What kind of eruption does krakatoa have

The line of fracture began at a point south of Lang Island, and formed an arc of a circle passing through the peak to the western side of the island. Boats from the U. Juniata entered the crater-like area, concave to the northward, and sounded along the face of the heights; but no bottom could be found with twenty fathoms of line. Prior to the eruption, Verlaten and Lang islands were green with trees and foliage; they are now covered with scoria. Eastward of Verlaten a small island had formed; small necks of land had been thrown out from the eastern side of Verlaten and the western point of Krakatoa.

The Polish Hat had disappeared, but a new rock, about twenty feet in height and as many in diameter, now existed in Krakatoa channel, near to the southern point of Lang Island. Within ten yards of this rock there were eight fathoms of water. At the place occupied by the Polish Hat the boats found no bottom with twenty fathoms of line, while at the spot where the volcano had been so active later soundings showed no bottom at one hundred and sixty-four fathoms, nearly one thousand feet.

To the northward and eastward two new islands, Steers and Calmeyer, had formed, where before the eruption were thirty to forty fathoms of water. It has been thought that the first great waves on the evening of the 26th were caused by a portion of Krakatoa being shot out northwards for eight miles, and dropped where now is Steers Island; while the terrific detonation on the 27th, and the greater wave accompanying it, resulted perhaps from that still more titanic effort which lifted the greater portion of Krakatoa, hurled it through the air over Lang Island, and plunged it into the sea where Calmeyer Island now blocks the old East Passage.

The captain of the Juniata stated in his report that he anchored off the site of Anjer, and that "the buoys which mark the line of the submarine cable to Telok Betong, Sumatra, and the base of the light-house at Fourth Point are the only monuments of Anjer.

The plain northward of Anjer peak was swept by the flood of waters, and nothing remains but the vine-like roots of the cocoa palm and some scattered and ghastly relics of the inhabitants Communication with Telok Betong is now interrupted by masses of floating pumice wedged in Lampong Bay. And yet another reported that on December 21, , in the S.

The tidal phenomena which followed this convulsion are particularly interesting. The waves formed in the narrow strait issued into the oceans east and west, and started on their journey around the globe.

The undulations were registered at Mauritius, the Seychelles, in South Africa, and on the shores of the Pacific Islands on the same day that the Java villages were swept away. The waves continued their course, crossed each other at the antipodes of Krakatoa, and returned to the spot from which they had started. Four times did they go around the earth before the equilibrium of the sea was so far restored as to be insensible to instruments.

At the same time an atmospheric wave also started around the globe. These disturbances were noted wherever there were barographs, and the dates are thus fixed when these undulations passed various places on the surface of the earth.

For instance, at St. Petersburg, on August 27th, there was a rise of the mercury, and immediately afterwards a fall. At Valencia, in Ireland, and at Coimbra, in Portugal, similar phenomena were noticed, and shortly afterward the disturbance was observed all over Europe, wherever a barograph was at hand.

At the western observatories the movement was more pronounced than at the eastern, but the general appearances of the curves at neighboring stations were about the same. This disturbance moved rapidly from east to west, requiring but two hours and twenty-five minutes to travel from St. Petersburg to Valencia, a distance of thirteen hundred and fifty miles.

On the 28th there was a somewhat similar disturbance which moved from west to east, requiring a little less than two hours to pass from Valencia to St. On the 29th there were two well-defined movements: one early in the morning, from east to west, occupying two hours and eight minutes from St. Petersburg to Valencia; and the other in the afternoon, from west to east, reaching St.

Petersburg one hour and twenty-five minutes after it was observed at Valencia. Similar phenomena, less defined, were noted on the 30th and 31st. Coincident with these atmospheric fluctuations, magnificent sunlight effects, lurid skies, prolonged dawns, and lengthened twilights were observed. He also reports that he noticed peculiar red sunsets in the South Atlantic several weeks before the Java eruption, and that he carried them through to Hong Kong, and from there nearly across to San Francisco.

