HR: 0830h
AN: V51E-0331    [PDF]
TI: Do the fractal dimensions of evolved lava-flow margins distinguish endogenous and exogenous growth?
AU: * Semple, A M
EM: amsemple@acsu.buffalo.edu
AF: University at Buffalo, Dept of Geology, 876 NSC, Buffalo, NY 14260-3050 United States
AU: Gregg, T K
EM: tgregg@geology.buffalo.edu
AF: University at Buffalo, Dept of Geology, 876 NSC, Buffalo, NY 14260-3050 United States
AB: Although there are recorded observations of active dacitic domes at Mount St. Helens, Soufriere, St. Vincent and Santiaguito, there is as yet no direct observation of an active rhyolite flow, dome or coulee. Thus, we must use numerical models and/or laboratory simulations to constrain the emplacement of evolved lavas. We have used fractals to describe the planforms of evolved flows and domes (both naturally occurring and simulated laboratory flows) in an attempt to quantify their emplacement styles. Bruno et al. [1994] used fractal analysis of basaltic lava flow margins and determined that a\'{ }a flows correspond to a fractal dimension (D) of 1.05-1.09 and pahoehoe flow margins display D = 1.13-1.23. Based on only a few examples, they concluded that evolved flow margins are not fractal. However, only a small number of evolved flows were examined and these were emplaced on relatively steep ($>$5$\deg$) slopes. More recently it has been suggested that the D ranges allocated to a\'{ }a and pahoehoe actually describe simple or complex emplacement, respectively. We have measured aerial images of evolved lava flows in the Cascades, the Inyo domes and the Andean Central Volcanic Zone to test the hypothesis that D values for lava flow margins reflect emplacement style rather than surface morphology. Preliminary results indicate that some evolved flows and domes do indeed exhibit a fractal behavior. A flow margin is determined to show fractal behavior if the R$^{2}$ value calculated on a Richardson plot of the margin is $>$0.95. The flows/domes that do exhibit fractal behavior fall within the range of 1.055 and 1.097. This range is almost identical to that of the simple flow emplacement (a\'{ }a-like), which may be indictative of endogenous (rather than exogenous) growth. Analyses of simulated flows in the laboratory will be used to further test this hypothesis.
DE: 5480 Volcanism (8450)
DE: 8400 VOLCANOLOGY
DE: 8429 Lava rheology and morphology
DE: 8450 Planetary volcanism (5480)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting