Is a river canyon realistic here? Why or why not?

[waldronate]

Additional information is always good! It was hard to guess about plausibility without a motion of scale. As NeonKnight pointed out, it's certainly possible to get what you're asking about.
I would add that information on the intended width of the canyon would be good. Something like a slot canyon the better part of a mile deep is very hard to do. Something like the grand canyon, zion canyon, or yosemite is much easier to do. However, getting that much erosion over that much distance straight down from mountain peaks might be difficult without l larger area up to to deliver a concentrated stream of water.

[eepjr24]

Additional information is always good! It was hard to guess about plausibility without a motion of scale. As NeonKnight pointed out, it's certainly possible to get what you're asking about.
I would add that information on the intended width of the canyon would be good. Something like a slot canyon the better part of a mile deep is very hard to do. Something like the grand canyon, zion canyon, or yosemite is much easier to do. However, getting that much erosion over that much distance straight down from mountain peaks might be difficult without l larger area up to to deliver a concentrated stream of water.

I don't think a slot canyon is what I am after as those are very narrow, narrow enough to jump or even touch both sides?

From earlier post:
"My best guess on the canyon depth would be about 4-5,000 feet deep at the start and drop to a few hundred feet deep where it meets the ocean. The widest point will be a couple miles (~ 3km) wide and the narrowest less than a mile (~ 1,500 m)."

Any of those figures are changeable if they would make the resulting canyon more realistic. As to other scales, the island is about 1,000 miles top to bottom. Total length of the river canyon would be in the 75-80 mile range. I know there are MUCH shorter river canyons (Tallulah Gorge in Georgia is 2 miles long and 1,000 feet deep, 200 feet to half a mile wide).

Does that answer the scale questions more thoroughly? If not, what else would be good to add?

- E