The tireless volcano watchers at Activolcans report that activity continues at Anak Krakatau (’child of Krakatau’), perhaps at slightly lower intensity than recently; low-level eruptive activity has been pretty much continual since October 2007, and the volcano has been at level III (orange) alert since April. Anak Krakatau is a young volcanic cone constructed within the caldera left by the 1883 Krakatau eruption. Since its emergence in 1927 it has been the site of frequent eruptions.

Anak Krakatau is continuously monitored by the Indonesia volcanological authorities, who have a website dedicated to the volcano which reports real-time data: KrakMon Online.

Information
Global Volcanism Program: Krakatau - summary information for Krakatau (0602-00=)
Pusat Vulkanologi & Mitigasi Bencana Geologi - News and information portal for the Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
KrakMon Online - Krakatau monitoring online

Reports from Indonesia today say that Soputan on Sulawesi Island, which is among Indonesia’s most active volcanoes, is currently erupting. ABC News (Australia) quotes an Indonesian volcanologist as saying that the volcano is ’sending heat clouds as far as four kilometres and throwing ash two kilometres into the air’. In Indonesia, ‘heat clouds’ generally means pyroclastic flows. There is as yet no order to evacuate but the authorities are maintaining a high alert and have imposed a 6km exclusion zone.

The Eruptions blog has more coverage.

Information
Global Volcanism Program: Soputan - summary information for Soputan (0606-03=)
Direktorat Vulkanologi Indonesia - Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
Pusat Vulkanologi & Mitigasi Bencana Geologi - News and information portal for the Directorate of Volcanology and Geological Hazard Mitigation, Indonesia

News
Volcano erupts in Indonesia - ABC News, 7 June 2008
Mount Soputan spewing sand and thick smoke - ANTARA News, 7 June 2008
Volcano erupts in Indonesia - Sydney Morning Herald, 7 June 2008

A correspondent has helpfully provided more information derived from the Indonesia media about the current alert at Semeru (reported here) and has translated local news reports, throwing more light on the nature of the volcano’s activity. The ‘heat clouds’ referred to in some reports clearly were pyroclastic flows.

The reports come from the Javanese Kompas newspaper and were apparently sent in by Blackberry from an observer on the spot. A 4-kilometre exclusion zone has been established around the volcano because of the danger posed by pyroclastic flows, and the Directorate of Volcanology and Risk Mitigtion warned on 23 May ‘although there is no cause yet for evacuation, residents should be alert up to 10km from the mountain centre in case of potential lahar, lava or pyroclastic flows’. A large number of earthquakes (more than 40) was registered between 00:00 and 18:00 on 23 May along with significant ash emissions. Since 15 May Semeru has released 12 pyroclastic flows with a range of up to 3 kilometres, and there is the potential for future flows to reach as far as 9 kilometres from the volcano.

It’s impossible to get any information from the Directorate of Volcanology and Risk Mitigation website at the moment because, as is not infrequently the case, the site is down. I hope no-one has to depend upon it for information in a crisis. Fortunately (perhaps) Indonesians are used to living with volcanoes: as my correspondent puts it, ‘The local villagers are so used to seeing these eruptions and so used to all the warnings etc it generally needs lava or a pyroclastic flow flowing through their back yard before they will move or evacuate’.

Information
Global Volcanism Program: Semeru - summary information for Semeru (0603-30=)
Direktorat Vulkanologi Indonesia - Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
Pusat Vulkanologi & Mitigasi Bencana Geologi - News and information portal for the Directorate of Volcanology and Geological Hazard Mitigation, Indonesia

News
Heat clouds raise Indonesian volcano alert - AFP, 21 May 2008
Mount Semeru volcano in Indonesia’s East Java heats up - Top News, India, 21 May 2008
Radius 4 Km dari Kawah Semeru Berbahaya - Kompas, 23 May 2008 (Indonesian)

The alert level for Mount Semeru, the tallest volcano on Java and one of the most active, has been raised to level three after it spewed ‘heat clouds’ down its slopes, media reports say. Do they mean pyroclastic flows? The Indonesian authorities have said that the activity poses no danger, and urged local residents to remain calm and stay put.

