1)
Do rivers have hands?!
1.
Rashi (from Shocher Tov): Nevi'im speak [in metaphors], in a way that one understands. Clapping hands is an expression of Simchah. Radak - "va'Yaku Chaf va'Yomeru Yechi ha'Melech" (Melachim II, 11:12).
2.
Malbim: There will be changes in the rivers, like there were in the Yarden and Nachal Arnon 1 .
1
Refer to 74:15:2:1, Bamidbar 21:16:1:2.
2)
Why will the mountains sing?
1.
Malbim: There will be changes in the mountains, like there was in Nachal Arnon 1 .
1
Refer to Bamidbar 21:15:2:1**.
