You select a 5-foot square area within range that acts as the center of the spell. A small gate to an evil alternate plane opens, expelling pure negative energy in a fountain of darkness, damaging anyone in its area of effect. On the first round of the spell, the eruption's energy deals 1d6 points of negative energy damage per caster level (maximum 20d6) to everything within 5 feet of the spell's center. On the second round, the eruption's area of effect grows to a 30-foot radius, after which it collapses and the gate vanishes. Undead affected by the eruption are healed of 1d6 points of damage per caster level (maximum 20d6), but cannot receive more hit points than their maximum.