He heard Aava, then. A blast of titanic heat, of power unimaginable, came roaring up at him.
Thor leaped outward, away from the bridge.
For a moment he hung a hundred feet above the jagged floor of the cave. In that instant, Aava hurled himself upward, filling the cave with radiance and intolerable heat.
Thor threw wide his arms, closed them on a stalactite dropping its thin rock formation from the roof. His legs spraddled the drooping stone, hugging it.
Aava raged, biting and burning at the stone bridge, seeking his quarry. Sullenly, he dropped back within the quartz oval.
Thor almost missed the bridge, leaping back for it. His hands scrabbled at the loose shale, sliding and slipping, before his fingers tightened on a rough projection.
With insane might, he flung himself and his axe again at the depression. Before Aava gathered himself once more, he had to do it.
The axe dug in. When he pulled it loose, a few flecks of sand slid with it. The thin grains showered downward, running in a steady stream.
"Earthling, stop! The sand must not come down on me. Stop and—"
The voice of Aava rose to a shrill crescendo, battering at his ears. But Thor worked on. His axe arm lifted. The crack widened. Tons of sand hung above that thin roof, on delicate balances. By opening the roof even so slightly as he had done, he was destroying that balance. An incredible weight of sand was waiting, waiting—