Proximal pyroclastic deposits from the 1989–1990 eruption of Redoubt Volcano, Alaska — stratigraphy, distribution, and physical characteristics
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Lahar
Lava dome
Dome (geology)
Pyroclastic fall
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
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During and after the 2006 eruption of Augustine Volcano, we compiled a geologic map and chronology of new lava and flowage deposits using observational flights, oblique and aerial photography, infrared imaging, satellite data, and field investigations. After approximately 6 months of precursory activity, the explosive phase of the eruption commenced with two explosions on January 11, 2006 (events 1 and 2) that produced snow-rich avalanches; little or no juvenile magma was erupted. Seismicity suggests that a small lava dome may have extruded on January 12, but, if so, it was subsequently destroyed. A series of six explosions on January 13–14 (events 3–8) produced widespread but thin (0–30 cm) pyroclastic-current deposits on the upper flanks above 300 m altitude and lobate, 0.5- to 2-m-thick pyroclastic flows that traveled down most flanks of the volcano. Between January 14 and 17, a smooth lava lobe formed in the east half of the roughly 400-m-wide summit crater and was only partially covered by later deposits. An explosion on January 17 (event 9) opened a crater in the new lava dome and produced a ballistic fall deposit and pyroclastic flow on the southwest flank. During the interval from January 17 to 27, a rubbly lava dome effused. On January 27, explosive event 10 generated a pyroclastic current that left a deposit, rich in dense clasts, on the north-northwest flank. Immediately following the pyroclastic current, a voluminous 4.7-km-long pyroclastic flow swept down the north flank. Three more explosive blasts on January 27 and 28 produced unknown but likely minor on-island deposits. The cumulative volume of erupted material from the explosive phase, including domes, flows, and fall deposits (Wallace and others, this volume), was 30×106 m3 dense-rock equivalent (DRE). The continuous phase of the eruption (January 28 through February 10) began with a 4-day period of nearly continuous block-and-ash flows, which deposited small individual flow lobes that cumulatively formed fans to the north and northeast of the summit. A single larger pyroclastic flow on January 30 formed a braided deposit on the northwest flank. Roughly 9×106 m3 (DRE) of magma erupted during this period. Around February 2, the magma flux rate waned and a northward lava flow effused and reached a length of approximately 900 m by February 10. Approximately 11×106 m3 (DRE) of magma erupted during the second half of the continuous phase. After a 23-day hiatus, lava effusion recommenced in early March (the effusive phase) and was accompanied by frequent (but volumetrically minor) block-and-ash flows. From March 7 to 14, extrusion increased markedly; two blocky lava-flow lobes, each tens of meters thick, moved down the north and northeast flank of the volcano; and a new summit lava dome grew to be ~70 m taller than the pre-2006 summit. This phase produced 26×106 m3 (DRE) of lava. Active effusion had ceased about March 16, but, in April and May, three gravitational collapses from the west margin of the north lava flow produced additional block-and-ash flows. The basic sequence of the 2006 eruption closely matches that of eruptions in 1976 and 1986.
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Peléan eruption
Lateral eruption
Pyroclastic fall
Phreatic eruption
Dome (geology)
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DOI: 10.17014/ijog.v8i3.163Merapi is an active strato volcano located in Central Java. This volcano is regarded as the most active and most dangerous volcano in Indonesia. Since the twentieth century, the activities have comprised mainly the effusive growth of viscous lava domes and lava tongues, with occasional gravitational collapses of parts of over-steepened domes producing pyroclastic flows, commonly defined as “Merapi-Type”. Since October 2010, however, explosive eruptions of a relatively large size have occurred to VEI 4, and some associated pyroclastic flows were larger and had farther reach than any produced on July 2006. These events may also be regarded as another type of eruptions for Merapi. On October26th, 2010 such event happened, even though it was not caused by pyroclastic flows of the dome collapses, about thirty people were killed including Mbah Marijan, known as the Merapi volcano's spiritual gatekeeper, who was found dead at his home approximately 4 km from the crater. The Yogyakarta Palace subsequently confirmed his death. This time the disaster was caused by a sudden directed blast that took place at 17:02 pm throughout Cangkringan, Kinahrejo Village, at the south flank of Merapi Volcano. The victims were the local people who did not predict the blast threatened their areas, because they believed that the pyroclastic flows from the dome collapses as long as they knew, did not threaten their areas, and pyroclastic flows would flow down following the Boyong River as the closest valley to their village. The blast swept an area about 8 km2, reaching about 5 km in distance, deposited thin ash, and toppled all trees to the south around the Kinahrejo and Pakem areas. The blast that reached Kinahrejo Village seemed to have moderate temperatures, because all trees facing the crater were not burnt. However, the victims were affected by dehydration and blanketed by fine ash.
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Lava dome
Dome (geology)
Debris flow
Pyroclastic fall
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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.
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Dome (geology)
Rainwater Harvesting
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