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| Titel |
Tube pumice kinematics using neutron tomography |
| VerfasserIn |
Asher Flaws, Kai-Uwe Hess, Donald B. Dingwell, Dominique Richard, Joan Martí |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039087
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| Zusammenfassung |
| Volume imaging using neutron computed tomography (NCT) offers a new window into
rheological processes and their kinematic consequences. In the past, the penetration power of
neutron scanning has been offset by its relatively poor resolution (order 1 mm). However, the
recent development of new scintillators has improved this resolution by almost an order of
magnitude to a voxel size of 20 μm (a range which is now useful for the geosciences). This
resolution, coupled with the penetration depth and good contrast of NCT imaging, makes this
an attractive method for large (order 1 to 10 cm) geomaterial samples. Here we quantitately
analysed the properties of bubbles in a tube pumice. The bubbles were isolated and
characterised by a purpose built software package. The resulting object database was then
tested against models of pure and simple shear. An analysis of the azimuthal variation in
maximum axis length perpendicular to the tube elongation reveals that simple shear is the
primary deformation. From the distribution of bubble shapes and sizes we were
able to infer the shear rate of the flow immediately prior to fragmentation, and
the cooling rate / internal heat transport of the pumice after fragmentation. The
method also provides an estimate of the post-fragmentational relaxation time. Further,
the 3-D imaging reveals that the curvature of the lineation provided by the tubes
is significant. The extraction of neutron tomographic data on these witnesses of
extreme volcanic fragmentation processes promises to provide new and uniques
insights into the conditions of explosive volcanic processes in the years to come. |
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