About 10 cm of ash was deposited on the saddle.
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Dies zeigt, ob die Metalle billig, durchschnittlich, teuer oder wirklich teuer sind. Das Ziel ist es, niedrig zu kaufen und hoch zu verkaufen. Ist Ihr Fahrplan zum allgemeinen finanziellen und wirtschaftlichen Umfeld. Wie alle Silberpreise spiegelt der aktuelle Silberpreis heute den inhärenten Wert von Silber und die relative Stärke der zugrunde liegenden Fiat-Währung wider. Die aktuellen Silberpreisgraphen zeigen, dass ein Graph der Silberpreise steigt, was bedeutet, dass Investitionen in Silber für Gewinn unter Berücksichtigung des Splitterpreises möglich sind.
Die billigsten Silberpreise können vom Silverspotpreis bezogen werden, da der Silberwertgraph 1 Troy Unzen Silberwert zeigt. Die 50 Tage und Tage gleitenden durchschnittlichen Silberpreise sind die Summe der durchschnittlichen Faserbandpreise für die letzten 50 oder Handelstage. Die monetären Metalle aus Gold, Silber und Platin sind eine gute Möglichkeit, um Reichtum zu speichern und können verwendet werden, um genaue Metall-Berechnungen von Wert mit Tools wie die Numeraire Spreadsheet durchzuführen.
Er arbeitet als Unternehmer, Investor, Journalist und Geldwissenschaftler. Folgen Sie ihm auf Twitter. Dies ist nur ein Artikel von 28 von Trace Mayer. Silber ist und wird eine wilde Fahrt. Wenn Sie nur lernen, wie zu handeln, können Sie beginnen, etwas wie Öl-weniger kurzfristige Volatilität. Regierungen können unbegrenzte Mengen an Geld drucken. Es gibt eine begrenzte Versorgung mit Silber auf dem Planeten. Die Weltbevölkerung nimmt zu.
Das Angebot und die Nachfrage von Silber umrissen durch diese langfristigen Faktoren sollten Sie darauf hinweisen, dass sein Preis wird mehr als oft nicht im Laufe der Zeit steigen. Kaufen, wenn Sie denken, dass der Preis von Silber steigen wird, verkaufen, wenn Sie denken, es wird zu fallen.
Um zu kaufen und zu verkaufen Silber, was Sie wirklich brauchen, ist ein Plan. Besser noch brauchen Sie ein Handelssystem. Das einfachste System zu folgen, verwendet eine technische Indikator genannt Tage gleitenden Durchschnitt.
Es ist im Grunde der durchschnittliche Schlusskurs der letzten Tage. Berechnen Sie die Tage gleitenden Durchschnitt von Silber, indem Sie die Schlusskurse von Silber über die letzten Tage und dann dividiert, dass durch Mit dem tägigen gleitenden Durchschnitt ist der erste Schritt zur Entwicklung Ihres eigenen silbernen Handelssystems. Sie versuchen, die Trends hier zu verwenden. Ash emission from two vents; frequent seismicity; lava dome extruded into summit crater.
Frequent, almost continuous, ash emissions m high continued in April from two vents. In mid-April, the most intense activity switched from Byobu-iwa vent. No earthquake swarms were recorded in April, but seismicity remained high.
A total of earthquakes was recorded and 27 felt. Most of the events were located a few kilometers W of Fugen-dake peak. The number of tremor episodes increased in April , compared to 99 in March , as did amplitudes and durations figure A swarm of microearthquakes, the first since July , began 13 May and continued as of 17 May. Ash emissions were at low levels during this period. Heavy rains on recently fallen tephra caused lahars in at least one flank valley.
The press reported that more than 1, people were evacuated on 19 May. A lava dome was extruded into the summit crater before dawn on 21 May. Small ash emissions occurred from the dome and fissures exposed its interior. On 3 June a large pyroclastic flow formed near the summit of Fugen-dake cone and moved down the E flank, reaching the outskirts of Kita-Kamikoba, 3 km from the 20 May lava dome.
The pyroclastic flow and accompanying fires destroyed more than 56 houses and portions of Shimabara were blanketed with wet ash. A larger pyroclastic flow, on 8 June, destroyed an additional 73 houses in Shimabara and Fukae, but no injuries were reported.
On 11 June, ejecta from an explosive event, not associated with pyroclastic-flow activity, damaged houses and car windows in Shimabara. Ashfall was reported km to the NE. Dome extrusion and pyroclastic-flow activity at Unzen continued as of 24 June. Premonitory activity and small ash emission. Increased seismicity was initially centered in Chijiiwa Bay, 13 km W, in November , and gradually migrated E in July-October , when seismicity increased further and the first volcanic tremor was recorded.
Following several earthquake swarms, including one on November centered 5 km W of the summit at shallow depth , the volcano erupted on 17 November, weakly emitting ash to heights of m from two newly formed vents Jigoku-ato and Tsukumo-jima within existing craters roughly m E of the summit figure Ash emissions, tremor, and swarm activity quickly ceased, but steam emission continued and seismicity remained at high levels.
An earthquake swarm occurred on 15 January and tremor resumed on 25 January figure A second eruption on 12 February produced m ash plumes from a new m-long line of small vents named Byobu-iwa m WSW of Jigoku-ato crater and m E of the summit.
Deposits of ash and lapilli reached 30 cm thick 10 m E of the vent but no incandescence was seen and no juvenile material was detected in the ash. Frequent small ash emissions continued from Byobu-iwa vent and seismicity remained at high levels. In early April, ash emissions resumed at Jigoku-ato vent, which widened and began to eject bombs. By mid-April, Jigoku-ato was the site of the most intense activity. Juvenile volcanic glass was first recognized on 12 May, although emissions remained small.
Shallow microseismicity beneath Jigoku-ato rose sharply the next day, and EDM measurements showed rapid inflation of the summit region. Debris flows, 15 and 19 May. Heavy rains on accumulated ash deposits triggered debris flows along the Mizunashi River on 15 and 19 May that destroyed two bridges and caused the temporary evacuation of about 1, people from Shimabara.
Lava extrusion, May. On 20 May, high-silica dacite table 6 lava extrusion began in Jigoku-ato crater. By the following day large fractures had appeared and the dome had separated into four parts.