The volcanic cloud that caused these peculiar effects seems to have followed a straight path, for they appeared on the east coast of Africa on the second day, on the Gold Coast on the third, at Trinidad on the sixth, and at Honolulu on the ninth day. It is impossible to say how high the lighter matter was carried; it is certain that months have been required for it to descend. The places situated below the direct path of the cloud were the first to have those ominous displays, which varied in intensity according to their time distance to the westward; for the cloud was at first elevated as a comparatively narrow column.

This column gradually spread out north and south, until the inhabitants of all lands obtained a view of the beautiful effects of broken and absorbed sunbeams, and a demonstration of the power of that steam which was imprisoned by the last convulsion of nature. The data from which this article is compiled has been taken from reports sent to the U. Hydrographic Office, from the preliminary survey of the U.

Juniata, and from the Proceedings of the Royal Geographical Society. They are cooler and stickier than basalt, allowing them to accumulate pressure before being set free.

Studies have shown in to be growing at a rate of 5 meters per year. Before , three volcanoes known as Rakata, Danan, and Perbuwatan combined to what then became Krakatoa island. Mount Krakatoa is an example of a stratovolcano, a tall, conical volcano with multiple strata of solidified lava, tephra, as well as volcanic ash.

Most of the popular eruptions have been made by stratovolcanoes. Other known stratovolcanoes are Mount St. Helens and Mount Pinatubo. Indonesia is the country that holds the biggest number of active volcanoes, at Iceland, another volcano-dotted country, holds about the same number of volcanoes but not all are as active as those in Indonesia.

They found no pumice. Observers on [Carita Beach] noted that lava glowed strongly in early May but had stopped by mid-June. As of 14 August glowing had not reappeared. Brodscholl and K. Activity resumes in March after 5 months of quiet; ash clouds and tephra ejection. Press reports have described renewed activity. Activity apparently began again on 19 March after about five months of quiet. At the end of March, thick black ash plumes rose m while "red flames and glowing lava" were observed at night to rise m.

Eruption noises like thunder could be heard at Carita Beach. Scientists from GMU stated in the newspaper Suara Pembaruan that their seismograph was not operational at the time of the eruption, but began functioning again on 26 March. Wimpy Tjetjep, Director of VSI, reported to the same newspaper on 6 April that volcanic materials had been thrown within a 3,m-radius from the crater.

Ash and tephra emissions were continuing, and weak volcanic earthquakes had been recorded in the previous week. Officials at the local observatory reportedly described the activity as "spouts of fire" and thick black ash emissions alternating with explosions.

Ejection of blocks as large as 1-m-diameter were also reported. Fishermen at Carita Beach described the April activity as "gigantic fireworks floating in the middle of the sea at night.

The most recent report of activity was on 5 May, when VSI volcanologists at the local observatory told the Antara News Agency that an eruption ejected lava m into the air. They also noted that as many as "eruptions" had been recorded on 3 May. All of the reports emphasized that the island remains off-limits to visitors. The height of the ash columns, measured from the [Pasuaran Observatory] during clear weather, ranged from to m above the summit, with incandescent projections evident at night.

The sporadic eruptions have deposited ash over almost the entire island. Occasionally, explosion sounds were heard and vibrations felt at the observatory. A similar report on 18 December stated that an ash cloud was as high as 3 km and drifting E.

On 26 July , J. Sesiano made observations from the sea, from the summit of the peak, and from the slopes of the active cone. Activity consisted of violent explosions averaging one every 15 minutes with ejecta small tephra and bombs erupted vertically to heights of m that fell back into the crater.

Finer particles were blown NW by winds. Longer intervals between eruptions minutes were followed by a single or series of very strong explosions that generated a dark plume 1,, m above the crater. A rough examination was done on two thin sections made from fresh lava samples collected while still hot. Phenocrysts were mostly zoned plagioclase, some augite, and rare olivine with reaction rims. The groundmass consisted of fine-grained opaque grains and scattered plagioclase, but no glass.

Based on these observations, the samples were identified as andesite to basaltic andesite. Information Contacts: J. Sesiano and J. Fox , ICAO. Explosions continue, sending ash plumes daily up to m above the summit. Volcanic activity continued through January-March , sending grayish white plumes m above the summit. Sounds like thunder were sometimes heard at the VSI observatory.

