Allah's saying:

فَكَانَتْ هَبَاء مُّنبَثًّا ﴿٦﴾

So that they will become floating dust particles.

Abu Ishaq narrated from Al-Harith, from Ali:

"It will become like the rising dust storm that soon fades away leaving no trace of itself behind.''

Al-`Awfi reported from Ibn Abbas about Allah's saying: فَكَانَتْ هَبَاء مُّنبَثًّا (So that they will become floating dust particles).

"It describes the rising embers from the fire when it is kindled, but when the embers land, they are extinguished quickly.''

Ikrimah said,

"The floating dust particles that the wind scatters all around,''

while Qatadah said, هَبَاء مُّنبَثًّ (floating particles),

"Like the dry parts of trees that the wind scatters all about.''

This Ayah is similar to several other Ayat that indicate that the mountains will be moved from their places, demolished and blown off their bases, becoming like carded wool on the Day of Resurrection.