Ho! there's his arm just breaking water.

嗬！他的胳膊刚刚露出水面了。

You know if the metaphore for the gradual change was the water breaking down stone, the metaphore for acute approach is taking a sledgehammer and breaking the water, breaking the stone.

如果用水冲刷石头来比喻渐进的改变，可以用拿大锤砸石头来比喻剧烈的改变。