Collaborative Research: Volatile sources, eruption triggers, and magma ascent rates for mafic alkaline magmas at Nyiragongo and Nyamulagira volcanoes, DR Congo, East African Rift

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Nyiragongo and Nyamulagira, in the East African Rift, are two of the most active volcanoes in the world, and they pose major hazards to large populations living nearby. Many volcanoes that pose great risks to large populations are well studied and highly monitored with scientific instruments, but there is still a fundamental lack of understanding of many basic aspects of the Nyiragongo and Nyamulagira systems. This investigation will improve our understanding of these systems by focusing on (1) how magma forms beneath the two volcanoes, (2) how deeply and for how long magma is stored beneath the volcanoes before eruption, (3) what triggers eruptions to occur on the flanks of the volcanoes, in and near populated areas, and (4) how fast magma moves towards the surface during an eruption and how much warning time people would have in advance of an eruption. In addition to these aspects focused on hazards, this project will investigate the source of the carbon that is released as carbon dioxide by these volcanoes. Large amounts of carbon are likely stored in solid minerals inside the Earth beneath thick, old continental crust like that in East Africa, and when the crust gets pulled apart by rifting as in the East African Rift, the carbon contributes to magma formation. Nyiragongo is one of the largest emitters of carbon dioxide gas of any volcano worldwide, and better understanding the connection between carbon in minerals and magma formation beneath this volcano will help us better understand the Earth’s deep carbon cycle. Much of the research for this project will be conducted by graduate students at the University of Oregon and University of Wyoming as part of their scientific training. Collaboration with scientists at the Goma Volcano Observatory in the Democratic Republic of the Congo will include periodic videoconferences to share research results important for volcanic hazards monitoring. Public engagement will include a National Geographic Explorer’s Blog and several short articles for a general audience on volcanic hazards at Nyiragongo and Nyamulagira and release of carbon dioxide from volcanoes.In detail, the primary goals of this project are (1) to understand the time-integrated effects of lithospheric metasomatism on magma generation beneath Nyiragongo and Nyamulagira, and (2) to use the results as the starting point for a source-to-surface investigation of the plumbing systems, magma storage timescales, eruption triggering processes, and magma ascent rates for these volcanoes. Although these volcanoes are only 15 km apart, their eruption behavior and the types of lava they emit are profoundly different, with Nyiragongo erupting some of the most unusual lava types found anywhere on Earth. To understand the roles of lithospheric mantle and metasomatic veins as magma sources, we will use existing major and trace element and isotopic data together with new data on volatile contents of olivine-hosted melt inclusions to establish parental melt compositions and source lithologies. Our data and modeling approach will also provide important constraints on parental magma CO2 and S concentrations and magma fluxes for each volcano. Our proposed work will use existing tephra and lava samples and will focus on the many parasitic cones and tuff rings on the flanks of Nyiragongo and Nyamulagira, as these erupt more primitive compositions than the volcanoes’ central vents. For investigating the plumbing systems, we will use (1) melt inclusion volatile data to determine crystallization depths, (2) U-series mineral isochrons to determine crystal and magma residence times, (3) mineral zoning and diffusion chronometry to identify recharge and mixing processes that may trigger eruptions and yield precursory seismic signals, and (4) diffusive loss of H from melt inclusions to infer magma ascent rates during eruption, which likely influence explosivity. Our overarching goal is to produce geologically well-grounded, state-of-the-art geochemical and petrological data that improves our understanding of these volcanic systems and thereby improves hazard assessment models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.