Over millions of years, 数百万年来

45. After ten months of drought,
    十个月的干旱以后
46. millions of tonnes of water
    百万吨降水
47. are dumped on the land in under an hour.
    在一小时内倾泻而下
48. Over millions of years,
    数百万年来
49. sand and gravel carried by the rampaging floods
    挟带着砂石的湍急洪水
50. have carved channels through the solid rock.
    在坚硬的岩石上切割出凹槽
51. Slot canyons, 150 feet deep.
    形成狭缝谷 深达四十六米

来自《行星地球 第二季 第四集 Planet Earth S02E04 沙漠》第 48 行