Are plumes predicted by realistic convection experiments and numerical situations? John Watson

Convection Experiments  Griffiths, RW – The differing effects of compositional and thermal buoyancies on the evolution of mantle diapirs  Laboratory experiment involving oils of different viscosities and temperature  Driving Forces for buoyancy INTRINSIC Vs TEMPERATURE  Entrainment Photograph taken from Campbell and Griffiths,. Implications of mantle plume structure for the evolution of flood basalts. Earth and plume structure for the evolution of flood basalts. Earth and Planetary Science letters, 99, 79-93

Convection Experiments part 2 Results of study  “Diapir convection is a function of the relative contributions of the two properties (intrinsic and temperature).”  Entrainment of surrounding material contributes to the driving forces.  Research leads onto the Griffiths and Campbell paper - Stirring and structure in mantle starting plumes

Convection Experiments part 3  A plume rises from the Core- Mantle-Boundary (CMB), via a “narrow conduit”, through which “buoyant liquid” flows.  Plume head spreads to 1000km in diameter until lithosphere causes the plume to spread laterally to around 2000km.  Cause of Flood Volcanism?  Diagram taken from P. Van Keken, Earth and planetary science letters, 148, 1997

Limitations of Convection experiments  Both these experiments and several others ignore PRESSURE as a parameter.  Griffiths et al state that the model cannot explain all hot-spot events.  Therefore the research cannot fully account for the original plume argument (Morgan, 1971).

Numerical and computer simulations  “Numerical simulations of plumes reproduce many of the geophysical observations.” (Courtillot et al, 2003) Picture taken from a.htm A Hotspot Alternative. The rise of a surface- related explanation is turning things upside down

Numerical and computer simulations part 2  Ribe, NM and Christensen UR – The dynamical origin of Hawaiian volcanism.  A model for eruption rate predictions and timing of volcanism.  Model ASSUMES plume model based on “surface signatures” e.g.;  The swell under Hawaii, Geoid anomaly  Flexural arch produced by loading of the elastic lithosphere

Numerical and computer simulations part 3  Tarduno et al – The Emperor Seamounts: southward motion of the Hawaiian hot-spot plume in Earth’s mantle.  Based around computer modelling of lithology inclination values from three seamounts from the chain.  Results are inconsistent with a fixed plume model.  Hypothesis: plume has remained fixed, but asthenospheric channelling of the plume alters course of the conduit, leading to bend in the Emperor chain.

Numerical and computer simulations part 4  Inclinations show a South/South-East motion of ° during the last 100myrs.  PROBLEM – no evidence in this paper for alteration of the plume conduit

Conclusions  Neither Convection experiments or Numerical simulations can prove Morgan's theory.  Key parameters overlooked.  The studies assume that their models are realistic when compared to actual mantle conditions.