Rheological properties and ages of lava flows on Alba Mons, Mars

Abstract

We present the results of our studies of the rheological properties and ages on Alba Mons lava flows. Previous studies have shown that the rheology of lava flows, such as yield strength and viscosity, as well as external parameters affecting flow characteristics, such as effusion rate and eruption duration can be derived by remotely sensed dimension measurements. The calculations made in this study are based on images obtained from the Context Camera (CTX) on board of NASA's Mars Reconnaissance Orbiter (MRO) as well as data from the Mars Orbiter Laser Altimeter (MOLA) on NASA's Mars Global Surveyor (MGS). Absolute model ages (AMAs) have been derived by performing crater size-frequency distribution (CSFD) measurements on CTX images. The main objectives of this investigation are not only the calculation of the rheological properties and ages, but also the analysis of possible correlations between the rheologies, ages and distances of the flows to the volcano's center. A comparison of the rheological properties of the investigated lavas with those reported for flows on other planetary bodies was also performed. The aim of the study is a better insight into the history of one of the largest volcanoes in the Solar System. We provide new information about the formation and composition of the volcano's lava flows, whether they changed over time, and until when Alba Mons has been active.In total, 29 lava flows close to the summit of Alba Mons were mapped and measured. The calculated yield strengths are 2.79 × 103 Pa on average, ranging from 4.00 × 102 Pa to 9.61 × 103 Pa. We found effusion rates between 46 m3 s−1 and 1528 m3 s−1 with an average effusion rate of 636 m3 s−1. The derived viscosity is on the order of 1.04 × 107 Pa s with values between 1.27 × 105 Pa s and 1.0 × 108 Pa s. The lavas have erupted over a period of 11 to 223 days, with an average eruption duration of 68 days. The rheological properties derived in this investigation are very similar to those of other volcanic regions on Mars, especially Elysium Mons and Elysium Planitia. However, they differ from calculated rheologies of previous studies of venusian lavas and lunar lava flows. Based on the derived yield strength and viscosity values, the composition of the lava flows can be inferred as basaltic/basaltic-andesitic, which is analog to terrestrial basaltic or andesitic a'a lava flows. Significant correlations between the rheological properties and the distance to Alba Mons' center have not been found. AMAs could be derived for 14 of the 29 lava flows investigated, because 15 lava flows have either reached the state of equilibration or have too few impact craters to derive reliable model ages. The AMAs range from 130 ± 40 Ma to 810 ± 60 Ma. The results indicate a late volcanic activity at Alba Mons. Correlations between the AMAs and distance to the volcano's center, as well as between the rheological properties and AMAs were not observed.