PhD Title: Explosive flood basalt volcanism
(see also Murray's MSc page)
1. Map of the Karoo LIP in southern Africa, after Marsh et al. 1997. The red dashed lines enclose outcrop of igneous rocks of the Karoo Central Area, and the red box locates the field area on the southern border of Lesotho.
Explosive flood basalt volcanism
Flood basalt provinces represent the largest volcanic events known, and have punctuated the history of Earth at irregular intervals coincident with periods when continents are breaking up and the fragments drifting apart. Until recently the eruptions that formed the flood basalts were thought to be fairly gentle, passive events resulting in effusion of lava flows that piled up to form broad sheets and shields. However, recent work shows that explosive volcanism during eruption of flood basalts produced widespread, thick ash deposits from crater-complexes kilometres to tens of kilometres across, driven by the interaction of the earliest flood basalts with water in shallow lakes, rivers and aquifers. My PhD will investigate the physical volcanology of large-scale interaction between rising basaltic magma, wet sediment and sedimentary rock during break-up of the African-Antarctic sector of the Gondwana in Early Jurassic time (183 million years ago). Here, continental break-up was preceded by rifting and rapid outpouring of Karoo Large Igneous Province (LIP) flood basalts, with the complex interplay between volcanic, sedimentary and tectonic processes during this break-up event recorded in superb, regional scale outcrop along the Drakensberg Escarpment of South Africa and Lesotho.
This work involves:
- Prof. Bruce Houghton (U. Hawaii)
- Dr. Ian Skilling (U. Pittsburgh)
- Prof. Goonie Marsh (U. Rhodes)
- Dr. James White (U. Otago)
- and is supported by the U.S. National Science Foundation
2. Map of volcaniclastic rocks in the foothills of the Drakensberg Mountains in South Africa showing the location of the Sterkspruit Complex near the town of Barkley East.
The Sterkspruit Complex
One of the best exposed volcanic complexes formed during explosive eruptions of the Karoo flood basalts is the Sterkspruit Complex, located in South Africa's Eastern Cape (Fig. 2). An area greater than 40 km2 was mapped at 1:10,000 scale over six months of 2002-03, with rock units differentiated on the basis of componentry, structure and texture. This geologic mapping delineated a large crater-complex surrounded by thick ash deposits. This work will quantify why early eruptions in the Sterkspruit complex were explosive but later ones gently effused lava flows, how individual vents within the crater-complex erupted, and how and how far ejecta was transported away from vents. I will examine the relative role of magmatic volatiles versus steam in driving explosivity, how single small craters coalesced to form very large composite craters, the intensity of eruptions, their discharge rate and the height and density of volcanic plumes. This project will combine the traditional techniques of thin section analysis, rock description and map-making with the more sophisticated techniques of microprobe analysis, x-ray diffraction and automated and manual image analysis. Initial results show that explosive volcanism there was of the same scale and intensity there as for similar volcanoes of the same age in Antarctica studied by other members of the University of Otago Geology Department.
3. Cartoon showing how the Sterkspruit Complex is inferred to have grown by coalescence of many small overlapping active centres to form a very large crater complex. Craters are filled with a mixture of rocks broken from crater walls, fragmented magma, blocks of lava and sediment washed or blown in during or after eruptions. From White & McClintock 2001
These explosive eruptions are important to our understanding of flood basalts, and volcanism overall, because (i) they represent the largest examples of explosive volcanism driven by the interaction of basaltic magma and water known; (ii) they form volcanoes larger and made up of a greater diversity of rocks than their closest analogues; (iii) they provide clues about the environment and landscape just prior to volcanism as the continents began to break apart; and (iv) their impact on the environment is potentially much greater than eruptions of lava, and any new information about them has relevance for models of past climates and mass extinctions. This study will contribute to this rapidly developing field by: (1) describing the range of volcanic, igneous and sedimentary rocks and their relationship to one another within one volcanic complex, thus achieving a realistic reconstruction of the ancient volcano they form; (2) testing and refining our current model of explosive eruptions during flood basalt volcanism, currently only based on Antarctic examples, so that we can decide which processes and landforms are applicable to all such eruptions, and which are site-specific; (3) providing quantitative data on processes of fragmentation, transport and deposition during explosive "wet" basaltic volcanism driven by magma-water interaction; and (4) evaluating how the injection of ash and aerosols such as sulphur and chlorine into the atmosphere impacted regional and global climate.
