Multiple flooding events in Martian outflow channels
Multiple flooding events in Martian outflow channels
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火星流出通道发生多起洪水事件
DOI：
10.1029/2007je002951
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发表时间：
2008
影响因子：
--
通讯作者：
R. Grimm
中科院分区：
文献类型：
--
作者：
K. Harrison;R. Grimm
[1]在火星克赖斯平原的大型流出通道上，被认为是由受限冰冻圈下的含水层排出的洪水切割而成。然而，传统的地下水流动模型需要乐观的高渗透率，才能在一次洪水事件中产生从渠道形态推断的流量和流量。此外，当混乱的地形裂缝重新冻结时，可能会停止排放，将其带到地表，进一步限制了一次洪水产生的水量。因此，可能需要多次地表径流事件，我们用区域地下水模拟来量化这一假设。每一次排放事件都是由渠道源区的超静岩水力压头引起的冰冻圈破坏触发的，并由冰冻圈裂缝重新冻结而终止。在下一次地震之前，允许Head在以前的全球地下水模型约束的远距离含水层补给的帮助下恢复。我们的基线模型模拟了开成河谷的源区，即使是对应于10−9 m2近地表数值的高深度平均含水层渗透率，也至少产生2,900次洪水事件。尽管其他环流河道所需的事件较少，但由一次洪水形成的可能性仍然很小。我们建议，可以通过另一种模型来绕过不切实际的高洪水，该模型涉及到局部积水形成站立水体。这些水体的间歇性破坏产生了洪水暴发，侵蚀了河道。
[1] The large outflow channels of Chryse Planitia, Mars, are thought to have been carved by floodwaters discharged from an aquifer beneath a confining cryosphere. However, conventional models of groundwater flow require optimistically high permeabilities to produce, in a single flooding event, the discharge rates and volumes inferred from channel morphology. Additionally, discharge likely ceased upon refreezing of chaotic terrain fractures carrying it to the surface, further limiting the volume of water produced in a single flood. It is thus probable that multiple surface discharge events were required, and we quantify this hypothesis with regional groundwater simulations. Each discharge event is triggered by cryosphere disruption due to superlithostatic hydraulic head at the channel source region and is terminated by cryosphere fracture refreezing. Before the next event, head is allowed to recover with the aid of distal aquifer recharge constrained by previous global groundwater models. Our baseline model, which emulates the source region of Kasei Valles, yields a minimum of 2900 flooding events even for high depth-averaged aquifer permeabilities corresponding to near-surface values of 10−9 m2. Although fewer events are required for other circum-Chryse channels, formation by a single flood remains improbable. We suggest that unrealistically high numbers of floods may be circumvented by an alternative model involving the local ponding of surface discharge to form standing bodies of water. Episodic failure of these bodies produces flood outbursts which erode the channels.