2020 April 13

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A Sailing Stone across Death Valley
Image Credit:
Keith Burke

Explanation: How did this big rock end up on this strange terrain? One of the more unusual places here on Earth occurs inside Death Valley, California, USA. There a dried lakebed named Racetrack Playa exists that is almost perfectly flat, with the odd exception of some very large stones, one of which is pictured here in April of 2019 beneath a dark, Milky-Way filled sky. Now the flatness and texture of large playa like Racetrack are fascinating but not scientifically puzzling — they are caused by mud flowing, drying, and cracking after a heavy rain. Only recently, however, has a viable scientific hypothesis been given to explain how heavy sailing stones end up near the middle of such a large flat surface. Unfortunately, as frequently happens in science, a seemingly surreal problem ends up having a relatively mundane solution. It turns out that in winter thin ice sheets form, and winds push ice sections laden with even heavy rocks across the temporarily slick playa when sunlight melts the ice.

Tomorrow’s picture: garbled galaxy

穿越死亡谷航行石
图片来源及版权:
Keith Burke

说明:在这片奇怪的土地上为什么会有这么大的石头呢?这一幕发生在地球上最不寻常的地方之一,美国加利福尼亚的死亡谷。那里有一片叫赛马场盐湖的干涸湖床。除了有一些非常大的石头,它几乎是完全平坦的。照片拍摄的就是2019年4月在一片黑暗的、银河高挂的天空下的大石头。像赛马场一样的大型干盐湖的平坦与纹理令人着迷,它们的成因也不再令人困惑—它们是暴雨后的泥浆流动、凝固、皴裂后形成的。然而,最近提出的可行的科学假说解释了在如此大的平面中间为什么会有这些又重又大的航行石。不幸的是,就像科学界常发生的那样,一个看似超现实的问题最终只会有一个相当平凡的解释。结论是,当冬季薄形成时,风吹着裹挟着大石头的冰块,临时滑过了光滑的干涸湖床。当阳光将冰融化后,石头就留在了那里。

明日一图预告:garbled galaxy

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敬明 李

汝之盛颜,无法言语,无人能及