Iroh followed more slowly, taking the time to check the tunnel for stability. Without any earthbending, he ran a risk in entering such an ad hoc passage, and he kept himself fully ready -- the right degree of fire could harden the earth, or defend him against whatever he might find, though with the Avatar ahead, he expected to at least have some warning.

Beyond the first few jagged turnings, places where the earth seemed to have ripped itself apart from the stresses to either side, the tunnel widened, into a uniform, though crooked, dimension. It seemed to have been bored through the earth in erratic stages. Occasionally, there were cracks to all sides, which increased Iroh's sense of urgency. He increased his pace to his fastest sustainable pace. The sooner he was out of this, the better.

But even as he sped up, he was aware that he was much slower than Korra, and probably wouldn't catch up with her until she had reason to stop.