Sulawesi

Sulawesi (pronounced SOO-lə-WAY-see, and also called Celebes) is one of Indonesia’s four Greater Sunda Islands and ranks as the 11th-largest island on Earth. It lies east of Borneo, west of the Maluku Islands, and south of Mindanao and the Sulu Archipelago. In Indonesia, only Sumatra, Borneo, and Papua cover more area, while only Java and Sumatra have larger populations.

The island’s shape is defined by four peninsulas: the Minahasa (northern), East, South, and Southeast. These are separated by three gulfs—Tomini (between the Minahasa and East peninsulas), Tolo (between the East and Southeast), and Boni (between the South and Southeast). The Makassar Strait runs along the western side, separating Sulawesi from Borneo.

The name “Sulawesi” may come from the words *sula* (“island”) and *besi* (“iron”), possibly referring to the historical export of iron from the rich deposits around Lake Matano. This name became common in English after Indonesian independence. “Celebes” was given by Portuguese explorers; it may be their rendering of the native name “Sulawesi,” though its direct meaning is unclear.

Covering about 186,064 square kilometers (including nearby minor islands administered as part of it), Sulawesi is the world’s 11th-largest island. Its central region is ruggedly mountainous, making the peninsulas historically remote from one another—sea travel has often been easier than road connections. The three gulfs (Tomini, Tolo, and Boni) divide the four peninsulas. The Makassar Strait lies to the west, with Borneo to the west, the Philippines to the north, Maluku to the east, and Flores and Timor to the south.

Several island groups are administratively part of Sulawesi: the Selayar Islands stretch south from Southwest Sulawesi into the Flores Sea; the Sangihe and Talaud Islands extend north from the northeastern tip; Buton, Muna, and neighboring islands lie off the southeast peninsula; the Togian Islands sit in the Gulf of Tomini; and Peleng Island and the Banggai Islands cluster between Sulawesi and Maluku. All these, along with many smaller coastal islands, belong to Sulawesi’s six provinces.

Geologically, the island rises from deep surrounding seas to a high, mostly non-volcanic, mountainous interior. Active volcanoes are concentrated in the northern Minahasa Peninsula and continue north to the Sangihe Islands—examples include Mount Lokon, Mount Awu, Soputan, and Karangetang. Plate reconstructions suggest Sulawesi formed from the collision of terranes from the Asian Plate (west and southwest) and the Australian Plate (southeast and Banggai), along with island arcs from the Pacific (north and east peninsulas). This complex tectonic history has left numerous faults, making the island prone to earthquakes, including deadly events in 2018 and 2021.

Off the eastern coast, the North Banda Sea formed through subduction rollback during the early Miocene, leaving evidence such as an extensive fault network, a volcanic seamount with ridges, and an accretionary wedge. Off the east coast and Banggai, late Miocene carbonate rocks—likely pinnacle reefs—accumulated, forming a platform about 180–770 meters thick. Unlike most islands in Wallacea, Sulawesi is not truly oceanic; it is a composite island at the center of the Asia-Australia collision zone. Parts were once attached to either the Asian or Australian continental margins and later separated by vicariant processes. In the west, the opening of the Makassar Strait separated West Sulawesi from Sundaland around 45 million years ago (Eocene). In the east, the older view of multiple micro-continental collisions has been largely replaced by the hypothesis that extensional fragmentation followed a single Miocene collision of West Sulawesi with the Sula Spur (the western end of a Late Paleozoic Variscan folded belt).

The Bone Basin lies between the southeastern and southern arms. Studies indicate it opened due to extensional forces, bounded by normal faults on each side, with uplifted basement rock around its edges and young sediments in the middle. Its geological history has allowed large carbonate accumulations, raising the potential for oil and gas, though the faults make the system complex.

The oldest evidence of humans on Sulawesi comes from stone tools made by archaic humans at the Calio site near Ujung in Soppeng Regency, southwestern Sulawesi. These tools date to at least 1.04 million years ago, possibly as old as 1.48 million years. Other archaic stone tools, from over 200,000 to 100,000 years ago, have also been found.