Debris flows along the Mizunashi River continued; after the fourth debris flow, at on 21 May, about 1, people were evacuated. Water level in the river dropped following a debris flow at , and people were allowed to return home at Chemical composition of eruptive products from Unzen.
Sample 1 - block from 24 May pyroclastic flow. Sample 2 - surface of lava dome 1 June Sample 3 - pumice block from 8 June pyroclastic flow.
Sample 4 - lava flow. Total Fe as Fe 2 O 3. The dome continued to grow, reaching about m diameter and 44 m height a few tens of meters above the crater rim on 23 May, when material began spalling from its margins down the steep outer slopes. Large blocks, to 5 m in diameter m 3 volume , were observed falling from the dome, and explosive events produced grayish clouds to m height. Pyroclastic flows begin, 24 May. At on 24 May, a large explosion was heard as a portion of the lava dome collapsed, producing a pyroclastic flow that traveled about 1 km down the E flank to within 2 km of Kita-Kamikoba.
The flow discolored trees and transported blocks 10 m in diameter. About 1, people were evacuated on 24 May because of increasing mudflow hazard along the Mizunashi River, as volcanic debris accumulated and heavy rains continued.
During the evening, workers dredged material from above a dam 2 km from the summit constructed after the November eruption to reduce the mudflow danger. By the following morning the evacuation recommendation was withdrawn and residents were allowed to return home. Heavy rain on 25 May made observation difficult, but dust and ash from a pyroclastic flow was seen at around Rain continued on 26 May, and ash plumes m high were reported, but little is known about activity at the dome.
At on 26 May, a pyroclastic flow traveled into the Mizunashi valley, injuring a worker 2. The flow traveled 3 km, to within m of Kita-Kamikoba, and deposited ash 5 km E on Shimabara.
Bursts of tremor accompanied this flow and the prior pyroclastic flow at , suggesting that the tremor signal could be used to detect and count pyroclastic flows figure The pyroclastic flow, and the continued accumulation of debris in the river channel, prompted the evacuation of around 3, people from the surrounding valley. Several mudflows were reported during that evening, and rain soaked previously-deposited dust and ash to create more mud.
Many people were allowed to return home the next day when the rain ceased. Observations of the dome 27 May revealed a v-shaped vent, from which a m-wide tongue of lava was being extruded. Pyroclastic flows spawned from the margins of the lava tongue traveled along E and SE paths that joined at mid-flank. On 28 May, fluid no longer blocky lava overflowed the crater's E rim and moved down the outer flank, reaching about m elevation by midnight.
The 26 May evacuation order was extended. Pyroclastic flows continued to form, reaching to within m of Kita-Kamikoba on the 29th, and within m on the 30th. Trees in the valley were burned to charcoal, suggesting that flow temperatures had increased. On 31 May, lava was observed emerging from the vent, and then avalanching 1 km down the steep slope in 30 seconds, producing a roaring sound that was heard 6 km E in Shimabara. Pyroclastic flow kills 41, 3 June.
At about on 3 June, an audible explosion and 6 minutes of recorded tremor signaled the collapse of a portion of the summit dome and lava flow. The core of the pyroclastic flow traveled about 3. An ash cloud surge apparently detached from the flow and traveled an additional 0.
Blasted zones occurred in places along the margins of the flow and surge. The volume of the deposits was estimated to be 7. All of the casualties were within an evacuated "forbidden" zone and all were caused by the detached surge. The victims consisted of: Of the 41 people listed dead, 27 bodies were recovered, four remain missing and are presumed dead, and 10 died in hospitals from burns. Pyroclastic flows continued over the next several days, hampering rescue and recovery efforts, but were less frequent.
One helicopter was grounded due to ash-related engine problems on 6 June. Observers reported that despite continued growth of the dome it had not yet recovered half of its pre-3 June size. Large pyroclastic flow, 8 June. An increase in pyroclastic flow activity occurred in the afternoon of 8 June, with numerous small flows over a 5-hour period leading to a larger flow at The evacuation zone was again widened, to include parts of Fukae, bringing the total number evacuated to about 8, Multiple pyroclastic flows began at Finally, from to , a continuous series of pyroclastic flows traveled 5.
The flows destroyed 73 houses, but no injuries were reported. Activity continued, with an explosion detected by infrared camera at and a small pyroclastic flow at Clasts 5 cm in diameter fell to 5 km.
Evacuation zones were expanded on 9 June and again on 10 June, to a total of 9, people. Mudflow hazards were considered high given the more than 1 x 10 6 m 3 of debris that completely filled the Mizunashi River channel and covered the surrounding valley. Large explosive event, 11 June. By 11 June, a m-wide dome partly filled the large horseshoe-shaped depression that formed 8 June on the E side of the summit dome. Dome extrusion and pyroclastic-flow formation continued at Unzen as of 24 June.
On 14 June, the dome was m wide and 50 m high; it grew another 20 m in height by 16 June. Cracks in the dome emitted gas to m height, and periodic explosions produced 1-km-high ash columns.
The evacuation area was again expanded on 17 June, bringing the total number of evacuees to more than 10, Actions by Coordinating Committee. Early in November, volcanic tremors were observed. We were very worried about an impending eruption, and asked the Ministry for financial aid for observations by university scientists.
On 9 November, the Ministry decided to provide financial aid for observations by 6 universities. The university team set up seismic and deformation nets, in cooperation with Shimabara Volcano Observatory of Kyushu Univ.
Shimozuru , Tokyo Univ of Agriculture; H. Continued lava dome growth; debris flows to 7. Lava extrusion from Jigoku-ato crater began on 20 May. As growth of the dome continued, its E side, advancing down the steep upper flank, became structurally unstable, and collapse episodes triggered pyroclastic flows that traveled E down the Mizunashi River beginning 24 May.
Pyroclastic flows were frequent in June, and continued as of mid-July table 7. A large pyroclastic flow on 3 June traveled 4. On 8 June, a pyroclastic flow advanced 5. Evacuations prevented any injuries. An explosion from the crater at on 11 June ejected pumice, up to 10 cm in diameter, that fell 10 km NE. No further explosions had occurred by 24 July.