The daily number of explosions in January and early February fluctuated between 50 and events. According to news reports at the end of May , authorities closed the volcano to tourists, permitting them to come no closer than 3 km. During March Strombolian eruptions had plumes that rose m. These eruptions spewed incandescent ejecta every minutes and were accompanied by sounds like "thunder-claps. Similar Strombolian eruptions continued from April through June , with the plume rising m above the crater VSI, b.

Incandescent volcanic materials were ejected to heights of m above crater rim. Between 1 April and 17 May , earthquakes occurred each day. During June there were unofficial reports of unusually loud noises heard on the W coast of Java. On 27 June, GMU scientists visited islands around Anak Krakatau and heard some very loud sounds; only some of which correlated to visual activity at Anak Krakatau.

The observers compared their observations to a visit, when the volcano emitted steam-bearing discharges accompanied by lightning. The eruptions on 27 June appeared dissimilar because they were ash-rich and without visible steam. In addition, the 27 June eruptions produced string-shaped columns with mushroom-shaped tops; lightning was absent.

The group deployed two seismometers for five hours of observation. A vertical-component long-period seismometer 0. Typical seismograms, showing two of the three components recorded on Sertung Island, appear on figure Other events also showed the same 8-second delay between the seismic signal and these air waves.

The case shown was correlated with a small eruption that generated a loud sound and ultimately spawned an ash cloud of undisclosed dimension. Assuming a shallow source for the eruption, the travel times for first arrivals of the strong impulsive signals across the 3.

Thus, the strong impulsive signals were probably due to pressure waves transmitted through the air. Information Contacts: Wahyudi and A. Brodscholl , GMU. During an approved visit on 6 November, the volcano was steaming but not erupting. A smaller sulfur-stained plug was farther S in another depression. The landing site on the SE shore was a black-sand beach with tiny dunes of white pumice. While climbing the SE slope of the older cone, the party crossed water-eroded fields of pyroclastic material dotted with volcanic bombs.

The ascent to the summit went through deep cinder deposits covered with a blanket of loose breadloaf-sized stones. From the summit complicated internal crater structures could be seen. The largest and most active fumaroles were inside this cone's S rim. A smaller cone within the larger one was almost horseshoe-shaped and steeper to the S. Bombs on the summit cone were as large as m in diameter.

At about on 29 September, a Qantas Airlines pilot reported a thick plume near Krakatau that rose to an altitude of 3, m and drifted NW at low levels and E at high levels. There was no definite signature on GMS satellite images. Although a pilot report described a 3. Lava flows during July-August reached the island's W coast and added to its size. Two vents emitted lava and Strombolian eruptions in the N part of the main crater. During October, ash explosions occurred every minute, followed by rumbling sounds and lava fountains as high as m above the crater.

The main crater produced all the activity during October with the other two craters remaining quiet. There were no lava flows released to the surface during October. However, weak red glow was occasionally observed at night from the Pasuaran observatory. Information Contacts: Wimpy S. Lyvers noted that the Indonesian government's 5-km exclusion zone around the island has not deterred local boat operators from anchoring offshore or even landing tourists on Anak Krakatau.

This cloud, however, was not seen in GMS satellite imagery. Members of the SVE visited the island twice in April. They learned that during March at Carita, a beach resort on the W coast of Java 40 km from the volcano, there were ashfalls and explosions from the volcano were heard. During April, emissions became less prominent and more irregular. During their first visit on April they did not observe any plumes.

After landing they ascended to the first crest line where the group encountered several bread-crust bombs and their substantial impact craters. As they were ascending the cone of the volcano the visitors felt the heated ground through their hiking boots. There were fumaroles on both the flank and the summit. The crater, m in diameter, was breached to the W; the crater floor was occupied by large blocks, and it was possible to distinguish two vents aligned on a fissure trending SE-NW.

The group returned on April, after another eruptive episode. This time they observed enormous new blocks at the summit. The S vent continuously emitted white steam; the N vent sporadically discharged brown-black ash that rose up to m above the vent.

One projectile landed very close to the observation point. The next morning, ash on the tents suggested that the volcano had another explosion.

