Barnard, a 121.1 km diameter crater along the southern rim of Hellas basin, is a well-preserved complex crater with a history of burial, excavation, and fluvial/glacial activity on its floor and walls. The interior of Barnard shows ice-rich deposits similar to other mid-to-high-latitude craters on Mars but is distinctive in that it also contains sinuous ridges. We have completed a geologic map of Barnard and surrounding materials using the global CTX mosaic. Mapping has identified and shown the distribution of features including sinuous ridges and fluvial channels, attributed to subglacial melting, and lobate debris aprons, mantling deposits, and arcuate ridges, indicative of the deposition and mobilization of ice within the crater. We have identified 13 geologic units on and around Barnard, including three distinct floor units, suggesting sustained periods of infill. We have conducted topographic and morphometric analyses using MOLA and HiRISE DTMs across Barnard and its interior landforms, which show significant infill on the crater floor (∼1 km thick), and local excavation of floor deposits indicating continued modification. Lobate debris aprons extending from the crater walls have maximum thicknesses of ∼300–350 m. Sinuous ridges on the crater floor range in height from ∼10 to 20 m. Crater counts on Barnard’s ejecta show that it formed ∼3.81 Ga in the Middle to Late Noachian, with subsequent periods of infill, excavation, fluvial, and wet-based glacial activity modifying its interior during the Late Hesperian/Early Amazonian, followed by further deposition and flow of ice-rich materials between ∼400 and 16 Ma into the Late Amazonian.

This study characterizes fluvial activity on Alba Mons using a combination of image and topographic data to inform photogeologic interpretation and hydrological modeling. We produced a comprehensive digital inventory of fluvial valleys that documents the extensive dendritic and parallel drainage patterns dissecting Early Amazonian volcanic materials. Drainage density was correlated with regional slopes. On the summit and southern flanks, valleys are sparse and regional slopes are less steep, between 0.0° and 0.3° (average 0.4° ± 0.2°). Areas with higher drainage density (average 0.24 km −1 ; locally >0.5 km −1 ) have steeper regional slopes, between 0.1° and 2.9° (average 1.0° ± 0.4°). Ridged lava tubes and tabular lava flows represent local topographic highs that exert a strong influence on drainage patterns, but are also locally eroded by fluvial valleys. Graben formation and ice‐rich mantle deposition complicate analyses by altering fluvial features. For two case studies, we employed an integrated approach that combined mapping and hydrological modeling to create watershed reconstructions that allowed robust morphometric analyses of drainage basins and the contained valley networks. Mapping shows well‐preserved drainage patterns with morphometry and hypsometry that support a prolonged history of erosion and development into mature drainage networks. Modeling provides characterization of the downstream parts of drainage basins that are largely obscured. These results have climate implications, suggesting fluvial dissection resulted from widespread precipitation with possible contributions from meltwater related to periodic accumulation of ice‐rich surface deposits.

Topography is a fundamental factor influencing the emplacement of lava flows. We assess the impact of topographic resolution on the thermorheological PyFLOWGO model, specifically with digital elevation model (DEM) resolutions commonly available for Earth and other planetary bodies where flow modeling is relevant. We examined PyFLOWGO output parameters (e.g., channel length, core temperature, and flow velocity) to assess model sensitivity to topography in order to document model uncertainties and optimize future application. This study uses rheologic and topographic data from the Tolbachik, Russia 2012–2013 eruption as model constraints. Using moderate to lower resolution topographic data overestimates the channelized flow length by up to 35% due to differences in the distribution of slopes topographic variability at different resolutions and resulting effects on the modeled lava velocity down channel. Determining the impact of topography on thermorheological lava flow models such as PyFLOWGO is important to correctly interpret the results for channelized flows.

