Mafic pyroclastic flows at Tyrrhena Patera, Mars: Constraints from observations and models

Tyrrhena Patera (22°S, 104°E), Mars, is a low-relief (1800 m maximum relief), central-vent volcano whose flanks are dissected with broad (∼5 km wide), flat-floored channels. The easily eroded nature of the shield materials, combined with extremely low flank slopes (≤ 2.0°), suggest that Tyrrhena Patera is composed of pyroclastic materials. These shield deposits are observed to crop out ≥ 600 km from the volcano's summit with measured thicknesses of 100-150 m at these distances. Such dimensions strongly suggest emplacement via pyroclastic flows. Currently available data indicate that these deposits have a mafic composition. Application of models derived for terrestrial pyroclastic flow emplacement reveals that, aside from environmental parameters (atmospheric density, gravity), if all else is held equal, a pyroclastic flow should travel a factor of 3 to 4 times farther on Mars than on Earth. The observed Tyrrhena Patera deposits extend even farther, suggesting that some emplacement mechanism may be enhancing pyroclastic flow runout distances on Mars.