River Blackwater Puzzle

JupiterKid · 05-06-2016 3:43am #1

When I was a geography student in college 20 years ago, our Geomorphology lecturer pointed out to us that the course of the River Blackwater was an enduring puzzle.

For most of its length, it runs from west to east, but then at Cappoquin in Waterford it turns abruptly south to enter the sea at Youghal. Our lecturer said that this didn't make geologic sense as the river had to cut through harder sandstone rock units in its southwards course.

I'm intrigued by this puzzle. In the past two decades, has it been solved? Or does it remain a mystery?

Coles · 05-06-2016 8:35pm

My understanding was that the ancient north/south river existed on a limestone landscape above the sandstone outcrop. As the land rebounded (or was forced upwards by some other process) the limestone eroded away and revealed the sandstone at this location. The flow of the river was sufficient to erode away the sandstone and the river maintained it's course.

tabbey · 06-06-2016 5:45pm

If it did not turn south, it would meet the Comeragh mountains, and have to turn towards the sea sooner or later.
A river will always seek the lowest terrain, it cannot ignore the law of gravity.

Coles · 06-06-2016 8:28pm

Frank Mitchell discusses it a bit in 'Reading the Irish Landscape'.

This page also touches on it.

http://www.askaboutireland.ie/reading-room/environment-geography/physical-landscape/Irelands-physical-landsca/the-formation-of-the-phys/a-mystery-of-irish-landsc/

Fathom · 06-06-2016 10:51pm

Plate tectonics. Uplift. Erosion.

Rebel_Kn1ght · 10-06-2016 7:46pm

According to Geoffrey Keating (Seathrún Céitinn), in late March 830 there was a "great convulsion of nature" in the province of Munster. This changed the flow of the River Blackwater moving its mouth from Whiting Bay and forming the harbour of Youghal.

I've seen this on Wiki and a few other places but have never seen any proof. Plus I live in Youghal and the mouth of the river is too wide to have been created just 1200 years ago

joebloggs32 · 10-06-2016 7:52pm

A process known as river capture would have diverted the course of the river. Its linked to a change in a river's base level due to isostatic rebouond, causing river rejuvenation.

Coles · 10-06-2016 9:02pm

Rebel_Kn1ght wrote: »

According to Geoffrey Keating (Seathrún Céitinn), in late March 830 there was a "great convulsion of nature" in the province of Munster. This changed the flow of the River Blackwater moving its mouth from Whiting Bay and forming the harbour of Youghal.

I've seen this on Wiki and a few other places but have never seen any proof. Plus I live in Youghal and the mouth of the river is too wide to have been created just 1200 years ago

Very interesting, but isn't that really just a change in the river's course as it enters the ocean?

http://kinsalebeg.com/chapters/ferrypoint/ferrypoint.html

River Blackwater Puzzle

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