The Krakatau edifice grew as one or more stratovolcanoes of dominantly hypersthene-augite andesite composition. The geology of Krakatau has been described by Effendi and others (1985, 1986), who identified five main evolutionary periods. Period 1 was an early growth phase that included accumulation of lavas and pyroclastics. Period 2 was marked by caldera formation, accompanied by pyroclastic flows and partly welded tuffs (ignimbrites). The cones of Rakata, Danan, and Perbuwatan grew during the third period and were largely destroyed during the fourth period, which included the paroxysmal eruption of August 1883. Another growth phase (period 5) began by December 1927, when Anak Krakatau was first noticed in submarine eruption. ...
Several years of regional seismicity culminated in the famous caldera-forming eruption of August 1883 (Verbeek, 1886; Judd, 1888). Earthquakes were felt in west Java and eastern Sumatra 5-6 years before the 1883 eruption, and in northern Australia in the 3 years before the eruption. On 1 September 1880, a strong earthquake damaged the First Point lighthouse on the west end of Java (70 kilometers south-southwest of Krakatau). more earthquakes were felt at First Point on 9-10 May 1883 and at Katimbang (40 kilometers north-northeast) during 15-20 May 1883. None of the above-mentioned earthquakes is known to have been of volcanic origin and centered beneath Krakatau; more likely, they reflect a buildup and release of tectonic stress in the sunda Strait area.
A mild ash and steam eruption began from Perbuwatan on 20 May 1883, and similar eruptions continued for 3 months. At times several vents were in eruption simultaneously. On 11 August, vigorous ash-laden gas columns rose from the main crater of Perbuwatan, the former vent of Danan, and from the foot of Danan; in addition, "no fewer than eleven other foci of eruption could be observed on the visible portions of the island, from which smaller steam-columns issued and ejections of ash took place" (Judd, 1888, p.13). At least some of the early ash was basaltic, suggesting that intrusion of basaltic melt into the silicic reservoir may have played a role in initiating these eruptions (Francis and Self, 1983). The small eruptions intensified on 24 August 1883 and culminated in the famous, climactic explosion of 27 August 1883 (Verbeek, 1886; Judd, 1888; Simkin and Fiske, 1983).
Earthquakes and rumbling, not demonstrably from Krakatau, were noted in 1898 (Koninklijk Magnetisch en Meteorologisch Observatorium te Batavia, 1899). On 13 August 1913, a strong tectonic earthquake occurred in the Bantam-Krakatau region, damaging the First Point lighthouse. Fishermen where were on the islands of Krakatau reported that part of the caldera wall collapsed. They also reported that at 1000 hours a "column of fire" rose out of the crater, whereupon they heard a cannonlike sound and fled (Visser, 1920). There are no independent reports of eruptions of Krakatau in 1913, and we suspect that only a landslide occurred.
Eruptions from December 1927 to 1981, mostly of basaltic andesite, built the Anak Krakatau ("child of Krakatau") cone in the center of the 1883 caldera ...
The August 1883 eruption of Krakatau is often cited as a classic example of caldera formation by collapse following eruption of large volumes of pumice (Williams, 1941; Williams and McBirney, 1979; Self and Rampino, 1981, 1982; Francis and Self, 1983). However, other workers have suggested alternate mechanisms for formation of the Krakatau Caldera. Yokoyama (1981, 1982) concluded that the caldera formed by explosive destruction and reaming of the preeruption edifice, and Camus and Vincent (1983) and Francis (1985) favored an origin by large-scale collapse of the northern part of Krakatau Island (similar to the volcanic landslide at Mount St. Helens on 18 May 1980). Regrettable, much of the evidence is sumbmarine and inaccessible, but we are impressed by the similarity of Krakatau and other, better-exposed calderas (for example, Crater Lake) that are thought to have formed by simple collapse following voluminous pumice eruptions. The volume of magma erupted in the plinian eruption (9 cubic kilometers) is adequate to explain the caldera without invoking a landslide origin. ...
Several years of regional seismicity culminated in the famous caldera-forming eruption of August 1883 (Verbeek, 1886; Judd, 1888). Earthquakes were felt in west Java and eastern Sumatra 5-6 years before the 1883 eruption, and in northern Australia in the 3 years before the eruption. On 1 September 1880, a strong earthquake damaged the First Point lighthouse on the west end of Java (70 kilometers south-southwest of Krakatau). more earthquakes were felt at First Point on 9-10 May 1883 and at Katimbang (40 kilometers north-northeast) during 15-20 May 1883. None of the above-mentioned earthquakes is known to have been of volcanic origin and centered beneath Krakatau; more likely, they reflect a buildup and release of tectonic stress in the sunda Strait area.
A mild ash and steam eruption began from Perbuwatan on 20 May 1883, and similar eruptions continued for 3 months. At times several vents were in eruption simultaneously. On 11 August, vigorous ash-laden gas columns rose from the main crater of Perbuwatan, the former vent of Danan, and from the foot of Danan; in addition, "no fewer than eleven other foci of eruption could be observed on the visible portions of the island, from which smaller steam-columns issued and ejections of ash took place" (Judd, 1888, p.13). At least some of the early ash was basaltic, suggesting that intrusion of basaltic melt into the silicic reservoir may have played a role in initiating these eruptions (Francis and Self, 1983). The small eruptions intensified on 24 August 1883 and culminated in the famous, climactic explosion of 27 August 1883 (Verbeek, 1886; Judd, 1888; Simkin and Fiske, 1983).
Earthquakes and rumbling, not demonstrably from Krakatau, were noted in 1898 (Koninklijk Magnetisch en Meteorologisch Observatorium te Batavia, 1899). On 13 August 1913, a strong tectonic earthquake occurred in the Bantam-Krakatau region, damaging the First Point lighthouse. Fishermen where were on the islands of Krakatau reported that part of the caldera wall collapsed. They also reported that at 1000 hours a "column of fire" rose out of the crater, whereupon they heard a cannonlike sound and fled (Visser, 1920). There are no independent reports of eruptions of Krakatau in 1913, and we suspect that only a landslide occurred.
Eruptions from December 1927 to 1981, mostly of basaltic andesite, built the Anak Krakatau ("child of Krakatau") cone in the center of the 1883 caldera ...
The August 1883 eruption of Krakatau is often cited as a classic example of caldera formation by collapse following eruption of large volumes of pumice (Williams, 1941; Williams and McBirney, 1979; Self and Rampino, 1981, 1982; Francis and Self, 1983). However, other workers have suggested alternate mechanisms for formation of the Krakatau Caldera. Yokoyama (1981, 1982) concluded that the caldera formed by explosive destruction and reaming of the preeruption edifice, and Camus and Vincent (1983) and Francis (1985) favored an origin by large-scale collapse of the northern part of Krakatau Island (similar to the volcanic landslide at Mount St. Helens on 18 May 1980). Regrettable, much of the evidence is sumbmarine and inaccessible, but we are impressed by the similarity of Krakatau and other, better-exposed calderas (for example, Crater Lake) that are thought to have formed by simple collapse following voluminous pumice eruptions. The volume of magma erupted in the plinian eruption (9 cubic kilometers) is adequate to explain the caldera without invoking a landslide origin. ...
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