Sinkhole Science

Sinkhole Science, written by Sean McCollum.

《天坑科学》，作者：肖恩·麦卡勒姆。

Two Huge Holes For a few weeks in 2007, people in a neighborhood of Guatemala City felt the ground tremble and shake. No one knew what was causing it. Then on February 23, a huge hole suddenly opened in the street. A dozen houses tumbled into the pit, and several lives were lost. The hole was more than three hundred thirty feet, one hundred meters, deep, deep enough to swallow two statues of liberty.

两个巨坑 2007年，一连好几周，危地马拉城一个社区的居民都感觉到地面在颤动摇晃。 没人知道震颤的原因是什么。 随后在2月23日，路面上突然裂开了一个大洞。 十几栋房屋掉进了坑中，不少人因此失去了生命。 这个洞深超过330英尺，也就是100米，深度足够吞没两座自由女神像。

In 2010, it happened again, 15 blocks from the first hole. This time, the hole swallowed a three -story clothing factory and left another gaping chasm in a major intersection. miraculously no one was injured. Sinkholes happen all over the world, in the middle of cities, and in the middle of nowhere. Though sinkholes take years to form, each time a new sinkhole opens up in the earth, it takes people by surprise. What Causes Sinkholes? The ground we stand on feels solid. Underground, however, a lot is happening. Water trickles and flows, slowly eroding rocks and soil. This creates underground spaces. These result in sinkholes. Sinkholes don't happen just anywhere, though. Most natural sinkholes form where there are certain kinds of soft bedrock. Bedrock is a layer of underground rock. The ground above it and on the surface is called the overburden.

2010年，同样的事再次发生，地点距离第一个天坑仅15个街区。 这一次，天坑吞没了一栋三层楼高的服装厂，在主干道交叉口留下了另一个巨大深坑。 神奇的是，没有人受伤。 天坑在世界各地都有出现，无论是城市中心，还是荒无人烟之地。 尽管天坑需要数年才能形成，但每一次新天坑在地表裂开，都让人们措手不及。 天坑是怎么形成的？ 我们脚下的土地摸起来十分结实坚硬。 可是在地下，一直有许多变化在发生。 水流不断渗过，慢慢侵蚀着岩石和土壤。 这个过程会形成地下空洞。 这些空洞最终就变成了天坑。 不过天坑并不是随便在哪里都会形成。 大多数天然天坑形成于拥有特定软基岩的区域。 基岩是地下的一层岩石。 基岩上方、地表的土层叫做覆盖层。

Rain or underground water drips and flows into this bedrock and erodes it. This creates open spaces, such as underground caves or caverns. Over time, these spaces get bigger. Eventually, the overburden may slowly drop down to form a sinkhole. Sometimes, though, sinkholes can open suddenly and swallow buildings, cars, and people. Two Types There are two main types of sinkholes. The first is a cover -subsidence sinkhole. Subside means to sink or settle. A cover -subsidence sinkhole forms when water wears a space in the underground bedrock. The overburden above the bedrock then shifts downward. Most sinkholes of this kind form slowly and may measure only a few yards across. The overburden may contain a lot of sand that easily slides into the underground space. These sinkholes often create a bowl shape on the surface. They may become ponds or wetlands if water has no way to drain out.

雨水或是地下水渗进基岩，不断侵蚀它。 侵蚀会形成空地，比如地下洞穴或者岩洞。 久而久之，这些空洞会变得越来越大。 最终，覆盖层可能慢慢下沉，形成天坑。 不过有时候，天坑会突然裂开，吞没建筑、汽车和行人。 天坑的两种类型 天坑主要分为两类。 第一种是覆盖沉陷型天坑。 沉陷的意思就是下沉、沉降。 当水流侵蚀地下基岩形成空洞后，这类天坑就开始形成。 之后基岩上方的覆盖层会向下移位。 大多数这类天坑形成缓慢，直径往往只有几码宽。 覆盖层可能含有大量沙子，很容易滑进地下空洞里。 这类天坑通常会在地表形成碗状凹坑。 如果水无法排出，它们还会变成池塘或者湿地。

The second type is a cover collapse sinkhole. This sinkhole forms when a space gets bigger and bigger under the surface. The overburden gets thinner as dirt, sand, and other sediment fall into the space. The ground around this kind of sinkhole may contain a lot of sticky clay. Clay helps hold the overburden together. Without warning, though, the surface may collapse into the underground space.

第二种是覆盖塌陷型天坑。 这种天坑形成时，地表下的空洞会变得越来越大。 随着泥土、沙子和其他沉积物掉进空洞，覆盖层变得越来越薄。 这类天坑周边的土层往往含有很多黏性黏土。 黏土能把覆盖层粘合在一起。 可即便如此，地表也会毫无征兆地塌陷，掉进地下空洞。

Areas that get a lot of sinkholes usually have bedrock made of karst. Karst is made of any type of rock that dissolves easily, such as limestone. Karst can also be formed of gypsum, dolomite, salt, or other minerals and rocks. Karst has many holes and cracks that water can flow into. When rainwater soaks into the earth, it picks up a mild acid from leaves and plants. The mild acid dissolves karst. This helps create the underground spaces that cause natural sinkholes.

多发天坑的区域，基岩通常都是喀斯特。 喀斯特由容易被溶解的岩石构成，最常见的就是石灰岩。 喀斯特也可以由石膏、白云石、盐或者其他矿物岩石构成。 喀斯特有很多孔洞和裂缝，水能顺着流进去。 雨水渗进地下时，会从树叶和植物那里带上弱酸。 这种弱酸会溶解喀斯特。 这个过程会催生地下空洞，最终形成天然天坑。