Question Regarding Long Sea Channels

[jbgibson]

If you're not picky about the definition of "large landmass", the passage behind Vancouver Island might be instructive. It looks like "drowned topography". Hmmmmmm ... so all you need is a bit of flat connecting some nonflat landmasses, erode some rivers that almiost cut the isthmus, then raise the water level. Voila: river valleys become an ocean strait, and the River Poilice can't do a thing about it :-).

Again, the Strait of Magellan is continent vs. island, but Tierra del Fuego is pretty big, and the passage is mighty skinny. And the Drake Passage south of Cape Horn is a certifiably lousy piece of ocean to traverse, so the horrible conditions of the Strait of Magellan have long been one choice of mariners. And it looks like fjiordland - really rough terrain, that got itself drowned.

Tectonically, how about if a subduction trench at the edge of an ocean got "stuck", and the ocean plate diving under the continent bulged upwards? Or what if the ocean plate being subducted was carrying some continent, complete with continental shelf dropoff - when the two get close for a little while (geologically) you could get abrupt dropoffs opposing each other - not only narrow but Way Deep.

Suppose the Great Rift Valley of Africa (equivalent) were open to ocean... how much of a sea level rise could YOUR planet get, if you melted all of a super-Antarctica ice cap?

[Korash]

You might also want to look at the Falkland Islands. I have attached something that I did a while ago but left the layout of the islands as is in RL. True, the scale is not on a continental scale, but it does match your channels quite nicely.