In subtropical volcanic environments, there are often few accessible outcrops. These are often highly weathered and of very poor quality. Soil development is rapid (1 cm/y) and small eruptions are unlikely to be preserved in the geological record. Reconstructing past eruptions and assessing hazards is a challenge. Here, we studied a poorly outcropping tuff ring (very poor, incomplete sections) with the best outcrop observed at a beach cliff (up to ca. 5 - 10 m high) at Batoke, to the south of Mt Cameroon volcano. Mt Cameroon has a few tuff rings, currently of unknown ages, near the SW coast of Cameroon. In the Batoke case, the sequence is dominated by gently dipping tuff beds varying in the proportion of lithics, juvenile clasts, and accretionary lapilli (acc-laps). Several beds are close-packed with acc-laps of up to 10 - 15 mm diameter. Part of the section is gullied by mud flow deposits. The rocks are highly weathered but differential weathering enhances relationships. Quantitative data can be extracted from a detailed study of outcrops’ external surfaces. The preserved section is close to where the deposits were initially thickest and where acc-laps were most abundant and largest. There is an empirical correlation between maximum acc-lap size in the thickest outcrop and eruption column height. This and the deposit features suggest that the Batoke eruption was pulsating but dominated by fallout, with a water and ice-rich eruption column reaching 10 - 15 km high. Recycling of water drops and ice-coated fine ash accumulated during eruption. At switch off, wholesale gravitational collapse of this material produced the mud flows, which gullied the previously-laid down deposits. Such ash fall and mud flows can represent a substantial hazard, e.g. they can gully down through towns and roads and cut evacuation routes. This study illustrates how, at subtropical tuff rings, it is possible to extract key data needed for hazard assessment from only 1 - 2 poor outcrops.
References
[1]
Deruelle, B., N’ni, J. and Kambou, R. (1987) Mount Cameroon: An Active Volcano of the Cameroon Line. Journal of African Earth Sciences, 6, 197-214.
https://doi.org/10.1016/0899-5362(87)90061-3
[2]
Njome, S., Suh, C.E., Chuyong, G. and De Wit, M.J. (2010) Volcanic Risk Perception in Rural Communities along the Slopes of Mount Cameroon, West-Central Africa. Journal of African Earth Sciences, 58, 608-622.
https://doi.org/10.1016/j.jafrearsci.2010.08.007
[3]
Wantim, M., Jacobs, P., Suh, E., Kervyn, M. and Ernst, G. (2012) Mapping and Modelling Lava Flow Dynamics and Hazards at Mount Cameroon Volcano. Afrika Focus, 25, 101-102. https://doi.org/10.21825/af.v25i1.18063
[4]
Del Marmol, M.A., Fontijn, K., Atanga, M., Njome, S., Mafany, G., Tening, A., Wantim, M.N., Fonge, B., Che, V.B., Aka, F., Ernst, G.G.J., Suh, E., Jacobs, P. and Kervyn, M. (2017) Investigating the Management of Geological Hazards and Risks in the Mt Cameroon Area Using Focus Group Discussions. In: Fearnley, C.J., et al., Eds., Observing the Volcano World: Volcano Crisis Communication, Springer, Berlin, 373-394. https://doi.org/10.1007/11157_2017_3
[5]
Njome, M.S., Suh, C.E., Sparks, R.S.J., Ayonghe, S.N. and Fitton, J.G. (2008) The Mount Cameroon 1959 Compound Lava Flow Field: Morphology, Petrography and Geochemistry. Swiss Journal of Geosciences, 10, 85-98.
https://doi.org/10.1007/s00015-007-1245-x
[6]
Suh, C.E., Sparks, R.S.J., Fitton, J.G., Ayonghe, S.N., Annen, C., Nana, R. and Luckman, A. (2003) The 1999 and 2000 Eruptions of Mount Cameroon: Eruption Behaviour and Petrochemistry of Lava. Bulletin of Volcanology, 65, 267-281.
https://doi.org/10.1007/s00445-002-0257-7
[7]
Dolgoff, A. (1996) Physical Geology. Heath and Company, Lexington.
[8]
Brata, A.G., Rietveld, P., De Groot, H.L.F. and Zant, W. (2013) The Krakatau Eruption in 1883: Its Implications for the Spatial Distribution of Population in Java. Economic History of Developing Regions, 28, 27-55.
https://doi.org/10.1080/20780389.2013.866381
[9]
Abdurrachman, M., Widiyantoro, S., Priadi, B. and Ismail, T. (2018) Geochemistry and Structure of Krakatoa Volcano in the Sunda Strait, Indonesia. Geosciences, 8, Article 111. https://doi.org/10.3390/geosciences8040111
[10]
Ngwa, C.N., Nche, L. and Suh, C.E. (2013) Physical Volcanology of Pyroclastic Tephra Deposit at Batoke Mt. Cameroon, West Africa: An Overview. Global Journal of Geological Science, 11, 27-35. https://doi.org/10.4314/gjgs.v11i1.3
[11]
Walker, G.P.L. (1992) Puu Mahana near South Point in Hawaii Is a Primary Surtseyan Ash Ring, Not a Sandhills-Type Littoral Cone! Pacific Science, 46, 1-10.
