英语听力文摘 English Digest 554、岩石怎么会出现在你的花园？

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　　I wonder how many of us went out this past spring to get our gardens ready for planting, smug in the thought that last year we got rid of all the rocks. There’s that nice big mound¹ of them in the corner of the garden where we piled them. Surely by now they are all cleaned out.

 

　　“Wait! What is this?!” A big stone, and another one, and another one! Where did they come from? Did some mischievous² kid bury a bunch of them for me to find this spring? Well, that could be,But maybe this time the kids were actually innocent.

 

　　Any place that has winters cold enough to freeze the ground might experience the magical appearance of rocks welling up from beneath the surface. This is so common in the eastern U.S. that the rocks are called “New England potatoes.”

 

　　Here’s what makes these stones mysteriously appear. Stones are better conductors of heat than soil, so the stone conducts heat away from the warmer soil beneath it. That colder soil under the rock then freezes before other dirt at the same depth.

 

　　Remember that when water freezes it expands. So, when the water in the soil under the rock freezes, it expands and pushes the rock up a little.

 

　　When the ground thaws³ a space is left under the stone which fills with dirt, so the stone rests a little higher. Over a period of time this repeated freezing, expanding, upward push, and filling underneath⁴ eventually shoves⁵ the rock to the surface.

 

 

　　岩石是怎么出现在你的花园？

 

　　我好奇有多少人在刚刚过去的春天修整了花园，准备大干一场，自以为去年早已清理干净了所有石块。看看花园角落里那一大堆战利品！现在所有石块肯定都被清理出来了。

 

　　“等等！这是什么？！”一块大石头，又一块，又一块！从哪里冒出来的？莫不是哪个调皮的小子专程埋了一堆石头好让我在春天来时挖出来？嗯，有可能，但或许这次你的确错怪了人家。

 

　　任何冬季寒冷到足以令地表结冰的地方，都会出现这一神奇的现象：岩石从地下冒出来。这种现象在美国东部尤其常见，以至于人们将岩石称为“新英格兰土豆”。

 

　　石头神秘现身的原因如下：较泥土而言，石头是更为良好的热导体，因此石头会将其下方温度更高的泥土的热量传递走。在同样的深度，岩石下方的泥土由于温度低便会更早结冰。

 

　　要知道当水结冰时体积会膨胀。所以，当岩石下方泥土中的水分结冰时，其体积变大膨胀并将岩石向上推高了一点。

 

　　当地表开始融化，石块下方的空间被泥土填满，石块便停留在高一点的地方。日积月累，冰冻-膨胀-向上推力-填充间隙的过程不断重复，最终推挤石块重现地表。

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