Ionian Paterae: New Insights from Observations, Numerical Modeling and Laboratory Simulations

To constrain the behavior of Ionian volcanic paterae in general, and Loki Patera in particular, we have used the following techniques in concert: 1) geologic mapping and analyses; 2) laboratory simulations; and 3) mathematical modeling. Here, we present preliminary results from the synthesis of these data. Loki Patera (310°W, 12°°N) is significantly different from the rest of the Ionian paterae for the following reasons: 1) its surface area falls 6 s outside the range for other Ionian paterae; 2) it is the only patera containing a bright "island" that is cut by dark lineaments; 3) at times of a thermal brightening event, it emits up to 15% of Io's global heat flux. Debate continues over whether Loki Paterae is an overturning lava lake, or a depression whose floor is periodically resurfaced by lava flows. Laboratory simulations, in which corn syrup or polyethylene glycol wax (PEG) were extruded into a square tank through 1 or 2 floor vents at a constant rate, were conducted to provide insight into Loki Patera's behavior. Results from both sets of experiments suggest that a single convection cell would be difficult to establish at Loki Patera. Crustal foundering of a lava lake may be possible under special conditions. Given the unique nature of Loki Patera and its island, we propose that the island may be similar to a resurgent dome in a terrestrial caldera complex composed primarily of evolved lavas, such as Long Valley Caldera, California. We examined other paterae that contain bright "islands" on their floors in an effort to constrain their origins. Geologic mapping, and shape analyses of the paterae and the islands they contain, suggest that most paterae islands are patches of cooled lava on the paterae floor. Only about 8% of paterae islands have morphologies and geologic relations that are consistent with a tectonic origin.