水下地下(Underwater underground)

墨西哥的尤卡坦半岛就像一块巨大的瑞士奶酪，布满了被称为洞穴的洞。当地下石灰岩溶解时，会形成洞穴，使地下水渗入。上面的岩石可能会塌陷，形成一个坑，露出凉爽的，通常是水晶般清澈的水，而其他的洞穴可能仍然隐藏着，未经勘探。洞穴的大小从很小到几十码不等，最近的发现表明，洞穴形成了一系列地下洞穴系统，其长度可以跨越几英里。
原文：
Like a giant block of Swiss cheese, Mexico’s Yucatan Peninsula is riddled with holes called cenotes. Cenotes form when subterranean limestone dissolves, allowing underground water to penetrate. The rock above may cave in, forming a pit and revealing the cool, often crystal-clear water, while other cenotes may remain hidden and unexplored. Cenotes vary in size from very small to several dozen yards across, and recent discoveries have shown that cenotes lead to a series of underground cave systems that can span several miles in length.
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