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A subset of the sinuous ridges (SRs) in the Aeolis/Zephyria Plana (AZP) region of Mars has been previously hypothesized to be inverted fluvial features, although the precise induration and erosion mechanisms were not specified. Morphological observations and thermal inertia data presented here support this hypothesis. A variety of mechanisms can cause inversion, and identification of the specific events that lead to fluvial SR formation can provide insights into the sedimentological, geochemical, and climatic processes of the region. Reconnaissance of two terrestrial lava‐capped ridges suggests some criteria that may be used to identify inverted fluvial features formed by lava infill on Mars, but these criteria are not satisfied by the majority of the AZP fluvial SRs. Armoring also appears inconsistent with terrestrial analogs. Layering and surface textures of fluvial SRs indicate that the most likely induration mechanism was geochemical cementation of fluvial sediments, and that the primary erosional mechanism that exposed the fluvial SRs was aeolian abrasion. This analysis of formation mechanism provides a foundation for estimating paleodischarge using an empirical form‐discharge approach, to which we have applied scaling, for Martian gravity. For those fluvial SRs meeting a set of criteria for accurate paleodischarge estimates, paleodischarge values generally range between 101 and 103 m3 s−1. The largest of these initial estimates are comparable to paleodischarge estimates for some late‐stage Noachian fluvial channels on Mars, and provide a constraint on the atmospheric conditions at this equatorial location during the late Hesperian to early Amazonian time frame.

Dating of extensive alluvial fan surfaces and fluvial features in the hyperarid core of the Atacama Desert, Chile, using cosmogenic nuclides provides unrivalled insights about the onset and variability of aridity. The predominantly hyperarid conditions help to preserve the traces of episodic climatic and/or slow tectonic change. Utilizing single clast exposure dating with cosmogenic 10 Be and 21 Ne, we determine the termination of episodes of enhanced fluvial erosion and deposition occurring at ~19, ~14, ~9.5 Ma; large scale fluvial modification of the landscape had ceased by ~2–3 Ma. The presence of clasts that record pre-Miocene exposure ages (~28 Ma and ~34 Ma) require stagnant landscape development during the Oligocene. Our data implies an early onset of (hyper-) aridity in the core region of the Atacama Desert, interrupted by wetter but probably still arid periods. The apparent conflict with interpretation that favour a later onset of (hyper-) aridity can be reconciled when the climatic gradients within the Atacama Desert are considered.

Hierarchical and branching river networks interact with dynamic watershed disturbances, such as fires, storms, and floods, to impose a spatial and temporal organization on the nonuniform distribution of riverine habitats, with consequences for biological diversity and productivity. Abrupt changes in water and sediment flux occur at channel confluences in river networks and trigger changes in channel and floodplain morphology. This observation, when taken in the context of a river network as a population of channels and their confluences, allows the development of testable predictions about how basin size, basin shape, drainage density, and network geometry interact to regulate the spatial distribution of physical diversity in channel and riparian attributes throughout a river basin. The spatial structure of river networks also regulates how stochastic watershed disturbances influence the morphology and ages of fluvial features found at confluences.

Flood is among the deadliest disasters in India, and the frequency of floods and extreme precipitation events is projected to increase under the warming climate. The frequency of floods in India varies geographically as some regions are more prone to floods than the others. The Kerala flood of 2018 caused enormous economic damage, affected millions of people, and resulted in the death of more than 400 people. Here we provide a hydro-climatological perspective on the Kerala flood of 2018. Using the observations and model simulations from the Variable Infiltration Capacity (VIC) model, we show that the 2018 extreme precipitation and runoff conditions that caused flooding were unprecedented in the record of the past 66 years (1951-2017). Our results show that mean monsoon precipitation has significantly declined while air temperature has significantly increased during 1951-2017 in Kerala. The drying and warming trends during the monsoon season resulted in a declined total runoff in large part of the state in the last 66 years. Apart from the mean hydroclimatic conditions, extreme precipitation, and extreme total runoff have also declined from 1951 to 2017. However, 1 and 2-day extreme precipitation and extreme runoff conditions in August 2018 exceeded substantially from the long-term 95th percentiles recorded during 1951-2017. Since there is no increase in mean and extreme precipitation in Kerala over the last six decades, the extreme event during August 2018 is likely to be driven by anomalous atmospheric conditions due to climate variability rather anthropogenic climate warming. The severity of the Kerala flood of 2018 and the damage caused might be affected by several factors including land use/land cover change, antecedent hydrologic conditions, reservoir storage and operations, encroachment of flood plains, and other natural factors. The impacts of key drivers (anthropogenic and natural) on flood severity need to be established to improve our understanding of floods and associated damage.

