[揽瓜阁精读] 54. 金星Long Channels (Canali)

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Most landtorms of the volcanic plains and rises are reasonably ascribed to basaltic lavas. However, in several places the basaltic plains are incised by long meandering channels, designated canal the fluid that cut the canali is not known. Canali are long channels, from 500 to 6800 km in length, singous and meandering, incised into volcanic plains (and rarely tesserae). Their widths are typically 3 km, ranging up to 10 km, and are constant over the lengths of each canale, Shorter channels are comparable to the lumar sinuous rilles, and can reasonably be ascribed to the flow of basaltic lava. But the longer canali, with their constant widths, are enigmatic.

1. 介绍背景：火山爆发 运河 岩石 是什么样的，怎么形成的

The challenge presented by canalis to understand what sort of fluid could flow, at Venus' surface, for the distance and time needed to produce channels 500 to 6800 kilometers long. Baker et al. [1992] showed that the canali required a low-viscosity fluid that was either very hot or had a melting temperature close to that of the Venus surface. Basaltic and komatitic lavas seem to be precluded by their rapid cooling rates on Venus. The rapid cooling could be reduced by formation of an insulating cover, partially as a roof (although the channels are too wide to be spanned to form a lava tube), and partially by solid plates floating on and carried by the flow. On the other hand subsurface flows of basaltic lava could conceivably produce long channels, but it is not clear if sub-surface flows could produce the observed meanders of the canali.

2.
canali 带来的挑战是理解金星表面流的是哪种液体，因为它要流500到6800千米
Baker指出canali要一种low-viscosity的流体，要么很热要么接近金星表面的温度
后面解释原因和原理（这几句没看的很明白，玄武质和科马提质熔岩似乎被金星上快速冷却的速度排除在外。快速冷却可以通过形成一个绝缘覆盖物来减少，部分是作为屋顶(尽管通道太宽，无法跨越形成熔岩管)，部分是通过固体板漂浮在流动上并被流动携带。）
另一个方面底下流动的岩浆可能产生长的通道，但是这样一种流动是否能产生蜿蜒曲折（meander）的canali还是未知的

Possible liquids other than basalts include liquid sulfur, carbonate-rich lavas (carbonatites), and even water if the channels formed when Venus' surface were considerably cooler than at present.
Liquid sulfur is a plausible（合理的） product of reaction between oxidized atmospheric sulfur and reducing silicate rocks, but its low vapor pressure in the Venus atmosphere may imply that it would evaporate too rapidly to produce long channels (Komatsu et al., 1992).
Carbonate-rich and carbonate-sulfate lavas were considered by Kargel et al. (1994] and shown to have appropriately low viscosities, erosive potentials, and melting temperatures. They also showed that carbonate-sulfate liquids could plausibly form in the shallow crust by burial of basalt rock that was weathered at the surface

3.
除了玄武岩，这个液体可能还包含液体硫，富含碳的岩浆，甚至是水如果金星表面的通道的温度比现在低很多
液态硫是大汽中硫化物和减少的硅化的石头（猜的，化学东西）的合理产物，但它在金星大钟的低气压可能暗示了它可能会在长的通道里蒸发过快
富含碳和硫碳岩浆被K等人认为有低粘滞性（viscosities），腐蚀的潜力和融化的温度，他们还说这些东西可以在空气和石头什么作用下面形成