Evidence for Recent Wet-Based Crater Glaciation in Tempe Terra, Mars.

[Introduction] Mars’ mid-latitudes host abundant putative debris-covered water-ice glaciers (viscous flow features; VFF). Eskers emerging from 110-150 Myr-old VFF in Phlegra Montes and Tempe Terra provide evidence for rare occurences of past, localized basal melting of their parent VFF, despite the cold climates of the late Amazonian (see this conf.). Eskers are sinuous ridges comprising glaciofluvial sediment deposited by meltwater flowing through tunnels within glacial ice. Here, we describe a population of sinuous ridges emerging from VFF in an unnamed ~45 km-diameter crater (38.47 N, 72.43 W) in Tempe Terra, ~600 km from the VFF-linked esker identified by Butcher et al. We consider two working hypotheses for the formation of the sinuous ridges; that they are either (1) eskers formed by melting of the glaciers from which they emerge, or (2) topographically inverted fluvial channels which formed prior to glaciation of the crater. We present observations from preliminary geomorphic mapping of the crater to start to test those hypotheses

3D Morphometries of Eskers on Mars, and Comparisons to Eskers in Finland

International audienceIntroduction: We present new, high-resolution measurements of the 3D morphometries of eskers associated with debris-covered glaciers in the Phlegra Mon-tes [1] and NW Tempe Terra [2] regions of Mars' northern mid-latitudes. We compare them with the ancient south polar 'Dorsa Argentea' eskers on Mars [3], and first large database (n > 20,000) of 3D morphome-tries of terrestrial eskers, from SW Finland [4]. Eskers are ridges of glaciofluvial sediment deposited by meltwater flowing through tunnels within or beneath glaciers. They are vital tools for reconstructing the dynamics, extent, and environmental drivers of wet-based glaciation on Earth and Mars. For example, reconstructions of Mars' climate conditions at the Noa-chian-Hesperian transition [e.g., 5] have relied heavily upon insights from the Dorsa Argentea eskers [e.g., 3], which record basal melting of a large south polar ice sheet ~3.5 Ga. Morphometric studies of candidate eskers on Mars are vital both for testing hypotheses of their origins as eskers [e.g., 3], and for informing insights into the magnitude and dynamics of meltwater flows that formed them [e.g., 5-6]. Previously, such work has been limited by a lack of large-scale surveys of the 3D morphometries of eskers on Earth, to which the martian landforms can be compared. A new database comprising >20 000 measurements of 3D esker morphometries from SW Finland provides new opportunities for such-comparisons, which we exploit in this study [4]. Methods: We used 1-2 m/pixel digital elevation models generated from High Resolution Imaging Science Experiment (HiRISE) images to measure esker heights (H) and widths (W) from cross-sectional tran-sects spaced at 10 and 20 m intervals along the Phlegra Montes and NW Tempe Terra eskers, respectively (fol-lowing [3]). We calculated average slopes across cross-sectional transects (θ) as: tan −1 (H/0.5W). We classified transects into sharp-, multi-, and round-crested morphologies according to the scheme of [6]. The NW Tempe Terra esker comprises two 'stacked' esker ridges (see [7], this conference) which we treat separately in the present study. Storrar and Jones [4] obtained similar H, W, and θ measurements at 10 m intervals along ~70 km of Qua-ternary-aged eskers in SW Finland, using 2 m/pixel elevation data from airborne LiDAR

Multi-Phase Sedment-Discharge Dynamics of Subglacial Drainage Recorded by a Glacier-Linked Esker in NW Tempe Terra, Mars

International audienceIntroduction: Our recent discoveries of eskers associated with 110-150 Myr old debris-covered glaciers in Phlegra Montes [1] and NW Tempe Terra [2], Mars, indicate that localised wet-based glaciation has occurred in at least two locations during the late Amazonian , despite cold climate conditions. Eskers are sedi-mentary ridges deposited by meltwater flowing through drainage tunnels within or beneath glaciers. In this study, we use new 3D measurements of the NW Tempe Terra esker (46.17 °N, 83.06 °W) to develop a conceptual model for the sediment-discharge dynamics of the esker-forming drainage episode(s). Methods: Following [3], we used a 2 m/pixel digital elevation model derived from High Resolution Imaging Science Experiment (HiRISE) images to measure ridge height (H) and width (W) every ~20 m along the esker. We exclude ridge portions obscured by the parent glacier (Fig 1), as well as transitions between morphological zones. Results: A scatterplot of the raw height and width measurements (Fig 2A) has multiple limbs which correspond to subzones of the esker with common morphological characteristics (Fig 1)

Eskers on Mars: Morphometric comparisons to eskers on Earth and implications for sediment-discharge dynamics of subglacial drainage

