美国国家航空航天局NASA每日一图-2017年7月7日

Winds Trigger Pond Growth

Wind is a force to be reckoned with. It can stir up monsoons, carry dust thousands of miles, and sculpt rock into sinuous arches. But sometimes, the effects of wind go unnoticed for years, like when it carves away slowly at the edges of a pond.

A new study shows that winds are responsible for the widespread growth of ponds in three watersheds along the Mississippi River. The paper, published in April 2017 in Geophysical Research Letters, shows that wind-driven waves can erode pond banks, leading them to migrate in the direction of the wind. In effect, researchers have shown that wind-driven erosion, which nibbles away coastlines and the edges of larger bodies of water, can also happen inland on small scales.

The researchers analyzed roughly 10,000 satellite images taken between 1982 and 2016, examining land and water pixels to look for inland change across the Mississippi River Delta. “Up until now, a lot of focus has been on coastal retreat,” said Alejandra Ortiz, a marine geologist at Indiana University, Bloomington. Instead, Ortiz and colleagues focused on internal fragmentation; that is, what happens when land becomes subdivided by inland erosion processes. “Our thinking was, can you see this on large scale?”

Ortiz and her co-authors found that ponds in the Mississippi Delta tended to expand in a southwesterly direction, which is the same direction as the prevailing winds (which blow out of the northeast). This was especially true in Terrebonne and Barataria basins, where 80 percent of the ponds are expanding. The other study basin, the Atchafalaya-Vermillion, was deemed stable, with nearly as many ponds contracting as expanding—roughly 30 percent.

The false-color image above shows the area of study along the Atchafalaya Delta. It was captured on December 1, 2016, by the Operational Land Imager (OLI) on Landsat 8. The colors emphasize the difference between land and water while allowing viewers to observe waterborne sediment, which is typically absent from false-color imagery.

References and additional images: NASA Earth Observatory

Image Credit: NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey and data from Ortiz, A. C., Roy, S., & Edmonds, D. A. (2017)
Caption: Pola Lem

Last Updated: July 7, 2017
Editor: Sarah Loff

风引发池塘的扩张

风是一个值得考虑的力量。 它可以搅拌季风,携带数千英里的灰尘,并将岩石雕成弯曲的拱门。 但有时候,风的影响多年来一直被忽视,就像当它在池塘边缘慢慢地雕刻出来的时候。

一项新的研究显示,风对于密西西比河三个流域的池塘的广泛发展负责。这篇论文于2017年4月发表在“地球物理研究通讯”中,表明风力波浪可能会侵蚀池塘银行,导致它们向风向移动。实际上,研究人员已经表明,风力侵蚀会使海岸线和大型水体的边缘萎缩,也可能发生在小规模的内陆地区。

研究人员分析了1982年至2016年期间拍摄的大约10,000颗卫星图像,检查土地和水域像素,以查找密西西比河三角洲的内陆变化。布卢明顿印第安纳大学的海洋地质学家亚历杭德拉·奥尔蒂斯(Alejandra Ortiz)说:“到目前为止,海岸撤退的重点还是很多。相反,Ortiz和他的同事专注于内部分裂;也就是说,当土地被内陆侵蚀过程细分时,会发生什么。 “我们的想法是,你能看到这个大规模吗?

Ortiz和她的合着者发现,密西西比河三角洲的池塘往往以西南方向扩张,这与当时的风吹向东方方向相同。在Terrebonne和Barataria盆地尤其如此,80%的池塘正在扩张。另一个研究盆地,Atchafalaya-Vermillion,被认为是稳定的,几乎有许多池塘缩小约30%。

上面的假彩色图像显示了沿着Atchafalaya三角洲的学习领域。它于二零一六年十二月一日由Landsat 8的营运土地拍摄者(OLI)捕获。这些颜色强调了陆地与水之间的差异,同时让观众观察到水中沉积物,而这些沉积物通常不存在于假色图像中。

参考和其他图像:NASA地球观测站

图片来源:美国宇航局地球天文台图片由Joshua Stevens,使用美国地质调查局的Landsat数据和Ortiz,A.C.,Roy,S.,&Edmonds,D.A。(2017)的数据,
图片:Pola Lem

最后更新:2017年7月7日
编辑:莎拉·洛夫

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