Shall not the land tremble for this? "This" is the coming judgment, or the oath with which God announced it in the previous verse and the prophet asks, "Shall not the land tremble as with an earthquake when the Lord comes to judgement?"
The LXX; rendering ἐπὶ τούτοις, takes the reference to be to the "works" or sins of the people (Amos 8:7); but the thought in these two verses is the punishment of the transgressions, not the transgressors themselves.
And it shall rise up wholly as a flood (Amos 9:5). The LXX; pointing differently, renders, καὶ ἀναβήσεται ὡς ποταμὸς συντέλεια, "And destruction shall come up as a river;" the Vulgate, Et ascendet quasi fluvius universus; it is best, however, to refer both clauses to the Nile: "Yea, it shall rise up wholly like the river"—the land shall heave and swell like the waters of the Nile at its annual rising.
And it shall be cast out and drowned, as by the flood of Egypt; better, it shall be tossed up and sink again, like the river of Egypt—a picturesque comparison, which would allude to a phenomenon well known to the Israelites.
It is as though the whole earth were turned into a sea, tossing and labouring under a tempestuous wind (comp. Isaiah 24:4).