Rwandan Geologist

Winter geological fieldwork
Challenging conditions, limited exposure, but essential data still collected.

Geology🥰

Where the ground split open for more than 30 miles—in just days. 😲🌍

It began quietly, with the ground trembling day after day beneath a remote desert landscape.

There was no towering eruption at first—just the Earth growing increasingly restless as hundreds of small earthquakes rippled through the ground, signaling that something far larger was unfolding below.

For nearly three weeks, the shaking continued.

Then, in late September, the activity intensified. Stronger earthquakes struck in rapid succession as magma forced its way through the crust, prying the land apart from within.

This dramatic sequence of events is known as the Manda Hararo–Dabbahu rifting event, which began in northeastern Ethiopia on September 14, 2005.

The seismic swarm lasted for about 20 days, peaking on September 25 with a magnitude 5.5 earthquake—the largest of the episode.

On September 26, 2005, the process finally broke the surface. An explosive eruption at Dabbahu volcano confirmed that magma had reached shallow levels.

At the same time, a massive underground magma intrusion known as a d**e was ripping apart the crust below.

In just days, a fracture more than 30 miles (48 kilometers) long split the landscape. Satellite data later revealed that the d**e widened the crust by an average of 13 feet (4 meters) at depths of 1 to 5 miles (2–8 kilometers), with some sections stretching even farther.

Above it, the land cracked and dropped several feet, forming deep grabens and permanently reshaping the surface.

This extraordinary event occurred at the Afar Triple Junction, where the African (Nubian), Somali, and Arabian tectonic plates are slowly pulling apart.

The geological processes here are the same ones that build new crust along the Mid-Atlantic Ridge—except in Afar, they’re happening on land, where scientists can observe them directly.

At this location, the land is spreading apart at a rate of about 0.8 inches (20 mm) per year.

Over geologic time, this continued stretching and thinning of the crust will allow seawater to flood the region. Eventually, Afar will become a new ocean basin, splitting eastern Africa from the rest of the continent.

Between 2006 and 2009, at least ten additional magma intrusions reshaped the region, giving scientists a rare, real-time view of how continents break apart and oceans are born.

For geologists, the Manda Hararo–Dabbahu rifting episode was a once-in-a-generation natural experiment.

For everyone else, it’s a powerful reminder that Earth is still under construction—and that the forces shaping future oceans can sometimes reveal themselves in just a matter of days.

Source: agupubs[dot]onlinelibrary[dot]wiley[dot]com/doi/10[dot]1029/2008JB005843

📌 Structural Geology Insight | Strike-Slip Faults and Mineralization

Many people assume that strike-slip faults, often linked to compressional tectonic settings, play little or no role in mineral deposit formation. This is a common misconception.

🔎 What this example shows:
The photo highlights the critical control of a left-lateral strike-slip fault on mineralization. During the evolution of strike-slip fault systems, individual fault segments commonly link together, forming a linking (step-over) zone.

⚙️ Why the linking zone matters:
• Linking zones are typically dominated by extensional fractures
• These fractures create high-permeability pathways
• Hydrothermal fluids can easily migrate, precipitate, and form ore bodies

💎 Exploration implication:
Rather than being uniformly distributed along the fault, mineralization is most likely concentrated in the linking zone, not along the main fault segments.
➡️ In the photo, the blue-circled area marks this key linking zone along the left-lateral strike-slip fault.

🧠 Key takeaway:
Effective mineral exploration requires a detailed understanding of structural architecture, not just fault type. Strike-slip systems can be highly prospective—if you know where to look.

📢 Earthquake Damage & Seismic Hazard Assessment in the East African Rift

I am also pleased to share another recent study focusing on the 26 May 2021 Mw 5.1 earthquake that struck the twin cities of Gisenyi (Rwanda) and Goma (DR Congo) during the Mount Nyiragongo eruption sequence.

Although moderate in magnitude, this earthquake caused significant damage in densely populated urban areas, highlighting critical vulnerabilities in the region.

🏙️ What we investigated:
This study presents detailed field-based observations on:
• geotechnical impacts and ground conditions
• patterns of building damage
• factors responsible for the unexpectedly high destruction

🏗️ Key findings:
• Masonry buildings lacking seismic detailing suffered the most severe damage.
• Most damaged structures were located on plains underlain by volcanic soils, particularly black cotton soil.
• Using building damage data and the European Macroseismic Scale (EMS-98), we estimated ground motion intensity across the affected area.

🗺️ Major results:
• An intensity distribution map was developed—the first of its kind for this region.
• Estimated intensities reached VIII–IX along the eastern basin-bounding fault and VII in Goma and Gisenyi.
• Elevated intensities near the fault zone indicate the need for a reevaluation of regional seismic hazard models.

