al-Qamar

فَفَتَحْنَا أبْوَابَ السَّمَاء بِمَاء مُّنْهَمِرٍ

وَفَجَّرْنَا الْأرْضَ عُيُونًا فَالْتَقَی الْمَاء عَلَی أمْرٍ قَدْ قُدِرَ

11. Therefore, We opened the gates of the heavens with water pouring forth.

12. And We caused springs to gush forth from the earth. Therefore, the waters from the earth and the heaven joined for a matter preordained.

The blessed Verses make a telling and awe-inspiring reference to the manner of their torment saying that following Noah's (as) invocation, We opened the gates of the heaven and an incessant and heavy rain poured down. The metaphor of opening the gates of the heaven is a beautiful one which is employed at the time of pouring down heavy rain. The metaphor is also used in the Persian tongue when it is said that it is as if the gates of heaven have opened and all the rain is pouring down.

The Arabic word munhamir ("pouring down, flowing down") derives from h-m-r ("pour down, flow") connoting heavy pouring down of rain or flowing of tears. The word is also figuratively employed to connote milking animals to the last drop. It would be of interest to know that according to some exegetes, they had been afflicted with famine for years and expected rain until a fatal rain, rather than a rejuvenating one, poured down. The blessed Verse 12 is saying that such heavy rain poured down that water gushed forth from the earth, as reflected in the blessed Verse in question. God Almighty cleft the earth asunder and made many a spring gush forth from the same. The two waters intermingled as it was preordained and encompassed all over the earth.

In short, water gushed forth from all over the earth and springs flowed and a heavy rain poured forth and the waters met and formed an immense and agitating ocean.