When wielding a two-handed weapon, your Obliterate deals 40% more damage, and all melee attacks deal an additional 10% damage.
Might of the Frozen Wastes is a passive death knight ability learned at level 74 for death knights with the frost specialization.
Patch changes
Patch 5.0.4 (28 August 2012): Updated; changed from When wielding a two-handed weapon, your melee attacks deal an additional X% damage and your autoattacks have a Y% chance to generate 10 Runic Power.
Patch 4.2.0 (28-Jun-2011): Now increases two-handed weapon damage by 3/7/10%, down from 4/8/12%.
Patch 4.0.6 (8-Feb-2011): Now also increases all melee damage by 4/8/12% while wielding a two-handed weapon.