The group witnessed another eruption as they were leaving the island by boat at Cyr a French tourist-guide saw plumes accompanied by projectiles. He described the ash as an unusual pink color. During the night, incandescent explosions were took place about every 30 minutes; several incandescent blocks fell over the dome's N side.

The next morning, during a boat tour around the island, some blue smoke rose from mid-way up the W-SW flanks of the dome, conceivably a sign of minor lava flows. During the afternoon and evening of 17 May, Mike Lyvers visited the island by boat.

The previous few days, when observed from Carita Beach, the volcano had been quiet. In contrast, on 17 May it erupted almost continuously, issuing minor amounts of ash and sometimes a few bombs. Occasionally, larger explosions sent incandescent ash high into the sky, generating a spectacular display of volcanic lightning and covering the cone with glowing bombs.

The volcano seemed to show no obvious pattern to its activity, with random fluctuations in the intensity of eruption. Activity decreased early during the week of March. Weak booming noises were heard twice on 9 and 10 March, but plumes were not observed. At the end of the week booming noises were rare, and a white-gray ash plume was seen on 14 March that rose m above the summit. The current activity is a continuation of eruptions that began in This report combines their observations.

Seismic activity preceding and coincident with the eruption went undetected because of ballistic bomb damage to seismometers. Until 3 April, activity typically involved explosions per day. Beginning at about on 3 April ash explosions became almost continuous figures 12 and During the interval on 4 April, the volcano erupted every minutes from a new crater a few hundreds of meters S of the summit crater that formed during Accidental blocks, lava bombs, and ash reached heights of m above the crater rim.

About a third of the eruptions were Strombolian, with showers of lava and bombs occasionally 1 m across ejected m above the vent and falling onto the upper flanks. Some ballistic fragments cm in diameter rose above the associated ash cloud and landed m from the vent on the upper flanks before rolling down to the shore.

Eruptions were often accompanied by thunderous blasts and rumbling sounds heard several kilometers from the crater, including at Pasauran and Kalianda observatories 42 km from Krakatau.

A wedge-shaped deposit of fresh ash and bombs was visible on the crater rim the rim is higher on the SE due to prevailing northwesterly winds that blow ash and other ejecta in that direction. Ash clouds were light gray. The ash was crystal-poor and frothy, suggesting that it was mostly juvenile material. Nearly a dozen other solfataras discharged steam and non-condensible gas and deposited bright yellow native sulfur around vents near the summit figure Another fumarolic area was centered at m elevation on the W flank below the active crater.

Scientists observed several boatloads of tourists who had landed on the accessible SE beach. Officials had closed an area of 3 km radius around the vent, but many tourists defied the prohibition and climbed to the ridge m from the summit vents.

Escaping gases continued to pose a very serious hazard. Caldera collapse, perhaps in AD, destroyed the ancestral Krakatau edifice, forming a 7-km-wide caldera. Remnants of this volcano formed Verlaten and Lang Islands; subsequently Rakata, Danan and Perbuwatan volcanoes were formed, coalescing to create the pre Krakatau Island.

Caldera collapse during the catastrophic eruption destroyed Danan, and Perbuwatan volcanoes, and left only a remnant of Rakata volcano. The post-collapse cone of Anak Krakatau Child of Krakatau , constructed within the caldera at a point between the former cones of Danan and Perbuwatan, has been the site of frequent eruptions since Information Contacts: Igan S.

From the end of April until the end of May, only several explosions were heard. On 26 April a weak explosion sent a white-gray ash plume m high. Between 4 and 17 May there were two blasts per week, each accompanied by a glow and white-gray ash reaching between and m high.

In the week from 18 to 24 May, in addition to two explosions, a shock on the morning of 20 May registered at 2 on the MMI scale. Anak Krakatau was very active from to , depositing 6.

White-gray ash was emitted in plumes up to m above the summit. Detonations were accompanied by the ejection of incandescent material. During many weeks of May and June thousands of explosions were recorded on seismographs. An earthquake of intensity MM II was recorded on 10 June and another of the same intensity occurred during the week ending 16 August. On several days during the reporting period the volcano could not be seen because of thick haze.