River incision results from interactions among tectonics, climate change, and surface processes, and yet the role of each process operating at different time scales remains poorly understood. In this study, we address this issue by reconstructing the late Quaternary spatiotemporal variation of aggradation and incision rates along the Lancang River (Upper Mekong River) in southeast Tibet. Our work combined field observations, topographic data analysis, and optically stimulated luminescence (OSL) and cosmogenic radionuclide (CRN) dating of geologically well-defined fluvial terrace deposits, and it reveals five levels of fluvial terraces with strath heights up to 200-240 m and a 300-km-wide knickzone along the Lancang River. The new data indicate that: (1) the Lancang River has experienced four aggradation events at >120-100 ka, 90-70 ka, 25-15 ka, and <9 ka, with each event followed by rapid incision at ca. 100 ka, ca. 45 ka, ca. 15 ka, and ca. 6 ka; (2) river incision rates since the late Pleistocene decrease upstream across the knickzone from <2.8-2.3 and <2.1-1.7 to <0.5 mm/yr; and (3) they decrease with time at the knickzone from <2.1 mm/yr at ca. 100 ka to <1.1 mm/yr at 15-6 ka. The terrace-derived incision rates since the late Pleistocene from this study are more than an order of magnitude higher than the existing landscape-scale erosion rates derived from both thermochronological dating of bedrock bounding the river valley at million-year scales and cosmogenic nuclide concentrations of river sand at millennial scales. These findings imply decoupling of hydrologically induced river incision rates since the late Pleistocene from regional erosion rates on million-year and millennial time scales. Specifically, the hydrologically driven incision in a large fluvial system like the Lancang River in southeast Tibet, most likely related to local climate conditions, is much more efficient than tectonically driven erosion at a time scale of 100-10 k.y.

Geomorphic features typically associated with extreme rainfall events in terrestrial settings, including extensive fluvial features and alluvial fans, have been detected on Titan’s surface. Methane flow from precipitation on Titan can transport sediments and potentially erode the icy bedrock, but averaged precipitation rates from prior global-scale modelling are too low by at least an order of magnitude to initiate sediment transport of observed grain sizes at low latitudes. Here, we quantify the regional magnitude, frequency and variability of extreme rainfall events from simulations of present-day Titan, with a general circulation model coupled to a land model partially covered by wetlands reservoirs that can capture Titan’s regionally varying hydroclimate. We find that the most extreme storms tend to occur in the mid-latitudes, where observed alluvial fans are most concentrated. Storms capable of sediment transport and erosion occur at all latitudes in our simulations, consistent with the observed global coverage of fluvial features. Our results demonstrate the influential role of extreme precipitation in shaping Titan’s surface. We therefore suggest that, similarly to Earth but differently from Mars, active geomorphic work may be ongoing in the present climate on Titan. Extreme methane rainstorms on Titan occur in mid-latitudes, where alluvial fans are most common, according to a general circulation model. Average precipitation rates are insufficient to actively shape Titan’s surface.

Simulations reproduce previously unexplained features of Titan’s methane cycle, attributing them to atmospheric instabilities and cold-trapping of methane in the polar regions. Operation of the methane cycle on Titan The atmosphere on Saturn's moon Titan features an Earth-like cycle, but with methane rather than water taking the pivotal role. The Cassini mission has discovered numerous lakes, dunes and clouds on Titan, and planetary scientists are developing models to explain the atmospheric dynamics involved. Here Schneider et al . report simulations of the methane cycle using a general circulation model that successfully reproduces observations of Titan's methane clouds and lakes. They find that methane is cold-trapped and accumulates in polar regions, mainly in the north. At low latitudes, rare but intense storms occur around the equinoxes, producing enough precipitation to carve surface features. Tropospheric clouds form primarily in mid and high latitudes. The model predicts that prominent clouds are likely to form in the northern polar region within about two (Earth) years and that lake levels are set to rise. Titan has a methane cycle akin to Earth's water cycle. It has lakes in polar regions 1 , 2 , preferentially in the north 3 ; dry low latitudes with fluvial features 4 , 5 and occasional rainstorms 6 , 7 ; and tropospheric clouds mainly (so far) in southern middle latitudes and polar regions 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 . Previous models have explained the low-latitude dryness as a result of atmospheric methane transport into middle and high latitudes 16 . Hitherto, no model has explained why lakes are found only in polar regions and preferentially in the north; how low-latitude rainstorms arise; or why clouds cluster in southern middle and high latitudes. Here we report simulations with a three-dimensional atmospheric model coupled to a dynamic surface reservoir of methane. We find that methane is cold-trapped and accumulates in polar regions, preferentially in the north because the northern summer, at aphelion, is longer and has greater net precipitation than the southern summer. The net precipitation in polar regions is balanced in the annual mean by slow along-surface methane transport towards mid-latitudes, and subsequent evaporation. In low latitudes, rare but intense storms occur around the equinoxes, producing enough precipitation to carve surface features. Tropospheric clouds form primarily in middle and high latitudes of the summer hemisphere, which until recently has been the southern hemisphere. We predict that in the northern polar region, prominent clouds will form within about two (Earth) years and lake levels will rise over the next fifteen years.

