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Volcanism has played a major role in modifying the Martian surface. The Tharsis volcanic province dominates the western hemisphere of the planet with numerous effusive volcanic constructs and deposits. Here, we present the results of an in‐depth study aimed at characterizing and modeling the emplacement conditions of 40 lava flows in the Tharsis volcanic province. These lava flows display a range of lengths (∼15–310 km), widths (∼0.5–29 km), and thicknesses (∼11–91 m). The volumes and flow masses range from ∼1 to 440 km3 and ∼1011 to 1014 kg, respectively. Using three different models, we calculated a range of eruption rates (0.3–3.5 × 104 m3/s), viscosities (104–107 Pa s), yield strengths (800–104 Pa), and emplacement times (8 h–11 years). While the flow lengths and volumes are typically larger than terrestrial lava flows by an order of magnitude, rheologies and eruption rates are similar based on our findings. Emplacement times suggest that eruptions were active for long periods of time, which implies the presence and persistence of open subsurface pathways. Differences in flow morphology and emplacement conditions across localities within Tharsis highlight different pathways and volumes of available material between the central volcanoes and the plains. The scale of the eruptions suggests there could have been eruption‐driven local, regional, and perhaps, global impacts on the Martian climate. The relatively recent age of the eruptions implies that Mars has retained the capability of producing significant localized volcanism. Plain Language Summary: Volcanoes have resurfaced a majority of the Martian surface. Understanding the volcanic history of Mars is critical to understanding the evolution of the planet. Lava flows are one of the most common volcanic features on Mars, and numerous examples are present in the Tharsis volcanic province on shield volcanoes and in vast volcanic plains. Using three different approaches, we characterized the eruption conditions of 40 lava flows. In addition, we measured their dimensions and calculated volumes and masses. We observed flow dimensions (e.g., lengths and volumes) larger than typical terrestrial lava flows. Viscosities and yield strengths were similar to terrestrial values; however, effusion rates were generally at the higher end of terrestrial rates. These results indicate that lava flows erupted on Mars did not require exotic compositions or exceptionally high eruption rates to be emplaced. However, this does imply longer eruption times, which requires the existence of long‐lived subsurface conduits capable of transporting magma to the surface. Key Points: The large thick lava flows in Tharsis are explained by basaltic and basaltic‐andesite compositions without resorting to exotic compositionsThe observed lava flows likely required longer‐lived eruptive conditions and larger active conduits than their terrestrial counterpartsSeemingly high eruption rates for some solitary flows are reasonable extrapolations of terrestrial conditions with higher supply dimensions [ABSTRACT FROM AUTHOR]

The temporal evolution of effusion rate is the main controlling factor of lava spreading and emplacement conditions. Therefore, it represents the most relevant parameter for characterizing the dynamics of effusive eruptions and thus for assessing the volcanic hazard associated with this type of volcanism. Since the effusion rate curves can provide important insights into the properties of the magma feeding system, several efforts have been performed for their classification and interpretation. Here, a recently published numerical model is employed for studying the effects of magma source and feeding dike properties on the main characteristics (e.g., duration, erupted mass, and effusion rate trend) of small‐volume effusive eruptions, in the absence of syn‐eruptive magma injection from deeper storages. We show that the total erupted mass is mainly controlled by magma reservoir conditions (i.e., dimensions and overpressure) prior to the eruption, whereas conduit processes along with reservoir properties can significantly affect mean effusion rate, and thus, they dramatically influence eruption duration. Simulations reproduce a wide variety of effusion rate trends, whose occurrence is controlled by the complex competition between conduit enlargement and overpressure decrease due to magma withdrawal. These effusion rate curves were classified in four groups, which were associated with the different types described in the literature. Results agree with the traditional explanation of effusion rate curves and provide new insights for interpreting them, highlighting the importance of magma reservoir size, initial overpressure, and initial width of the feeding dike in controlling the nature of the resulting effusion rate curve. Key Points: The effects of magma source and feeding dike properties on the evolution of small‐volume effusive eruptions are studied numericallyTotal erupted mass is mainly controlled by magma reservoir conditions (in particular, dimensions and overpressure) prior to the eruptionDifferent types of effusion rate curves were modeled, classified, and compared with the effusion rate trends defined in the literature [ABSTRACT FROM AUTHOR]

