But on the moon such geologic features usually occur following collapses of lava tubes, which formed long ago in the moon's history.

但是在月球上，这些地质特征却往往是伴随着熔岩管(很久以前就已经出现在月球上了)崩塌而出现的。

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It is believed there may be many different formation mechanisms including ancient magma flows and the collapse of subterranean lava tubes.

据信可能是由于多种原因造成的，包括古岩浆流动和地下熔岩道的崩塌。

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Fossil skeletons found in lava tubes on the island, though, show that the nene was not originally alone.

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"The terrain where we were working was really dramatic, with all kinds of lava tubes and crevices, " said Phoenix business-development manager Pete LeHardy in Largo, Md.

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