Indonesia's ethnic, religious, and linguistic melting pot has produced a fittingly wide range of faiths and religious practices. Blending elements from different faiths is at least as common as adhering to the tenets of one religion. Though the vast majority of Indonesians are Muslim (roughly 85 percent), many combine Islam with animism, sometimes also mixing in Hindu or Buddhist ideas. And while most Balinese are Hindu, many Indonesians living in the eastern reaches of the archipelago blend Christianity brought by missionaries with ancient cultural practices centering on prehistoric megaliths. Stricter interpretations of Islam are seen in west Java, southern Sulawesi, and northern and western Sumatra, where the Islamic law known as Sharia has been introduced.
Details of beliefs and rituals can even vary depending on which part of a volcano one calls home: Villagers on the southern flank of Mount Merapi, in Java, worship a volcano deity named Kyai Sapu Jagat, while those who live on the northern flank refer to him as Mbah Petruk. But volcano deities are consistently seen as neutral rather than inherently good or bad. Many interpret an eruption on Merapi as a sign that the volcano deity has been disrespected by improper behavior or thought. Offerings are made to appease the spirit and bring prosperity, and sometimes to mimic sacrifices made in revered religious legends. Some people even say that a volcanic eruption is a way for a deity to expand his or her kingdom or to expel unwanted material—the volcano is, so to speak, merely blowing off steam.