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Subsurface lateral magma propagation from Nyiragongo volcano (DRC): an interplay between rifting-induced extension and edifice loading

Virginie Pinel1, Catherine Mériaux2, Mohamedahmed Mirghani Hassan Mohamed2

  • Affiliations: 1.Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, Univ. Gustave Eiffel, Grenoble, France 2. ICTP-East African Institute for Fundamental Research, University of Rwanda, Kigali, Rwanda

  • Presentation type: Talk

  • Presentation time: Friday 10:30 - 10:45, Room R290

  • Programme No: 1.8.4

  • Theme 1 > Session 8

Abstract

In rift zones, it is common to observe lateral propagation of magma characterized by vertical dykes developing parallel to the rift direction. Depending on the competition between vertical and lateral magma migration, these dykes either feed an eruption or not. In this context, the topography that includes the load of the edifice acts against the rise of magma and favors lateral and radial migration away from the edifice. Here, we study the combined effect of the rifting-induced extension and the topographic loading of the Nyiragongo volcano located in the western branch of the East African Rift. Using analytical and numerical models, we show that the path of a dyke originating from the volcanic edifice is first influenced by the load of the volcano, leading to a radial propagation. Beyond 5 km, however, the rift-induced extensional stress field dominates leading to a north-south propagation towards Lake Kivu, consistently with the path of the magma inferred by geodetic and seismic studies during the last two eruptions of the Nyiragongo volcano. We then determine the direction of propagation within the propagation plane as a function of the direction of the maximum stress gradient, a method which we have validated using analogue experiments. It shows that the lateral propagation over more than 20 km is controlled by depth-dependent extension and reduced magma buoyancy and, to a lesser extent, the downslope towards Lake Kivu and the slight increase in rift extension towards the south.