For over 150 years Geologists and Geographers have been puzzled by the fact that the Munster Backwater makes a 90 degree turn at Cappoquin to flow South to Youghal Harbour instead of continuing in its more natural Easterly direction to reach Dungarvan Harbour like shown the map below. Why does the river make a dramatic change of course for no apparent reason?
On researching as to why this is the case, I came across about six different proposals (or variations on) as to why the river runs wild! The sixth explanation is generally the most accepted theory…..read on.
One: J.B.Jukes, in 1862, proposed a theory that the present North-South flowing stretch of the Blackwater is very old and that there was a section of it directly north of Cappoquin that does not exist anymore. Also he thought that the present West-East flowing upper reaches of the river was only a tributary of the original Blackwater.
Two: G.H. Kinehan (19th century) said that a crustal fissure determined the course of the river south from Cappoquin. In other words the river followed the line of a crack in the surface of the Earth that caused it to deviate from its course.
Three: Hull (19th century) thought there must have been a physical barrier East of Cappoquin. This would be most likely have been a glacier which blocked the East-West flow of the river and diverted it Southwards through relatively higher ground.
Four: Similarly, Lewis and Porter (19th century) blamed a Moraine which is related to glacier activity for the 90 degree bend.
Five: In 1975, Gordon Herries Davies and J.B. Whittow came forward with a theory directly opposite to Jukes’ idea. They argued that the West - East flowing Blackwater above Cappoquin is the older section and the North - South flowing river to Youghal is the newer part, due to the erosion of Carboniferous rocks and the resulting formation of a new drainage system in the karstic landscapes. This is known as a type of river capture.
Six: Finally most scholars agree on the river capture idea but slightly different to Davies and Whittow above. This idea is a little complicated when described in words and especially if you are unsure of the local geography but have a look at my map and see what you think.
The old River Suir originally flowed North South through Ardfinnan, Newcastle and Cappoquin. Somewhere near Newcastle and a long time ago a smaller river which flowed through Clonmel “captured” the old River Suir and changed its course. This mechanism involves a smaller river which is able to tap and so capture the discharge of a neighbour. The capturing stream normally extends by headward erosion along an outcrop of soft rock until it meets and diverts the second river. A right-angled bend, the ‘Elbow of Capture’ is typical of the junction between capturing and captured rivers. As you can see from the map there is a notable change of direction of the present day River Suir at Newcastle which represents the ‘Elbow of Capture’
Meanwhile, downstream of this point obviously dried up until a point where a tributary joined the old river (The green river on my map). This happened at Cappoquin where a tributary joined at 90 degree to the old river. This formed into its own river system and continued on to the sea at Youghal harbour. So, what looks to the eye like one river, the Blackwater, changing course dramatically at Cappoquin was once, in fact, two rives.
By the way, I’m using the local towns as landmarks, as they didn’t exist when all this was going on – possibly as far back as 70 million years.
The cache is a magnetic attachment, please rehide with care. Parking at waypoint, very near another cache! Enjoy.