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In my world, there is an archipelago that is home to the Coorabar Alps, the highest mountain range in the entire known galaxy (quite a few peaks here surpass 30,000 feet, and they form a plateau on their land-facing side similar to Tibet or the Andes with an average altitude of 20,000 feet. However, the location for these alps is tropical and often directly coastal (think of Norway or New Zealand's mountains but on the equator). Would it be possible for snow-capped peaks to rise directly off of a tropical beach like this, and if so, how ludicrously steep would these be?

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  • $\begingroup$ Define what you mean by "directly". E.g. if you have 30K ft cliffs, you aren't going to have much of a beach. OTOH, it's quite common to have snow on the mountains of Hawai'i: bigislandvideonews.com/2020/01/13/… $\endgroup$
    – jamesqf
    Sep 28, 2020 at 17:24
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    $\begingroup$ Olympus Mons rises 72000 feet... $\endgroup$
    – ths
    Sep 28, 2020 at 17:25
  • $\begingroup$ @jamesqf what I mean by "directly" is that coasts with the mountains will have no more than a football field's worth of flat beach, if that, before the terrain shoots up. $\endgroup$ Sep 28, 2020 at 17:31
  • $\begingroup$ Mount Kilimanjaro is straight Equatorial, has permanent snow, and is a stratovolcano. Stratovolcanos can raise wherever they please; Kilimanjaro rises majestically out of a plain, but Mount Fuji is indeed close to the coast. $\endgroup$
    – AlexP
    Sep 28, 2020 at 17:48
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    $\begingroup$ Snow capped Mauna Kea is about 15 miles away from the tropical beaches of the Big Island. $\endgroup$
    – Alexander
    Sep 28, 2020 at 18:52

3 Answers 3

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The Island of Hawaii has two mountain peaks (Mauna Kea and Mauna Loa) with elevations of over 13,000ft that are only about 10-15mi inland from the Ocean. Both of these peaks receive annual snowfall.

enter image description here

If you mean directly on the beach, then no. The tallest sea cliffs¹ in the world (Also in Hawaii) are at Kalaupapa. While they are pretty impressive, at only about 3000ft, they are not nearly tall enough to get snow capped. Your world would need a place like Hawaii, but much more extreme to have snow caps on a raised beach.

enter image description here

1. As per comments: sea cliffs are geologically different than fjord cliffs. There are some taller fjord cliffs in the world very close to the ocean, but fjord cliffs are formed by glaciers, not sea erosion; so, you generally do not find very big ones in tropical zones.

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  • $\begingroup$ Nitpick: Your second picture shows steep slopes, not cliffs, and Mt. Thor on Baffin Island is about a third taller in vertical drop: en.wikipedia.org/wiki/Mount_Thor $\endgroup$
    – jamesqf
    Sep 29, 2020 at 4:08
  • $\begingroup$ @jamesqf Oh, it gets even more nitpicky than that, hehe! Mt Thor is a fjord cliff whereas Kalaupapa is a sea cliff. Kalaupapa is the official record for tallest "sea cliff" based on the definition used by Guinness Book of World Records, although this record is sometimes contested based on "what is a sea cliff". Torsukattak Strait and Piopiotahi are also sometimes called the world's tallest sea cliff, but they are both fjord cliffs which are geologically different. Fjord cliffs can be quite taller than sea cliffs, but are not generally found in the tropics since they are formed by glaciers. $\endgroup$
    – Nosajimiki
    Sep 29, 2020 at 13:38
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Tropical glaciers can be found (or could once have been found) not far from the equator in Papua: Ngga Pulu, just under 16,000 feet high, sports an ice cap.

As for the steepest elevation, 30,000 feet may not be completely realistic but you might take inspiration from Mt Thor, Canada, the steepest vertical drop on Earth at 4,101 feet:

Thor Peak, Nunavut, Canada

The cliff was created by glacial erosion scouring a steep wall as it formed the adjacent valley. The cliff's angled at 105° or more vertical than vertical!

To get your 30,000 feet you'll have to do some planetary engineering: lower gravity to start. See: What is the highest possible mountain on an Earth-like world?.

Further thoughts:

Getting glaciers eroding valleys to sea level in the tropics will prove difficult, so your likely options here are:

  1. The cliff was eroded long before the continent it's attached to migrated to the tropics; or

  2. The erosion took place during an icehouse phase; the melting of all that ice raised sea levels so high the valley flooded and joined the open ocean; and/or

  3. The cliff is on the continental-mainland-facing side of an island arc in a back-arc basin; it eroded just before the basin opened.

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    $\begingroup$ I have been sipping a drink poolside in Tucson, Arizona - enjoying sunshine while watching plumes of Snow blowing from the top of nearby Mt. Lemmon ( 10,000 ft) $\endgroup$
    – Joe
    Sep 28, 2020 at 17:39
  • $\begingroup$ @Joe While I get your point, Arizona isn't tropical, it's arid/semi-arid. Arizona has examples of every Köppen category but Tropical. $\endgroup$
    – rek
    Sep 28, 2020 at 17:50
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Have you ever heard of a place called Hawaii? A tropical paradise with palms, sandy beaches, pineapples and coconuts all year round, right?

Hawaii beach

Well, this is precisely there, raising 13000 feet above the sea level:

Mauna Loa

According to google maps it's just 90 km drive from the beach to the peak, and that's reported as a gentle slope, as to be expected from a basaltic volcano.

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  • $\begingroup$ 3 minutes... you beat me by 3 minutes... lol $\endgroup$
    – Nosajimiki
    Sep 28, 2020 at 19:13

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