According to the rescue headquarters, an initial investigation showed that the cause of the accident was the local gas explosion underground.

据事故抢险指挥部介绍，现已初步查明，事故原因为井下局部瓦斯爆炸。

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Twenty-nine of them died in an explosion at an underground mine in West Virginia on April fifth,twenty-ten.

VOA: special.2011.07.01

Panetta said U.S. technical experts are still assessing available data to learn more about the underground explosion.

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"Well No. 4 in this area was being drilled at this site here when suddenly an underground steam explosion managed to get its way to the surface, " he explains.

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Shatter cones are surface features with distinctive wavy patterns that are known to be created only by the tremendous force of a meteorite impact or an underground nuclear explosion.

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