What greeted Alice as she waited for a reply was a sudden roar — one so sharp it seemed to pierce the ears and so loud it seemed to reach the heavens.
Literal
Reply [object-を] waiting Alice [toward-に] directed was sudden roar. That [topic-は] ears [object-を] pierce [as-if-んばかりに] sharp, heaven [to-に] reach [as-if-んばかりに] greatly resounding thing was.
Literary narrative prose. 咆哮 (ほうこう, 'roar, howl') is dramatic vocabulary. ~んばかりに is a literary grammar pattern meaning 'as if about to, to the point of almost' — used twice in parallel for rhetorical force (耳を貫かんばかりに鋭く, 天に届かんばかりに大きく). The passive 向けられたのは inverts the sentence for dramatic reveal: what was directed at Alice was... a roar. The formal でした closes the storybook narration.