SHORT SCIENTIFIC COMMUNICATION Soil temperature and CO 2 degassing, SO 2 fluxes and field observations before and after the February 29, 2016 new vent inside Nyiragongo crater Charles M. Balagizi 1 & Mathieu M. Yalire 1 & Honoré M. Ciraba 1 & Vicky B. Kajeje 1 & Abel S. Minani 1 & Annie B. Kinja 1 & Marcellin M. Kasereka 1 Received: 29 April 2016 /Accepted: 2 August 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Nyiragongo volcano threatens ∼1.5 million inhabi- tants of Goma (DR Congo) and Gisenyi (Rwanda) cities and people living in the surrounding villages. In 2002, the volcano produced lava flows which invaded Goma and destroyed the economic district of the city, forced a mass exodus of the population and caused the loss of several lives. Nyiragongo volcanic activity is therefore closely followed by the inhabi- tants, and any news related to increased activity agitates peo- ple in the area, especially those in Goma. Here, we report a short time series of soil temperature and carbon dioxide degassing for four locations, and plume sulphur dioxide fluxes preceding and following the opening of a new vent inside the main Nyiragongo crater on February 29, 2016. The observed sudden and unexpected changes in Nyiragongo activity raised the fear of a new volcanic eruption and led to panic in Goma and the surroundings, inducing some people to leaving the city. We use the dataset and field observations before and after the opening of the new vent, in conjunction with published information about Nyiragongo’ s eruptive mechanism and of the volcano’ s plumbing system geometry (mainly the crater), to show that the new vent was fed by magma intruded from the lava lake or the upper conduit. Keywords Nyiragongo volcano . Lava lake activity . SO 2 emissions . Soil temperature . CO 2 soil degassing . Volcanic monitoring Nyiragongo volcanological settings and eruptive background Nyiragongo is a stratovolcano (3470 m a.s.l.) located on the floor of the western branch of the East African Rift. Nyiragongo along with Nyamulagira shieldvolcano (3058 m a.s.l.) are the presently active volcanoes in a group of eight major edifices forming the Virunga Mountains, though Visoke also erupted in 1957 (Global Volcanism Program, accessed in June 2016 ). Both Nyiragongo and Nyamulagira hold an active lava lake inside their main craters, and these lakes have persisted since May 2002 and early April 2013, respectively. Nyiragongo has erupted only two times (January 10, 1977 and January 17, 2002) since its first exploration in the late nineteenth century, and the two eruptions occurred when the volcano was holding a closed up lava lake, i.e. a lake with a solidified surface (Tazieff 1977; Pottier 1978; Ueki 1983; Durieux 2004a, b; Komorowski et al. 2004; Tedesco et al. 2007). The 1977 and 2002 Nyiragongo eruptions were dike-fed fissural eruptions triggered by rift movement that caused the opening of an N-S-oriented system of fractures (Fig. 1), which led to drainage of the lava lakes (Tazieff 1977; Durieux 2004a; Komorowski et al. 2004; Tedesco et al. 2007; Wauthier et al. 2012). During the 2002 eruption, this fracture network further extended to the south through Goma and Gisenyi and even beneath Lake Kivu, which is rich in carbon dioxide (CO 2 ) and methane (CH 4 ). The magma intrusion yielded to opening of a new vent in Munigi (Fig. 1), and from there, one of the two major lava flows was emitted that invaded and destroyed 10–15 % of Goma and one third of the airport runway (Baxter and Ancia 2002; Tedesco et al. 2007; Smets et al. 2010). Nyiragongo’s 2002 eruption also destroyed the houses of ∼120,000 people, forced a Editorial responsibility: T.P. Fischer * Charles M. Balagizi balagizi.charles@gmail.com 1 Goma Volcano Observatory, 142, Av. du Rond-point, Goma, Democratic Republic of Congo Bull Volcanol (2016) 78:64 DOI 10.1007/s00445-016-1055-y