Volcanic activity at Unzen along with injuries and major damage, and actions taken by the Coordinating Committee for the Prediction of Volcanic Eruptions, November July The pyroclastic-flow rate increased briefly on 19 June between and with some of the larger flows traveling 2 km E. Ash elutriated from pyroclastic flows fell to the NE in June and July.
By the end of June, the crater dome was about x m and 80 m thick, and pyroclastic flows were recorded seismically times daily figure On 30 June, heavy rainfall caused a large debris flow down the Mizunashi River, injuring one person, and destroying 87 houses [a total of were damaged] near the coast 7. The area affected by the flow was entirely within the evacuation zone designated in early June a 5 x 5 km zone E of the summit, including parts of Shimabara and Fukae , with a pre-evacuation population of 12, The dome continued to grow E, reaching x m and 80 m thick by 21 July.
The eruption rate calculated from dome and pyroclastic deposit volumes was 0. Continuous ash emission to 1, m height began 13 July, echoing a similar period in mid-June. Summit seismicity was at lower levels in June and July than in May, with earthquakes recorded in June, compared to in May.
The monthly number of tremor episodes increased dramatically in June, apparently associated with small dome collapses. An earthquake swarm, from 23 June to early July, was centered 18 km SW of the summit, at 10 km depth figure Nine of the earthquakes were felt. However, seismicity near the volcano and to its W in Tachibana Bay was lower in June and July than in previous months.
Continued dome growth and pyroclastic flow generation; dome history reviewed. The dome in Jigoku-ato crater continued to grow in an easterly direction in July, at a rate of 0.
The magma supply rate remained unchanged in August, but the direction of growth became westerly. By 15 August, the dome was estimated to be x m and m thick. On 19 July it had been x m, with a volume of 5. A total of pyroclastic flows were recorded in July down from in June , and during August. Event durations were shorter than in previous months when flow signals occasionally lasted more than seconds.
The longest events lasted seconds in July and seconds in August. Pyroclastic flows continued to travel as much as 2 km E down the Mizunashi River. None of the flows reached the evacuated areas of Shimabara and Fukae, which remained closed with 12, inhabitants relocated.
Ash clouds from the larger pyroclastic flows rose 2 km, with ash falling mainly NE on Shimabara. Prevailing winds remained unchanged since May. Continuous ash emission from vents in the crater near the dome occurred in mid-July Explosive ejections of incandescent blocks to m height were observed from midnight to on 12 August, presumably from a vent on the W end of the dome that continuously emitted ash throughout the day.
In contrast to the drop in pyroclastic flows on 12 August, the number of summit earthquakes and tremor episodes increased sharply on 11 August. This followed reduced seismic activity in June recorded earthquakes and July , compared to April More than earthquakes had already been recorded in August by the 15th. Earthquake magnitudes were small and no shocks were felt, nor were changes in ground deformation detected by tiltmeters or EDM lines near the summit.
Following the peak on 12 August, seismicity began to decrease. The increase in seismicity may be related to the incandescent ejections on 12 August, the active continuous ash emission, and the westward growth of the dome. A man died on 8 August from burns suffered on 3 June, bringing the total casualties to 39 dead and three missing. The following is a report from Setsuya Nakada on dome growth and morphology in June. The E half of the lava dome collapsed during the eruption of the 3 June pyroclastic flow, leaving a m-wide horseshoe-shaped depression opening to the E figure The volume of dome material left behind referred to as W dome was about 0.
A new lava dome formed within the depression by 8 June, obtaining pre-3 June volumes. An extensive area of trees was burnt by the accompanying ash clouds. Pyroclastic surge ash-cloud surge deposits, such as those in the deposits from 3 June, were not clearly identified. Breadcrust bombs 5 cm in diameter were ejected to 3 km NE of the crater. Half of the W dome and the entire E dome post-3 June material were destroyed, widening the horseshoe-shaped depression to m.
As a result, a depression m in diameter formed within the crater, just above the former Jigoku-ato crater. On 17 June a continuous eruption column was observed rising from the W dome, for the first time since the start of lava extrusion.
The surface of the lava dome had the form of a petal with two lobes. These were created by extrusion near the summit of the E dome. By the end of June the horseshoe-shaped depression was filled with dome material, and lava blocks began to overflow NE onto the caldera floor.
Bulletin of the Volcanological Society of Japan, v. Nakada , Kyushu Univ. Lava extrusion continued at Jigoku-ato crater through mid-September, generating destructive pyroclastic flows that advanced down two valleys. More than 12, people remained evacuated and no new casualties were reported. A summit seismic swarm that began 11 August peaked August figure 29 , then gradually declined through the 19th. Incandescent block ejection was seen between and on 12 August, followed by continuous ash emission through the day.
The number of seismically detected pyroclastic flows from the lava dome decreased suddenly to a few events daily on 12 August.
A new lava dome, first recognized from the air on 13 August, emerged W of the former dome, and began to produce pyroclastic flows on 25 August. Pyroclastic flows had previously traveled down the Mizunashi River valley but those from the new dome C dome; see below moved ENE down the Oshigatani Valley, which extends N of and parallel to the Mizunashi, then joins it several kilometers downstream. Some of the larger pyroclastic flows from the new dome advanced 3 km down the Oshigatani valley from late August through mid-September, and pyroclastic surges burned vegetation.
The mayor of Shimabara city ordered the evacuation of about people from an area Senbongi 3. Frequent pyroclastic flows during the afternoon of 3 September included one of about 1 x 10 5 m 3 volume that advanced down the Oshigatani Valley at The accompanying cloud rose about 1, m and ash fell to the N part of Shimabara city. Ashfalls from pyroclastic flow elutriation clouds disrupted traffic around Shimabara city throughout the following day; the cloud from a flow at was 2, m high.
Another seismic swarm began beneath the crater on 6 September, and a pyroclastic flow that evening at advanced about 3. Hypocenters and seismic wave characteristics were similar to those of mid-August, although the September swarm was more vigorous. By 12 September, the lava dome had broken into numerous small blocks.
Seismic activity declined through 14 September but increased again on the 15th. Seismometers near the summit began to record larger pyroclastic flows, with longer durations than any since 8 June, on 15 September at seconds followed by others at seconds , seconds , and the largest at seconds.
