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I'm currently working on two connected continents for the world I'm building. They've created a convergent boundary where they meet, which has given rise to an east-west mountain range, in addition to a north-south range on the northern continent. There's also a deep bay or sea that will eventually close. The relevant section looks like this:

The problem is, the two continents have come together somewhere around my world's equator, and thus the fjords that formerly populated the northern continent in the northern polar region find themselves regularly enduring temperatures of 100 degrees Fahrenheit.

Actually, the above explanation - a continental merger - is not what I want. I'd rather have the two continents form together, where they are now, rather than have continental drift send one down from the north. This is because the east-west mountain range is inconvenient for the purposes of a story I've set in this world. However, I couldn't come up with a better explanation for equatorial fjords, although I did consider having a version of the Snowball Earth, which should cover the tropics.

Therefore, I turn to Worldbuilding Stack Exchange. Is it possible for fjords to form on the equator? If so, how?

It's worth noting, as I just found out, that Slartibartfast designed Africa with fjords for the Earth, Mark II, but he's not around for consultations.

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    $\begingroup$ Looks like it, but you would need some pretty heavy glaciation of the planet, which implies a geological period of extremely low temperatures toward the poles. I might write up a proper answer later if nobody beats me to it. $\endgroup$ – a CVn Jul 13 '16 at 14:20
  • $\begingroup$ @MichaelKjörling I'd be interested to read that. The Snowball Earth was the closest I could get to something like that, but I don't know just what it would leave behind. $\endgroup$ – HDE 226868 Jul 13 '16 at 14:23
  • $\begingroup$ Well in that case hold off on answer acceptance and I just might see what I can do later. :-) Don't have the time to write up a proper answer now. $\endgroup$ – a CVn Jul 13 '16 at 14:24
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    $\begingroup$ "In this replacement Earth we're building they have given me Africa to do and of course I'm doing it with all fjords again, because I happen to like them; and I'm old fashioned enough to think give a lovely baroque feel to a continent. And they tell me "It's not equatorial enough"... hrumph ...what does it matter?! Science has achieved some wonderful things, but I'd far rather be happy than right any day!". "And are you?" "No.... that's where it all falls down of course". — Slartibartfast & Arthur Dent, The Hitch Hiker's Guide to the Galaxy, Fit the Fourth $\endgroup$ – MichaelK Jul 13 '16 at 14:59
  • $\begingroup$ Heh, saw your subscript comment after I typed up the one above. :) $\endgroup$ – MichaelK Jul 13 '16 at 15:00
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You probably can't get tropical fjords, since they're glacially formed by definition and likely to erode before an arctic environment can become tropical, but you can achieve similar effects with a rift valley.

enter image description here

Rift valleys form at a divergent plate boundary, where two continental plates are moving apart. In the case of the Great Rift Valley (pictured above), the valley is forming at a point where the African continental plate is splitting in half. Plate boundaries, of course, can form at any latitude, from the arctic to the tropics.

For a fjord-like rift valley, your best bet is probably to have a relatively young rift valley forming at a point where a continental plate dips beneath the ocean, such as the Eastern Seaboard of the US in the modern day or the coasts of the Western Interior Seaway, a vast, shallow sea that covered much of the North American interior during the Cretaceous. Such a valley would form a steep-walled ocean inlet superficially very similar to a fjord, though formed by a very different process.

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    $\begingroup$ As an addendum: if your "fjord" is actually a rift valley, your mountains surrounding it will probably be relatively small volcanoes. (Think Iceland.) $\endgroup$ – ckersch Jul 13 '16 at 20:49
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Technically Fjords are formed by glacial action, so they are unlikely to be found in the tropics, unless your world has undergone some very serious climate changes or the land itself has moved as you speculated.

You could still have Fjord like landforms formed in other ways, but technically they wouldn't be fjords.

https://en.wikipedia.org/wiki/Fjord#False_fjords

One option is a Ria these landforms can be quite similar to fjords, but are caused by former river valleys being flooded by rising ocean levels.

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Fjords are inlets formed by glacial erosion. For glacial erosion to occur near the equator, you would need a global ice age, which has happened in Earth's history. I don't know how long a fjord will last, so I don't know how long ago it could have been.

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  • $\begingroup$ Indeed, I knew about this (see my first edit), but I didn't know if it would leave many fjords behind in the long term. $\endgroup$ – HDE 226868 Jul 13 '16 at 14:24
  • $\begingroup$ It probably would leave behind many fjords, however, fjords would disappear over time on account of other geological processes, so maybe, it left behind many fjords, but only one has survived the amount of time since. $\endgroup$ – Jarred Allen Jul 13 '16 at 14:33
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You may go with Cliffed coasts if you want fjords for the looks: https://en.wikipedia.org/wiki/Cliffed_coast It might be possible for them to occur the way you draw them in your map. They are the coasts that contain soft rocks which are eroded by waves.

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Ria coasts can look so much like fjords they are commonly mistaken for them: http://www.ocvts.org/classroomconnect/classrooms/jwnek/documents/Oceanography/Presentations/Ria%20Coast.pdf

As others have said, in the time it takes for a continent to move from where fjords would form down to the equator, the fjords would likely have eroded into a less rugged landscape.

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