This report covers the period of 29 May June Cloud cover made visual inspection impossible on 29 May but inspection on 30 May revealed a dark gray ash plume rising m into the air. During June seismicity remained elevated. Bad weather inhibited visual observation throughout the rest of the reporting period. Three booming explosions on 17 June coincided with a decrease in the number of volcanic earthquakes, as well as a marked increase in small explosion earthquakes.

Krakatau remained at alert level 2 on a scale of 4. Eruptive activity through late October ; infrasonic earthquakes detected. Krakatau activity continued after the previous report BGVN through October although intensity decreased relative to the 29 May eruption. The volcano's hazard status, however, did not exceed 2 on a scale of within the report period. During 27 June-2 July explosions sent ash to heights up to m, and booming sounds could be heard on three occasions.

VSI reports resumed as of July when seismographs recorded 1, explosion earthquakes, compared to about a month earlier. An infrasonic sensor detected 37 events. Satellite imagery did not detect a significant plume on this date, and no additional ash advisories were dispatched.

Activity remained similar through August. Frequent booming was heard, and high numbers of explosion and infrasonic earthquakes were detected. A volcanic ash advisory was issued on 20 August although it indicated that plumes were sparse, did not reach high altitudes, and dissipated quickly.

During 22 August-4 September a white, low-density plume rose 50 m above the summit. No visual observations could be made due to heavy fog, clouds, or smog masking the summit from view during 5 September October, although seismicity indicated persistent activity.

During September, 3, explosions and 17 infrasonic events were recorded. Audible booming, however, ceased on 12 September, and activity decreased dramatically through the end of October. Deep volcanic A-type earthquakes stopped occurring as of 10 October, although a low number of small explosion earthquakes and tectonic earthquakes continued through 30 October.

No further VSI reports were issued for Krakatau in Increase in seismicity during July through August ; ash and bomb ejection. The Volcanological Survey of Indonesia VSI did not report any further activity until mid-March , when the number of shallow volcanic B-type earthquakes rose to 79 from 25 the previous week. The number of shallow volcanic earthquakes decreased again in late March to In early April, seismic activity at Krakatau increased again. The seismographs detected 7 deep volcanic A-type earthquakes, 54 shallow volcanic earthquakes, and 7 tectonic events.

Local tour operators reported a significant increase in seismic activity at Krakatau beginning during July and continuing through August. During July there were shallow volcanic earthquakes registered. The explosion was recorded by an infrasonic microphone sensor installed at the Pasuaran post observatory.

John Seach visited on 12 August and found that the volcano was not erupting then, but was steaming vigorously on the N side of the summit crater. Pulses of steam every minute reached 20 m above the summit. Lava bombs, 0. The bombs left 1. The fresh impact craters were caused by both lithic and lava bombs.

Observers on a boat 1. The top m of the active cone was steaming from multiple locations. On the NW side, 60 m below the summit, a fumarole emitted blue gas. During September the number of explosion and volcanic earthquakes increased, but the number of small explosion earthquakes sharply decreased September. Seismic activity increases during mid-August ; Alert Level remains at 2.

A thick white plume reached 25 m above the summit several times during October through December During 27 August through 16 September at Krakatau, available seismic data were dominated by explosions and shallow volcanic earthquakes table 1.

The seismograph broke on 16 September but was repaired by 26 August , when it showed a slight increase over the previous interval when data were available. No surface activity accompanied the increased seismicity. Volcanic events decreased during early September.

The volcano remained at Alert Level 2 through at least 8 September. Table 1. Earthquakes registered at Krakatau during 27 August through 8 September The seismic system was down during 16 September August Courtesy of VSI. Seismicity dominated by volcanic earthquakes through at least December During 9 September through at least late December , seismicity at Krakatau was dominated by A-and B-type volcanic earthquakes table 2.

