School evocation [force]; Level sorcerer/wizard 4
Casting Time 1 immediate action
Range 5 ft.
Effect 5-ft.-radius hemisphere of force centered on you
Duration 1 round/level (D)
Saving Throw None; Spell Resistance no
As wall of force, except you create a hemispherical dome of force with hardness 20 and a number of hit points equal to 10 per caster level. The bottom edge of the dome forms a relatively watertight space if you are standing on a reasonably flat surface. The dome shape means that falling debris (such as rocks from a collapsing ceiling) tend to tumble to the side and pile up around the base of the dome. If you make a DC 20 Craft (stonemasonry), Knowledge (engineering), or Profession (architect or engineer) check, the debris is stable enough that it retains its dome-like configuration when the spell ends, otherwise it collapses.
Normally this spell is used to buy time for dealing with avalanches, floods, and rock-slides, though it is also handy in dealing with ambushes.