The melting of the earth is imagery used to emphasize the awesome power of God. A mere touch from him causes the earth to melt like ice. The rising of the Nile likely refers to the land shaking like an earthquake, moving up and down. It was common knowledge in Israel that there were times when the Nile River was in flood and it would rise and spread out over a large area before receding. The prophet Jeremiah also uses the rising of the Nile as a picture of judgment (Jeremiah 46:7–8).1
5 The Lord GOD of hosts, he who touches the earth and it melts, and all who dwell in it mourn, and all of it rises like the Nile, and sinks again, like the Nile of Egypt;