A detailed geomorphological map of the Mt. Babia Góra Massif (1725 m a.s.l.), at a scale 1:10,000 is presented. A slope, glacial, periglacial and fluvial features were mapped on the base of the coupled field studies and LiDAR DEM analyses. This study underlines the complexity of rock slope failures (RSFs), in shaping the morphology of compact and isolated upland, exhibiting one of the highest incidences of RSFs yet recorded in Europe (29% for a whole massif, and 45% for the north face). A total of 212 RSFs were mapped of which 18 failures are large landslides (>0.25 km 2 ), among them is one of the largest known (2.6 km 2 and 150 × 106 m 3 ) in the Polish Flysch Carpathians. The mapping and Schmidt-hammer results shed light on the problem of glacial relief of the massif, documenting the remnants of glacial deposits beyond the tongues of landslides in the Szumiąca Woda valley.

The Aeolis and Zephyria Plana contain the western‐most portion of the Medusae Fossae Formation (MFF), an enigmatic and extensive light‐toned deposit located in the Martian equatorial region and dated from the Hesperian to Amazonian epochs. This area hosts a large population of sinuous ridges (SRs), interpreted as inverted fluvial features, formed by precipitation, indurated by chemical cementation, buried by subsequent deposition, and finally exhumed. This interpretation of SRs as uniformly fluvial represents a modification to an earlier hypothesis for one particular SR of possible glaciofluvial (i.e. esker) formation. These SRs provide a tool to investigate the degree and character of post‐fluvial modification processes in this region. We combined digital terrain models made from Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) stereo image pairs with individual data points from the Mars Orbiter Laser Altimeter (MOLA) to estimate relief, cross‐sectional profiles, longitudinal profiles and slope directions of selected SRs. Longitudinal profiles of several SRs display undulations with amplitudes of up to order 100 m. While some of the lower amplitude undulations may be due to differential erosion, undulations having amplitudes in excess of SR relief require alternative explanations. Our combined morphologic and topographic analysis suggests that multiple post‐flow processes, including compaction of the deposits and tectonic displacements, have modified the original SR profiles. Specification of the type(s) and magnitudes of these modification processes will contribute to understanding both the potential of post‐flow modification of fluvial profiles elsewhere on Mars as well as the nature and properties of the MFF. Key Points Topographic profiles of inverted fluvial features show post‐flow deformation Compaction or tectonics may have occurred in the Medusae Fossae Formation

On Mars, the presence of extensive networks of sinuous valleys and large channels provides evidence for a wetter and warmer environment where liquid water was more abundant than it is at present. We undertook an analysis of all major channel systems on Mars and detected sharp changes in elevation along the river long profiles associated with steep headwall theatre-like valleys and terraces left downstream by channel incision. These breaks in channel longitudinal slope, headwalls and terraces exhibit a striking resemblance with terrestrial fluvial features, commonly termed ‘knickpoints’. On Earth, such knickpoints can be formed by more resistant bedrock or where changes in channel base-level have initiated erosion that migrates upstream (such as tectonic uplift or sea level change). We observed common elevations of Martian knickpoints in eleven separate channel systems draining into the Martian Northern lowlands. Numerical modeling showed that the common elevations of some of these knickpoints were not random. As the knickpoints are spread across the planet, we suggest that these Martian knickpoints were formed in response to a common base level or ocean level rather than local lithology. Thus, they potentially represent a record of past ocean levels and channel activity on Mars.