Acoustic instruments on the submarine told us that there was a ridge at the bottom of the ocean, sitting transverse to the flow of ice.

潜艇上的声波仪器告诉我们，在海洋底部有一道海脊，横向坐落在冰流方向上。

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The road dips a precipitous path along the ridge from where the deep geological gash of the Great Rift Valley cascades downwards to meet its bottom at the Dead Sea, 400m below sea level.

BBC: Travelling the slow route to Petra