Although most of the large volcanic landforms on Mars have been extensively studied, this is not the case for kilometer-sized landforms whose origin remains uncertain and which might provide important insights into the evolution of Martian volcanism. Previously, different populations of small-scale putative scoria cone volcanoes have been described in Tharsis, specifically in areas where the heavily fractured crust of the Noachian- and Hesperian-age escaped Amazonian resurfacing by younger lava flows. Therefore, we decided to explore a region of old fractured crust in Tharsis, Claritas Fossae, to search for signs of local-scale volcanic activity. Here, we present the results of a mapping campaign focused on the morphological and spectral properties of small-scale constructional mounds in the Noachian-age Claritas Fossae region that was affected by Hesperian- to early Amazonian-aged fracturing. By using data from Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE), we mapped 39 mounds superimposed on the ancient crust and determined their morphological and morphometrical properties. The majority of the mounds are elongated (WNW- trending) with steep flanks and without associated flow units. The general appearance of studied edifices is consistent with a volcanic origin and their shapes suggest that they have been emplaced by effusion of viscous, volatile poor lavas incapable of significant flow. In addition, a spectral investigation utilizing the data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) reveal that some of the mounds showed evidence for high concentrations of low-calcium pyroxenes (LCP). Based on the relative stratigraphy, we demonstrate that volcanic activity is responsible for their formation and postdates the main N-S-trending fracturing of the Claritas Fossae, suggesting the formation of a volcanic field in the period spanning through the Late Hesperian and the Early Amazonian. However, morphological evidence such as well-preserved volcanic fissures and fresh-appearing slopes of some of the edifices might suggest even younger age. Among the mapped edifices, we found a well-preserved circular-shaped cone with a short-distance flow-like unit spreading from a caldera-like structure that challenges a scenario in which all the edifices are old. Such relatively young ages of volcanic activity combined with LCP-rich compositions might have critical implications for understanding the temporal evolution of magma compositions on Mars. Moreover, the observed shapes and spectral characteristics of the studied edifices appear to be quite different from other volcanic fields of similar geological settings observed so far on Mars. Therefore, we underline the importance of studying old and heavily fractured terrains that escaped later resurfacing by widespread younger lava flows, in order to search for evidence of small-scale volcanism and better understand local Martian magmatic systems. • Noachian-aged fractured crust of Claritas Fossae hosts 39 volcanic edifices • Volcanoes are superimposed on the N-S fractures and postdate their formation • Volcanoes are spatially associated with low-calcium pyroxenes • They were formed by the low-voluminous effusive eruptions of viscous magma • Volcanism might be associated with Amazonian-age partial melting beneath Claritas Fossae [ABSTRACT FROM AUTHOR]

Historic and recent (last 2,000 years) eruptions on the active volcanic island of Tenerife have been predominantly effusive, indicating that this is the most probable type of activity to be expected in the near future. In the past, lava flow invasion caused major damage on the island, and as the population and infrastructure have increased dramatically since the last eruption, lava flows are the most important short-term volcanic risk on Tenerife. Hence, an understanding of lava flow behaviour is vital to manage risks from lava flows and minimise future losses on the island. This paper focuses on the lava flows from the historic eruptions in Tenerife, providing new data on the volumes emitted, advance rates and the timing of the emplacement of flows. The studies show three main stages in the development of unconfined flow fields: the first stage, corresponding to the fast advance of the initial fronts during the first 24-36 h of eruption (reaching calculated velocities of up to 1.1 m/s); the second stage, in which fronts stagnate; and a third stage, in which secondary lava flows develop from breakouts 4-7 days after the initial eruption and farther extend the flow field (velocities of up to 0.02 m/s have been calculated for this stage). The breakouts identified originated at sites both proximal and distal to the vent and, in both cases, caused damage through lengthening and widening the original flow field. Hence, the probability of damage from lavas to land and property is highest during stages 1 and 3, and this should be accounted for when planning the response to a future effusive eruption. Tenerife's lava flows display a similar behaviour to that of lava flows on volcanoes characterised by basaltic effusive activity (such as Etna or Kilauea), indicating the possibility of applying forecasting models developed at those frequently active volcanoes to Tenerife. [ABSTRACT FROM AUTHOR]

The Ilopango caldera in central El Salvador is the source of at least 13 voluminous rhyolitic eruptions over the last two million years, including the 431 CE Tierra Blanca Joven (TBJ) which blanketed areas inhabited by the Mayan civilization, and the 1.707 ± 0.022 Ma Olocuilta ignimbrite, one of the largest Quaternary eruptions in Central America. These rhyolitic deposits have been the subject of numerous detailed studies. In contrast, the abundant effusive and monogenetic eruptions at Ilopango have not been studied. These small-volume eruptions range from basalt to rhyolite (49.7–72.8 wt% SiO 2) and occur both within the caldera margin and on the south flank of the Antiguo Ilopango stratovolcano. Here we present 28 new 40Ar/39Ar ages and geochemical data from domes, lavas, dikes, and ignimbrites from the Ilopango caldera and the Antiguo Ilopango stratovolcano as well as from adjacent volcanic systems. Collectively, these new data are used to construct a revised eruptive sequence for the Ilopango caldera that spans almost three million years. The new chronostratigraphy for Ilopango is highlighted by two volcanic cycles. Each cycle starts with rhyolite dome effusions, and then a prolonged period of explosive rhyolitic volcanism followed by a ~120–175 kyr period of less evolved eruptions. The spatio- and chemo-temporal patterns in the Ilopango eruptive sequence are similar in many ways to those observed in other well-studied Quaternary silicic centers. • We have new ages and geochemical data from 28 units from the Ilopango caldera system. • The new chronostratigraphy for Ilopango suggests there have been at least two volcanic cycles. • Evolution of the Ilopango magma system is similar to other Quaternary silicic systems. [ABSTRACT FROM AUTHOR]