This figure shows a model of a mantle plume in spherical axisymmetric geometry,
created using the finite-element model SCAM. The axis of symmetry runs
along the center of the plot. Contours are temperature. Colors indicate
radial velocity. More intense colors denote higher velocity. Red denotes
radial outward flow; blue denotes inward flow.
What is a mantle plume?
In 1971, W. J. Morgan suggested that intraplate volcanism such as
the hotspot at Hawaii derives from hot upwelling plumes in the
mantle. Our current understanding of the mantle suggests that
convection takes the form of subducting plates and upwelling,
approximately axisymmetric plumes. According to this model, hotspots
are the surface manifestation of mantle plumes. In terms of heat flow,
plumes are relatively minor; Davis (1988) and Sleep (1990) used the
topography and gravity anomalies associated with hot-spots to estimate
that actively upwelling mantle plumes account for about 10% of the
total heat loss of the Earth.
Nevertheless, the hotspots are of interest, because they have given
us such geological features as Hawaii, Iceland, Yellowstone, etc.
In addition, plumes may be an important mechanism for heat transfer
from the interior of Venus.
Some open questions about plumes
- Where do plumes come from?
The source of mantle plumes remains a matter of considerable debate. A
widely accepted picture is that in the Earth's mantle, a hot thermal plume
originates as an instability at a thermal boundary layer, forming a large
mushroom-shaped head as it grows. This head eventually rises from the boundary
layer followed by a narrow tail. These tails probably take the form of
pipe-like features that are less than a few hundred kilometers in diameter,
probably just barely detectable by seismic methods in a few specific favorable
- What do plumes look like as they rise?
Lab and numerical models suggest that plumes may start out with large,
mushroom-like heads followed by narrow tails. These "mushroom heads"
have been associated with flood basalts by a number of investigators. However,
this model is far from complete; development of a plume head depends on
just the right combination of plume rheology, thermal entrainment, etc.
- How do plumes interact with the lithosphere?
Plume modeling at U.C. Davis
We are looking at these and other questions using numerical models of
mantle plumes. Recent and ongoing work includes:
- Using a combination of numerical simulations and geochemical
studies to determine how plumes interact with a spreading center - for
instance, at Iceland and the Galapagos Islands (Feighner et al, 1995;
Fram et al., AGU abstract, Fall 1996, and paper in preparation). Click
here for a recent AGU abstract on this subject.
- Determining how the temperature-dependent rheology of plumes
creates a large, but anomalously cool, plume head if the plume rises
from the core-mantle boundary (Kellogg and King, EPSL, 1997).
- Examining how plumes behave through time using a spherical,
axisymmetric finite-element model and examining how the geoid and
topography evolve through time. For more information, click
here or perhaps you'd like to
view the color figures from our recent paper on this research
(Kiefer and Kellogg, PEPI, 1998)