也可能是由某种长期变化导致而成，比如积聚的温室气体(或可以想象成笼罩上了一层层的烟雾)。

Or it might be something driven by a long-term change, such as the build-up of greenhouse gases (or, conceivably, layers of sooty smog).

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他们在白天几乎不停地进食来积聚一层脂肪，用来在寒冷的夜晚慢慢消耗。

They feed almost constantly during daylight to accumulate a layer of fat that will burn slowly through the cold night.

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这座高达2582米（9357英尺）的成层火山（百科看 这里——译注）顶部被一层30平方公里的冰川（10平方英里）所覆盖，大部分冰雪都积聚在山顶南部和东部因岩浆喷发所形成的盆地中。

The 2,582-meter (9,357-foot) stratovolcano is mantled by a 30-square-kilometer (10-square-mile) glacier field, most of it amassed south and east of the summit in a basin made by a caldera depression.

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