The latter moved down the Oshigatani valley, entered the Mizunashi valley, and continued to within m of highway 57, a total of 5. The main body of the pyroclastic flow turned east into the Mizunashi valley, where it damaged 50 houses in Shimabara city, but the pyroclastic surge continued about m southward, destroying 26 houses and 74 other buildings including those of a primary school in Onokoba district, Fukae town.
All of the affected area had previously been evacuated, so there were no casualties. The largest pyroclastic flow was associated with the collapse of a section of the new lava dome about m wide, m long, and 50 m thick, a volume exceeding 3 x 10 6 m 3. Two days later, a new lobe had grown to x m and 30 m high 0. A total of pyroclastic-flow events was recorded in August, down from in July, but the more frequent episodes toward mid-September raised that month's total to as of the 17th.
September earthquake counts had reached through the 17th, up from in August and in July. The following, from Setsuya Nakada, describes eruption products through early September. However, collapse episodes from the E lava dome remained frequent and lava blocks had filled the narrow headwaters of the Mizunashi River, along which the 3 and 8 June pyroclastic flows had descended. As a result, cliffs along the valley disappeared, and valley-fill deposits talus became thick enough to act as a cushion to soften the shock of falling blocks.
The E dome flowed southeastward on the valley-fill deposits. After the end of June, the horseshoe-shaped depression had filled with dome materials, and lava blocks began to fall northeastward onto the floor of Myoken caldera figure They filled the E end of the floor with talus, which overflowed the caldera rim at the end of July.
Lava blocks then fell down the E and NE flanks as pyroclastic flows and their paths widened northeastward. Some reached the N bank of the Mizunashi River. The E margin of the E dome widened; because the NE slope under the dome was steeper than the SE slope, the northern half of the E dome migrated northeastward, while the southern half did not move and solidified.
By the middle of August, the caldera rim NE of the dome had been eroded away by the falling lava blocks. At the beginning of August, the ash-laden plume from the small vent at the northern base of the remnant W dome became stronger, and new lava was extruded on the western part of the E dome. On 5 August, many bubbles were observed coming from an old water-filled crater near the W dome. The small explosions that took place from the W dome on 12 August see above enlarged the vent to 20 m across and built a tuff cone around it.
The E dome temporarily thickened for a few days prior to the new lava extrusion; the western part of the E dome, just above the former Jigoku-ato Crater, had swelled vertically.
By the time new lava appeared 13 August, magma supply into the E dome had stopped, since the E dome did not lengthen and the surface of the dome did not move eastward figure It was difficult to accurately estimate the change in magma supply rate; talus and pyroclastic flows were deposited over an extensive area with irregular topography, which causes difficulties in calculating volumes of talus plus pyroclastic deposits.
At the end of August, the new dome central, or C dome was m long, m wide, and m high. The C dome grew eastward and northeastward, keeping a constant thickness. It covered the E dome and talus, plus a part of the old volcanic edifice, which was bulldozed by the growing dome from the former crater wall to the caldera rim. Talus also formed on the E dome. At the end of August, the volume of C dome was about 4 x 10 6 m 3 and the total volume of the domes was about 12 x 10 6 m 3.
The resulting dome growth rate is about 0. The upstream area of the valley was the source area for lahars on 30 June. The pyroclastic flows traveled a maximum distance of 3 km from the dome, and had associated ash-cloud surge and seared zones like those of 3 and 8 June figure Flows moving down the Oshigatani Valley changed course southeastward when they encountered a high point dividing the valley and a residential area.
Ash-cloud surges climbed the barrier, burning or searing trees, but block-and-ash flows did not. The devastated area was widest for pyroclastic flows that took place within the first week. By mid-September, Oshigatani Valley had been almost filled by pyroclastic-flow deposits.
Average speeds of pyroclastic flows were estimated using travel distances observed by Ground Self-Defense Force radar and durations of tremor signals. The higher the average speed of a pyroclastic flow, the longer its travel distance: Nakada , Kyushu Univ; M.
Dome collapse triggers large pyroclastic flow, then new dome extruded. Lava dome growth continued in Jigoku-ato crater through early October, generating frequent pyroclastic flows by partial dome collapse. A seismic swarm began beneath the crater on 6 September, peaking September and again on September.
Seismicity was similar to that of mid-August when dome 3 formerly called the central dome, or C-dome began to grow, although September activity was more vigorous. Extruded lava pushed the crater wall NE, leading to a collapse of the crater wall and the adjoining dome 3 at on 15 September. Red-colored ash plumes were observed intermittently earlier in the day, becoming stronger and more frequent by the start of a 2-hour increase in the number and size of pyroclastic flows at The activity culminated in a major pyroclastic flow that generated an minute seismic signal, the longest since 8 June, composed of 6 successive events including one that lasted 4 minutes beginning at An ash cloud surge detached from the flow at the confluence of the Oshiga with the Mizunashi River, continuing SE into the Onokoba area of Fukae city.
A car previously burned by June pyroclastic flows was thrown about 60 m by the surge. Although it appeared that the surge rapidly lost force when it detached from the rest of the pyroclastic flow, its temperature remained high.
The volume of collapsed dome lavas and pre-existing summit rock was estimated to be 3. Using aerial photos, the Ministry of Construction estimated the volume of 15 September pyroclastic-flow deposits at 4 x 10 6 m 3 , indicating that the main flow was the largest since the start of activity in May. Flow deposits were about 5 m thick, and although the interior was still hot 3 weeks after deposition, no gas-pipe structures were observed.
Lava blocks in the deposits were massive, without the breadcrust or cauliflower surfaces seen in the 8 June pyroclastic-flow deposits. The biotite hornblende dacite composition of the blocks was the same as that of lava fragments from the 3 and 8 June flows and the pumice ejected from Jigoku-ato crater on 11 June.
Peripheral surge deposits consisted of a lower coarse sand layer, and an upper reddish ash layer. A total of earthquakes was recorded on 16 September, the most in one day since July , but seismicity rapidly declined, reaching former levels by the following morning. Dome 4 began to grow in the horseshoe-shaped depression about m wide and m long formed by the collapse of dome 3 figure By 20 September, it had grown to about 1. Following the pattern of dome 2, the length of dome 4 stopped increasing at the end of September, as continuing collapse of its distal end generated small-scale block-and-ash flows.
