What happens at the end of gears of war 2

At the end of Gears of War 2, Marcus and Dom enter the Locust hollow on the back of a Brumack. After a large "slaughter" of fleeing Locust, the two drive the Brumack into a pool of imulsion to destroy 3 pillars. These pillars hold up a section of Jacinto and the collapse of these allows some King Raven helicopters to enter the hollow to evac Marcus and Dom and to destroy the rest of Jacinto with a light mass bomb as suggested by Adam Phoenix, Marcus' father. This would flood the hollow and kill the Locust for good. The Raven with the bomb is shot down and the Brumack goes Lambant just as Marcus and Dom get off. They realize that the Brumack is a bomb and destroy it with the Hammer of Dawn and sink Jacinto. At the end all of delta squad (minus Carmine) leave in Ravens and watch the city burn and sink. Lastly after the credits, Adam Phoenix is heard asking "What have you done?!!".