Clint Conrad
Associate Professor


Office: Post 804
Phone: 808-956-6649
Fax: 808-956-5152
E-mail: clintc@hawaii.edu

Department of Geology and Geophysics
SOEST, University of Hawaii
1680 East-West Road
Honolulu, Hawaii 96822


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Conrad Group Research Topics

My research program is primarily directed toward gaining a better understanding of the dynamics of Earth's interior and surface, but this effort has led in several different directions. Below I describe some of the topics that have interested members of my research group lately.


Exoplanets

ExoplanetsRecent astronomical observations have detected planets orbiting stars outside of our solar system. Many of these planets have sizes, densities, compositions, and temperatures that distinguish them from any known bodies in our own solar system. Thus, these "exoplanets" are likely to host planetary processes that have never been previously considered. Our work has contributed to undestanding how convection within exoplanet mantles may affect plate tectonics, geodynamos, and volcanism on these planets.
  1. van Summeren‡, J., C.P. Conrad, and E. Gaidos, Mantle convection, plate tectonics, and volcanism on hot exo-Earths, The Astrophysical Journal Letters, 736, L15, 2011. [online version] [reprint]
  2. Gaidos, E., C.P. Conrad, M. Manga, and J. Hernlund, Thermodynamic limits on magnetodynamos in rocky exoplanets, Astrophysical Journal, 718, 596-609, 2010. [online version] [reprint]

Sea Level and the Solid Earth

Sea Level and the Solid EarthSea level change is one of the more dramatic consequences of modern-day climate change, and has periodically transgressed and regress from continental boundaries in the geologic record. The solid earth influeces sea level change on timescales ranging from decades to billions of years. On the shortest timescales, redistributions of water loads on the Earth's surface cause elastic and viscous deflections of the earth's solid surface as well as gravitational deflections of the sea surface. These deflections affect sea level locally but can also change global sea level. On timescales of millions of years and longer, the volume of the ocean basins (and thus sea level) can change due to variations in seafloor spreading rates, ocean area, sediment cover, seafloor volcanism, and dynamic deflection of the seafloor. Our work has helped to constrain the relative importance of several of these sea level change mechanisms.
  1. Ruban, D., C.P. Conrad, and A.J. van Loon, The challenge of reconstructing the Phanerozoic sea level and the Pacific Basin tectonics, Geologos, 16, 237-245, 2010. [online version] [reprint]
  2. Ruban, D., S. Zorina, and C.P. Conrad, No global-scale transgressive-regressive cycles in the Thanetian (Paleocene): evidence from interregional correlation, Palaeogeography Palaeoclimatology Palaeoecology, 295, 226-235, 2010. [online version] [reprint]
  3. Fiedler§, J.W., and C.P. Conrad, Spatial variability of sea level rise due to water impoundment behind dams, Geophysical Research Letters, L12603, doi:10.1029/2010GL043462, 2010. [online version] [reprint] [highlighted in Nature] [response model]
  4. Conrad, C.P., and L. Husson, Influence of dynamic topography on sea level and its rate of change, Lithosphere, 1, 110-120, 2009. [online version] [reprint]
  5. Husson, L., and C.P. Conrad, Tectonic velocities, dynamic topography, and relative sea level, Geophysical Research Letters, 33, L18303, doi:10.1029/2006GL026834, 2006. [online version] [reprint]
  6. Xu, X., C. Lithgow-Bertelloni, and C.P. Conrad, Global reconstructions of Cenozoic seafloor ages: Implications for bathymetry and sea level, Earth and Planetary Science Letters, 243, 552-564, 2006. [online version] [reprint]
  7. Conrad, C.P., and B.H. Hager, Spatial variations in the rate of sea level rise caused by the present-day melting of glaciers and ice sheets, Geophysical Research Letters, 24, 1503-1506, 1997. [online version] [reprint]
  8. Conrad, C.P., and B.H. Hager, The elastic response of the earth to interannual variations in Antarctic precipitation, Geophysical Research Letters, 22, 3183-3186, 1995. [online version] [reprint]

