Thank you for your enjoying this poem! I love both, too. Yeah, the images are very wonderful.

The surging Chu River/Yangtze River seems to split the Mountain Tianmen in half when running from the west to east in Dangtu county. Then it turns north and arrives in Nanjing, pouring into East China sea by Shanghai in the end. (It is also very interesting for myself to learn something new when I read this poem again.) The mountains on both sides gradually unfold themselves as if to greet the ship by which the young poet Li Bai began his journey.

(Oh, maybe I should add one point: Tianmen is the pinyin/phonics of 天门. 天 means sky or heaven; 门 means gate. So in the second version, the translator calls it as Mountain Heaven's Gate.)