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If a movie is not displayed, please use the links in the caption to download it to your computer.
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Movie 1. The
solution with small mass source intensity M0=30 m/yr (no
ice-stream). The large panel on the right shows the velocity field
(colors represent dimensionless speed), the top-left panel shows
v(x,y=0.5), and the lower-left panel shows the total mass source
influx (blue) and the total mass out-flux (magenta) across y=0.5. This
mass source is too weak to drive the flow across the bottom
shear-stress threshold (&tauc1) and therefore the velocity
is everywhere lower than vc1. The total outflow mass flux
converges to the value of the total influx within ~1000 years and the
flow settles in a steady state.
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Movie 2. The
solution with large mass source intensity, M0=150 m/yr
(steady ice-stream). Panels are described in the caption of Movie 1.
A wide stream-like pattern is formed near the mass source, and
advances downstream. The shear-margins then converge towards the
stream center until a steady pattern of ice-stream is reached within 15-20 years.
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Movie 3. The
solution with intermediate mass source intensity, M0=100
m/yr (relaxation-oscillation). Panels are described in the caption of
Movie 1. A stream-like pattern is formed near the mass source, and
advances downstream as the stream margins move away from the center
(x=0.5). The margins then converge back towards the stream center, and
the outflow mass flux declines simultaneously. The distance between
the margins declines significantly so that they overlap. Consequently,
the stream pattern collapses to a no-stream flow (time=~6.5 years) and
a new cycle initiates. The motion of the shear-margins with respect to the ice-stream
center (x=0.5) is related to the presence of ice thickness gradients,
as explained in the text.
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Movie 4. The
solution with intermediate mass source intensity, M0=100
m/yr (relaxation-oscillation-mode). Top panel shows the thickness
field, h(x,y) (aspect ratio 1:140) and lower panel shows the velocity
field (u,v) as in Movie 3. This shows how the evolution in the
thickness distribution and the velocity are coupled. The flow
accelerate as the ice surface slopes increase upstream. At t=3 years,
a stream-pattern is formed and the out-flow mass flux sharply
inclines. As a result, the ice thickness diminishes rapidly, and the
slopes get smoothed. Once the stream collapses, surface slopes build
up again up-stream, driving a new cycle.
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© 2008 Cambridge University Press