How is this work useful to society?
The ultimate goal of the proposed PhD project is to learn more about the violent eruptions that occur when magma is brought abruptly into contact with surface or underground water, so that volcanologists, government and emergency managers can better predict and react to future eruptions and mitigate their effects on society and property. New Zealand's largest and fourth largest cities are built on or close to active volcanic fields that have erupted less than 800 years ago (Auckland) and 120 years ago (Hamilton). As a consequence of our well-watered climate almost all recent eruptions in New Zealand have involved some magma-water interaction that increased their violence and far-field effects; well-known examples include Ruapehu (1995-96) , White Island (1976-82), Tarawera-Rotomahana (1886) and Taupo (181 AD). The eruption of Ruapehu in 1995-96 provides a useful example of the social and economic cost wrought by a fairly minor eruption even when the physical effects are limited to a small area around the volcano, ranging from shutting down skifields and crop damage to re-routing aircraft to avoid ash damaging their jet engines. Eruptions can have long-lived effects on society if loose, unstable debris can be remobilised by rain or, as is the present concern at Ruapehu, catastrophic flooding from a crater lake to form lahars (mudflows). Specific outcomes applicable to New Zealand problems include a better understanding of: (i) the plumbing system of basaltic volcanoes (such as those at Auckland and Tarawera); (ii) how magma and water come into contact and what the resulting mixture looks like before it explodes; (iii) how volcanic craters form and how crater size relates to eruption duration or the type of rock that it forms in; and (iv) how ejecta is transported away from vents, and how far it goes. Studying extinct volcanoes allows us to extract many of the details of the eruption from the volcano in safety – not always possible on active volcanoes – plus erosion allows us to see deep inside the volcano and study sites where explosions were taking place when the volcano was active. These physical studies have downstream social and economic benefits through reducing the impact of volcanic hazards on people and the impact of volcanic disasters on infrastructure and production.
4. Photo of part of the Sterkspruit Complex at Glengarry. The Sterkspruit River runs from right to left in the centre of the photo, with volcanic (black) and sedimentary (white) rocks exposed in the valley walls and layered lava forming hilltop plateaus.
5. Photo showing poorly sorted, polymict coarse lapilli tuff typical of the Sterkspruit Complex at Glengarry.
This PhD project dovetails neatly with studies of volcanoes in Antarctica by members of the University of Otago Geology Department, including the PhD work of Pierre-Simon Ross and the MSc work of Simone Hood Hills and Gillian Lockett. As well as Antarctica and South Africa, volcanology at Otago has involved work on ancient and active volcanoes in New Zealand, Hungary, USA, the Canary Islands, and Germany.
I am grateful to the landowners of the Barkley East district for permission to access the field area, and for the hospitality we enjoyed there. Sarah Sharp's cheerful field assistance is much appreciated. My participation in this study has been supported by Fulbright New Zealand, the NSF, the School of Ocean & Earth Science & Technology at the University of Hawaii and the University of Otago.
- McClintock, M. and White, J.D.L., 2005. Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP. Bulletin of Volcanology. DOI: 10.1007/s00445-005-0001-1
- Ross, P.S., Peate, I.U., McClintock, M.K., Xu, Y.G., Skilling, I.P., White, J.D.L. and Houghton, B.F., 2005. Mafic volcaniclastic deposits in flood basalt provinces: A review. Journal of Volcanology and Geothermal Research, 145(3-4): 281-314.
- McClintock, M., White, J.D.L., Houghton, B.F. and Skilling, I.P., in press. Physical volcanology of a large crater-complex within the Karoo flood basalt, Sterkspruit, South Africa. In: I.P. Skilling and J.D.L. White (Editors), Journal of Volcanology and Geothermal Research Special Issue on the Physical Volcanology of Large Igneous Provinces.
