[Tagging] Map a divide?

Kevin Kenny kevin.b.kenny at gmail.com
Thu Oct 4 23:45:10 UTC 2018

On Thu, Oct 4, 2018 at 6:26 PM Warin <61sundowner at gmail.com> wrote:
> A land form ridge too me is a long, narrow raised part of a high edge formed by hill/mountains and there associated bits.
> A land form of a dividing range or continental divide does not have to be narrow,
> The 'dividing line' marks the separate water flow from one side to the other and should be 'long'.

That divide is, ipso facto, a ridge line, because water flows downhill
- it is a line that's higher than the basins on either side. It runs
from peak to saddle to peak to saddle (admittedly, the 'peaks' may be
of but little prominence) for the length of the divide.

In any case, the place where I mean to map the divide is terrain of
considerable complexity, topographically. Its high point is the most
topographically prominent feature between Vermont and West Virginia.
The divide unquestionably runs for the most part along high ridges.
The 'ridge' nature gets lost only at a handful of saddles that are in
relatively high-elevation wetlands - but those flat lands are still
some hundreds of metres above the valley floors of the two rivers
whose basins it divides. The complexity comes from the fact that the
place is not a mountain range geologically. It is a 'dissected
plateau', whose 'peaks' are actually arêtes between chasms excavated
by glacial action. The direction of glacial flow was not consistent
among the glacial epochs, so the ridges tend to run higgledy-piggledy,
and one reason for mapping the divide is that it is otherwise tricky
to follow visually. It wanders quite a lot.

I live among some of the oldest exposed rock on the planet -
surrounding me are sediments from the early Palæozoic, and to the
north is the Canadian Shield, with its oldest rock dating to the
Hadean Æon, with its oldest samples having an estimated formation of
4.2 × 10⁹ years ago. Consequently, the mountains here are all rounded
and eroded. The ridges, except for the cols at the boundaries of
glacial cirques, are therefore broader and flatter-topped than you
appear to imagine - but they still rise distinctly above the
surrounding valleys.

Can we agree that https://www.flickr.com/photos/ke9tv/9514469053,
https://www.flickr.com/photos/ke9tv/10031459724 and
https://www.flickr.com/photos/ke9tv/14799708048 are all indeed views
of a ridge? (In the last photo, ignore the mountains on the horizon,
they're in a different range - the ridge runs diagonally away from the
right foreground).

Or check out the contour lines (elevations in feet; my users are
American) along the Devil's Path
and tell me that I'm not dealing with a ridge!

Open question - which I'll resolve for myself - is how much
topographic prominence to use when labeling peaks and saddles.  I
think I'll probably follow the local hiking clubs, and say, '150 feet
(about 45 m) of prominence, and 1 km separation' for mapping peaks and
their key cols, and at this point I care about the key cols mostly so
as to keep the topology of the divide continuous - although I'll
surely map the names of the saddles where I know them! (They do have
local names, even though they aren't listed in GNIS or appear on very
many maps. But the locals could tell you where to find Mink Hollow,
Stony Clove, Lockwood Gap, Winisook Pass or Pecoy Notch - and yes, we
use all those words in toponyms, reflecting the Babel of languages
that our settlers spoke.)

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