Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.v31d..02g&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #V31D-02
Mathematics
Logic
8400 Volcanology, 8429 Lava Rheology And Morphology, 8450 Planetary Volcanism (5480)
Scientific paper
Observations of active basalt, dacite, and polyethylene glycol (PEG) flows suggest that the channel-forming process is similar through various scales and is independent of composition. Specifically, analysis of subaerial and simulated flows shows the systematic formation of channel zones (stable, transitional, zone of dispersed flow), as described by Lipman and Banks [1987] to characterize a 27 km-long a'a channel from the 1984 Mauna Loa (MLV), Hawaii eruption, are observed in all viscous fluid channels. A channelized dacite flow, emplaced from 1999-2002 on Santiaguito volcano (SV), Guatemala, displays similar downstream transitions in structure and morphology along its 3.75 km flow length. We observed the formation of these zones in meter-scale pahoehoe breakouts in active flows from the Pu'u O'o Mother's Day flow in 2002-2003, and in solidified flows from Mauna Ulu, Kilauea volcano (KV), Hawaii. Controlled laboratory simulations produce the structural and morphologic zones on the centimeter-scale (< 70 cm long) as warm PEG (22-24 ° C) is emplaced into a cold sucrose solution (6-12 ° C) on a range of underlying slopes (8-30° ). As an initial comparison, we measured the fraction of the flow length characterized by the stable, transitional, and zone of dispersed flow for MLV, SV, KV, and PEG flows. The stable zone dominates kilometer-scale flows, covering the majority of the flow length for MLV (0.49) and SV (0.64). Pahoehoe breakouts on Mauna Ulu have a lower range for stable zones of 0.25-0.49, while in PEG flows <0.28 of the flow length is stable. The fraction of flow contained within the transitional zone varies, with meter-, and kilometer-long flows ranging from 0.13-0.31, whereas PEG flows are >0.30 of the flow. The zone of dispersed flow dominates the flow length on centimeter- (>0.40) and meter-scale (0.25-0.54) flows, but is much less (0.20) of the flow length for MLV and SV. The time-scales for the emplacement of the channels ranges from minutes for PEG and pahoehoe breakouts, weeks for the a'a channel on MLV, to years for the dacitic flow on SV, yet each channel displays the same systematic downstream variation in morphology. The fraction of flow-length characterized by each zone at various length-scales may be attributed to the timescale of the eruptions, whereas longer emplacement times allow for maturity of the stable and transition zones downstream. To better understand the fundamental similarities of channel formation in the solar system, we will continue to analyze lava channels on greater length-scales (100's km), and in various environments including Venus, Mars, and Io.
Garry Brent W.
Gregg T. K.
Harris Jessica A.
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