The upper reaches of the Oshiga valley were filled with debris shed from the domes, and large pyroclastic flows were rare. A total of seismically determined pyroclastic-flow events and earthquakes were recorded in September, increases from and , respectively, in August. There were no felt shocks in either September or early October.
Growth of the lava dome. Seismicity had declined to relatively low levels since extrusion of dome 4 started in mid-September. A seismic swarm began beneath the dome on 24 October, gradually increasing through mid-November. The seismicity buildup was similar to those of August and September, which culminated in the appearance of domes 3 and 4, respectively, although the rate of increase was slower for the current swarm.
Uplift at the boundary between domes 3 and 4, first noted from the air on 25 October, was continuing in mid-November, suggesting magma intrusion under or into dome 4. As of 14 November, dome 4 was m long, m wide, and m high. Dome and pyroclastic flow volumes were used to estimate a total of about 4 x m 3 of magma erupted between May and the end of October.
Pyroclastic flows, mainly from dome 4, moved down the Oshiga and Mizunashi valleys, as in September. Most have been relatively small since the eruption's largest pyroclastic flow on 15 September. Ash clouds generated by the larger flows reached about 2 km height. The number of pyroclastic flows, counted seismically, declined gradually through October to , from in September and markedly since 11 November.
Lava extrusion has continued. Extrusion of the 4th in a series of lava domes began after the 15 September collapse of dome 3, which spawned a major pyroclastic flow. A seismic swarm began beneath the crater on 24 October and inflation of the upper part of dome 4 was first noted the next day. Inflation continued through November and seismicity increased gradually until 1 December, then declined. On 3 December, a new lobe emerged on the S side of dome 4, and it was continuing to grow a week later.
The number of seismically counted pyroclastic flows was relatively low until late November, when frequent flows resumed. The flows, generated mainly from dome 4 and its early-December lobe, moved down the same valleys Oshiga and Mizunashi as in previous months. Ash clouds elutriated from the larger flows reached about 2 km height. The following information, from Setsuya Nakada, describes November-early December surface activity. Growth of lava dome 4 has continued in the depression left by the collapse of dome 3 on 15 September.
By the end of October, dome 4 was m long, with two lobes forming a crudely petal-shaped structure. Rough pressure ridges, convex downslope and of long wavelength, formed on the surface of dome 4, and thick lava layers piled atop each other were observed on its southern cliffs. New magma reached the surface along the narrow space between domes 2 and 4 and between the head of dome 4 and the remnants of dome 3, where it built new irregularly shaped lobes. Significant intrusion was indicated by swelling of the dome and uplift of the talus between domes 3 and 4.
As the uplifted area expanded southward and northward, reddish blocky lava replaced the talus. Older domes were pushed S-SW, causing radial cracking in dome 3, where deformation was continuing in early December. Dome 4 has advanced little since early November, as frequent rockfalls from the dome front compensated for the additional magma supply. Rockfalls eroded and buried dome 2, but did not develop into pyroclastic flows as often in October and November as in previous months.
The early-November flow started from the head of dome 4, advanced across the dome, then entered the Oshiga valley. Its average speed was calculated at Continued dome extrusion and pyroclastic flows; vigorous seismicity; more than 8, still evacuated.
Lava domes continued to grow through early January, with growth occurring both exogenously and endogenously figures 35 and Talus from the domes buried their SE slopes. Extrusion of a new lava dome 6 toward the SE began in early December. By late December, its initial 2-lobed petal structure had become poorly defined and its advance had nearly stopped, as lava blocks began falling directly from the head of the dome, eroding the southern margin of dome 4.
On 7 January, dome 6 was about m long, m wide, and 80 m high. Collapsed dome material eroded and buried dome 2, which was no longer visible by mid-December. Dome 5, emerging since 21 November at the head of dome 4, grew upward about 50 m in mid-December to become the highest of the six domes. Its peak, at about 1, m above sea level, had reached the height of the volcano's summit Fugen-dake. A crack formed in the top of dome 5, roughly perpendicular to the NW-SE-trending graben that developed on the lava-supply vent and widened in late December.
Pyroclastic flows, generated mainly from dome 6, advanced as much as 2. Ash clouds generated by pyroclastic flows, reddish brown to dark brown early in the eruption, had become milky colored, and those from the largest flows reached 2 km height.
Failure of dome portions as large as 5 m 3 in volume seldom triggered pyroclastic flows, but remained simple rockfalls.
This suggested to geologists a decline in the fragmentation force and perhaps the auto-explosivity of falling lava blocks, probably implying a decreased pore pressure. Plumes from the NW margin of the former Jigoku-ato Crater had become weaker and less frequent by mid-December, and ash-laden columns were rare.
White-bluish, sulfur-rich, acidic gas was discharged continuously from Jigoku-ato through cracks in dome 3. Strong steam-rich gas emission accompanied the bluish plumes, especially the day after heavy rains. The seismic swarm that began beneath the dome on 24 October was continuing as of mid-January, becoming the longest and most vigorous since lava extrusion began in May. Earthquakes recorded in December totaled , the highest monthly figure since activity began to increase in July table 8 and figure Monthly seismicity and number of seismically recorded pyroclastic flow events at Unzen, The evacuation zone has remained almost unchanged since September, with a total of 8, evacuees in December 5, from Shimabara city, 2, from Fukae town.
Shimabara Railway traffic resumed on 27 December. Lava dome growth continues; dome collapses spawn pyroclastic flows. Dome growth continued through early February, mainly endogenously, and pyroclastic flows were generated by collapse from the edges of domes 5 formed in late November and 6 appeared 3 December. Talus from the domes continued to bury the SE slope of the dome complex. Magma was supplied primarily to the head of dome 6 m long, m wide, and 50 m thick , causing the dome to thicken to 80 m , especially over the vent area, as it was shortened by collapse.
Magma intrusion in dome 6 caused uplift of older dome materials behind the vent, where a small graben had formed earlier. The peak of the resulting cryptodome surpassed the summit of dome 5, previously the highest point in the dome complex 1, m elevation.
