因为他不是在火山活动期间形成的，弹坑的外壁是由沉积岩而不是火山石组成的。
Because it wasn't formed during volcanic activity, the walls of the crater are composed of sedimentary rather than volcanic rock.
沿大裂谷形成的火山大爆发这个问题和其他“大弹坑，”以及在底部渣锥。
Large volcanic eruptions along the Great Rift formed this and other "big craters," as well as the cinder cones at the bottom.
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