Semeru has effectively been in a continuous state of eruption since 1967.

Information
Global Volcanism Program: Semeru - summary information for Semeru (0603-30=)
Direktorat Vulkanologi Indonesia - Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
Pusat Vulkanologi & Mitigasi Bencana Geologi - News and information portal for the Directorate of Volcanology and Geological Hazard Mitigation, Indonesia

News
Heat clouds raise Indonesian volcano alert - AFP, 22 May 2008
Indonesia raises alert level for Java volcano - Radio Australia, 22 May 2008

Inspired by the theme of the current Accretionary Wedge, which is ’significant geological events’ (hosted at Harmonic Tremors), Ole Nielsen has written an interesting article about the supervolcanic eruption of Toba about 71,500 years ago, on the eminently reasonable grounds that ‘an event that nearly wiped out all human beings could be called significant’.

Toba - A Significant Geological Event

Mount Kelut (also known as Kelud), situated in the east of the island of Java, is one of the most active and hazardous volcanoes in Indonesia. Over the past six centuries the 1730m volcano has erupted at least thirty times and has been responsible for approximately 15,000 fatalities. On 19 May 1919 it was the site of one of the deadliest volcanic eruptions of the twentieth century, killing over 5100 people when water ejected from the crater lake formed lethal lahars that travelled nearly 40 kilometres and destroyed more than 100 villages.

The 1919 eruption is interesting not only for itself but for the response it generated. At the time Java was under Dutch colonial rule, and the Dutch authorities reacted to the disaster both institutionally, by establishing the forerunner of today’s Indonesian volcanological authority, and technologically, by creating a drainage system intended to manage the hazard posed by the crater lake.

The presence of a substantial crater lake has been the main reason why Kelut is a very lahar-prone volcano, but also significant are its deeply eroded flanks and abundance of loose sediment. During the 19 May 1919 eruption 38 million cubic metres of water was expelled from the crater lake, radiating out through the deep drainage channels and accumulating vast quantities of sediment and volcanic material to produce fast-moving lahars that inundated over 30 square kilometres of the surrounding countryside.

Above: map of Kelut, showing the extent of the 1919 lahars. Adapted from Thouret et al, Bull. Volc., 59:7 (1998), fig. 1.

Even before the 1919 catastrophe the colonial authorities recognized the danger Kelut posed and had, in 1905, constructed a dyke intended to protect the nearby city of Blitar. The 1919 lahars, however, overwhelmed this construction. The Dutch response was to abandon the mitigation of lahars and concentrate instead on preventing them developing by enabling the drainage of the crater lake. The work took until 1926 to complete: a system of seven drainage tunnels was constructed, which reduced the volume of the lake by more than 2 million cubic metres, lowering the level by 50 metres. In 1951 the volcano erupted again, but the successful operation of the drainage system meant that little water was present in the crater and no lahars resulted. A second catastrophe had been averted.

The eruption itself, however, deepened the lake and destroyed the drainage tunnels. Only after another deadly eruption in 1966, in which more than 200 people died, was a new deeper tunnel excavated. The most recent large-scale eruption, in 1990, would certainly have been much more destructive to life and property had the crater lake not been largely drained.

Kelut’s most recent period of restlessness occurred in the autumn of 2007 and resulted in evacuations, although there was no large-scale eruptive activity. A lava dome which has grown since the autumn 2007 eruption now fills the crater lake site (see pictures Université Libre de Bruxelles here; h/t to commenter Hawkeye) and has overwhelmed the drainage inlets.

Information
Global Volcanism Program: Kelut - summary information for Kelut (0603-28=).
Kelud Volcano - information and analysis from the Université Libre de Bruxelles, Belgium (ULB). The volcanic lake specialists at ULB are currently collaborating with the Volcanological Survey of Indonesia in monitoring Kelut.
Le volcan Kelut - account of the 1919 eruption and a detailed history, with illustrations, of the various drainage systems built since to drain the crater lake (in French).

