Colo volcano forms the isolated small island of Una-Una in the middle of the Gulf of Tomini in northern Sulawesi. The broad, low volcano, whose summit is only 507 m above sea level, contains a 2-km-wide caldera with a small central cone. Only three eruptions have been recorded in historical time, but two of those caused widespread damage over much of the island. The last eruption, in 1983, produced pyroclastic flows that swept over most of the island shortly after all residents had been evacuated.

The NE-most volcano on the island of Sulawesi, Tongkoko (also known as Tangkoko) has a summit that is elongated in a NW-SE direction with a large deep crater that in 1801 contained a cone surrounded by lake water. The slightly higher Dua Saudara stratovolcano is located only 3 km to the SW of Tongkoko, and along with Tongkoko, forms the most prominent features of Gunung Dua Saudara National Park, a noted wildlife preserve. Eruptions occurred from the summit crater of Tongkoko in the 17th century and in 1801. The prominent, flat-topped lava dome Batu Angus formed on the east flank of Tongkoko in 1801, and, along with an adjacent east flank vent, has been the source of all subsequent eruptions.