卡卡是由地下碳酸钙。>为什么它只发生在干旱的土壤?因为这是碳酸钙在潮湿的环境中会发生什么:[![在这里输入图像描述][1]][1]它溶解,形成一个山洞。碳酸钙、或方解石,溶于酸性温和的解决方案。雨水是弱酸性,因为2有限公司<子> < /订阅>从大气中溶解,所以它永远不会允许土壤中的碳酸钙沉积的形成。至于为什么在干旱的土壤,它形成的维基百科页面(钙质层)[2]解释:>钙质层一般形式在矿物浸出的上层土壤(A层)和积累下一层(B层),在3到10英尺的深度下的表面。它通常由碳酸盐在半干旱地区干旱地区,更难溶矿物质形成钙质层毕竟碳酸盐可以从土壤中过滤出来。沉积碳酸钙accumulates-first形成颗粒,然后小团,然后一个明显的层,最后,厚,固体床。作为钙质层层形式,逐渐变得更深,并最终进入母材,坐落在上层土壤的视野。> >然而,钙质层在其它方面也形成。 It can form when water rises through capillary action. In an arid region, rainwater sinks into the ground very quickly. Later, as the surface dries out, the water below the surface rises, carrying up dissolved minerals from lower layers. This water movement forms a caliche that tends to grow thinner and branch out as it nears the surface. Plants can contribute to the formation of caliche, as well. Plant roots take up water through transpiration, and leave behind the dissolved calcium carbonate, which precipitates to form caliche. It can also form on outcrops of porous rocks or in rock fissures where water is trapped and evaporates. In general, caliche deposition is a slow process, but if enough moisture is present in an otherwise arid site, it can accumulate fast enough to block a drain pipe. (photo from http://www.naturephoto-cz.com/karst-cave-photo-24442.html) [1]: https://i.stack.imgur.com/QGxn8.jpg [2]: https://en.wikipedia.org/wiki/Caliche