Throughout the report period, clouds obscured the view of the summit. Krakatau remained at Alert Level 2. Table 2. Earthquakes registered at Krakatau during 9 September December No data were available during September. Courtesy VSI. Volcanic earthquakes continue; thermal alerts during July-September Seismicity at Krakatau was dominated by volcanic and tectonic earthquakes during 30 December March table 3. The hazard status remained unchanged at Alert Level 2. Table 3. Seismicity at Krakatau during 30 December March The first alert occurred on 31 July when one alert pixel was detected with an alert ratio of The anomalies increased during August and on 9 August the anomaly consisted of two alert-pixels with a maximum alert ratio of Other major anomalies occurred on 1 September four alert-pixels with maximum alert ratio of These anomalies correspond to an increase of activity at Krakatau characterized by ash and bomb emission during August and an increase in the number of explosion and volcanic earthquakes during the first half of September , reported by the Volcanological Survey of Indonesia BGVN and The coordinates of the centers of the alert pixels are tightly grouped around the summit of the main cone.

Bearing in mind that each pixel represents radiance from an area of ground more than 1 km across, the alert pixels could represent radiance from the active vent or from hot ejecta close to the vent. According to reports from the Volcanological Survey of Indonesia VSI , no visual observations were made this month due to foggy weather. The volcano remained at alert level 2 for the month. They also noted that relatively few volcanic and tectonic earthquakes were recorded during the weeks of and June Specifically, the June record consisted of 9 deep volcanic earthquakes, 19 shallow volcanic earthquakes, and 5 tectonic earthquakes; the record of June consisted of 6 deep volcanic earthquakes, 17 shallow volcanic earthquakes, and 4 tectonic earthquakes.

In the week of June, a significant increase in shallow volcanic earthquakes was observed, although no tectonic earthquakes were recorded. The sesimic record for that week showed 11 deep volcanic earthquakes and 63 shallow volcanic earthquakes. Both volcanic and tectonic earthquakes were recorded for the week of June, with 7 deep volcanic earthquakes, 61 shallow volcanic earthquakes, and 2 tectonic earthquakes detected. Due to continued foggy weather, no visual observations could be made at Krakatau during July and through 17 August.

Throughout this period the volcano remained at Alert Level 2. Seismicity reported by the Volcanological Survey of Indonesia VSI between 30 June and 17 August consisted mostly of shallow volcanic events table 4 , although 36 deep volcanic earthquakes were recorded during the week of 30 June-6 July.

Table 4. Seismicity at Krakatau, 30 June August A report of activity at Krakatau for the period August was provided by the Volcanological Survey of Indonesia. There was increase in volcanic earthquakes during this time, while tectonic earthquakes decreased. No visual observations were made due to foggy weather. Seismicity consisted of 12 deep volcanic earthquakes, 56 shallow volcanic earthquakes, and three tectonic events.

The hazard status was at Alert Level 2 on a scale of Intense activity occurred at Anak Krakatau beginning on 4 July , when gas and steam emissions increased. Based on the increased activity, the hazard status was upgraded to Alert Level II yellow on 16 July; visitors were not allowed to approach the summit or crater.

Seismicity recorded at the Kalianda station after 18 July through 15 August was variable, but did not exhibit the high numbers recorded in the first half of July. Table 5. Seismicity at Krakatau, 4 July August Minor eruptions beginning October ; seismic data for Eruptive activity in recent years was low at Krakatau. Seismic data collected during this period figures 15 and 17 , although intermittent and variable, suggests mainly low-level activity discussed in more detail below.

Starting on 23 October reports noted multiple gray plumes from eruptions lasting minutes; these vented from a crater near the summit of Anak Krakatau figure Similar eruptions were continuing in early November figure Activity during April September On 13 April increased seismicity prompted authorities to raise the Alert Level to 2 on a scale of Seismic activity decreased over the next four days to a normal level.

Visitors were banned from the summit and crater of Anak Krakatau due to toxic gas emission. Another increase in seismic activity was reported around 16 May. Elevated seismicity was also recorded on 24 September , 8 December , and June figure On figure 15, a conspicuous, longer period of high seismicity occurred during most of December , when tremor and low-frequency events also increased. That peak on figure 15 ended prior to the end of the month. No eruptions were noted in available reports by CVGHM for these episodes of elevated seismicity in or For the intervals where data were available during the first eight months of , seismicity was generally moderate to low.

