Kevin's Watch

I have wondered this a lot of about the Sunbane - how does it only encompass part of the Land?
Linden says that she knows it doesn't really come from the sun, so where does it come from?

Spoiler

It is like Kevin's Dirt, but only localized to part of the Land?

Or, if it is some atmospheric 'lens' of some sort, how come it only work on part of the Land after all those years gone by?
Lastly, the Banefire went to the Sun - why? What did it feed? And wouldn't it have been diminished once extinguished?
As I enter the final chapter of WGW, I couldn't shake these questions...

(Moderator: I spoilerized references to the Final Chronicles)

This was explained in TWL. Basically, the Sunbane is a corruption of Earthpower, and it arises out of the earth. Only the Upper Land is affected by it, that seems to be the area where the corruption is extant. By it's nature, the power of the Sun which passes through the air in the corrupted area is warped.

In [u]The Wounded Land[/u] was wrote:"This is the line." She spoke in bursts of excitement, comprehension. "Landsdrop. It's like a border." Her hands traced consequences in the air. "You'll see. When the sun passes over the cliff - at noon - the Sunbane will be as strong as ever."

Covenant swallowed thickly. "Why?"

"Because the atmosphere is different. It doesn't have anything to do with the sun. That corona is an illusion. We see it because we're looking at the sun through the atmosphere. The Sunbane is in the air. The sun doesn't change. But the air -"

He did not interrupt. But in the back of his mind he sifted what she said. Some of it made sense: the power required literally to change the sun was inconceivable.

"The Sunbane is like a filter. A way of warping the normal energy of the sun. Corrupting it." She aimed her words at him as if she were trying to drive insight through his blindness. "And it's all west from here. The Upper Land. What you see out there" - she jerked her head eastward - "is just spillover. That's why it looks weak. The Clave won't be able to reach us anymore. And the Sarangrave might be just as you remember it."

All -? Covenant thought. But how? Winds shift - storms -

Linden seemed to see his question in his face. "It's in the air," she insisted. "But it's like an emanation. From the ground. It must have something to do with the Earthpower you keep talking about. It's a corruption of the Earthpower."

A corruption of the Earthpower! At those words, his head reeled, and his own vague intuitions came into focus. She was right. Absolutely. He should have been able to figure it out for himself. The Staff of Law had been destroyed -

And Lord Foul had made his new home in Mount Thunder, which crouched on the edge of Landsdrop, facing west. Naturally, the Despiser would concentrate his Sunbane on the Upper Land. Most of the east already lay under his power. It was all so clear. Only a blind man could fail to see such things.