Cryptodome growth pushed dome 5 NE, and caused its partial collapse northeastward and eastward. Rockfalls from dome 5 eroded the surface of dome 4, and began to bury it with talus. A group of parallel to radial cracks developed on the surface of dome 4, forming a central groove that divided it into N and S parts by early February. The N part appeared to be pushed eastward by the movement of dome 5 and the cryptodome. Pyroclastic flows traveled mainly SE and E from dome 6 and the cryptodome, with ash clouds from the larger flows rising to 2 km.
Some small pyroclastic flows and rockfalls occurred NE and E of domes 4 and 5. A total of flow events were recorded seismically in January compared to in December ; activity increased somewhat in early February. Seismicity beneath the dome complex continued at high levels in January, when the highest monthly total 5, earthquakes since the start of dome growth was recorded. Two blocks at the front of dome 6 estimated block volume, x 10 5 m 3 collapsed on 2 February at , forming a larger-than-normal pyroclastic flow.
Associated ash decreased visibility to 30 m in Fukae 4 km ESE immediately after the flow, and nearby roads were briefly closed. Despite initial estimates from TV-monitor footage and eyewitness accounts that the pyroclastic flow traveled 3 km, the area 2. Compared to pre-October pyroclastic flows, more recent ones were less energetic, with lower velocities and a narrower area of devastation.
However, the quantity of co-ignimbrite ash had not changed noticeably. Small horseshoe-shaped depressions, up to m wide, were created by the rockfalls. The pyroclastic flows all descended along the same path, eroding a narrow v-shaped groove in the accumulated talus, which terminated at the top of a m cliff. The flows spread at the base of the cliff, depositing material on the gentler slopes. Some of the southward-moving flows were deflected by the N face of Iwatoko hill roughly 1.
The pyroclastic flows traveled about another m, to a total of 2. Continued dome growth; occasional pyroclastic flows; large debris flow nearly reaches coast. Summit lava dome growth continued through early March, with frequent pyroclastic flows generated by partial dome collapse. Most of the growth of dome 6. The area around the dome swelled upwards, and complicated "petal" structures formed on its surface.
Continued thickening of dome 6 forced dome 5. The surface of dome 5 was very reddish, implying that it was composed of older, oxidized lavas, and was dominantly a cryptodome. Rockfalls from the E and N faces of dome 5 produced reddish block-and-ash flow deposits and left behind numerous small cliffs figure Dome 5 in turn pushed dome 4 split into N and S parts , especially its N part, which moved more than 50 m to the E during mid-February-early March. Much of dome 4 was eroded or buried by material from other domes, bringing the talus slope flush with its top.
Incandescence and strong gas emissions were observed along cracks and pit craters in and near dome 3. Emission of ash-laden plumes became continuous from Jigoku-ato Crater in early March.
Lava blocks frequently fell from near the head and front of dome 6, generating pyroclastic flows to the SE and occasionally to the E and NE figure Clouds of elutriated ash descending to the S sometimes reached the N cliff of Mt. Iwatoko, but the accompanying block-and-ash flows stopped about m short of this point. Thus, trees on the N slope of the cliff were covered by the elutriated ash clouds, but they were neither bent over nor burned.
Larger pyroclastic flows occurred on 2 and 12 February. Flows at and on 12 February had durations of and seconds, respectively, the longest since 15 September. Heavy rainfall triggered a large debris flow at on 1 March, along the E flank's Mizunashi River, following the route of the previous large debris flow on 30 June The flow reached a point m from the coast, 8 km E of the summit, crossing Routes 57 and , and burying a m section of the Shimabara Railway.
No damage occurred in previously untouched areas, and rail service was resumed within 6 days. As of early March, roughly 7, people remained evacuated. February's 6, recorded earthquakes represent the largest monthly total since the eruption began, but seismicity started to decline on 4 March. Seismicity has been at very high levels since October.
Lava extrusion persists; new dome follows increased seismicity; strong pyroclastic-flow activity. The length of dome 6 did not increase significantly, and the complex "petal" surface structures remained close to the vent, now the highest point in the dome complex. Increased seismicity in early April preceded the extrusion of a new dome 7 , which was growing rapidly at mid-month.
During March, pyroclastic flows were seismically recorded, up from in February. A large pyroclastic flow, generated by collapse of large blocks between domes 5 and 6 on 1 April, traveled 3 km down the Mizunashi River, reaching the evacuated town of Kita-Kamikoba where 43 people were killed by the 3 June flows. The 1 April block-and-ash-flow deposit was thinner, and its ash-cloud surge deposit was thinner and distributed over a much smaller area than those from the 3 June flows.
The 1 April pyroclastic flow was the largest since the 15 September flows, whose deposit surface and lava blocks continued to steam as of early April. Small pit craters to 30 cm diameter were visible on the surface of the September deposit. Heavy rainfall triggered three large debris flows in March.
The 1 March debris flow reached a point m from the coast 8 km E of the summit crossing Routes 57 and , and burying a m section of the Shimabara Railway.
Both highways were crossed, and a m section of the railway was buried by 0. A smaller debris flow occurred along the same route on the morning of 23 March, burying a m section of Route Roughly 7, people remained evacuated as of mid-April.
During March, 5, earthquakes were recorded on the dome complex, down slightly from in February. Seismicity declined through mid-March, increased to the highest level of the eruption, and then declined again at the end of the month. The number of earthquakes increased during the first few days of April, before declining once more on 6 April, as a new dome 7 began to emerge.
The new dome had grown to x m by 12 April figure Continued lava dome growth; frequent avalanches and pyroclastic flows. Lava dome growth continued through mid-May, accompanied by frequent avalanches and pyroclastic flows produced by partial collapse of the lava dome complex m E-W, m N-S, and m high by mid-April. The youngest dome 7 , which first appeared on 6 April, grew slightly faster than material was removed by collapse along the leading edge. Its viscous lava formed "banana peel-like" structures with several radial lobes.
These structures had typically been observed on the surfaces of newly extruded lava that overrode older domes dome 3 over dome 2, and dome 5 over dome 4.
By mid-May, dome 7 was about m long, m wide, and 90 m high, and had the highest extrusive vent of the dome complex. The cryptodome that formed among domes 3, 4, 6, and 7 continued to swell, and small reddish oxidized pieces, probably from its interior, were exposed on the surface. Intrusion and erosion rates were balanced, keeping the peak shape and height nearly stable. Gullies developed around the cryptodome, extensively eroding its ENE side, where rockfalls frequently occurred.
