The most destructive effusive eruption in modern history: Nyiragongo (RD. Congo), January 2002.
Abstract
Nyiragongo volcano (3470 m a.s.l.), built on the western branch of the East African Rift, has long contained in its summit crater a highly fluid, actively degassing lava lake of nephelinite composition that was studied on several occasions since the mid XXth century [1]. In 1977, for the first time in recent history, this lava lake suddenly drained out through flank fractures, causing some 60 casualties [2]. A new lava lake gradually refilled the crater from 1982 to 1994 [3] but, subsequently, its surface solidification evidenced a drop in the magma supply rate. On 17 January 2002, after several months of increased seismicity and fumarolic activity, a second drainage of the lava lake occurred through a 18 km long N-S fracture system that propagated in a few hours from 2800 m down to 1550 m elevation along the southern volcano flank. Voluminous flows of fluid pahoehoe and aa lavas ran across villages, banana fields and crops and, finally, through the city of Goma from which 350,000 inhabitants fled in a hurry. About 15% of the city, including its main centre and the housing of 120,000 people, were engulfed by flows which ultimately poured into the nearby gas-charged Lake Kivu, raising concern about a possible Nyos-type lethal gas burst [4]. Despite its limited death toll (about 45), this eruption had the most destructive impact ever recorded in history for an effusive eruption. Understanding its triggering mechanism is fundamental since a new lava lake may reform soon in Nyiragongo crater, further threatening the Goma region. Different field observations and measurements carried out soon after the eruption allowed us [4] and UN-OCHA colleagues [5] to recognize that the 2002 eruption had likely been triggered by tectonic spreading of the Kivu Rift, manifested in the occurrence of intense post-eruptive seismicity, regional ground subsidence, fracturing and minor CO2-CH4-rich gas explosions, rather than by simple magma overpressure and intrusion. This interpretation is supported i) by the similarity in the volumes of erupted flows (ca. 30-40x106 m3) and of summit crater collapse, and ii) by the identical major and trace element chemistry of the 2002 and 1977 lavas, as will be discussed. Monitoring tectonic movements in the Kivu rift thus reveals extremely important for anticipating future volcanic risks from Nyiragongo. [1] Tazieff H. et al., Bull. Volcanol., 23, 69-71, 1960; [2] Tazieff H., Bull. Volcanol., 40, 189-200, 1977; [3] Global Volc. Bull. Reports; [4] Allard P. et al., French-UK Concorde Report, 38 pp., 8 March 2002; [5] Tedesco D. et al., UN-OCHA Report, 52 pp., 30 March 2002.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....11970A