⚠️ Why it matters:
This work strengthens the link between ground conditions, construction practices, and earthquake damage, and provides a critical dataset for urban planning, building code improvement, and seismic risk mitigation in the East African Rift.

📘 A step toward safer cities in active rift environments through evidence-based seismic hazard assessment.

Link: https://link.springer.com/article/10.1007/s11069-024-06637-7

📢 Volcanic Morphology, Stress Fields & Seismic Hazards (Jeju Island, Korea)

I am also excited to share the findings from my recent study on Jeju Island, South Korea, which focuses on how volcanic cone morphology can be used to infer hidden magma-feeding fractures and paleo-stress conditions.

🌋 Why Jeju Island?
In intraplate volcanically active regions like Jeju, subsurface fractures are often concealed by thick volcanic deposits, making direct structural observation difficult. Reconstructing paleo-stress fields is therefore challenging—yet essential for understanding volcanic and seismic hazards.

🔍 Our approach:
We applied an indirect morphometric analysis to 152 Quaternary volcanic craters, measuring:
• crater ellipticity
• maximum crater diameter
• breaching azimuth
• coeval cone alignment
• line connecting depressed crater points

🧭 Key results:
• Two dominant Pre-Pleistocene magma-feeding fracture systems were identified: E–W and NE/ENE-trending.
• These fracture orientations are consistent with Pre-Neogene E–W and Miocene NE-trending structures previously reported around Jeju Island.
• The results suggest a rotation of the maximum horizontal stress direction (σHmax) through time.

⚠️ Why it matters:
Identifying concealed subsurface structures is crucial for seismic hazard assessment, as the reactivation of pre-existing fractures can trigger devastating earthquakes. This study demonstrates how volcanic morphology can serve as a powerful proxy for unraveling buried tectonic controls.

📘 A clear example of how volcanic landforms preserve tectonic memory, even when structures are hidden from view.

Link: https://doi.org/10.1016/j.qsa.2024.100169

📢 New Research Publication | Volcanic Hazards & Tectonic Stress

I am pleased to share my recent publication focusing on volcanic hazard assessment in the western branch of the East African Rift System.

While most hazard studies concentrate on active volcanoes, this research highlights a critical gap: dormant volcanoes can be reactivated when stress conditions change. By integrating volcanic morphology with regional stress analysis, the study provides new insights into eruption potential and volcano–tectonic processes.

🔍 What we did:
We analyzed morphometric parameters—such as crater alignment, ellipticity, breaching direction, and crater diameter—for 231 volcanoes in the Virunga Volcanic Complex and Toro–Ankole Volcanic Field.

🔥 Key findings:
• Actively erupting volcanoes (e.g., Nyiragongo and Nyamuragira) are associated with WNW–ESE to E–W extensional stress, crustal thinning, and magma-driven stress perturbations.
• Volcanoes aligned along NW–SE, E–W, and NE–SW trends remain largely dormant, likely due to unfavorable stress orientations.
• Dormant volcanoes can still erupt when local stress changes—highlighted by the 1957 eruption of Mount Bisoke.

🌍 Why it matters:
This study moves beyond treating tectonics and volcanic hazards separately. By coupling morphometric analysis with stress field reconstruction, it improves eruption forecasting, vent location prediction, and hazard map refinement. The approach is also transferable to other tectonically active volcanic regions worldwide.

Link: https://link.springer.com/article/10.1007/s00445-025-01885-2

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Geochemical Characterization of Nyamyumba Hot Spring, Northwest ...

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https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ajol.info/index.php/rjeste/article/view/210591%23:~:text%3DRwanda%2520hosts%2520million%2520tons%2520of,Compressed%2520Natural%2520Gas%2520(CNG).&ved=2ahUKEwjtyKXImJb3AhWwgP0HHVS9AUAQFnoECAUQBQ&usg=AOvVaw1bv8k_rw_E4mJKBFg_1eMR

Organic Geochemistry of Peat Deposits in southwest Rwanda | Rwanda Journal of Engineering, Science, Technology and Environment Organic Geochemistry of Peat Deposits in southwest Rwanda Theophile Mugerwa Francois Hategekimana Olugbenga A. Ehinola Ibrahim A. Oladosu Digne Rwabuhungu Theophile Bimenyimana Fils V. Byiringiro Cedrick Nsengiyumva DOI: 10.4314/rjeste.v4i1.15 Keywords: Biomarkers, depositional environment, n-alkane...

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Lake Kivu Water Chemistry Variation with Depth Over Time, Northwestern ...

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Brittle Deformation History Based on the Analyses of Dikes and Faults ... - 지질공학

지질공학 · 대한지질공학회 본 연구는 방해석 내 쌍정을 이용하여 조선누층군 풍촌석회암층의 고응력장을 규명하기 위함이다. 이를 위해 조선누층군 두위봉형의 풍촌석회암에서 6개의 시료를 채취하여 방해석 c-축의 …