Title: Magma-Assisted Extension and Crustal Deformation in the Kivu Rift: Geodetic Constraints on the 2021 Nyiragongo Dike Intrusion. 

PhD Defence: Derrick Murekezi

Committee: Dr. Andy Newman (Advisor), Dr. Samer Naif, Dr. Zhigang Peng, Dr. Winnie Chu, Dr. Kyle Murray

Abstract

The East African Rift System (EARS) is one of the most tectonically and magmatically active continental rifts on Earth, offering critical insight into the mechanisms governing the transition from continental extension to seafloor spreading at divergent plate boundaries. Within its western branch, the Kivu Rift is a volcanically and structurally dynamic segment where repeated dike intrusions and eruptions at Nyiragongo and Nyamuragira volcanoes accommodate regional strain. The May 2021 Nyiragongo dike intrusion and eruption provided a unique opportunity to quantify how a transient magmatic event perturbs the regional stress field, reorganizes crustal strain accommodation, and advances long-term rift evolution within this portion of the EARS.

In this work, we integrate Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) observations to constrain the geometry, kinematics, and spatio-temporal evolution of deformation associated with the 2021 intrusion. A joint elastic dislocation model identifies a near-vertical dike between 3–6 km depth, with a maximum tensile opening of nearly 10 m beneath Goma and a total length of 25 km southward of Nyiragongo. The intruded volume (~1.8 × 10⁸ m³) exceeds the erupted lava volume by nearly an order of magnitude, confirming that the event was predominantly intrusive. The geodetic moment (~5.5 × 10¹⁸ N·m) accounts for more than 95 % of the total deformation energy, indicating that strain was accommodated almost entirely aseismically. The close alignment between the modeled dike, mapped faults, and co-eruptive seismicity indicates a structurally guided intrusion, consistent with strain localization along pre-existing fault corridors observed in other active rift zones such as Afar and Iceland.

Sentinel-1A/B InSAR time-series analysis (2019–2025), integrated with continuous GNSS measurements, captures the three-dimensional and temporal evolution of deformation across the Kivu Rift. Interferograms processed using the InSAR Scientific Computing Environment (ISCE) and its Dolphin module employed robust techniques to mitigate decorrelation and atmospheric noise in the mountainous Virunga region. The derived displacement fields reveal uplift and westward motion on the western flank and subsidence with eastward motion on the eastern flank, consistent with dike opening parallel to the regional fault architecture and principal extensional axis. Time-series results show that the 2021 intrusion accelerated rift extension by nearly a decade of tectonic strain within days, while persistent post-intrusion deformation indicates a long-lived modification of the regional stress field and shallow crustal rheology. Collectively, these results demonstrate that the 2021 event was a structurally controlled, dominantly aseismic dike intrusion that localized extension and efficiently transferred magma through the brittle crust, underscoring the importance of sustained geodetic monitoring for understanding magma–tectonic coupling and improving hazard preparedness in the Goma–Gisenyi region.