Investigating Volcano-Tectonic Interactions in the Natron Rift, East Africa with Implications for Understanding Volcanic Eruptive Processes

An early phase continental rift is an emerging plate boundary where tectonic forces stretch and thin the continental lithosphere, shaping the Earth's surface. Continental breakup and its progression are typically driven by the interplay between repeated magmatic and tectonic activities, which have been explored through both tectonic and magma-assisted rifting models. Understanding volcano-tectonic interactions is key for evaluating the role of magmatic fluids in facilitating the initiation of continental breakup during early phase rifting. This study applies the magma-assisted rifting model to the Natron Rift and investigates volcano-tectonic interactions during early phases of continental breakup associated with observed changes in the volcanic plumbing system of the active volcano Ol Doinyo Lengai. The Natron Rift is a magma-rich rift in the southern segment of the Eastern Branch in northern Tanzania providing an ideal setting to explore the interactions between tectonic and magmatic processes in the early stages of rifting. To investigate tectonic and magmatic interactions, we began by characterizing the magmatic plumbing system of Ol Doinyo Lengai using Global Navigational Satellite System (GNSS) data from our TZVOLCANO network and Interferometric Synthetic Aperture Radar (InSAR) observations. We inverted the GNSS and InSAR data independently to identify potential deformation sources using the software dMODELS. We then conducted a joint inversion of both datasets and found results that were consistent with the independent inversions within 2-sigma uncertainty. Our findings suggest that Ol Doinyo Lengai is fed by an offset multi-tiered reservoir system, consisting of a shallow magma reservoir located east of the volcano connected to a deeper reservoir through a network of fractures. This magmatic system likely influences the nature, style, and magnitude of volcanic activity at the edifice. We also assessed temporal and spatial changes in surface motion observed with GNSS stations associated with magmatic activity to help mitigate risks to nearby communities, tourism, and air traffic. Detecting transient deformation is essential for forecasting eruptions since these signals often precede eruptive events. To detect transient signals using GNSS data from the TZVOLCANO network, we employed the Targeted Projection Operator (TPO) program which projects GNSS time-series data onto a target spatial pattern. We analyzed seven years of continuous GNSS data and divided the observations into three-year intervals. The TPO method detected rapid uplift between March 2022 and December 2022 followed by steady-state uplift through August 2023. The method also identified quiescent periods and non-eruptive inflation signals that enhance our understanding of the dynamic magma plumbing system of Ol Doinyo Lengai. When integrated with the TZVOLCANO network, which streams real-time GNSS data, this approach enables continuous monitoring and early detection of potential volcanic hazards. Ongoing monitoring is crucial for assessing volcanic risks and improving emergency response plans. Finally, we examined the role of interactions between tectonic and magmatic processes in the Natron Rift during the early stages of continental breakup, focusing on the evolution of the magma plumbing system beneath Ol Doinyo Lengai. Using the code PyLith, we developed a 3D model of the region. The modeling experiments test both homogeneous and heterogeneous medium, with and without topography to estimate surface deformation and stress changes on the Natron fault due to geodetically constrained magma source inflation and deflation. Our analysis focused on stress transfer from the magma sources to assess the likelihood of fault slip, considering the typical 0.1 MPa threshold for triggering slip in magmatic rift settings. Results indicate that during the inflation period from 2016 to 2023, slip on the Natron fault is inhibited adjacent to the volcano under all scenarios. During the magma source deflation phase that occurred from 2007 to 2008 due to explosive eruptions, slip on the Natron fault was promoted adjacent to the volcano under all scenarios. Shear stress change analyses reveal that during the magma deflation scenario, slip of the Natron fault is consistent with oblique normal fault movement that is dominated by normal faulting and has components of strike-slip motion. Finite numerical modeling results demonstrate that topography considerably influences stress changes caused by dynamic magma sources as compared to material heterogeneity highlighting the importance of incorporating topography in volcano-tectonic settings. This work suggests that the potential ongoing magmatic activity at Ol Doinyo Lengai and its proximity to the Natron Fault influence the development of the youthful Natron Rift during early phase rifting. However, this influence likely inhibits fault slip at present on the adjacent section of the Natron fault due to magma source inflation.