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The Indonesia Region
The vast Indonesian archipelago consists of more than 13,000 islands, spread over an area approximating that of the width of the conterminous United States. Its population of more than 237 million is three-fourths of the US's, but with only one-fifth of the land area. More than 75% of Indonesian residents live within 100 km of a Holocene volcano, the highest number of people of any of the world's volcanic regions. Indonesia was the subject of the first CAVW in 1951, authored in Holland by Meir Neumann van Padang, who had grown up in Indonesia and worked there as a geologist. He went on to spearhead the CAVW series, authoring or co-authoring 6 catalogs and overseeing publication of 21 before retiring, at the age of 73, in 1967.
Although Chinese records show a Krakatau eruption in the 3rd century CE, and some 20 additional historical eruptions are reported, mostly from Kelut as well as Krakatau, through the 15th century, uncertainty surrounds many of them. Europeans first began to document eruptions in 1512 (Sangeang Api and Gunungapi Wetar), about the time Portugal gained control of the Mollucan clove trade. The Dutch East India Company controlled the islands from 1602 through 1780, followed by the Dutch government. Britain took temporary control of the islands in the early 19th century, but the Dutch returned and unrest marked much of the century. The disastrous Krakatau eruption of 1883 was followed by several devastating eruptions on other islands and in 1920 a Volcano Survey was established by the government, leading to much improved volcano monitoring and reporting. The islands were occupied by Japan from early 1942, and WW-II was followed by a 4 year war of independence, with sovereignty gained at the end of 1949. The Volcanological Survey of Indonesia (VSI), now known as the Centre of Volcanology and Geological Hazard Mitigation (CVGHM), operates a network of 76 volcano observatories continuously monitoring 66 volcanoes.
The great sweep of the Sunda Arc, over 3000 km from NW Sumatra to the Banda Sea, results from the subduction of Indian Ocean crust beneath the Asian Plate. This arc includes 78% of the region's volcanoes, but those on either end are tectonically more complex. To the NNW, the basaltic volcanism of the Andaman Islands results from short spreading centers, and to the east the Banda Arc reflects Pacific Ocean crust subducted westward. North of this arc, tectonic complexity increases, with converging plate fragments forming multiple subduction zones, mainly oriented N-S, that in turn produce the Sulawesi-Sangihe volcanoes on the west and Halmahera on the east of the collision zone. Indonesia leads the world in many volcano statistics. It has the largest number of historically active volcanoes (78), its total of 1250 confirmed eruptions is only exceeded by Japan's 1469, and these two regions have combined to produce nearly 1/3 of the known pyroclastic-flow producing eruptions. Indonesia easily leads the world in numbers of residents living within 30 and 100 km of a Holocene volcano, and has more than double the number of the next highest region of those within these distances of volcanoes with eruptions since 1500 CE. The combination of a densely packed population in a volcano-rich country has led to Indonesia suffering the highest numbers of eruptions producing fatalities (114) and damage to human infrastructure (195). In recent years, however, the VSI (now CVGHM) has compiled an enviable record of evacuating populations before eruption disasters occur. As shown in the evacuation table later in this compilation, Indonesia has had many more recent evacuations than any other nation, and fatalities have been avoided in all but a few eruptions. Indonesia also ranks at the top of regions with tsunamis and crater lake eruptions, the former best known for the major 1883 tsunami from the eruption of Krakatau that swept the coasts of Sumatra and Java, and the latter seen in the frequent eruptions from Kawah Ijen on Java and the renowned multi-hued crater lakes at Kelimutu on Flores Island. Indonesia lies near the top of the list in eruptions producing lava domes (second only to Kamchatka), and mudflows: the volcanological term lahar used for mudflows in volcanic terrain derives from Indonesia.
More than four-fifths of Indonesian volcanoes with dated eruptions have erupted since 1900 CE, and history shows the danger of volcanoes that have not erupted in recent centuries. Relatively few stratigraphic studies of older volcanic deposits have been completed in Indonesia, and only 0.4% of known Indonesian eruptions have been dated by other than historical techniques, emphasizing the need for more study of the prehistoric record in this region.
List of Holocene volcanoes in the Indonesia region.