Saturday, April 25, 2015

Sinkholes and the Perched Pond

Some of you have probably been wondering exactly what these 'sinkholes' that I'm talking about really are.  They're not those large sinkholes that you sometimes see pictures of where a car or two have collapsed into a large cavity that opens up under the street.  They are simply cracks in between the rocks where water runs downward into the limestone beneath.

Here's a group on a Bruce Trail hike in the fall two years ago, heading down into the depression surrounding a sinkhole, and back out again.  At the moment, this would be under that flooded field.

And this is what they're looking at, just a tiny stream of water, about 4" wide and 2" deep, dropping down the crack between two large pieces of bedrock.

This is what the same sinkhole looks like in the early spring before it's flooded.  The hole at the bottom is the only evidence of water draining away.  We paddled across this last week.

This is the main cluster of sinkholes taken two years ago, just after the spring flood had ceased and water levels were back down to normal.  That year the spring flood was very brief!  Two sinkholes are in the lower right, against the shadowed rock outcrop, and one is in the upper left.

The sinkhole is simply a stream of water disappearing downwards between the rocks.  In my mind, none of these are big enough to have 'caves' below them, but the literature does refer to such caves, and I've heard local stories of people crawling through them - but you certainly couldn't tempt me to even try!!


This is the last and lowest sinkhole of the main cluster, almost always with at least a small pool of water in it, and a bit of a whirlpool pattern in the water.

If you stand at that sinkhole, and look upwards, you can see where the 'perched pond' is, about 18' higher.

And if you stand where that fellow is in the shot above, looking beyond, this is the perched pond.  It's known as a 'perched pond', because it's perched right beside a flowing stream, but it's higher and hydrologically seperate in the landscape.

Even the government topographic maps get this one wrong, showing the stream flowing into this pond, which it doesn't.  I think a number of people interpret the pond as the sinkhole, incorrectly.

I always wondered how the pond possibly got its water, which seems stable all summer long.  I began to guess that maybe the spring flood reached high enough to refill it each year, which seemed amazing to me when I first thought of it.  It wasn't until we first paddled in there last year, here paddling from the flooded field back into the perched pond, that I realized it was true.  Another fascinating side to this interesting drainage system.


17 comments:

  1. You're right, it's fascinating. Thanks for all the information about the interesting area where you live. I'm learning a lot. :-)

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  2. That is an interesting drainage system. I don't think I've ever seen something like this out west.

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  3. Wonderful photos and explanations. Such a geologically interesting area where you live.

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  4. I know there are places along the Escarpment where there are caves or crevices. It's all a matter of time. Geological time, not our time.

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  5. I have never seen the water draining down into the crevice. I understand it now when you describe where all the rock is and how it relates to the rest of their development. Great job of explaining you sinkholes.

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  6. This makes it lots clearer, and so interesting. Lovely ones of the blue water just a tiny swirly pattern, no wonder you so enjoy the times when you can get out on the water.

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  7. Great photos and very interesting about the sink holes. Thanks for explaining them.

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  8. This is all so very interesting. Great photos. It does look like a beautiful place to paddle.

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  9. We have a lot of Karst scenery in Northern England, but the limestone supports few trees. Is there a thin layer of glacial deposits on top of the rock in your part of the world, or has sheep farming stripped all the vegetation from ours?

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    1. Usually there is a layer of glacial deposits, so the only exposed limestone is in the bed of the creek. Don't know about your sheep!

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  10. A fascinating and beautiful landscape - one I think I could only properly get to grips with by being shown around in person. Sometimes such works of nature are almost frightening; maybe I'm a wimp but its complexity sometimes inspires an awe that's almost overwhelming.

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  11. the sinkholes are interesting but a little bit scary!! it's a beautiful place and i enjoyed your images!!!!

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  12. Very interesting... I wonder if you have to be careful where you walk ---when there is no water around to warn you???? Thanks for sharing your 'sinkholes'.... Amazing.
    Hugs,
    Betsy

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    1. Yes you do have to watch where you walk. Not just for sinkholes, but for crevices in the rock too.

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  13. Thanks for answering my questions about the sink holes. Such an interesting landscape. I can't imagine trying to crawl down into one of them to find caves below but I suppose some adventurous types do and that's how things are discovered.

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