I don't suppose you can turn the plains of Lothlann into a mountain range while escorting those people?

I'm not sure I could do that quickly enough to help even if I wasn't carrying people. You saw how slow I was destroying those mountains, and in general breaking is easier than making.

A gaping crevasse would also be useful. Take them to Thargelion, they're probably going to be too shaken up for a long walk once you land them.

Fair point. I still probably shouldn't try it while carrying people. It would be bad if my concentration slipped enough that I dropped one, even for a minute. I can try it on the way back, though.

Thank you.

She takes them to Thargelion. She has to go slower, making sure to not drop anyone and if she goes supersonic she has to carry enough air and muffle the sound well enough not to make them any more anxious than was inevitable, and every minute chafes, but she gets there, and she leaves her charges with someone who can presumably smooth their justifiably ruffled metaphorical feathers, and then she zips back to the plains of Lothlann and attempts to render them impassable.

How wide does the crevasse need to be?

Thirty feet, if you can manage it.

So she...pries the earth apart, compacting the earth into stone until she has a hole in the ground thirty feet square and deep enough that it should be a serious problem. Then she does it again, adjacent. Then again. How long does it need to be?

Everywhere you do it is a place we're going to have an easier time holding. The plains are a hundred miles across but I'm recalling you as soon as anything changes because the Enemy must have realized by now that he ought to target you. 

My brother has magic that generally enhances others in some respect - resilience, tiredness, will, energy. We intended to test whether his abilities can help you use yours. Care to test that now?

YES

He is on his way.

Thank you. Dig dig dig compress.

He rides up a short time later. This is impressive. We should have started you on it a week sooner - not that we could have anticipated this. Can anything plausibly go wrong if this works as well as we hope and you're suddenly much stronger?

Don't stand where you might fall in if the part of the chasm I'm currently working on were suddenly much wider.

He rides around to be well clear of it, then starts singing. The clouds of ash in the air start moving as if caught in a windstorm.

Ooh.

The chasm-bit she's currently working on jerks outwards to a bit more than thirty feet, and she starts parting the land from there like butter under a hot knife. The chasm still isn't extending faster than a horse could run, but it's much swifter and smoother than before.

He smiles, and they keep that up until the sky darkens further.

There's something coming, Maedhros says. Odette, get back here. Cáno, if you can't hold the Gap get your people to Himring -

Maglor's response isn't in the language Odette is familiar with.

Is Cáno you? she asks Maglor. I don't know all the names everyone seems to have.

You are unfamiliar with that name because it is not legal and outside our heads it would be costly to speak it. My brother is being sentimental, or pretending to be sentimental, or something like that, because it is unclear to him how we'll hold the Gap and yet we really really can't afford not to.

I already got the linguistic blackmail explanation from Celegorm. I won't say it aloud.

A  substantial part of those among my forces who have leave to enter Doriath have run off today to do so. If we survive this there will be lots of racial resentment that is awkward to fix. We can at a minimum not compound it.

As I said, I won't say it aloud.

Odette, come in. We are not risking you against unknown enemies.

Coming! She zooms back as fast as she can push herself.

Thank you. It occurred to me too late that I did not know you well enough to know if you'd listen to us on that. Once we know more about whatever's coming you are welcome to go make its life difficult.