All data are acquired continuously and are transmitted to the Pasauran Observatory western Java via digital radio telemetry. In Pasauran, the data are collected and transmitted to a server in Jakarta. Three stations are located on Anak Krakatau figure A fourth station on Sertung island consists of a short-period seismometer and a digital camera with a view of Anak Krakatau. During October , minor eruptions occurred at Anak Krakatau BGVN , an island and active vent on the rim of the famous larger caldera whose name often is misspelled as "Krakatoa.

Villagers and tourists were advised not go within 3 km of the summit. According to an Associated Press news article, "red-hot lava flares" from Anak Krakatau rose m above the S crater on 6 November. Officials said, that on that day there were eruptions coupled with 11 volcanic earthquakes, 54 shallow volcanic shocks, eight deep volcanic tremors and 44 shallower tremors. The volcano spewed "smoke" 29 times. As reported by VolcanoDiscovery 's Tom Pfeiffer, who visited there from November, emissions were relatively constant.

He noted that all activity occurred from the newly formed crater on the upper S flank just below the old summit crater figure On 21 November, the new crater had an oval shape, approximately 50 x 70 m. Dense, dark brown, billowing ash clouds escaped in pulses from the crater at near-constant intervals of about 2 minutes, rising typically m above the crater and drifting E. A few blocks were ejected along with the ash clouds figure Pfeiffer also reported that at more irregular intervals, about min apart, more violent, small vulcanian explosions interrupted the weaker ash venting events.

The more violent explosions consisted of a sudden spray of mostly solid rocks and few incandescent scoria, followed by more powerful and turbulent ash plumes that rose up to 1 km above the crater figure Generally, these vulcanian explosions occurred after a slightly longer quiet period and, in most cases, the length of the quiet period correlated with the force of the explosion.

Pfeiffer noted that several more powerful explosions occurred at intervals of approximately hours. The strongest, on November, showered the whole island with incandescent blocks, ignited bush fires, and produced a very loud cannon-shot noise that rattled windows on the W coast of Java, 40 km away figure Other, unusually large blasts occurred at around on 21 November and at around and on 23 November figure Early on 23 November, activity became more ash-rich and the vigor of the individual events increased slightly over the next two days.

The pace of single explosions stayed at near-constant intervals of about 2 minutes. During November, ash plumes typically rose to over 1 km above the crater and were easily visible from the W coast of Java.

The thermal alerts occurred on twelve occasions between 27 October and 9 December Seven of these took place between 16 and 26 November Variable eruptive activity from late to mid; plumes to 3 km altitude. This small but growing post-caldera cone first gained attention with a eruption Simkin and Fiske, The detailed chronology of behavior during October to 3 July is sometimes sketchy, but activity was apparently quite variable.

Although one or more lulls may have occurred, eruptions clearly continued into The Alert Level was lowered and raised again throughout and into as activity warranted.

People were advised not to go within 1. Activity through August According to a news article, by 22 November , seismicity had declined in frequency. Based on an Antara News article, this decline in seismic activity was interrupted by incandescent rock ejections on 20 January accompanied by plumes that rose to altitudes of 2. Seismicity again declined in early February , and eruption plumes and ejected incandescent material were not seen during 4 February to mid-April Seismicity increased during April , with the number of events per day peaking on 20 April.

Ash plumes accompanied by ejected incandescent rocks were noted during CVGHM field observations on 16, 17, and 18 April.

During 22 June-1 July , the number of seismic events decreased significantly and booming noises were less frequently heard. On July ash emissions declined, although on 1 and 2 July low level ash plumes rose to an altitude less than 3 km and drifted NW.

According to an article in Antara News, eruptions increased in frequency during August On 12 August, monitoring personnel reported that active lava flows and dense emissions of "smoke" continued, but that the frequency of earthquakes and eruptions had declined.

Monitoring personnel during that period observed plumes, active lava flows, and rock ejections. Activity during March-May Seismicity increased significantly during March and remained high through 5 May.

During periods of clear weather on 25 March, white-to-gray plumes rose m above the volcano. During March and 1 April clear weather revealed ash plumes rising m. On 2 April an ash eruption was seen on satellite imagery and reported by a pilot.

