Ma'arif al-Qur'an
Mufti Muhammad Shafiفالْتَقَى الْمَاءُ عَلَىٰ أَمْرٍ قَدْ قُدِرَ (so the water [ of both kinds ] met together for a destined event....54:12). In other words, the rain water pouring down from the skies in torrents and also bubbling water gushing forth from under the ground, caused the Deluge [ a huge flood ] which engulfed the entire land, and thus the Divine decree was fulfilled, destroying the people of Nuh (علیہ السلام) to the last man, and even the peaks of the mountains could not give them any shelter.