Strategically positioned between the Pacific and Indian oceans, Indonesia is an archipelagic nation containing over 18,000 islands. Of those, the larger islands of Sumatra, Java, Kalimantan (which comprises two-thirds of the island of Borneo), Sulawesi, and Irian Jaya are quite mountainous, with some peaks reaching 12,000 ft.
The highest elevations (over 16,000 ft) are found on Irian Jaya in the east, with the highest point being Puncak Jaya at 16,502 ft. (5,030 m).
Indonesia's former tallest peak, Mount Tambora (8,930 ft, 2,722 m), is an active stratovolcano whose 1815 eruption was the largest ever in recorded history - killing nearly 71,000 people.
The explosion alone was heard as far west as Sumatra island, some 1,200 miles (2,000 km) away, and ash falls were recorded on the islands of Borneo, Sulawesi, Java and Maluku.
Located along the Ring of Fire, Indonesia has about 400 volcanoes within its borders, with at least 90 still active in some way.
The most active volcanoes are Kelut (which has erupted more than 30 times since 1000 AD) and Merapi (which has erupted more than 80 times since 1000 AD) on Java island.
Due to its location between numerous tectonic plates, including two continental plates: the Eurasian Plate (Sunda Shelf) and the Australian Plate (Sahul Shelf); and two oceanic plates: the Philippine Sea Plate and Pacific Plate; natural disasters are common in Indonesia.
In addition to the mountainous landscape, much of the islands are covered in thick tropical rainforests that give way to coastal plains.
Significant rivers of Indonesia include the Barito, Digul, Hari, Kampar, Kapuas, Kayan and Musi; as well, there are also scattered inland lakes which are relatively small in size.