Prelude
Starting with 13th of October 2010 random earthquakes are reported in the major cities and zones of Azeroth. In response, the faction leaders of the Alliance and Horde have gathered in Stormwind and Orgrimmar respectively to deal with this turn of events.
On 16th of October 2010 the earthquakes have longer durations. Whenever there are earthquakes near the Orgrimmar or Stormwind Auction houses, or the bank in Ironforge, dust comes down from the ceilings.
On 27th of October the earthquakes become more frequent.
Phase 1
This phase released on the 1st of November, 2010. Portals have begun to spawn randomly in all questing zones, spawning elementals; the spawn timers are erratic, and not tied to the beginning of the hour. The first phase of the quest chains are now active.
To obtain the Feat of Strength [Tripping the Rifts], players must obtain a buff from each type of elemental portal that spawns in Kalimdor, Eastern Kingdoms, Outland and Northrend (Earth, Fire, Water, and Wind). Players do not have to kill rifts of their level to qualify for the achievement. The daily quest Hammering It Out, obtained from the mysterious devices left after the portals have faded, does require the death of level-appropriate elementals, however.
Phase 2
This phase has not yet been turned on for the live realms.
Phase two will open up a few more quests in Thunder Bluff / Ironforge.
Phase 3
Invasion preparation
Before every invasion event starts, a herald will yell, warning players and citizens about incoming danger. At this time, players are instructed to grab barricades/sandbags from stockpiles around their major city and place them in zones directed by a red arrow. Low-level players unable to participate in this event are instructed to evacuate to the nearest portal activated by several guards. When all barricades are placed or 5 minutes have elapsed, the battle against the invasion begins.
Combating the invasion
Viewing a city's map during an invasion will display all the districts and which are still under attack by elementals or need citizens freed. All of the districts of the invaded city will be attacked by elementals spawning from opened rifts. Every elemental has about 320,000 HP and every rift will spawn elementals until 32 are destroyed. Several citizens are trapped in these districts and must be freed by an [Earthen Ring Unbinding Totem] provided by Earthen Ring Defenders. Players must clear the city of every rift and rescue every citizen within an hour in order to win the event.
After players defeat 32 elementals surrounding a rift, the rift will close and a buff will be applied to all players nearby:
Tips
Unlike other phased events such as Battle for the Undercity, Operation: Gnomeregan, or Zalazane's Fall, you are not buffed into invulnerability against these powerful mobs. If you are assaulting a rift by yourself or with a few players without a healer present, only attack one elemental at a time.
Bring an unbinding totem provided by the Earthen Ring Defenders with you. If your allies get trapped by an elemental, they must be freed or healed immediately or they might die within the time of the prison's stun.
The elementals' prisons are cast in a frontal AoE cone. It has a very short range, so it is possible to avoid it by simply running away during the cast.
After the invasion
If an hour has elapsed since the start of the event, Earthen Ring Defenders will intervene and suddenly halt the invasion, removing all elementals from the city. However, players will not benefit and will have to wait until the next event occurs.
If players successfully secure a major city, two portals are available to enter for the next 30 minutes to fight one of the four lieutenants Cho'gall commands:
Grand Ambassador Flamelash
Crown Princess Theradras
Kai'ju Gahz'rilla
Prince Sarsarun
Phase 4
Zarhym has stated "There are four stages of the event. We're on the first." Details of the fourth phase are as yet unknown.