Determining Emplacement Conditions and Vent Locations for Channelized Lava Flows Southwest of Arsia Mons

The lava flow field southwest of Arsia Mons, Mars has complex volcanic geomorphology. Overlapping flows make observations of their total lengths and identification of their source vents impossible. Application of flow emplacement models, which rely upon physical parameters such as flow length, using only the exposed flow may produce inaccurate estimates of effusion rate, viscosity, and yield strength. We use an established terrestrial thermorheological model (PyFLOWGO), modified to Mars conditions, to estimate effusion rates, viscosities, yield strengths, and possible vent locations for five Mars flows. Our investigation found a range of effusion rates from 2,500 to 6,750 m3 s-1 (average of ∼4,960 m3 s-1). These results are an order of magnitude higher than terrestrial channelized basaltic flows. Corresponding modeled viscosities and yield strengths ranged from 9.4 × 103 to 6.6 × 105 Pa s (average of 5.5 × 104 Pa s) and 66 to 381 Pa (average of 209 Pa), respectively. A novel secondary application of PyFLOWGO that assumes upslope channel narrowing provided estimates of the entire channel length, which is on average four times longer than the exposed portions. Projecting these lengths upslope shows that four of the five flows may have a common vent location, which shares morphologic similarities to other Tharsis region vents. This modeling approach for partially-exposed lava flows makes it possible to not only determine eruptive parameters, but also to estimate total channel lengths and thereby identify possible source vents.

Taxonomic Characterization and Microbial Activity Determination of Cold-Adapted Microbial Communities in Lava Tube Ice Caves from Lava Beds National Monument, a High-Fidelity Mars Analogue Environment

Martian lava tube caves resulting from a time when the planet was still volcanically active are proposed to contain deposits of water ice, a feature that may increase microbial habitability. In this study, we taxonomically characterized and directly measured metabolic activity of the microbial communities that inhabit lava tube ice from Lava Beds National Monument, an analogue environment to martian lava tubes. We investigated whether this environment was habitable to microorganisms by determining their taxonomic diversity, metabolic activity, and viability using both culture-dependent and culture-independent techniques. With 16S rRNA gene sequencing, we recovered 27 distinct phyla from both ice and ice-rock interface samples, primarily consisting of Actinobacteria, Proteobacteria, Bacteroidetes, Firmicutes, and Chloroflexi. Radiorespiration and Biolog EcoPlate assays found these microbial communities to be metabolically active at both 5°C and -5°C and able to metabolize diverse sets of heterotrophic carbon substrates at each temperature. Viable cells were predominantly cold adapted and capable of growth at 5°C (1.3 × 10⁴ to 2.9 × 10⁷ cells/mL), and 24 of 38 cultured isolates were capable of growth at -5°C. Furthermore, 14 of these cultured isolates, and 16 of the 20 most numerous amplicon sequences we recovered were most closely related to isolates and sequences obtained from other cryophilic environments. Given these results, lava tube ice appears to be a habitable environment, and considering the protections martian lava tubes offer to microbial communities from harsh surface conditions, similar martian caves containing ice may be capable of supporting extant, active microbial communities.

Cold-based glaciation of Pavonis Mons, Mars: evidence for moraine deposition during glacial advance

The three large volcanoes in the Tharsis region of Mars: Arsia, Pavonis, and Ascraeus Montes all have fan-shaped deposits (FSDs) on their northern or western flanks consisting of a combination of parallel ridges, knobby/hummocky terrain, and a smooth, viscous flow-like unit. The FSDs are hypothesized to have formed in the Amazonian during a period of high spin-axis obliquity which redistributed polar ice to the equatorial Tharsis region resulting in thick (> 2 km), flowing ice deposits. Based on previous ice flow simulations and crater surveys, the ridges are interpreted to be recessional drop moraines formed as debris on the ice sheet surface was transported to the ice margin-forming a long ridge sequence over an extended (∼100 Myr) period of ice sheet retreat. We test this hypothesis using a high-resolution, thermomechanical ice sheet model assuming a lower ice loss rate (~ 0.5 mm/year) than prior work based on new experimental results of ice sublimation below a protective debris layer. Our ice flow simulation results, when combined with topographic observations from a long sequence of ridges located interior of the Pavonis FSD, show that the ridged units were more likely deposited during one or more periods of glacial advance (instead of retreat) when repetitive pulses (approx. 120 kyr periodicity) of ice accumulation during high obliquity produced kinematic waves which advected a large volume of surface debris to the ice margin. If ridge deposition does occur during glacial advance, it could explain the cyclic pattern of ridge spacing and would link the dominant, 120 kyr periodicity in obliquity to the time interval between adjacent ridges. By measuring the spacing between these ridges and applying this timescale, we constrain the velocity of glacial margin to be between 0.2 and 4 cm/Earth year-in close agreement with the numerical simulation. This re-interpretation of the FSD ridged unit suggests that the timescale of FSD formation (and perhaps the duration of the Amazonian high obliquity period) was shorter than previously reported.

Volcanism and tectonism across the inner solar system: an overview

Volcanism and tectonism are the dominant endogenic means by which planetary surfaces change. This book, in general, and this overview, in particular, aim to encompass the broad range in character of volcanism, tectonism, faulting and associated interactions observed on planetary bodies across the inner solar system – a region that includes Mercury, Venus, Earth, the Moon, Mars and asteroids. The diversity and breadth of landforms produced by volcanic and tectonic processes are enormous, and vary across the inventory of inner solar system bodies. As a result, the selection of prevailing landforms and their underlying formational processes that are described and highlighted in this review are but a primer to the expansive field of planetary volcanism and tectonism. In addition to this extended introductory contribution, this Special Publication features 21 dedicated research articles about volcanic and tectonic processes manifest across the inner solar system. Those articles are summarized at the end of this review.

Magma generation on Mars: amounts, rates, and comparisons with Earth, moon, and venus

Total extrusive and intrusive magma generated on Mars over the last approximately 3.8 billion years is estimated at 654 x 10(6) cubic kilometers, or 0.17 cubic kilometers per year (km(3)/yr), substantially less than rates for Earth (26 to 34 km(3)/yr) and Venus (less than 20 km(3)/yr) but much more than for the Moon (0.025 km(3)/yr). When scaled to Earth's mass the martian rate is much smaller than that for Earth or Venus and slightly smaller than for the Moon.