Emplacement of channeled flows in subaerial, submarine, simulated, and extraterrestrial environments.

摘要

Channeled lava flows are observed in a range of volcanic environments including shield volcanoes in Hawai'i, in submarine lava flows along mid-ocean ridges, and on the flanks of volcanoes in the Tharsis Region on Mars. Observations of the final channel morphology are a primary means for interpreting how the lava flow was emplaced, including rheologic properties of the lava, effusion rates, and eruption duration. To better understand the emplacement of lava flows, I performed laboratory simulations using polyethylene glycol wax (PEG). These channeled flows reflect a range of compositions (PEG, basalt, dacite), lengths (centimeters to kilometers), and emplacement durations (minutes to years). I find that all the flows show a downstream change in morphology, consistent with morphologic zones (stable, transitional, zone of dispersed flow, flow toe) described by Lipman and Banks [1987] regardless of scale or composition. Lava channels in the extraterrestrial environments can have greater dimensions than terrestrial flows. One particular channeled lava flow near Ascraeus Mons volcano on Mars is 690 km long. I analyze this Ascraeus Mons flow using high-resolution (4.5 to 32 m/pixel) images from Mars Orbiter Camera (MOC) and Thermal Emissions Imaging System (THEMIS) and elevation data from the Mars Orbiter Laser Altimeter (MOLA). I calculate a minimum effusion rate of 19,000--29,000 m3/s from the Graetz number and durations of ∼100--250 days assuming constant flow rates and a continuous eruption. Textures that form in channeled PEG flows are similar to textures observed in submarine channeled lava flows along the East Pacific Rise (9°--10°N). Channeled PEG flows consistently display the following surface textures in the channel: smooth, folded, lineated, and chaotic, which are analogous to smooth, folded, lineated, and jumbled textures in submarine channels. Observations of the formation of surface textures in the PEG channels are applied to the formation of textures in submarine lava channels. I mapped the surface textures preserved in the final flow morphology of 10 channeled PEG flows and 9 submarine lava channels. (Abstract shortened by UMI.)