HR: 0830h
AN: NG11A-0166 [PDF]
TI: Visualiztion of Viscous Heating in the Earth's Mantle
Induced by Glacial Loading
AU: Hanyk, L
EM: lh@karel.troja.mff.cuni.cz
AF: Dept. of Geophysics, Faculty of Physics
Charles Univrersity, Prague, 18000
Czech Republic
AU: Matyska, R
EM: cm@karel.troja.mff.cuni.cz
AF: Dept. of Geophysics, Faculty of Physics
Charles Univrersity, Prague, 18000
Czech Republic
AU: Yuen, D A
EM: davey@msi.umn.edu
AF: Minnesota Supercomputing Institute and Dept. of Geology and Geophysics, University of Minnesota,
Minneapolis, MN 55455 United States
AU: * Kadlec, B J
EM: kadlec@msi.umn.edu
AF: Minnesota Supercomputing Institute and Dept. of Geology and Geophysics, University of Minnesota,
Minneapolis, MN 55455 United States
AB:
We have studied the a possible mechanism of transferring gravitational
potential
energy into viscous heating in the mantle via glacial loading during the
ice ages. Shear heating associated with the transient flow occurring
over a short timescale on the order of tens of thousand of years can cause
a non-negligible amount of heat production in the mantle.
We have applied our initial-value approach to the modelling of viscoelastic
relaxation of spherical compressible self-gravitating Earth models
with a linear viscoelastic Maxwellian rheology.
We have focussed on the magnitude of deformations, stress tensor
components and corresponding dissipative heating for ice sheets of the size
of the Laurentide ice mass and cyclic loading with a fast unloading phase
two orders of magnitude less than that associated with mountain building
and vertical tectonics.
Much to our surprise, we have found that this kind of
internal heating can represent
a non-negligible internal energy source with, however, an exogenic origin.
The volumetric heating by this fast rate of deformation can be locally higher than
the chondritic radiogenic heating during peak events with short timescales.
In the presence of an abrupt change in the ice-loading,
its time average of the integral over the depth corresponds
to equivalent mantle heat flow of the order of magnitude
of milliwatts per m$^2$ below the periphery of ancient glaciers
or below their central areas.
However, peak heat-flow values in time are almost by about two orders
higher.
On the other hand, nonlinear rheological models can potentially increase
the magnitude of localized viscous heating.
To illustrate the spatial distribution of the viscous heating
for various Earth and glacier models,
we have employed the powerful 3-D visualization system Amira.
( www.amiravis.com ). With this type of data format we can
animate very easily the temporal evolution of the data
fields on a moving curvilinear mesh, which spreads
over outer and inner mantle boundaries and mantle cross-sections.
Amira movies can reveal the complex nature of
dissipative heating of the PREM model with a lower-mantle viscosity hill
at the end of the recent Pleistocene ice age. This viscoelastic model can be
employed in other dynamical situations with fast dynamical timescales, such
as the aftermath of a meteoritic impact or other global cryospheric events.
UR: http://www.amiravis.com
DE: 3210 Modeling
SC: Nonlinear Geophysics [NG]
MN: 2003 Fall Meeting