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Overspilling small craters on a dry Mars: Insights from breach erosion modeling
Earth and Planetary Science Letters ( IF 5.3 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.epsl.2020.116671
A.O. Warren , S. Holo , E.S. Kite , S.A. Wilson

Abstract Understanding when, where, and how frequently liquid water was stable on Mars since the Late Noachian/Early Hesperian (3.2-3.9 Ga) is important for understanding the evolution of Mars' climate and hydrology. Some relatively young features on Mars require multiple wetting events to form, whereas others are consistent with single wetting events. Small and rare exit breach craters or “pollywogs” are craters between 0.5 and 15 km in diameter with valleys leading away from the lowest point on their rims but no visible inlet valleys. These craters must have been filled with water to the point of overspill to form the observed valleys. The two possible water sources are precipitation and groundwater. In this paper we use measurements from Digital Elevation Models (DEMs) of 18 pollywog craters (21 outlet valleys) and a fixed channel width 0-D breach erosion model to determine whether pollywog exit breach valleys are consistent with a single crater overspill event, or if their formation requires multiple overspill events. Our model, which we compare to a selection of dam breaching events on Earth, predicts runaway erosion for two pollywog exit breaches. No runaway erosion is observed. We discuss potential explanations for this mismatch between the data and our model. We show that the majority of pollywog craters on Mars are consistent with formation during a single crater overspill event, incorporating a work around for the long-standing problem of unknown grainsize into our approach. Three pollywog craters require either multiple events or sustained water supply to drive erosion. We discuss potential source mechanisms for crater-filling water and conclude that pollywogs either formed in a single erosion event, driven by groundwater discharge, or through many small erosion events, driven by draining of small meltwater lakes formed on crater-filling bodies of ice.

中文翻译:

在干燥的火星上溢出的小陨石坑:来自破坏侵蚀模型的见解

摘要 了解自晚诺亚世/早西伯利亚 (3.2-3.9 Ga) 以来,液态水在火星上稳定的时间、地点和频率对于了解火星气候和水文的演变非常重要。火星上一些相对年轻的特征需要多次润湿事件才能形成,而另一些则与单一润湿事件一致。小型且罕见的出口缺口陨石坑或“pollywogs”是直径在 0.5 至 15 公里之间的陨石坑,其山谷从其边缘的最低点延伸,但没有可见的入口山谷。这些陨石坑一定已经被水充满到溢出点,从而形成了观察到的山谷。两种可能的水源是降水和地下水。在本文中,我们使用来自 18 个 Pollywog 陨石坑(21 个出口谷)的数字高程模型 (DEM) 和固定通道宽度 0-D 裂隙侵蚀模型的测量结果来确定 Pollywog 出口裂隙谷是否与单个陨石坑溢出事件一致,或如果它们的形成需要多次溢出事件。我们的模型与地球上的一系列大坝溃坝事件进行了比较,预测了两个波利沃格出口溃坝的失控侵蚀。没有观察到失控侵蚀。我们讨论了数据和我们的模型之间这种不匹配的潜在解释。我们表明,火星上的大多数 Pollywog 陨石坑与单个陨石坑溢出事件期间的形成一致,将解决长期存在的未知颗粒大小问题的方法纳入我们的方法。三个pollywog 陨石坑需要多次事件或持续供水来推动侵蚀。我们讨论了火山口填充水的潜在来源机制,并得出结论,Pollywogs 要么在单个侵蚀事件中形成,由地下水排放驱动,要么通过许多小侵蚀事件形成,由在填充火山口的冰体上形成的小型融水湖的排水驱动。
更新日期:2021-01-01
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