Mount Suswa last erupted during the late Holocene, with the most recent eruptive activity likely occurring within the past 1,000 years, although no exact date has been established. Stratigraphic and morphological evidence—particularly the fresh phonolitic lava flows from the Eululu Formation (Stage S8) along the southeastern ring trench and south flank—suggests geologically recent activity.
These flows lack significant weathering or soil development, supporting a late-stage eruption age. Earlier K-Ar dating by Baker et al. (1988) places the initial shield-building phase (Angat Kitet Formation) at approximately 0.24 ± 0.01 million years ago, with subsequent explosive caldera-forming events and lava flows occurring between ~200,000 and <10,000 years ago.
Although no historic eruptions have been documented, the volcano remains classified as dormant rather than extinct, and continued geothermal activity (e.g., fumaroles and warm ground) further indicates that Mt. Suswa retains potential for future eruptions.
📚 Summary of Academic Evidence on Suswa’s Eruption History
The volcanic evolution of Suswa is traditionally divided into eight stages (S1–S8), including two major caldera-forming events. Much of what we know comes from foundational studies including:
- Johnson (1969): Stratigraphy and morphology
- Hay et al. (1976, 1979): Globule ignimbrites and eruptive dynamics
- Baker et al. (1988): Radiometric dating and evolution of central Kenya Rift volcanoes
- Macdonald et al. (1993): Petrology and immiscibility evidence
- Skilling (1993, 1994): Caldera collapse mechanics and pyroclastic stratigraphy
⏳ Key Dates in Suswa’s Eruptive Timeline
| Stage | Event | Estimated Age (Ma) | Dating Method |
|---|---|---|---|
| S1 | Pre-Caldera I shield-building (Angat Kitet Formation) | ~0.24 ± 0.01 Ma (240,000 years ago) | K-Ar (Baker et al., 1988) |
| S2–S5 | Caldera I collapse & associated explosive eruptions | ~0.2–0.1 Ma (approximate range) | Stratigraphy, K-Ar (inferred) |
| S6 | Post-Caldera I phonolitic lavas | Likely Holocene (<11,700 years) | Stratigraphy, unconformities |
| S7 | Formation and collapse of Ol Doinyo Onyoke cone (Caldera II) | Possibly within the last 10,000 years | Inferred from morphology and fresh lava fields |
| S8 | Ring trench & south flank lavas (Eululu Formation) | Possibly <1,000 years ago | No radiometric date; inferred from freshness and lack of erosion (Macdonald et al., 1993; Skilling, 1993) |
🔥 Most Recent Eruptions: What the Evidence Suggests
While no historical eruption has been recorded, several geological indicators point to very recent volcanic activity at Mt. Suswa:
- S8 lavas, found along the southeastern ring trench and southern flanks, appear unweathered and topographically fresh, suggesting Holocene age.
- Lack of soil development or vegetation cover on these flows implies they may have erupted within the last few centuries, possibly even in the last 500–1,000 years.
- The inner caldera shows evidence of fumarolic activity and warm ground, indicating that the volcano is dormant but not extinct.
📌 Why There Is No Exact Year
There is currently no absolute date (e.g., carbon-14 or tree-ring correlation) available for the most recent flows. The primary challenges include:
- The absence of organic material for radiocarbon dating.
- Limited K-Ar dating resolution for very young (sub-100 ka) lavas.
- Lack of tephra layers or cultural disturbance that could tie an eruption to known archaeological records.
However, given geomorphic freshness, lack of deep erosion, and analogs with other rift volcanoes (e.g., Longonot and Menengai), researchers like Skilling (1993) and Macdonald et al. (1993) have cautiously suggested a late Holocene age for the most recent eruptions.
🧠 Expert Conclusion
Mount Suswa last erupted sometime in the Holocene epoch—most likely within the last 1,000 years—but no exact date can yet be confirmed.
The evidence points to episodic volcanic activity throughout the late Quaternary, with two major caldera collapses and ongoing low-level volcanic processes. Though dormant, Suswa should be considered potentially active, and further geochronological work (e.g., Ar-Ar dating, paleomagnetic studies, or tephrochronology) could help refine its eruptive timeline.
🗂️ Key References
- Baker, B.H., Williams, L.A.J., Miller, J.A., & Fitch, F.J. (1988). Stratigraphy, geochronology and evolution of the Kenya Rift Valley volcanoes. Journal of the Geological Society of London.
- Skilling, I.P. (1993). Calderas and ring fracture volcanism: Suswa, Kenya Rift. Journal of Volcanology and Geothermal Research.
- Macdonald, R., Smith, M., & Thomas, R.J. (1993). Carbonatite-trachyte immiscibility at Suswa volcano. Contributions to Mineralogy and Petrology.
- Hay, R.L., et al. (1979). Globule ignimbrites of Suswa, Kenya. Bulletin Volcanologique.
- Johnson, R.W. (1969). Volcanic history of the Suswa Complex. Geological Society of East Africa.