[Tagging] Feature Proposal - Voting - Couloir 2

[Kevin Kenny]

On Thu, Feb 18, 2021 at 7:22 PM Bert -Araali- Van Opstal <
bert.araali.afritastic at gmail.com> wrote:

> Gully or gorge = created by flowing water or ice, also applicable for
> desert
>
> Couloir = similar appearance but not created by erosion but by other
> phenomena which only appear in mountains.
>
> That's a part of the description that I found confusing, because in my
part of the world, virtually all surface topography is erosional.

Even the large couloir for which I posted a video link earlier (I since
discovered a trip log with excellent images at
https://alavigne.net/Outdoors/ImageGallery/2015/06-27-TrapDike/?n=2#id=54959)
has a complex history. The rock on either side is anorthosite gneiss, and
is among the oldest rock on the planet, being on the fringes of the
Canadian Shield.  The gneiss is broken by a newer intrusion of a narrow
dike of gabbro (essentially, a coarser-grained form of basalt).  Over the
eons, repeated glaciations, avalanches, and freeze-thaw cycles have eroded
the gabbro away leaving the deep, narrow, steep chute that we have today.
Because the climate here is relatively wet, a stream does flow in the
couloir (and the hardest part of the route is ascending the two
waterfalls).

Farther south, the Catskill Mountains aren't mountains at all,
geologically, but rather aretes of sedimentary rock in a dissected
plateau.  They still have features of similar topography.
https://i0.wp.com/mountain-hiking.com/wp-content/uploads/2019/10/Twin-Cave.jpg
and https://i.redd.it/ho2zisofspn41.jpg are sculpted purely by erosion.
(They don't look like alpine couloirs, because they're below the tree line,
but they get the same sort of conditions in winter and offer similar lines
of ascent.)

I would agree that you see couloirs only in mountains (or other cliffy
features such as canyon walls), because only mountains are steep enough to
have them.

To me, the distinguishing features are that a couloir has rock walls on
both sides and a steep gradient. Usually the climbing is at least class 3
on the Yosemite scale, and may be considerably more technical, particularly
when there's ice about.
-- 
73 de ke9tv/2, Kevin
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