On volcanoes, a fissure is an elongated fracture or crack at the surface from which lava erupts. Fissure eruptions typically dwindle to those at a central vent after a period of hours or days. Nyiragongo has a complex system of fissures, which extend from its summit crater all the way down to the city of Goma on its lower flanks. Lava can burst out of these fissures without warning, as occurred in 2002 at the edge of the city, killing more than 100 people, leaving over 120,000 homeless, and destroying 40 percent of the city. Scientists believe a fissure could open directly underneath Goma in a future eruption, precipitating a catastrophe.