On the second day of creation God fashioned an expanse over the waters of the earth and called the expanse heaven
(Genesis 1:6–8). This expanse called heaven
(sky
here in Revelation 6:14) now disappears and is rolled up as the Lamb opens the sixth seal and God comes in judgment. This action represents the decreating of what God created on the second day.
14 The sky vanished like a scroll that is being rolled up, and every mountain and island was removed from its place.