Each time the periodic damage of Flame Shock damages an enemy, there is a 20% chance to gain a charge of Lava Surge, which stacks up to three times and lasts until used, or until you are out of combat where it decays at the same rate as Holy Power and Chi.
Casting Lava Burst normally, does not consume a charge of Lava Surge.
Attempting to cast Lava Burst (or Flame Shock?) when you would otherwise be unable to, such as while moving and/or while the spell is on cooldown, will instead consume a charge of Lava Surge and cause Lava Burst to cast instantly.
Lava Surge needs to be more reliable. Perhaps increase it's chance to proc with each tick of Flame Shock that doesn't proc Lava Surge?
And am I the only one who thinks Shocks sharing a cooldown is outdated?