What language is that?
“Cwm” is Welsh.
For some unknown reason, Welsh has had a disproportionate influence in the mountain climbing community.
Col is a loanword into English from French. It comes originally from Romanic dialects that are spoken in the Alps, and turns up in the names of a lot of Alpine features. Mountaineers who encountered the term in the Alps are responsible for bringing it into English in the mid-nineteenth century.
(It’s ultimately from the Latin collum, a neck.)
Cwm is a loanword from Welsh into English. The long-established English word coomb, which describes a different kind of valley and now is mostly used only in place-names, is related. Again, the borrowing of the Welsh word occurred in the mid-nineteenth century.
On edit: I think it was geographers or geologists, rather than mountaineers, who first borrowed cwm, but I could be wrong.
I thought it was crossword puzzle designers who needed the word; then geologists and mountaineers picked it up from them.
In case this isn’t a whoosh… Wales is the nearest mountainous area to southern and central England, so it makes perfect sense that specific, “technical” mountain-related terms would be borrowed by English from Welsh.
I’d bet there are analogous situations in certain other languages – e.g., Tibetan borrowing from Mandarin for ocean-related terms, perhaps.
(By “mountainous,” I mean Wales has rugged areas with visually obvious evidence of recent glaciation, unlike England.)
A rough synonym to cwm, also from Britain, is the Scottish term corrie, which comes from the Gaelic coire.
Other terms in common use:
[ul]
[li]Cairn - pile of rocks used for marking a route above treeline (from the Scottish)[/li][li]Gendarme - a rock pinacle or spire, often blocking a route (from the French)[/li][li]Arête - narrow ridge of rock formed by glaciers (from the French)[/li][li]Bergschrund - a deep fissure near the top of a glacier where it pulls away from rock or stable ice (from the German)[/li][/ul]
Mountaineering borrowed terms from lots of languages.
True…unsurprisingly, from languages spoken in places near England that include these features.
Also serac, a column of ice, borrowed from the Swiss French sérac.
Don’t forget “mountain,” which comes from Old French. 
Some more, a few from non-European languages
[ul]
[li]Talus - French, rock debris at the base of a cliff[/li][li]Scree - Norse, collection of broken rock found in various mountain locations[/li][li]Sherpa - Nepali, anyone who hauls gear for others [/li][li]Nunatak - Inuit, mountain or ridge that sticks up out of surrounding ice[/li][li]Monadnock - Abenaki/Native American, solitary mountain that rises from a plain[/li][li]Névé - French, snow/ice that has been subjected to repeated freeze/thaw cycles[/li][/ul]
And people who needed a example when asked “OK, when* is *‘W’ a vowel??”
rappel and abseil, from French and German terms respectively for the same climbing technique of descending by rope.
carabiner, a metal loop with a spring gate, from the German Karabinerhaken, “spring hook.”
couloir, a narrow, steep, gully, from French
crevasse, a crack in a glacier, from French
Krummholz, the twisted trees at timber line, from the German for “twisted wood.”
I had always understood cwm to be specific to Welsh mountains. As noted above the Scottish equivalent is corrie and the ‘proper’ geological name being cirque. Both terms appear frequently as feature names on maps in their respective countries.
https://en.wikipedia.org/wiki/Western_Cwm - Western Cwm on Everest is probably the most famous.
Snowdonia in wales was the venue of choice for training for more exotic mountain ranges. It is also home the oldest serious climbing society (as with many things you can’t really claim the Victorian British invented mountain climbing, but they were the first to form a club around it and write down rules).
The inn where Tenzing and Hilary stayed before their Everest attempt is a particular nice spot if you ever have a chance to visit.