If we can't overcome the defenders inside Thor Modan, the iron dwarves can hold out forever. The Earthen are bravely taking on the constructs built by the sons of iron, but they cannot break into the city.
The tunnels narrow too quickly for my fellow giants to be of use, so our options are few. Would you be willing to venture into the city and kill the dwarf commanding the resistance?
You will be able to choose one of these rewards:
Were you able to kill the commander?
Well done, <name>. The loss of the iron dwarf commander should be enough to break the remaining defenders. The Earthen should be able to deal with the survivors.
The Iron Thane is near the (NE) end of the trench. If you cannot fly and don't want to wade through all the mobs (possibly "again") to get to the thane, you could climb onto any of the middle pillars and jump into the water. There are also some (many?) spots where a fall is not necessarily fatal.