Nova Blast

A Nova Blast is when a Toa exerts all of their Elemental Energy at once, releasing an extremely powerful explosion of that Element. Once a Toa has done one of these, they cannot use Elemental powers until their Elemental Energy has recharged. They were not so often used because of their destructive and usually deadly force.

Known Uses of the Nova Blast
In the BIONICLE story, so far only one Nova Blast has been used. Toa Nuva Gali used one as a last resort when fighting the Makuta Icarax in Karzahni. She summoned a huge flood of water that destroyed the entire realm using all of her power. Unfortunately, Icarax escaped, presumably by the Rahkshi power of teleportation.

Toa Metru Vakama had once considered a Nova Blast during his fight against a creature made entirely of fire, but decided against it, because it would kill everything in a huge radius.

In Comic 11: Death of a Hero Toa Mahri Jaller almost unleashed a Nova Blast before he was teleported back to Metru Nui. Once there, he had to force down his powers in order to avoid destroying the whole city.

Makuta
Makuta could perform something similar to a Nova Blast. Makuta Mutran did this in BIONICLE Legends 9: Shadows in the Sky when he gathered all his shadow energy and unleashed it all in a massive explosion.

Trivia

 * Toa Hordika cannot perform Nova Blasts as they lacked the focus necessary. Although it has been hinted that they could charge their Rhotuka to near-Nova Blast levels.
 * Turaga are unable to perform Nova Blasts, as they lack the power needed.
 * Toa Ignika can preform one despite not being a real Toa.