And the mountains are removed and will be [but] a mirage. (78:20)

Almuntakhab Fi Tafsir Alquran Alkarim

and the mountains are set in motion and into a mirage as if transmigrated

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(78:20) and the mountains will be set in motion and become a mirage. *13

And the mountains are removed and will be [but] a mirage. meaning

*13) One should bear in mind the fact that here also, as at many other places in the Qur'an, the different states of Resurrection have been mentioned all together. In the first verse, mention has been made of what will happen at the final sounding of the Trumpet and in the following two verses of the state which will appear at the second sounding of the Trumpet. This we have already explained in E.N. 10 of Surah Al-Haaqqah above. "The heavens shall be opened" means: All obstacles in the heavens will be removed and every heavenly calamity from every side will be befalling freely as though all doors for it were open and no door had remained closed to obstruct its happening. "The mountains will be set in motion till they become as a mirage" means: In no time will the mountains be uprooted from their places and then will be scattered away in particles leaving nothing but vast, empty sand plains behind. "This same state has been described in Surah Ta Ha, thus: They ask you: well, where will the mountains go on that Day? Say to them: My Lord will reduce them to fine dust and scatter it away. He will turn the earth into an empty level plain, wherein you will neither see any curve nor crease." (vv. 105-107 and the corresponding E. N . 83! .
 

And the mountains are removed and will be [but] a mirage. meaning in Urdu

اور پہاڑ چلائے جائیں گے یہاں تک کہ وہ سراب ہو جائیں گے