Intraplate Volcanism and the Shear-Driven Upwelling

Intraplate Volcanism and the Shear-Driven Upwelling

Several mechanisms have been proposed to explain volcanism occurring away from tectonic plate boundaries. Although mantle plumes may produce most of the high-volume intraplate volcanism (e.g., Hawaii), low-volume examples likely require an alternative explanation. We have proposed a new mechanism: The "shear-driven upwelling" (SDU), in which mantle upwelling is driven by the action of asthenospheric shear on viscosity heterogeneity (either "topography" on the base of the lithosphere, or a low-viscosity "pocket" embedded within the asthenosphere). The energy for this upwelling arises from global mantle flow (which induces asthenospheric shear), rather than local density heterogeneity. We have shown that SDU can drive upwelling sufficient to induce low-volume basaltic volcanism with a surface expression that is distinct from that of hotspots. We have also shown that regions of the asthenosphere that are shearing rapidly also tend to have higher rates of intraplate volcanism.

  1. Conrad, C.P., T.A. Bianco‡, E.I. Smith, and P. Wessel, Patterns of intraplate volcanism controlled by asthenospheric shear, Nature Geoscience, 4, 317-321, 2011. [online version] [reprint] [online supplement] [news & views]
  2. Conrad, C.P., B. Wu†, E.I. Smith, T.A. Bianco‡, and A. Tibbetts, Shear-driven upwelling induced by lateral viscosity variations and asthenospheric shear: A mechanism for intraplate volcanism, Physics of the Earth and Planetary Interiors, 178, 162-175, 2010. [online version] [reprint] [highlighted in Nature Geoscience] [summary on MantlePlumes.org]
  3. Smith, E.I., C.P. Conrad, T. Plank, A. Tibbetts, and D. Keenan, Testing models for basaltic volcanism: implications for Yucca Mountain, Nevada, American Nuclear Society, Proceedings of the 12th International High-Level Radioactive Waste Management Conference, 157-164, 2008. [printed version] [reprint]

Dynamics and Tectonics of Earth's Lithosphere

Dynamics and Tectonics of Earth's LithosphereEarth's lithosphere moves and deforms in response to the stresses exerted on it by topographic loads, tectonic forces, and viscous coupling to convective processes occurring in the underlying mantle. The dynamics of the lithosphere in turn influence mantle heat flow, plate motions, and a variety of tectonic processes such as mountain building. Our work has examined the interaction between lithospheric tectonics and mantle dynamics, and has constrained this interaction using a variety of geological and geophysical observations.
  1. Naliboff, J.B., C.P. Conrad, and C. Lithgow-Bertelloni, Modification of the Lithospheric Stress Field by Lateral Variations in Plate-Mantle Coupling, Geophysical Research Letters, 36, L22307, doi:10.1029/2009GL040484, 2009. [online version] [reprint] [AGU journal highlight in EOS]
  2. Cooper, C.M., and C.P. Conrad, Does the mantle control the maximum thickness of cratons?, Lithosphere, 1, 67-72, 2009. [online version] [erratum] [reprint]
  3. Becker, T.W., C.P. Conrad, B. Buffett, and R.D. Müller, Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport, Earth and Planetary Science Letters, 278, 233-242, 2009. [online version] [reprint]
  4. Meade, B.J., and C.P. Conrad, Andean growth and the deceleration of South American subduction: Time evolution of a coupled orogen-subduction system, Earth and Planetary Science Letters, 275, 93-101, 2008. [online version] [reprint] [Discovery Channel Article] [highlight in Nature Geoscience]
  5. Husson, L., C.P. Conrad, and C. Faccenna, Tethyan closure, Andean orogeny, and westward drift of the Pacific basin, Earth and Planetary Science Letters, 271, 303-310, 2008. [online version] [reprint] [highlight in Nature Geoscience]
  6. Loyd, S.J., T.W. Becker, C.P. Conrad, C. Lithgow-Bertelloni, and F.A. Corsetti, Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for Earth's thermal evolution, Proceedings of the National Academy of Sciences, 104, 14266-14271, 2007. [online version] [reprint] [Geology Times article]
  7. Conrad, C.P., and C. Lithgow-Bertelloni, Faster seafloor spreading and lithosphere production during the mid-Cenozoic, Geology, 35, 29-32, 2007. [online version] [reprint] [highlight in Nature] [spreading rate data]
  8. Conrad, C.P., and C. Lithgow-Bertelloni, Influence of continental roots and asthenosphere on plate-mantle coupling, Geophysical Research Letters, 33, L05312, doi:10.1029/2005GL025621, 2006. [online version] [reprint] [lithosphere thickness model]