[12]
Mattox, T.N. and Mangan, M.T. (1997) Littoral Hydrovolcanic Explosions: A Case Study of Lava-Seawater Interaction at Kilauea Volcano. Journal of Volcanology and Geothermal Research, 75, 1-17. https://doi.org/10.1016/S0377-0273(96)00048-0
[13]
Aranda-Gomez, J.J. and Luhr, J.F. (1996) Origin of the Joya Honda maar, San Luis Potosi, Mexico. Journal of Volcanology and Geothermal Research, 74, 1-18.
https://doi.org/10.1016/S0377-0273(96)00044-3
[14]
Hanson, R.E. and Elliot, D.H. (1996) Rift-Related Jurassic Basaltic Phreatomagmatic Volcanism in the Central Transantarctic Mountains: Precursory Stage to Flood Basalt Effusion. Bulletin of Volcanology, 58, 327-347.
https://doi.org/10.1007/s004450050143
[15]
Lorenz, V. (1986) On the Growth of Maars and Diatremes and Its Relevance to the Formation of Tuff Rings. Bulletin of Volcanology, 48, 265-274.
https://doi.org/10.1007/BF01081755
[16]
Lorenz, V. (1974) Vesiculated Tuffs and Associated Features. Sedimentology, 21, 273-291. https://doi.org/10.1111/j.1365-3091.1974.tb02059.x
[17]
Wohletz, K.H. and McQueen, R.G. (1984) Experimental Studies of Hydromagmatic Volcanism. In: Explosive Volcanism: Inception, Evolution, and Hazards, National Academy Press, Washington DC, 158-169.
[18]
Go, S.Y. and Sohn, Y.K. (2021) Microtextural Evidence for Vesiculated Tuff Formation in Songaksan Tuff Ring, Jeju Island, Korea. Journal of Volcanology and Geothermal Research, 417, Article ID: 107311.
https://doi.org/10.1016/j.jvolgeores.2021.107311
[19]
Giaiotti, D., Gianesini, E. and Stel, F. (2001) Hueristic Considerations Pertaining Hailstone Size Distributions in the Plain of Fruili-Venezia Giula. Atmospheric Research, 57, 269-288. https://doi.org/10.1016/S0169-8095(01)00080-1
[20]
Rosi, M. (1992) A Model for the Formation of Vesiculated Tuff by the Coalescence of Accretionary Lapilli. Bulletin of Volcanology, 54, 429-434.
https://doi.org/10.1007/BF00312323
[21]
Mueller, S.B., Kueppers, U., Huber, M.S., Hess, K.U., Poesges, G., Ruthensteiner, B. and Dingwell, D.B. (2018) Aggregation in Particle Rich Environments: A Textural Study of Examples from Volcanic Eruptions, Meteorite Impacts, and Fluidized Bed Processing Bulletin of Volcanology, 80, Article No. 32.
https://doi.org/10.1007/s00445-018-1207-3
[22]
Schumacher, R. and Schmincke, H.U. (1991) Internal Structure and Occurrence of Accretioanary Lapilli: A Case Study at Laacher See Volcano. Bulletin of Volcanology, 53, 612-634. https://doi.org/10.1007/BF00493689
[23]
Brown, R.J., Branney, M.J., Maher, C. and Dávila-Harris, P. (2010) Origin of Accretionary Lapilli within Ground-Hugging Density Currents: Evidence from Pyroclastic Couplets on Tenerife. Geological Society of America Bulletin, 122, 305-320.
https://doi.org/10.1130/B26449.1
[24]
Lane, S.J. and Gilbert, J.S. (1992) Electric Potential Gradient Changes during Explosive Activity at Sakurajima Volcano, Japan. Bulletin of Volcanology, 54, 590-594.
https://doi.org/10.1007/BF00569942
[25]
Miura, T., Koyaguchi, T. and Tanaka, Y. (2001) Measurements of Electric Charge Distribution in Volcanic Plumes at Sakurajima Volcano, Japan. Bulletin of Volcanology, 64, 75-93. https://doi.org/10.1007/s00445-001-0182-1
[26]
Alvarado, G.E. and Soto, G.J. (2002) Pyroclastic Flow Generated by Crater-Wall Collapse and Outpouring of the Lava Pool of Arenal Volcano, Costa Rica. Bulletin of Volcanology, 63, 557-568. https://doi.org/10.1007/s00445-001-0179-9
[27]
Koyaguchi, T. and Ohno, M. (2001) Reconstruction of Eruption Column Dynamics on the Basis of Grain Size of Tephra Fall Deposits: 1. Methods. Journal of Geophysical Research, 106, 6499-6512. https://doi.org/10.1029/2000JB900426
[28]
Koyaguchi, T. and Ohno, M. (2001) Reconstruction of Eruption Column Dynamics on the Basis of Grain Size of Tephra Fall Deposits: 2. Application to the Pinatubo 1991 Eruption. Journal of Geophysical Research, 106, 6513-6533.
https://doi.org/10.1029/2000JB900427
[29]
Suh, C.E., Ayonghe, S.N. and Njumbe, E.S. (2001) Neotectonic Earth Movements Related to the 1999 Eruption of Cameroon Mountain, West Africa. Episodes, 24, 9-12.
[30]
Manville, V., Hodgson, K.A. and Nairn, I.A. (2007) A Review of Breakout Floods from Volcanogenic Lakes in New Zealand. New Zealand Journal of Geology and Geophysics, 50, 131-150.
