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Volcanoes of Indonesia

Geography of Indonesia is dominated by about 150 volcanoes of all types and dimensions that were formed due to subduction processes occurring along the collision zone separating the Eurasian and the Indo-Australian tectonic plates. Some of the Indonesian volcanoes became especially notable for their eruptions, for instance, volcano of Lake Toba is famous for its super-eruption at c. 74,000 BC, which caused a long 6-year volcanic winter. Mount Tambora volcano is known for its most violent eruption in 1815, and the Krakatoa explo-sion in 1883 became noted for its global effects.

Figure 76 was reproduced from a monthly geographical journal edited by German cartographer H. Zollinger (1858). In the upper part of the panel, cross sections of three volcanic groups were plotted, namely of the southern part of the Indonesian archipelago: Tennger (East Java), Bator volcano (Bali), and Rinjani (Lombok). The profi les were accompa-nied by a map of the Indian islands or Malasia (the territory of present Malaysia and Indonesia), together with a part of New Guinea, Philippines, Formosa (=Taiwan), Hainan, and a substantial part of southeastern Asia.

Indonesian volcanoes create one segment of the Pacifi c Ring of Fire. They can be subdivided into six geographical regions, four of which belong to volcanoes of the Sunda Arc Trench system, one group includes volcanoes of Halmahera, Sulawesi, and the Sangihe Islands, and another group covers the Philippine volcanoes. At present, the most active volca-noes are Kelut and Merapi on the Java Island, which have brought about thousands of casualties in the region.

An annihilating blow of Krakatoa, located in the Sunda Strait between Java and Sumatra, occurred on 28 August, 1883 (Fig. 77). During the eruption, more than 25 km3 of rocks, ashes, and pumices were ejected, generating the loud-est sound historically reported; two thirds of the island of Krakatoa disappeared during the eruption. The number of casualities in the Sunda Strait and in its vicinity was assessed between 35,000 and 70,000. Giant sea waves reached the height of 40 m and propagated through the whole Indian Ocean as plotted in the map by Hermann Berghaus (1886) (see Fig. 25). Already this map, published 116 years before

the recent damaging tsunami catastrophe following the 2004 Sumatra earthquake, pointed out the deadly potential of the earthquakes occurring in Indonesia for the coastal settle-ments of the Bay of Bengal and Indian Ocean. Seismic and volcanic consequences of the 1883 Krakatoa explosion were even more devastating than the 2004 tsunami. Gigantean tsu-nami waves of 1883 smashed down not only the coastal regions of the Indian Ocean and eastern Africa as in 2004, but also ran around the Cape of Good Hope and hit South American Patagonia. The 1883 eruption was accompanied by gigantic emissions of volcanic ashes and gases expelled in a monstrous column of cloud reaching high up to the strato-sphere, which then enveloped the whole globe.

That time reports, unfortunately rather fragmentary, informed that the ash clouds had caused twilight for several days and changed days into dark nights in some places, and also the sky had became dark red at sunrise in another locali-ties. The explosion sound could be heard as far as in Australia, Japan, or in Istanbul (!). However, the 1883 Krakatoa event might represent a smaller episode in comparison with the prodigious eruption (equal to a potential collision with a sizeable asteroid), which had allegedly happened in Krakatoa region in AD 535. Although this common disaster causing a 2-year volcanic winter was mentioned and discussed in many early Middle Ages Arabic written sources, a clear unambigu-ous and verifi ed description of the event has not yet been documented (Keys 1999).

We cannot close our considerations on Indonesian volca-noes without mentioning the work of outstanding German naturalist Franz Wilhelm Junghuhn (1812–1864), who spent many years in Indonesia (from 1835 to his death). He repeat-edly made expeditions into that time little-known mountain regions of Java and Sumatra and visited most of the main Indonesian volcanoes. During his journeys, he made detailed sketches of the visited localities in several size levels: from the most detailed portrayals of individual craters, lava streams, and other structural elements, up to general pat-terns and prospects of long volcanic mountain chains (Junghuhn 1845).

J. Kozák and V. Čermák, The Illustrated History of Natural Disasters,© Springer Science+Business Media B.V. 2010

104 Volcanoes of Indonesia

Fig. 76 “Skizzen aus dem Indischen Archipel”. Three profi les of volcano groups and a map of south-east Asia (Malesia). German hand colored lithographic panel. Private collection, Prague

Volcanoes of Indonesia 105

Fig. 77 Krakatoa Island and volcano before the 1883 eruption. Xylography, late 19th century illustration (Verbeeck, 1884). Private collection, Prague