- Ross, P.-S., White, J.D.L. and McClintock, M., in press. Physical volcanology of mafic volcaniclastic deposits, lavas and intrusions in the Coombs-Allan Hills area, Ferrar large igneous province, Antarctica. In: I.P. Skilling and J.D.L. White (Editors), Journal of Volcanology and Geothermal Research Special Volume on the Physical Volcanology of Large Igneous Provinces.
- McClintock, M.K. & Cooper, A.F. (2003) Geochemistry, mineralogy and metamorphic history of kyanite-orthoamphibole-bearing Alpine Fault mylonite, South Westland, New Zealand. New Zealand Journal of Geology and Geophysics 46 1: 47-62
- McClintock, M.K. & White, J.D.L. (2002) Granulation of weak rock as a precursor to peperite formation: Coal peperite, Coombs Hills, Antarctica. Skilling, I., White, J.D.L., McPhie, J. (eds) Peperites: processes and products of magma-sediment mingling. Journal of Volcanology and Geothermal Research 114 1-2: 205-217
- White, J.D.L. & McClintock, M.K. (2001) Immense vent complex marks flood-basalt eruption in a wet, failed rift: Coombs Hills, Antarctica. Geology 29 10: 935-938
Conference abstracts (presentation type)
- McClintock, M.K., Houghton, B.F., Skilling, I.P. & White, J.D.L. (2003) Evolution of a Large-Volume Explosive Vent-Complex at the Base of the Karoo LIP: Sterkspruit Complex, South Africa. AGU Fall Meeting, San Francisco, USA. EOS Trans. AGU (oral)
- McClintock, M. K. (2003) The Volcaniclastic Initiation of Karoo Flood Basalt Volcanism. University of Hawai_i Tester Symposium, Honolulu, USA. Pacific Science (oral)
- McClintock M.K. & White, J.D.L. (2002b) Mawson Formation at Coombs Hills, Antarctica records conditions within a surtseyan vent complex. AGU Chapman Conference on Explosive Subaqueous Volcanism, Dunedin, NZ: 22 (oral)
- McClintock, M.K., Houghton, B.F., Skilling, I.P. & White, J.D.L. (2002) The volcaniclastic opening phase of Karoo flood basalt volcanism: Drakensberg Formation, South Africa. AGU Fall Meeting, San Francisco, USA. EOS Trans. AGU 83(47): F1445 (poster)
- McClintock M.K. (2000) Mawson Formation at Coombs Hills, Antarctica, records a novel phreatomagmatic precursor to supercontinent fragmentation. Geological Society of New Zealand, Wellington, NZ. GSNZ Misc. Pub. 108A: 99 (oral)
- McClintock, M.K. & White, J.D.L. (2000a) Phreatomagmatism at Coombs Hills, Antarctica: Large-scale laterally quarrying eruptions as a precursor to flood basalt volcanism. First International Maar Conference, Daun, Germany. Terra Nostra, 6: 336-341 (oral)
- McClintock M.K. & White, J.D.L. (2000b) Coombs Hills, Antarctica: Large scale lateral quarrying in a phreatomagmatic flood-basalt precursor eruption. AGU Western Pacific Geophysics Meeting, Tokyo, Japan: WP224
- White, J.D.L. & McClintock M.K. (2003) Mawson Fm., Ferrar Group, SW Allan Hills; deposits of large basaltic pyroclastic flows? New Zealand Antarctic Conference, Dunedin, NZ.
- White, J.D.L. & McClintock, M.K. (2000) Huge, shallow-seated root-zone deposit at Coombs Hills, Transantarctic Mountains, records a novel phreatomagmatic eruption style in the Ferrar LIP. AGU Fall Meeting, San Francisco, USA. EOS Trans. AGU: F1335
- McClintock, M.K., 2001. Phreatomagmatism at Coombs Hills, Antarctica: Magma-water super-volcanism in a wet, failed rift. Unpublished MSc thesis, Geology Department, University of Otago, New Zealand, 189 pp.
- McClintock, M.K., 1999. Makawhio Geology: Alpine Fault Zone structure and tectonometamorphic evolution, Makawhio River, South Westland. Unpublished BSc (Hons) thesis, Geology Department, University of Otago, New Zealand, 104 pp.
- McClintock, M., 2002. Digging for fire in the Drakensberg. Barkley East Reporter, 116(31): 6.