First posted January 5, 2023 For additional information, contact: Astrogeology Science CenterU.S. Geological Survey2255 N. Gemini Dr.Flagstaff, AZ 86001 Xanthe Terra is a high-standing cratered plain located southeast of Lunae Planum and south of Chryse Planitia in the western equatorial region of Mars. It contains landforms shaped by diverse geologic processes, including various scales of channels and valleys, chaotic terrains, delta fan deposits, and landslides. An extensive outflow channel system is located within Xanthe Terra and the surrounding circum-Chryse region, including Shalbatana and Ravi Valles, thought to have formed by catastrophic flooding during the Hesperian to Amazonian Periods. The study region within Xanthe Terra is defined by Mars Transverse Mercator (MTM) quadrangles 00042 and 00047 (2.5° to −2.5° N, 310° to 320° E) and includes Orson Welles crater (124.5 km diameter, the source region for Shalbatana Vallis), the southernmost portion of Shalbatana Vallis, Aromatum Chaos (the source region for Ravi Vallis), the westernmost portion of Ravi Vallis, and the source area of Nanedi Valles. The Mars Odyssey Thermal Emission Image System (THEMIS) IR daytime mosaic (100 m/pixel) was used as the primary base map. We constructed the geologic map of the source region of Shalbatana Vallis at 1:750,000 scale. We defined 16 geologic units in the map area, which we divided into the following groups: plains units, channel units, crater units, chaos units, flow units, and surficial units. Mapped linear features include ridge crests, scarp crests, channels, crests of crater rims, crests of buried or degraded crater rims, graben traces, grooves, troughs, and faults. Surface features include secondary crater chains and dark ejecta material. The geologic history of the map region can be summarized as follows. During the Noachian Period, ancient highland materials in the Xanthe Terra region, including lava and any ancient sedimentary units present, were reworked by impacts during the heavy bombardment. In particular, the impact that formed a basin that later underwent widespread resurfacing, likely as a combination of lava flows, reworked crater materials, and sedimentary deposits resulting in the flat-lying, smooth plains of Chryse Planitia. The Hesperian Period was characterized by the impact that formed Orson Welles crater and the subsequent formation of Shalbatana Vallis, as well as Aromatum Chaos and Ravi Vallis. During this period, depressions were filled with smooth material that was subsequently modified by collapse, subsidence, and flooding. Water filled and overflowed the tops of Orson Welles crater and other depressions. The Amazonian Period was characterized by ongoing collapse, as well as the formation of flow and surficial materials, including a lava flow that extends from Aromatum Chaos.

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.

Much has been discovered about volcanism on Mars over the past fifty years of space exploration. Previous reviews of these discoveries have generally focused on the volcanic constructs (e.g., Olympus Mons and the other volcanoes within the Tharsis and Elysium regions), the analysis of individual lava flows, and how volcanic activity on Mars has evolved over time. Here we focus on attributes of volcanology that have received less attention and build upon characteristics of terrestrial volcanoes to pose new questions to guide future analyses of their Martian equivalents either with existing data sets or with new types of measurements that need to be made. The remarkable lack of exposed dikes at eroded ancient volcanoes attests to an internal structure that is different from terrestrial equivalents. Enigmatic aspects of the origin of the ridged plains (commonly accepted to be volcanic but with few identifiable flow fronts and only rare vents), the style(s) of volcanism during the earliest period of Martian history (the Noachian), and the possible mode(s) of formation of the Medusae Fossae Formation are considered here. Martian meteorites have been dated and are volcanic, but they cannot be correlated with specific geographic areas, or the chronology of Mars derived from the number of superimposed impact craters. Some of these questions about Martian volcanism can be addressed with existing instrumentation, but further progress will most likely rely on the acquisition of new data sets such as high-resolution gravity data, the return of samples from known localities, the flight of a synthetic aperture imaging radar, penetrators sent to the Medusae Fossae Formation, and detailed in situ field observations of selected volcanic sites.

