THREAT IN VIRUNGA: UNDERSTANDING EXPLOSIVE ERUPTIONS OF NYAMURAGIRA

Nyamuragira volcano (D.R. Congo, Africa), located in the western branch of the East African Rift, is among the most active volcanoes in Africa, erupting every ~2 years since 1980, and one of the largest emitters of volcanic sulfur dioxide (SO₂) on earth. Some Nyamuragira events have produced more SO₂, were more explosive, and/or injected gas and ash to higher altitudes than others. For example, the 1912 eruption was one of the most explosive Nyamuragira events in its recorded history. Due to limited data available for the 1912 event, further study is needed in order to understand the role of volatiles in Nyamuragira eruptions, and the processes that can lead to more hazardous volcanic explosions. This is particularly important in light of the fact that ~700,000 people live within 30 km of the volcano.

Olivine and pyroxene crystals from the 1912 Nyamuragira eruption have been handpicked from bulk lava, and suitable melt inclusions (MI; portions of magma caught within solidifying crystals that are brought to the surface within lava during eruptions) have been identified. These MI will be prepared and analyzed for sulfur, chlorine, and fluorine, as well as major and minor element concentrations using electron microprobe analysis. With this information, we will evaluate the degassing and crystallization history of the 1912 magma prior to eruption. Preliminary data from one 1912 MI show a higher magmatic sulfur concentration (3700 ppm) compared to 1938, 1948, 1986, and 2006 samples (1000-2000 ppm). Gathering additional MI data on the 1912 Nyamuragira eruption will help us determine why this particular eruption was more explosive than other eruptions of this volcano.