The rockfalls commonly traveled E and NE, and rarely N, producing reddish to pink-colored ash clouds. Many cracks appeared on the head of dome 6, pushed by the swelling cryptodome. The foot of dome 6 reappeared from the talus deposits, while dome 4 E of the cryptodome was buried by talus. Dome 2 was similarly buried in mid-December The E part of dome 3 was also pushed, and covered by reddish lava blocks from the cryptodome. The daily number of seismically recorded pyroclastic flows ranged from 4 to 28, almost unchanged from previous months, totaling in April.
Flows originating at dome 7 traveled down the SE flank of the dome complex toward Iwatoko-yama and the Akamatsu River valley. Pyroclastic deposits buried the gentle slope along the Akamatsu River valley. April's longest flow extended 3. Geologists suggested that this may indicate a decrease in the auto-explosivity of the lava blocks. On 22 April, repeated lava-block falls from the toe and sides of dome 7 generated multiple pyroclastic flows that cascaded down the steep SE slope made of pre volcanics, forming a gully 50 m deep, m wide, and up to m long.
By mid-May, the gully had been buried by rockfall talus. From mid-April to mid-May, blue gas was emitted continuously from dome 3, and sporadically from the heads of domes 6 and 7, and the cryptodome. Ash emission was weak and infrequent. Roughly 7, people remained evacuated as of early May. The samples had specific gravities of 2. Bombs erupted directly from the magma conduit on 8 and 11 June had specific gravities of 0.
Lava-dome growth continued through mid-June, and pyroclastic flows were frequently generated by partial collapse of the dome complex. The new dome 7 which first appeared on 24 March correction to Lava extrusion formed "banana peel" and sometimes "petal" structures petal with two lobes. Swelling of the cryptodome raised its summit to 1, m elevation, 30 m higher than the pre-eruption summit. Earthquakes, probably occurring within the dome complex, frequently triggered collapse of the cryptodome, causing it to develop a conical shape with a relatively smooth surface.
Collapses occurred at both sides of the growing lobes on dome 7, as well as at the dome front. One rockfall, measured by the GSJ with a theodolite, was estimated to have a volume of 1.
Pyroclastic flows generated from rockfalls traveled primarily down the dome complex's SE flank towards Mt. Iwatoko and into the Akamatsu valley, extensively burying its gentle slope figure Ash clouds accompanying the flows rose to about 1, m, with a maximum height of 1, m on 19 May. The pyroclastic-flow-deposit distribution was little changed from previous months.
Longer flows had a tendency to erode the steeper, upstream area, then deposit in the middle and downstream areas. The eroded upstream channels were subsequently filled by less-energetic flows. The low magma-supply rate reflects the low level of activity in April, when the lava domes grew very little, large pyroclastic flows were rare, and seismicity was at low levels. Geologists believe that the supply rate has probably fluctuated considerably since February.
Continued geomagnetic measurements by Kyoto Univ scientists show that the degree of demagnetization around the dome complex had decreased from mid-March. Demagnetization was strongest when lava first appeared in May , and continued steadily until February A total of 3, earthquakes was recorded in May, similar to April. The daily number of seismically detected pyroclastic flows ranged from 5 to 17, with a total of events, similar to previous months.
The evacuated area E of the volcano, in Shimabara and Fukae town, was reduced somewhat in June, decreasing the number of evacuees from 7, in May [to] about 6, by 11 June. Growth of the lava dome continued through early July. Partial collapses of the dome complex frequently generated pyroclastic flows. Dome 7, which had begun to emerge in late March, grew exogenously against dome 6 figure 43 , which was buried and eroded by dome 7's lava blocks.
Petal or peel structures, which had always appeared on the dome's surface during periods of rapid lava extrusion, were not evident, perhaps indicating a declining magma supply rate. The cryptodome, including dome 5, grew endogenously, frequently generating small rockfalls that were probably triggered by earthquakes within or beneath the dome complex. Volcanic gas was emitted continuously from the E part of dome 3, as well as from the depression between domes 3 and 7.
The depression divides the cryptodome area into a conical NE section that includes the dome's summit, and a lower SW section with a flat top. Deposits of the pyroclastic flows that cascade down the SE flank continue to bury the Akamatsu valley. On 23 June, the ash-cloud surge from a pyroclastic flow struck the saddle, but the main flow did not reach the cliff. Bark and leaves were not burned, but leaves in the area died.
About 10 cm of ash was deposited on the saddle. Thin lead foil, set in a stainless-steel hole to detect the pressure of the ash-cloud surge, was hollowed, and aluminum foil was broken. Debris flows that have occasionally occurred during the current rainy season eroded pyroclastic flow deposits in the valley. Pyroclastic-flow material was deposited along the valley's N side and in its upper reaches. This deposition pattern, erosion by debris flows, and the declining magma-supply rate delayed the overflow of the lowest part of the saddle by southern-cliff pyroclastic flow deposits.
In early July, the Nagasaki prefectural government began to construct a steel fence, 35 m wide and 10 m high, in a stream originating from the saddle, hoping to prevent ash-cloud surges from entering the stream. JMA reported that the daily number of seismically detected pyroclastic flows ranged from 6 to 21 in June.
The total of in June was almost unchanged from previous months. The longest June flow extended 3 km SE from the dome. Most ash clouds generated by the flows rose about 1, m, with the highest, to 1, m, on 13 and 17 June. The June total, 3, recorded earthquakes, was similar to previous months.
Dome growth slows, but rockfalls and heavy rain trigger destructive pyroclastic and debris flows. The lava dome complex continued to grow through mid-August table 9. Viscous lava did not continuously reach the surface, although magmatic intrusion caused some endogenous growth. Earthquakes had been frequent during periods of endogenous growth at the higher magma-supply rate, but recently there have been few seismic events in the absence of lava extrusion, implying that magma is no longer being continuously supplied to the dome complex.
