Eruption
#2
Exp #89 in Zhang et al. (1997, J. Geophys. Res.,
102, 3077)
The movie shows the slow motion of the experiment
by a factor of 133. This is a close-up view of the eruption front.
The whole height is only 2.6 cm. Initial test cell pressure was 5
bar, and tank pressure was 0.11 bar. A polymer was added so that
the viscosity is 18 times that of water (18 millipascal-second).
You can see the oscillation of the front at the beginning of the experiment
due to shock wave reflection. Only in such close-up views, are individual
bubbles clearly distinguishable. Almost all bubbles appear at the
same time. That is, bubble nucleation is “instantaneous”, lasting
only ~ 1 ms. Very few bubbles form before or after this event.
This is confirmed by the similar size of the bubbles. Bubble growth
data were obtained from such experiments. Even though there is a
rapid vertical flow, bubbles are not stretched vertically. A nice
foam forms and is stable. You may think that there are bubbles inside
bubbles. These are actually bubbles behind bubbles. You can
see that bubbles near the center rise more rapidly than bubbles near the
wall. Near the end of the film, there is some coalescence.
A foam is defined as a bubbly liquid in which the bubbles occupy
more than 74% of the volume (i.e., the vesicularity is greater than 74%).
In a foam, the liquid is the continuous phase and the gas is not, even
though gas bubbles account for most of the volume. Greater than this
vesicularity, spherical bubbles have to deform into polygonal surfaces
in order not to break. The deformation of spherical bubbles to polyhedral
bubbles accounts for the honeycomb appearance of the foam.
Eruption
#3
Exp #90 in Zhang et al. (1997, J. Geophys. Res.,
102, 3077)
The movie shows the slow motion of the experiment
by a factor of 133. This shows again a close-up view of the eruption
front. A polymer was added but the viscosity is only 5 times that
of water (5 millipascal-second). Initial test cell pressure was 5.2
bar, and tank pressure was 0.07 bar. There was a foam layer on top
of the liquid column before the experiment, simulating the case of a magma
chamber with a top bubble-rich layer. Because of this bubbly layer,
the eruption starts very violently. Individual bubbles can be seen
clearly and bubble growth data were obtained. Bubbles are nicely
spherical and not stretched vertically. A foam forms but is not very
stable.
More?
The original video tape with six eruption experiments is deposited
with American Geophysical Union Publication Office. To obtain a copy,
please call 1-800-966-2481, or send your request (indicate production code:
96JB0318V) with a US $25 payment (payment must accompany order; more payment
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