Chapter culture of Spain

Geology

Main article: Geology of Indonesia
See also: Volcanoes of Indonesia
Major volcanoes in Indonesia. Indonesia is in the Pacific Ring of Fire area.
Tectonically, most of Indonesia's area is highly unstable, making it a site of numerous volcanoes and frequent earthquakes.[90] It lies on the Pacific Ring of Fire, where the Indo-Australian Plate and the Pacific Plate are pushed under the Eurasian plate, where they melt at about 100 kilometres (62 miles) deep. A string of volcanoes runs through Sumatra, Java, Bali and Nusa Tenggara, and then to the Banda Islands of Maluku to northeastern Sulawesi.[91] Of the 400 volcanoes, around 130 are active.[90] Between 1972 and 1991, there were 29 volcanic eruptions, mostly on Java.[92] Volcanic ash has made agricultural conditions unpredictable in some areas.[93] However, it has also resulted in fertile soils, a factor in historically sustaining the high population densities of Java and Bali.[94]
A massive supervolcano erupted at present-day Lake Toba around 70,000 BCE. It is believed to have caused a global volcanic winter and cooling of the climate and subsequently led to a genetic bottleneck in human evolution, though this is still in debate.[95] The 1815 eruption of Mount Tambora and the 1883 eruption of Krakatoa were among the largest in recorded history. The former caused 92,000 deaths and created an umbrella of volcanic ash that spread and blanketed parts of the archipelago and made much of the Northern Hemisphere without summer in 1816.[96] The latter produced the loudest sound in recorded history and caused 36,000 deaths due to the eruption itself and the resulting tsunamis, with significant additional effects around the world years after the event.[97] Recent catastrophic disasters due to seismic activity include the 2004 Indian Ocean earthquake and the 2006 Yogyakarta earthquake.

Nearly nine-tenths of the Indonesian population professes Islam. There are, however, pockets of Christians scattered throughout the country, particularly in Flores, Timor, northern Celebes, the interior of Kalimantan, and the Moluccas. Most are Protestant or independent Christian, and the remainder are mainly Roman Catholic. Many Chinese in the cities are also Christian, but some follow Buddhism or Confucianism, sometimes blended with Christianity. Hindus account for less than 2 percent of all Indonesians, although Hinduism is the dominant religion on Bali and has many adherents in Lombok. Local religions are practiced in some remote areas.

Palembang
The Great Mosque in Palembang, South Sumatra, Indonesia.
The major religions of Indonesia were all introduced on the coast and, except in such open areas as Java and southern Sumatra (which were free of natural impediments), penetrated slowly inland. Regions such as central Kalimantan and western New Guinea, the mountains of northern Sumatra, and the interiors of other mountainous islands long remained virtually untouched by outside religions. However, much 20th-century Christian missionary activity has focused on these inland-dwelling peoples.

stupas at Borobudur
Stupas at Borobudur, central Java, Indonesia.
The earliest recorded Indonesian history shows extensive religious influences from India; the early Indonesian states that centred on Java or Sumatra evolved through many forms of Hinduism and Theravada and Mahayana Buddhism. During the 9th century CE, both Hinduism and Buddhism were practiced as court religions; Shiva and Buddha were looked upon as manifestations of the same spiritual being. The blending of the two religions continued until the 14th century, when Islam, brought by Muslim traders primarily from South Asia, emerged as the dominant religion along the coasts of Java and Sumatra. By the 15th century, Islam had gained a firm footing in coastal areas of other islands of the archipelago as well.
Throughout all the religious changes on the court level, the common people adopted part of each new religion as an additional layer on top of their traditional local beliefs. Consequently, Islam is expressed differently in Indonesia than it is in the Middle East. The religion is most strictly practiced in Aceh, western Sumatra, western Java, southeastern Kalimantan, and some of the Lesser Sunda Islands. On Java, Muslims who follow orthodox practices are referred to as the santri. By contrast, the abangan adhere to a more syncretic tradition, strongly influenced by ancestral beliefs and practices. With the growth of a more religion-conscious middle class, especially since the late 20th century, the abangan way of believing has been in retreat, while more-orthodox Muslim practices have been on the rise. However, the many local rituals connected with birth, death, and marriage are carefully observed by people at all levels, and ceremonies (selamatan) are held on all special occasions.