The hills melted like wax at the presence of the Lord (comp. 5:5; Isaiah 64:1; Micah 1:4). The earth itself is regarded as not only shaken (Psalms 97:4), but as melting and crumbling away at the descent of God from heaven to earth.
At the presence of the Lord of the whole earth (comp. Joshua 3:11, Joshua 3:13.; Micah 4:13; Zechariah 4:14; Zechariah 6:5).