I have created and bound Alluvius using the Horn of Elemental Fury. He will respond to the horn's call when you stand near the southernmost sinkhole in the Geyser Fields.
The quake Alluvius will unleash should collapse the Nerubian tunnels and put an end to their flanking attack. I wouldn't be surprised if the Nerubian commander showed himself after the quake. If the collapse of the tunnels doesn't break the back of their assault, the defeat of their leader surely will.
Your efforts against the Nerubians have given us a reprieve from the overwhelming Scourge assault. Thanks to your accomplishments, we can strike at the Scourge fortress to the northeast without fear of attack from the west.
As for the horn, I will safeguard it until next we need its power. Stormhoof gave his life to secure the horn and we cannot suffer its loss again.