During March through 25 April , an episode of heightened seismicity produced thousands of eruptive signals table 6 ; however, the seismic station shut down overnight during April, and completely shut down during April. CVGHM believed that this shutdown was the result of either blockage of sunlight from reaching the solar panels by tephra collecting there or because of impact-induced damage to the panels.

Table 6. Type and number of earthquakes and tremor recorded at Krakatau during 27 March-6 May Values shown are daily averages except the following: 1 and April: during hour period daylight ; 2 30 April: starting at local time from a new, safer location; 3 06 May: during to local time.

No data was recorded during April. During April observers reported grayish-white to black plumes that rose to , m above the crater. They heard many loud booms. Some of the lofted ash blew E to SE and caused fallout up to 5 km away. According to a news article on 29 April , some residents in southern Sumatra near Krakatau evacuated because they had observed increased volcanism during the previous week.

For example, observers reported loud blasts, lava flows, and ash plumes. In clear weather on 5 May "smoke" rose m above the crater. An Antara News article published on 18 June indicated that in the previous several days the number of small eruptions increased tremendously. It said that, according to Anto Prambudi, head of the monitoring post in Pasauran village, at least small eruptions were recorded during June In later , comparatively few alerts occurred, but became more prevalent again during mid-January After that, they were few or absent until mid-April; alerts were common and strong during the week ending 4 May.

Consistent alerts were the pattern until the week ending 7 June, which had no alerts, but some continued in the next few weeks. After that, alerts again became common again, particularly abundant during April an episode of eruptions and heightened seismicity and continued regularly through at least 3 July The gap in alerts may have been influenced by downward biasing from poor weather conditions.

On the other hand, for the cases with high numbers of alerts, false positives due to fires for example were unlikely on the desolate landscape of Anak Krakatau.

Simkin, T. On 25 March activity increased significantly, with the recording of 19 eruptions. Eruptive activity then continued without pause until 6 May when the hazard status was elevated to Alert Level 3 Siaga. The VAAC did not detected the plume on satellite imagery. Visual observations of the summit were often obstructed by fog, although a gray cloud rising as high as 1, m above the summit was observed at a clear moment on one undisclosed day in August.

Booming eruptive sounds were recorded 49 times in August and once in September. Table 7. Seismically detected signals at Krakatau, including tremor and earthquake, registered by the Pasauran observation post during August through 29 October Instrument locations were discussed in BGVN although the status of these stations was not discussed. Where reported the table also presents ranges of amplitudes in millimeters, mm , duration in seconds, s , and S-wave minus P-wave arrival times S-P.

CVGHM also reported two major seismic events over the reporting period at distance from Krakatau with little discernable impact there. On 16 October , a tectonic earthquake originating from Ujung Kulon-Jawa Barat, located at the W tip of Java, occurred with a magnitude of 6. CVGHM stated that the volcanic seismic signals at Krakatau following the earthquakes on 16 August and 16 October do not indicate an increase in volcanism.

Anak Krakatau the active post-collapse cone of the infamous Krakatau volcano, figure 23 began another eruptive phase around 25 October , characterized by up to hundreds of explosions per day e.

In November , Arnold Binas documented explosive activity, ballistic bombs, column collapse generating pyroclastic flows, and volcanic lightning in some spectacular photographs figure Ash fall in early January covered the solar panels running seismometers monitoring Anak Krakatau, rendering them inoperative until rainfall cleared the ash from the solar panels. In March , the activity at Anak Krakatau decreased and the eruption was considered to be over. According to a local news service TO:DAY , the head of the Anak Krakatau monitoring post reported that in the previous month, volcanic earthquakes became fewer and at greater focal depths.

They had ranged from a high of shallow earthquakes per day, declining to dozens per day in March In August, Andi Rosadi reported on the Volcano Discovery website that the seismometer monitoring Anak Krakatau was again damaged by explosions venting from the summit crater, noting "many quite big new bombs around the old crater.

Rosadi also described and photographed large areas of incandescence within the summit crater on 8 August , reporting a lava dome or "dry lava lake glowing in the central crater" figure On 30 September, CVGHM reported that the seismometers were again operational following 18 September, and increased the Alert Level from 2 to 3 on a scale from 1 to 4 , citing visual and seismic observations.