Compact Atmosphere

Using an extreme amount of concentration and resource, compress (#hp*1000) cubic meters of the atmospheric environment into 1/100th of its normal size. 
Upon dispel or trigger, the [compacted atmosphere] expands back to it's normal state in a fraction of a second, dealing 1d12*(total-hp/10)+5 damage to all entities and buildings. Damage varies depending on nearness to epicenter.

Nearness is calculated based on the dimension of the total pre-compacted atmosphere. (i.e., if 50^3 cubic meters of gas is compressed, then the dimension of measurement would be 50 meters and the 'Damage from epicenter' percentage would be of the 50 meters. 

Damage from epicenter:
0-100% - 150% of damage
101-300% - 100% of damage
301-500% - 50% of damage
>500% - 25% of damage

Either the caster or the [compacted atmosphere] can be moved to a safer location, but it's extremely perilous.

The shockwave can be felt up to 5000% of the dimension away, and can be heard up to 50000% of the dimension away.