Arcane Cataclysm Proc - Cataclysm Set

How exactly does this proc work? Specifically wondering what the 1 sec duration is for.

It says on critical attack,

1.5 recharge
1 sec duration
xx elemental damage
1.5 sec stun

It seems, from what i can tell, the proc creates 1 lightning nova from the target which was crit, which i assume will take xx elemental damage, and will presumably hit anyone in a 4m radius. what is the 1 second duration for? I doesnt seem to me like the proc hits again, unless i’m mistaken (which is entirely possible).