Observations of Global Mantle Flow

Observations of Global Mantle FlowViscous flow within the Earth's mantle ultimately drives plate tectonics and most of the time-dependent geological deformation that we observe at the Earth's surface. Seismic constraints on mantle structure, coupled with improved computational abilities, have allowed us to constrain patterns of flow presently occurring in the Earth's mantle. My research group has been constraining such models of global mantle flow using various geological and geophysical observations. This effort has led to a greater understanding of how surface tectonic and mantle dynamics interact to drive geological deformation and modulate mantle convection.
  1. Conrad, C.P., and M.D. Behn, Constraints on lithosphere net rotation and asthenospheric viscosity from global mantle flow models and seismic anisotropy, Geochemistry Geophysics Geosystems, 11, Q05W05, doi:10.1029/2009GC002970, 2010. [online version] [reprint] [theme issue] [mantle flow model]
  2. Métivier‡, L., and C.P. Conrad, Body tides of a convecting, laterally heterogeneous, and aspherical Earth, Journal of Geophysical Research, 113, B11405, doi:10.1029/2007JB005448, 2008. [online version] [reprint] [auxiliary material]
  3. Conrad, C.P., M.D. Behn, and P.G. Silver, Global mantle flow and the development of seismic anisotropy: Differences between the oceanic and continental upper mantle, Journal of Geophysical Research, 112, B07317, doi:10.1029/2006JB004608, 2007. [online version] [reprint] [auxiliary material] [flow model and anisotropy code]
  4. Steiner†, S.A., and C.P. Conrad, Does active mantle upwelling help drive plate motions?, Physics of the Earth and Planetary Interiors, 161, 103-114, 2007. [online version] [reprint]
  5. Conrad, C.P., C. Lithgow-Bertelloni, and K.E. Louden, Iceland, the Farallon slab, and dynamic topography of the North Atlantic, Geology, 32, 177-180, 2004. [online version] [reprint]
  6. Behn, M.D., C.P. Conrad, and P.G. Silver, Detection of upper mantle flow associated with the African superplume, Earth and Planetary Science Letters, 224, 259-274, 2004. [online version] [reprint]
  7. Conrad, C.P., and M. Gurnis, Mantle flow, seismic tomography and the breakup of Gondwanaland: Integrating mantle convection backwards in time, Geochemistry Geophysics Geosystems, 4, 1031, doi:10.1029/2001GC000299, 2003. [online version] [reprint]

Plate Tectonics and Subduction

Plate Tectonics and SubductionPlate subduction is one of the key processes that facilitates plate tectonics on Earth. By linking models of subduction to numerical models of plate motions and mantle flow, we have developed new constraints on the interaction between plate motions and subduction. In particular, we have shown that subducting slabs provide the largest driving force for plate tectonics, and couple to plate motions both directly (via guiding stresses transmitted within the slab) and indirectly (by inducing mantle flow that pushes on the base of plates).
  1. Wu†, B., C.P. Conrad, and A. Heuret, C. Lithgow-Bertelloni, and S. Lallemand, Reconciling strong slab pull and weak plate bending: The plate motion constraint on the strength of mantle slabs, Earth and Planetary Science Letters, 272, 412-421, 2008. [online version] [reprint] [table 1]
  2. Jahren, H.J., C.P. Conrad, N.C. Arens, G. Mora, and C. Lithgow-Bertelloni, A plate tectonic mechanism for methane hydrate release along subduction zones, Earth and Planetary Science Letters, 236, 691-704, 2005. [online version] [reprint]
  3. Conrad, C.P., and C. Lithgow-Bertelloni, The temporal evolution of plate driving forces: Importance of "slab suction" versus "slab pull" during the Cenozoic, Journal of Geophysical Research, 109, B10407, doi:10.1029/2004JB002991, 2004. [online version] [reprint]
  4. Conrad, C.P., and C. Lithgow-Bertelloni, How mantle slabs drive plate tectonics, Science, 298, 207-209, 2002. [online version] [reprint] [online supplement] [U. Michigan press release] [Geotimes article]
  5. Conrad, C.P., and B.H. Hager, Mantle convection with strong subduction zones, Geophysical Journal International, 144, 271-288, 2001. [online version] [reprint]
  6. Conrad, C.P., and B.H. Hager, Effects of plate bending and fault strength at subduction zones on plate dynamics, Journal of Geophysical Research, 104, 17551-17571, 1999. [online version] [reprint]
  7. Conrad, C.P., and B.H. Hager, The thermal evolution of an earth with strong subduction zones, Geophysical Research Letters, 26, 3041-3044, 1999. [online version] [reprint]

