Overbank
Stratovolcano
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Volcano is located in the Narino Province, South of Colombia. It is an andesitic strato-volcano, which structure was formed by the interchange of lava flows and pyroclastic deposits of different sizes. In the last 4500 years, six major eruptions have been identified (4500, 4000, 2900, 2300, 1100 years before present and in the XIX century), with eruptive columns of small size and producing small pyroclastic flows. In the past 500 years, the eruptions have been characterized by gas and ash emissions, small lava flows and explosive eruptions which have also produced pyroclastic flows. Since INGEOMINAS started the monitoring in 1989, it has been recorded several manifestations of its activity, starting from its re-activation characterized by frequent phreatic eruptions (at the end of 1988 and beginning of 1989), the gradual arise of a viscous magma and its emplacement as a dome in the bottom of the main crater (second semester of 1991), and subsequent explosive eruptions related with the dome destruction and volcanic process development (eruptions on July 16,1992; January 14, March 23, April 4, April 13 and June 7, 1993)), as well as, the record of seismic sequences of Volcano-Tectonic events, related with fracturing process, located in the neighborhood of the volcanic edifice (April and November, 1993 and March, 1995). Since 1997, this volcano is the focus of the implementation and development of what here is called the Galeras Multiparameter Station, a project which consists in technological adequacy and research, and is carried out by the Institute for Research and Geoscientific, Mining - Enviromental and Nuclear Information (INGEOMINAS - Colombia) and the Federal Institute for Geosciences and Natural Resources (BGR - Germany). The INGEOMINAS - BGR Project is proposed in order to investigate the Volcanic activity through the combination of various geophysical and geochemical disciplines like broadband seismology, electro-magnetic methods, gas chemistry, thermography, gravimetry and geodesy in a continuos telemetric experiment for long time observations.
Lava dome
Peléan eruption
Phreatic eruption
Phreatic
Stratovolcano
Pyroclastic fall
Volcanic hazards
Dome (geology)
Effusive eruption
Phreatomagmatic eruption
Strombolian eruption
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Existence of volcanic fluid in the shallow crust beneath active volcanoes is considered to be closely related to the generation process of volcanic earthquakes such as the nucleation of shear faulting due to the reduction in effective normal stress on the faults and the creation of tensile faults. In addition, the movement of volcanic fluids sometimes causes earthquake swarms and migration of hypocenters. Therefore, the observation and understandings of fluid-related phenomena associated with volcanic earthquakes would be important for understanding of volcanic phenomena. In this presentation, as an example of such interaction between volcanic earthquakes and volcanic fluids, I will report the detection of small inflation phase prior to the occurrence of volcanic earthquakes observed at Azuma volcano, Japan. Azuma volcano is one of the quaternary volcanoes located at the volcanic front of the Northeast Japan arc, and it consists of overlapping stratovolcanoes of shield volcanoes, lava domes, and pyroclastic cones. Historical eruptions of Azuma volcano were mostly small phreatic eruptions at Issaikyo and O-ana crater at the northern end of the Higashi-Azuma volcanic complex. Just beneath the O-ana crater, occurrence of various types of volcanic earthquakes including volcanic, tremor, low-frequency earthquakes, monotonic/harmonic earthquakes, and Tornillos as well as the volcano-tectonic earthquakes have been reported, and these facts suggest the existence of hydrothermal system and fracture system beneath the volcano. Since 2014, the activity of Azuma volcano become rather high, and subtle ground deformation and increase in seismicity are observed. In addition, there is an earthquake swarm in the middle of January 2015. To understand the nature of this earthquake swarm, we carefully analyze the seismic and geodetic (tilt) records observed at nearby stations, and detect the existence of small inflation phase just prior to the occurrence of volcanic earthquakes. The inflation phase starts about five seconds before the occurrence of earthquakes, and observed displacement and tilt vectors roughly point to the epicenteral area. The depth of the inflation source determined by fitting of displacement and tilt waveforms is around 2 km, and thus the location of inflation source is just below the source of thermal demagnetization/magnetization detected by the repeating magnetic field survey in this area. These results provide a direct evidence of the interaction between volcanic earthquakes and volcanic fluids, and further study may reveal the generation and triggering processes of shallow volcanic earthquakes.
Stratovolcano
Volcanic hazards
Volcanic plateau
Shield volcano
Lava dome
Volcanic cone
Caldera
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