Mars’ present climate is extremely cold and arid. Until recently, it was widely thought that debris-covered glaciers in Mars’ mid-latitudes have been pervasively cold-based since their formation 10s–100s Myr ago. However, we recently discovered eskers associated with ~110–150 Myr old glaciers in the Phlegra Montes [1] and NW Tempe Terra [2] regions of Mars’ northern mid-latitudes. Eskers are sinuous ridges comprising sediments deposited in glacial meltwater conduits. Therefore, eskers associated with existing mid-latitude glaciers on Mars indicate that localised wet-based glaciation did occur during Mars’ most recent geological period. Eskers are important tools for reconstructing the nature, extent, and dynamics of wet-based glaciation on Earth, and have similar potential for Mars. We used 1–2 m/pixel resolution digital elevation models derived from 25–50 cm/pixel High Resolution Imaging Science Experiment stereo-pair images to measure the planform and 3D morphometries of the Phlegra Montes and NW Tempe Terra eskers, and compare them with the morphometries of Quaternary-aged eskers in Canada [3] and SW Finland [4]. We found that the Martian eskers have remarkably similar lengths, sinuosities and heights to terrestrial eskers, but that the Martian eskers are typically wider and have lower side slopes. Large width-height ratios of the Martian eskers are consistent with our previous measurements of ancient (~3.5 Ga) eskers close to Mars’ south pole [5], and may arise from differences in either: esker degradation state, or fundamental glacio-hydrological controls on esker formation between Mars and Earth. Portions of the two Martian eskers with comparable crest morphologies (e.g., sharp- or round-crested) have similar width-height relationships, suggesting that glacio-hydrological processes may exert controls upon the observed relationships between esker morphology and morphometry. Our morphometric analyses also reveal that the Martian esker in NW Tempe Terra has a ‘stacked’ morphology: the crest of a wide, round-crested underlying ridge is superposed by a narrow, sharp- to multi-crested ridge. Based on morpho-sedimentary relationships observed along terrestrial eskers [6], we interpret this transition to represent waning sediment supply and meltwater discharge towards the end of the esker-forming drainage episode(s). Direct sedimentary insights into Martian eskers are not yet possible so we emphasise that such inferences should be rigorously grounded in observations of analogous landforms on Earth. This work was funded by STFC grant ST/N50421X/1. References: [1] Gallagher, C., and Balme, M.R., (2015), Earth. Planet. Sci. Lett. 431, 96-109, [2] Butcher, F.E.G., et al. (2017), J. Geophys. Res. Planets. 122(12), 2445-2468, [3] Storrar, R.D., et al. (2014) Quat. Sci. Rev. 105, 1-25, [4] Storrar, R.D., and Jones, A., Unpublished, [5] Butcher, F.E.G., et al. (2016), Icarus 275, 65-84, [6] Burke, M.J., et al. (2010) Geol. Soc. Am. Bull. 122, 1637-1645

Geomorphological signature of topographically controlled ice flow-switching at a glacier margin: Breiðamerkurjökull (Iceland) as a modern analogue for palaeo-ice sheets

Ice low-switching, which can involve changes in ice flow velocity and direction, is crucial to a full understanding of ice masses and their response to climate change. A topographically controlled ice flow switch near a glacier margin was recently documented at Breiðamerkurjökull, southeast Iceland, where the central flow unit migrated eastward in response to variations in subglacial topography and the influence of Jökulsárlón glacial lagoon. This site provides an opportunity to study the geomorphic response to ice-margin reconfiguration. Investigating contemporary processes can offer valuable insights into analogous landforms created during the deglaciation of palaeo-ice sheets. The landform assemblage and topographic setting of our Icelandic study site is compared to a palaeo-example from Alberta, Canada, which was once covered by the Laurentide ice sheet. Uncrewed aerial vehicle-(UAV) derived data was used to assess the geomorphic response to this switching and related processes across a 1.5 km2 area of the central flow unit which deglaciated between 2010 and 2023. From 2010 to 2017, the landscape featured streamlined subglacial material, a stable subglacial esker system and proglacial lakes (Landsystem A), shifting to a spillway-dominated system between 2018 and 2023 (Landsystem B). Since 2018 this section of Breiðamerkurjökull has been retreating across a reverse slope bed, resulting in the formation of quasi-annual ice-marginal spillways. Meltwater impoundment at the ice margin, formed ice-contact lakes which eventually initiated ice-margin parallel spillways draining proglacial meltwater along the local land-surface gradient, towards Jökulsárlón. As the ice retreats, an ice-contact lake forms again at the new margin and initiates the erosion of the next ice-marginal spillway. The geomorphological signature demonstrates how subglacial topography and ice-flow switching can significantly influence ice and meltwater dynamics. Since the glacier flow-switch, part of the central unit is now lake-terminating with areas of the margin evolving into a stagnant system, as it is now cut off from the accumulation centre. Therefore, Landsystem B could be analogous to regions of ice stream shut down and where ice masses retreated across reverse slope beds. For example, the Pakowki Lake region of Southeastern Alberta displays a similar landform assemblage and is presented as a palaeo-example in this work. Such insights are important for assessing the efficacy of numerical models in reconstructing the finer scale dynamics of past ice sheets during retreat

Manual mapping of drumlins in synthetic landscapes to assess operator effectiveness

Mapped topographic features are important for understanding processes that sculpt the Earth's surface. This paper presents maps that are the primary product of an exercise that brought together 27 researchers with an interest in landform mapping wherein the efficacy and causes of variation in mapping were tested using novel synthetic DEMs containing drumlins. The variation between interpreters (e.g. mapping philosophy, experience) and across the study region (e.g. woodland prevalence) opens these factors up to assessment. A priori known answers in the synthetics increase the number and strength of conclusions that may be drawn with respect to a traditional comparative study. Initial results suggest that overall detection rates are relatively low (34–40%), but reliability of mapping is higher (72–86%). The maps form a reference dataset

Eskers associated with buried glaciers in Mars' mid latitudes: recent advances and future directions

Until recently, the influence of basal liquid water on the evolution of buried glaciers in Mars’ mid latitudes was assumed to be negligible because the latter stages of Mars’ Amazonian period (3 Ga to present) have long been thought to have been similarly cold and dry to today. Recent identifications of several landforms interpreted as eskers associated with these young (100s Ma) glaciers calls this assumption into doubt. They indicate basal melting (at least locally and transiently) of their parent glaciers. Although rare, they demonstrate a more complex mid-to-late Amazonian environment than was previously understood. Here, we discuss several open questions posed by the existence of glacier-linked eskers on Mars, including on their global-scale abundance and distribution, the drivers and dynamics of melting and drainage, and the fate of meltwater upon reaching the ice margin. Such questions provide rich opportunities for collaboration between the Mars and Earth cryosphere research communities