In contrast to rain or a storm, which can be fairly easily imitated on stage, an avalanche completely engulfs the scene, unleashing a destructive power that also threatens musical form.
Unleashing refers to the act of releasing or setting free something that has been confined or restrained.
This can apply to emotions, potential, energy, or any other force that can be controlled or held back.
If you say that someone or something unleashes a powerful force, feeling, activity, or group, you mean that they suddenly start it or send it somewhere.
Then he unleashed his own, unstoppable, attack..