Chronology of eruptive events at Unzen, July to mid-August Dome 7 figure 44 , which began to emerge in late March, grew exogenously in late July, creating petal and peel structures on its surface. A few days after dome 7 stopped growing, the axis of the petal structures was buried by material that collapsed from the dome above it, and its surface became reddish, implying that magma supply had nearly ceased.
Geologists believe that the plug may represent a magma conduit inclining westward beneath Jigoku-ato crater that was the source of viscous lava when the magma-supply rate was high.
A grayish fresh lava surface with step-growth wrinkles appeared along the circular fault. Ash frequently fell on inhabited areas around the volcano including Shimabara city and Fukae town, which extend to within 7 and 4 km of the dome, respectively, and the Unzen spa area. Rates in late July were the highest since March, and the July total of 5, was also the largest since March.
Seismometers began to record a burst of pyroclastic flows, the most vigorous since 22 April, on 8 August at Sixteen were recorded by , including events with durations of seconds at , seconds at , and seconds at Heavy rains and dense clouds from a typhoon, which passed near the volcano that morning, obscured the volcano and prevented determination of pyroclastic-flow lengths and directions.
An additional house burned on 9 August at about , but the cause of the fire was not known. No houses had been burned by pyroclastic flows since the destruction of on 15 September Debris flows were frequent along the Mizunashi River on 8 August between and The largest extended 7 km E of the dome, burying highways and the Shimabara railway, and damaging 72 houses in Shimabara city and Fukae town. Rain that fell from about noon on 12 August until the next morning caused 2 more large debris flows, at about on the 12th and on the 13th.
The flows again traveled along the Mizunashi river, burying highways and the railway, and destroying 55 houses along both sides of the river's lower reaches. Structural damage from the August debris flows was the first since 30 June Highways were reopened by the evening of 13 August, but railway traffic was still halted as of 16 August. Forty more houses were destroyed along the Mizunashi River by a rain-induced debris flow early on 15 August.
Weather prevented observations of changes in dome morphology, as the succession of large pyroclastic flows and debris flows occurred for about a week in mid-August. When geologists examined the debris flows, they were steaming vigorously, and contained hot fragments of lava blocks derived from the youngest pyroclastic flows.
Debris flows were generated in the middle sections of the Oshiga NE flank and Akamatsu valleys. The middle portion of the Mizunashi valley was always covered by a sequence of new pyroclastic-flow deposits when visited by geologists. None were reported injured by the activity. Continued dome growth; dome 8 extruded; pyroclastic and debris flows damage many buildings. Endogenous cryptodome and exogenous growth in August produced a new dome 8 , which began to emerge 11 August at the upper part of dome 7.
Collapses reduced the size of the dome complex until mid-August, then volume increased again, mainly from endogenous growth. Based on digital mapping by the Geographical Survey Institute, the volume of the dome complex is estimated at 5 x m 3 , with the total amount of magma erupted since 20 May estimated at 11 x m 3.
Dome 7 resumed growth in mid-August as new lava extruded from the magma-supply vent joined lava emerging from the circular fault that appeared on the east-central part of the cryptodome in early August. A NW-SE-trending graben up to 50 m wide formed on dome 8 in late August along part of the former circular fault.
Upward growth of dome 8 in early September increased the width of the graben until the graben wall collapsed. The growth of dome 8 caused the W half of dome 7 to collapse as a series of rockfalls on August. The E half of dome 7 was pushed E until it hung over dome 6.
Partial collapses of the dome complex often generated pyroclastic flows. One SE-flank pyroclastic flow burned 17 houses from to on 8 August. Heavy rains triggered debris flows along the Mizunashi River. No additional damage had been caused by pyroclastic flows as of mid-September.
Pyroclastic flows from Jigokuato crater in late August traveled almost 4 km along the Mizunashi River, longer than the fatal 3 June flow and the longest since 15 September The flows frequently struck the N cliff of Mt. Iwatoko on the S side of the Akamatsu valley , just reaching the top of its lowest saddle, and ash clouds entered a small valley extending m from the saddle.
Since mid-August, pyroclastic flows moving NE from the cryptodome overflowed from the Oshiga Valley extending NE from the summit into another small valley north of Taruki Height. The Height is a barrier between the Oshiga Valley and Shimabara city, and the small valley is the headwater of a river flowing into the city.
The upper portion of the Oshiga Valley near the head of Taruki Height had been completely filled with pyroclastic-flow deposits until small debris flows eroded them. Cut off by debris flows in early August, the Shimabara railway resumed operation on 1 September. Summary of damage from volcanic activity at Unzen, , showing inhabited houses totally and partially destroyed or inundated, uninhabited houses damaged, deaths, and injuries.
Ash fell to the E on Shimabara city, Fukae town, and Unzen spa. The number of evacuees was halved to 3, on 9 September. Volcanic gas was emitted from dome 3 and a graben area. A total of 3, earthquakes was recorded in August, at rates of per day.
The events recorded on 11 September were a new high for the current activity. Earthquake swarms were detected on , 17, and 31 August.
Seismic activity in Tachibana Bay had been low since August Five shocks from the swarms were felt at UWS. The largest shock was M 4. The period mid-September to mid-October was characterized by exogenous growth of dome 8 on the SE part of the lava-dome complex.
Lava emerged from the SE end of an arc-shaped crack described as a circular fault in The part of dome 8 that formed along the crack in mid-August and subsequently stopped growing has been uplifted and pushed E. Rockfalls continued to occur on the E flank figure 45 , increasing the thickness of talus deposits around the dome complex. Ash clouds from the flows rose about 0. Relatively large pyroclastic flows generated by rockfalls from dome 7, which was pushed above dome 6 during the growth of dome 8 in mid-August, occurred at on 27 September, on 3 October, and on 10 October.
These pyroclastic flows reached the Kita-Kamikoba and Kami-Onokoba Fukae town areas, after traveling 3.
No damage was done, and the surrounding forest was not burned or destroyed. The rockfall volume that generated these pyroclastic flows was estimated at 0. Seismic duration of the flow was seconds.
The main block-and-ash flows were the longest in and traveled slightly farther than those of 3 June The main flow split in two after striking a large block. One portion traveled 3.
The videotape showed ash clouds moving steadily rather than surging on the ground in the area S and SW of Kami-Onokoba. An inspection from the air 6 hours later showed thick ash covering trees and houses.