The Indonesian volcanological authorities have raised the alert levels for Ibu and Anak Krakatau to level III, orange, following recent ash eruptions and an increases in seismic activity at both volcanoes. This is the second-highest alert level. No evacuations have been ordered but people have been warned not to approach either volcano closer than 2 kilometres, and the local inhabitants around Ibu have been advised to wear masks to protect themselves from ash.

Indonesia now has three volcanoes on level III orange alert: Egon, Ibu, and Anak Krakatau. A guide to the Indonesian volcano alert system can be found here.

For all our coverage of Indonesian volcanism: Indonesia << The Volcanism Blog.

Information
Smithsonian Institution Global Volcanism Program - summary information for Ibu (0608-03=)
Smithsonian Institution Global Volcanism Program - summary information for Krakatau (0602-00=)
Direktorat Vulkanologi Indonesia - Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
Pusat Vulkanologi & Mitigasi Bencana Geologi - News and information portal for the Directorate of Volcanology and Geological Hazard Mitigation, Indonesia

News
Indonesia’s Krakatau, Ibu volcanoes put on second-highest alert - Bloomberg, 22 April 2008
Alert levels raised for Indonesia’s Krakatau, Mount Ibu volcanoes - Earth Times, 22 April 2008
Alert for Indonesia’s Krakatau, Mount Ibu volcanoes - Bangkok Post, 22 April 2008
Indonesia raises alert for two volcanoes - Reuters, 22 April 2008

The alert level for Mount Papandayan in Java has been raised to level II following an increase in seismic activity at the volcano.

Papandayan, just 51 kilometres south-east of Bandung (population c. 3 million) is potentially one of Indonesia’s most dangerous volcanoes.

Information
Smithsonian Institution Global Volcanism Program - summary information for Papandayan (0603-10=)
Direktorat Vulkanologi Indonesia - Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
Pusat Vulkanologi & Mitigasi Bencana Geologi - News and information portal for the Directorate of Volcanology and Geological Hazard Mitigation, Indonesia

News
Alert raised on Indonesia’s Mount Papandayan volcano - Radio Australia, 17 April 2008

Mount Egon on Flores Island, Indonesia, erupted a 4 kilometre ash plume late on Tuesday 15 April, causing the evacuation of hundreds of villagers from nearby communities. The Indonesian Directorate of Volcanology and Geological Hazard Mitigation bulletin reports that the eruption was phreatic in nature and occurred at 22:15 local time (13:15 GMT) on 15 April. The alert level for Egon has been raised to level III, orange (the Indonesian term for this alert level is Siaga).

Information
Smithsonian Institution Global Volcanism Program - summary information for Egon (0604-16=)
Direktorat Vulkanologi Indonesia - Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
Pusat Vulkanologi & Mitigasi Bencana Geologi - News and information portal for the Directorate of Volcanology and Geological Hazard Mitigation, Indonesia

News
Indonesian volcano spews ash, residents evacuated - Reuters, 16 April 2008
600 flee erupting Indonesian volcano - Associated Press, 16 April 2008
Hundreds flee as Indonesian volcano erupts - AFP, 16 April 2008

The Malaysian news agency BERNAMA reports today that Ibu volcano in Halmahera, Indonesia, has ’spewed thick smoke [sic] up to 500 metres into the sky in the last few days’. Quoting Indonesia’s Antara news agency, BERNAMA reports that an average of 40 earthquakes a day have been shaking the volcano, but that the current activity is not regarded as dangerous and no evacuations have been ordered.

Information
Smithsonian Institution Global Volcanism Program - summary information for Ibu (0608-03=)
Direktorat Vulkanologi Indonesia - Directorate of Volcanology and Geological Hazard Mitigation, Indonesia
Pusat Vulkanologi & Mitigasi Bencana Geologi - News and information portal for the Directorate of Volcanology and Geological Hazard Mitigation, Indonesia

News
Mount Ibu spews thick smoke - BERNAMA, 11 April 2008