冰山是断裂的冰川滑入水中的一部分,它们漂浮一段时间,最终融化。现在漂浮着的冰山是由以往漫长岁月里飘落的雪花形成。它们承载的雪是数百年乃至数千年前落下的,有的还可能是100万年前的。雪飘落在极地和寒冷的高山上,仅仅融化一点或根本就不融化,年深日久逐渐达到了很深的厚度。
覆盖在表面的雪年复一年地累积,蒸发和融化使雪花逐渐失去了羽状边角,变成细小的冰粒。当新雪落在旧雪上时,也变成了冰粒。就这样,雪和冰粒层层重叠,变得非常厚,以致上层的重量紧紧压住了下层。随着时间的推移以及来自上层的压力,众多细小的冰粒互相结合并转变为更大的水晶,最终深层的水晶融合成巨大的坚冰。
测试题
1.The author states that icebergs are rarely seen as they appear in_______________of the world.
2.From the passage,we can know that the shape of icebergs is___________________.
3.According to the passage,icebergs are scary and dangerous because they are likely to_______________________suprisingly.
4.What glaciers become when they break off and drift into the water?
5.What are the major factors in the process of the many small ice grains being merged into icebergs?
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