There is still a debate here about whether glacial meltwater has played a big role in the cutting of these gorges. Will investigate further -- but in the meantime, just enjoy the photos!!
Thursday, 6 October 2011
Nahanni Labyrinth and Cheddar Gorge
There is still a debate here about whether glacial meltwater has played a big role in the cutting of these gorges. Will investigate further -- but in the meantime, just enjoy the photos!!
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12 comments:
Brian
"There is still a debate here about whether glacial meltwater has played a big role in the cutting of these gorges."
To consider this seriously, details of how much water would be needed to cut such a gorge?
Recent Geologists theories suggest the same action caused both the North and South Downs - a far bigger area and hence greater amount of water - but exactly how much?
As scientists until the maths is done and can equates to known sea level rises at that time, the idea is only speculation.
RJL
Robert -- re glacial meltwater -- "Recent Geologists theories suggest the same action caused both the North and South Downs" -- what on earth are you talking about? I really have no idea.....
Brian
What I have read on the internet and seen in your blogs about the extent of past ice age glaciations, has shown that the ice sheets only reached Hornchurch (following the Thames River) to Bristol maximum.
IF that is true, the only way you can have the massive dry valleys in the North and South Downs as the likes of the Devil's Dyke - is through ice water release like the Cheddar Gorge.
So how much water needed to be released?
RJL
"......the only way you can have the massive dry valleys in the North and South Downs as the likes of the Devil's Dyke - is through ice water release like the Cheddar Gorge." That's nonsense. Why are you so obsessed with catastrophic floods?
I see no reason to doubt the normal explanation of chalk dry valley development, maybe with some assistance from permafrost conditions, and maybe over a very long period of time (ie several glacial / interglacial cycles).
Brian you write,
“There is still a debate here about whether glacial meltwater has played a big role in the cutting of these gorges.”
From previous exchanges you know my thinking on this. It does not seem to me that these gorges were initially formed as glacier meltwater channels. I still think such gorges were formed in somewhat analogous way to 'bread crust cracks' in thick crusty loaf. These beautiful photos only reenforce that impression.
The bedrock being limestone makes these gorges similar to the Mendips – in contrast to Salisbury Plain where the bedrock is chalk and where such gorges to not exist.
Of course, my view avoids all the pitfalls Kallaway stepped on explaining these Mendips gorges as formed by glacier meltwater.
Kostas
Kosta & Brian
If we ever get a straight answer to a simple question - how much water is needed to cut such a gorge - we may have a better idea on how they were truly formed!
RJL
Robert,
I just don't believe such gorges were 'cut by water'. I could be wrong, of course. But I am just sharing my 'intuitive insight'.
Such rugged and sharp zig-zag landscape at the bottom of a valley can only be the result of 'cracks' on the limestone bedrock when the hot strata encountered freezing conditions, in my humble opinion.
Of course, I have no 'expertise' to back up such opinions. But then that enables me to make them. I see no harm in considering such possibilities! Do you?
Meltwater could of course later use such gorges and associated sinkholes to drain into deep caverns and collect underground. And make the existing cracks much wider through rock dissolution.
But the cracks were probably already present. Otherwise, wont we get such impressive gorges happening everywhere glaciers existed over limestone bedrock?
My view on this explains why, for example, some of the “meltwater channels” at the Mendips flow opposite to the expected direction of the glacier retreat. What I think discredited Kallaway's otherwise correct glacier transport claims. If these gorges were initially created by hot/cold cracks in the limestone strata, these cracks would occur in almost any direction.
Just thinking out aloud! Am I being ostracized for thinking?
Kostas
Kosta
You could be right - I'm not a geologist. I don't have a ulterior motive in asking just curiosity in if anyone has done the maths on this idea?
As a archaeoloist when I read that the 'south and north downs' was formed by a glacier cutting the chalk top off what would been half the county of Kent - I naturally think 'wow' where is the chalk version of Kent now - floating in the bottom of the North Sea or are the geologists just guessing?
RJL
Robert -- it's fairly obvious that you are neither a geomorphologist nor a geologist! Goodness knows where you got this latest idea from -- you have profoundly misunderstood something or other. Please go off and do some homework -- there are plenty of perfectly good text books out there....
re the amount of water needed to cut a gorge -- this is a nonsense question, since there are so many variables in ersosion -- involving time, the nature of the bedrock and the processes (both chemical and mechanical) involved. Every valley has a different history, and you'd be better off concentrating on looking at the field evidence of sediment sequences etc if you want to know what has happened in the past.
Brian is correct here-you must have misread almost everything. I do not know anyone- including Brian at his most expansive- who has suggested a glaciation in Kent;'cutting the chalk off' cannot have been meant literally it would be a poetic way of saying eroded.
Do not even think Klippen!
GCU In two minds
Not my ideas Guys! I just read this rubbish in complete disbelief.
Even with this current popular theory on periglacial erosion - where has all the material gone? It can't just vanish leaving North and South Downs untouched in comparison - The gorge I can accept that it was washed away into the Bristol channel and then the sea (although an idea on the volume would be useful)- but this Kent Weald Dome its huge!!
In a strange sense the ice cutting the top off the dome seems a more sensible solution than erosion (its this word used like the archaeologists word 'ceremonial' when you don't know?).
Lots of textbooks with lots of words - but no answers!
RJL
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