The Martian drainage system and the origin of valley networks and fretted channels
The Martian drainage system and the origin of valley networks and fretted channels
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火星排水系统以及山谷网络和微动河道的起源
DOI：
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发表时间：
1995
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影响因子：
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通讯作者：
M. Carr
中科院分区：
文献类型：
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作者：
M. Carr
流出通道为火星表面附近丰富的水和广泛的地下水系统提供了强有力的证据。地表塌陷到某些渠道意味着除了地表水流的侵蚀外，还有大规模的地下侵蚀和/或溶蚀作用。平坦的地面、陡峭的墙壁、纵向的条纹和山脊，条纹从渠道壁向下游偏转，以及缺乏河道，这些都表明，微动的渠道主要是由大量浪费形成的。提出了一种两步法工艺。在第一阶段，地下水从坡面渗入碎屑流，有利于谷头沟谷的扩展。碎屑在碎屑底部间隙地下水的帮助下向下游移动，可能具有高孔压。在第二阶段，由于气候变化或较低的热流，地下水不能再渗入山谷中的泥石流，它们的运动几乎停止，形成更多粘性的冰润滑泥石流围裙。几乎所有海拔高于+1公里的高地都被山谷网络切割，尽管排水密度比地球上的典型排水密度低一个数量级。河谷网络在平面形状上类似于陆地河流系统，但U形和矩形的横截面、堤状的外围脊、中间脊、分支和重新连接的图案以及没有河道的平坦地板表明，这些网络可能不是真正类似于陆地河流流域的网络。认为它们与微动河道一样，主要由大量浪费形成，地下水渗入大量废弃碎石中为辅。每年只需要几毫米到厘米的运动就可以解释河道的长度。大多数山谷的形成在低纬度地区很早就停止了，因为近地表逐渐脱水，这是水升华和/或地下水排水到较低海拔地区的结果。山谷的形成持续到后来，在陡峭的斜坡上，如火山口和峡谷的墙壁上，和/或在高热流和水的存在下，如在一些火山上。
Outflow channels provide strong evidence for abundant water near the Martian surface and an extensive groundwater system. Collapse of the surface into some channels suggests massive subsurface erosion and/or solution in addition to erosion by flow across the surface. Flat floors, steep walls, longitudinal striae and ridges, downstream deflection of striae from channel walls, and lack of river channels suggest that fretted channels form dominantly by mass wasting. A two-stage process is proposed. In the first stage, extension of valleys at valley heads is favored by seepage of groundwater into debris shed from slopes. The debris moves downstream, aided by interstitial groundwater at the base of the debris, possibly with high pore pressures. In the second stage, because of climate change or a lower heat flow, groundwater can no longer seep into the debris flows in the valleys, their movement almost stops, and more viscous ice-lubricated debris aprons form. Almost all uplands at elevations greater than +1 km are dissected by valley networks, although the drainage densities are orders of magnitude less than is typical for the Earth. The valley networks resemble terrestrial river systems in planimetric shape, but U-shaped and rectangular-shaped cross sections, leveelike peripheral ridges, median ridges, patterns of branching and rejoining, and flat floors without river channels suggest that the networks may not be true analogs to terrestrial river valleys. It is proposed that they, like the fretted channels, formed mainly by mass wasting, aided by groundwater seepage into the mass-wasted debris. Movements of only millimeters to centimeters per year are needed to explain the channel lengths. Most valley formation ceased early at low latitudes because of progressive dehydration of the near surface, the result of sublimation of water and/or drainage of groundwater to regions of lower elevations. Valley formation persisted to later dates where aided by steep slopes, as on crater and canyon walls, and/or by high heat flows and the presence of water, as on some volcanoes.