Integrated analyses of Thermal Emission Imaging System (THEMIS) IR, Context Camera (CTX), and Mars Orbiter Laser Altimeter (MOLA) data sets have been used to characterize the western flank of the Martian volcano Alba Mons, which hosts a prominent population of lava tube systems. Identification and mapping of lava tube systems is based on both morphologic and topographic analyses, including the presence of chains of collapse depressions and elongate, sinuous ridges. Lava tubes and adjacent tabular lava flows with lengths of 100 + km form an extensive lava flow field. Analyses of topographic data sets, including slope maps, suggest continuity of the radial flow field pattern across the full western flank. Concurrent surface activity across the western flank is consistent with age constraints from geologic mapping and crater size‐frequency distributions that indicate Early Amazonian ages. The mapped population of 331 lava tube systems in the western flank geologic map quadrangle has a mean length of 36.2 km and a total length of ∼12,000 km. Individual lava tube systems extend up to ∼400 km. Orientation and slope data for lava tube systems show small deviations compared to regional values in 50‐km grid cells defined by the MOLA Digital Elevation Model, suggesting a strong coupling of lava tubes to the current slopes of Alba Mons. Mapping of lava tube systems documents segments both showing collapse and with no collapse, indicating the potential for extensive subsurface cavities that would be important astrobiological targets.

The Medusae Fossae Formation (MFF) is hypothesized to be an enormous deposit of pyroclastic material, generated during explosive eruptions from unknown volcanic vents. Investigation of these materials has been hampered for decades by dust that hides the surface rocks from easy remote observation. The MFF materials have been sculpted by sand and wind into massive eroded ridges called yardangs, with layers of variably erodible rock exposed in many places. Apollinaris Mons is hypothesized to be a potential source for MFF deposits, but the immense volume of the MFF materials far exceeds the volume of this volcano. The northern lowland plains have many examples of explosion pits called pseudocraters, interpreted to be the result of hot volcanic materials being emplaced on top of subsurface ice or wet materials.

Robotic missions to Mars are in various stages of development. Many will provide new understanding of volcanic materials. The InSight lander continues to explore the interior from the volcanic plains in the Cerberus region. The Perseverance rover should land in Jezero crater in 2021, where it will search for chemical traces of ancient bacterial life and collect drill cores for later return to Earth. The ExoMars rover will explore the Oxia Planum region after 2022. Orbiters were launched by China and the United Arab Emirates during 2020. The Mars Sample Return mission should recover the rock cores cached by Perseverance (hopefully including many volcanic rocks), launch the samples into Mars orbit, and return them to Earth. No definite date is set for human missions to Mars, but such missions will allow on-site human assessment for selecting and collecting samples. Mars will long continue as a major objective in planetary science.

The Elysium Province is the second largest volcanic region on Mars after the Tharsis Province. It is evidently slightly older than Tharsis and is dominated by Elysium Mons volcano, but two other volcanoes (Hecates Tholus and Albor Tholus) are also found here. Some of the best candidates for explosive volcanism, as well as hydromagmatic volcanism, are found within Elysium, and it is likely that vast amounts of water and sediments were released from fractures west of Elysium Mons to form giant lahars. These eruptions may also have interacted with a transient ice cover. South of Albor Tholus, a fracture system within Cerberus Fossae has been the site of potentially the youngest major eruptions on the planet. Located to the east of the InSight landing site (which is to the SW of Elysium Mons), the potential exists for marsquakes to provide new information on the internal structure of this region.

The Tharsis Province is the largest and youngest volcanic region of Mars, and includes the giant shield volcanoes Olympus Mons and the three Tharsis Montes (Arsia, Pavonis, and Ascraeus Montes). Extensive studies of the styles of volcanic activity within Tharsis have been conducted over the past 45 years, and have identified numerous lava flows in excess of 150 km long, multiple caldera collapse events, and the possibility that explosive volcanism (perhaps due to phreatomagmatic activity) took place. Glacial and tectonic events have also been described. By virtue of the apparent age of the lava flows found in this area, the Tharsis Province is the most likely source of Martian meteorites.