Nooh's flood encompassed the entire earth
27-9-2014 | IslamWeb
Question:
assalam alikum I was just wondering was noahs flood a local flood or was it a global flood that it flooded the whole world because what would be the point of allah flooding the whole world if noahs people were the only people on earth and did any of the 80 people on the ark what was saved from the flood did they have any chirdren or was it just noahs sons what had chirdren what populated the earth or like I said did any of the 80 people have chirdren and they populated the earth also and if the 80 people did have chirdren how would we explain chapter 37 verse 77 because that verse makes it sound like only noahs chirdren had chirdren jazzakkallah :)
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Nooh (Noah)'s flood encompassed the entire earth, as stated by the scholars of Tafseer (interpretation of the Quran) and other scholars; the evidence for this is the saying of Allaah (which means): {[Nooh] said, "There is no protector today from the decree of Allaah, except for whom He gives mercy."} [Quran 11:43] and (which means): {Then We opened the gates of the heaven with rain pouring down. And caused the earth to burst with springs.} [Quran 54:11-12]; which means that the entire earth became springs.
The following is presented in Ibn Katheer's Tafseer about the words of Allaah (which mean): {And it sailed with them through waves like mountains...}[Quran 11:42] : “This means that the ship sailed with them on the surface of the water, which had completely covered the earth until it enveloped the mountain tops.”
Tafseer Al-Lubaab by An-Nu’maani reads: “The flood covered the entire earth from north to south and from east to west.”
The Stories of the Prophets by Ibn Katheer reads: “The flood covered the entire earth, from north to south and from east to west, its valleys and cliffs, its mountains, its deserts, and its sands, and everyone who was on the surface of the earth died without exception. As regards the eighty people who were with Nooh, they did not leave any progeny as Allaah says (what means): {And We made his descendants those remaining [on the earth].} [Quran 37:77]"
A group of scholars stated this; for instance, Ibn Katheer said: “It is related that ‘Ali ibn Abi Talhah related that Ibn ‘Abbas said: ‘It was only the offspring of Nooh that remained.’” Sa'eed ibn Abi ‘Aroobah said that Qataadah said: “All people are from the descendants of Nooh.” [End of quote]
At-Tabari said: “All the people – after the people of Nooh had been destroyed until today – are from the descendants of Nooh.” [End of quote]
Ibn Hajar 
said in Al-Fat-h: “After the flood, the people who remained were only the offspring of Nooh who was from the lineage of Sheeth; Allaah says (what means): {And We made his descendants those remaining [on the earth]}; and with him on the ship were eighty people, and they were those whom Allaah referred to in the saying (which means): {But none had believed with him, except a few.} [Quran 11:40] However, it was only the descendants of Nooh who remained, and they populated until they filled the earth.”
Mu‘jam Al-Buldaan (by Yaqoot al-Hamawi) 2/84 reads: “Thamaneen (eighty): A small town at Mount al-Joodi near the island of Ibn Umar At-Taghlabi above al-Mawsil city; the first person who settled in it was Nooh 
when he went out of the ship and with him were eighty people. They built houses for them in that place and they dwelt in it, and so, the place was named after them. Then they were afflicted with an epidemic disease and the eighty people died whereas Nooh and his children survived, so he is the father of all mankind.” [End of quote]
As for the wisdom behind making the flood encompass the entire earth while it was only the people of Nooh who were on the earth, we have not come across a scholar who clarified the wisdom behind it, but there is no doubt that the Acts of Allaah are all for a great wisdom and it is probable that the flood encompassed the entire earth so that no one would find a place to escape.
Allaah Knows best.