Patterns of Global Seismicity

Patterns of Global Seismicity Earthquakes represent brittle deformation of the Earth's lithosphere in response to imposed stresses. Thus, observations of spatial and temporal patterns of seismicity can tell us something about lithospheric stresses. We have used observations of the timing and location of earthquakes to constrain the importance of tidal and tectonics stresses for lithospheric deformation. In particular, we have shown that earthquakes are slightly more common during certain phases of the earth tides, and that both large and deep subduction zone earthquakes are correlated to the tectonic environment at the subduction zone.
  1. Métivier‡, L., O. de Viron, C.P. Conrad, S. Renault, M. Diament, and G. Patau, Evidence of earthquake triggering by the solid earth tides, Earth and Planetary Science Letters, 278, 370-375, 2009. [online version] [reprint] [New Scientist Article] [Geo.de Article (in German)] [Johns Hopkins News-Letter] [MSNBC-Discovery]
  2. Bilek, S.L., C.P. Conrad, and C. Lithgow-Bertelloni, Slab pull, slab weakening, and their relation to deep intra-slab seismicity, Geophysical Research Letters, 32, L14305, doi:10.1029/2005GL022922, 2005. [online version] [reprint]
  3. Conrad, C.P., S. Bilek, and C. Lithgow-Bertelloni, Great earthquakes and slab pull: interaction between seismic coupling and plate-slab coupling, Earth and Planetary Science Letters, 218, 109-122, 2004. [online version] [reprint]

Convective Instability

Convective Instability The upper and lower boundary layers to convection are gravitationally unstable. As a result, small-scale convective instability can develop on either boundary layer. For the top boundary layer, this instability takes the form of "drips" that descend from the dense lithosphere into the hotter mantle. This processes can remove the lower mantle lithosphere and ultimately lead to surface uplift and volcanism. For the lower bounary layer, this instability produces "plumes" that rise from the core-mantle-boundary and can eventually reach the surface, producing volcanism. We have investigated the fluid dynamics of both types of instability, and related them to observations of lithospheric drips and mantle plumes on Earth.
  1. Lithgow-Bertelloni, C., M.A. Richards, C.P. Conrad, and R.W. Griffiths, Plume generation in natural and thermal convection at high Rayleigh and Prandtl numbers, Journal of Fluid Mechanics, 434, 1-21, 2001. [online version] [reprint]
  2. Conrad, C.P., Convective instability of thickening mantle lithosphere, Geophysical Journal International, 143, 52-70, 2000. [online version] [reprint]
  3. Conrad, C.P., and P. Molnar, Convective instability of a boundary layer with temperature- and strain-rate-dependent viscosity in terms of "available buoyancy", Geophysical Journal International, 139, 51-68, 1999. [online version] [reprint]
  4. Molnar, P., G.A. Houseman, and C.P. Conrad, Rayleigh-Taylor instability and convective thinning of mechanically thickened lithosphere: Effects of non-linear viscosity decreasing exponentially with depth and of horizontal shortening of the layer, Geophysical Journal International, 133, 568-584, 1998. [online version] [reprint]
  5. Conrad, C.P., and P. Molnar, The growth of Rayleigh-Taylor-type instabilities in the lithosphere for various rheological and density structures, Geophysical Journal International, 129, 95-112, 1997. [online version] [reprint]
§ an undergraduate student working in my research group
† a graduate student working in my research group
‡ a postdoctoral scholar working in my research group