Thursday, 28 February 2019

Wensleydale Waterworks!

Waterfalls of Old Yoredale

Wensleydale was not scoured just as deep by its glacier as neighbouring Bishopdale, and so a 'step' of limestone was left along the valley foor.  This step, part of the Yoredale Series of limestones, sandstones and shales, is the major reason for the abundance of waterfalls .. some of which are spectacular indeed!

The 'Yoredale' series are named from the old name for Wensleydale - 'dale of the Yore or Ure' and are superbly seen along the length of this fine glaciated valley.  About 320 million years ago in the late Carboniferous, fluctuating sea levels on a regular pattern produced this lovely 'sandwich cake' of rocks, well seen here at West Burton Force.  At the top here can be seen Gayle limestone, one of the lowest limestone bands in the sequence, with sandstone and shale beneath.  The sandstone and shale were formed when sea levels lowered to allow river deltas to wash in sands, gravels and muds.  Once the sea level rose again for marine life to flourish, limestones were once again laid down.

The Yoredale series is well seen here at Penhill, as we drive from Bishopdale into Wensleydale.  Each 'step' is a resistant layer of limestone, marking where shales and sandstones have been undercut beneath.  The layers of limestone were named by lead miners in the past.  The highest step here - the 'main' limestone, is the same as that seen just below the summits of the Three Peaks.  The massive plinth of Great Scar Limestone on which Ingleborough sits is nowhere in sight here, being buried far beneath our feet, as the Dales rocks all rest on a foundation, the 'Askrigg Block' which dips to the north and hence hides the Great Scar Limestone in all but a few places.  

Here at the lovely Cauldron Falls, at West Burton - we see two of the lower layers of limestone in the Yoredale Series well displayed.  The beck falls over Gayle Limestone (named from the area of the dale in which it is prominent) and onto Hawes Limestone.  The undercutting of thin shales and sandtones is forming a small cave to the left of the force.  There are many fossils in both the limestone and shale beds here.  The Hawes Limestone is famous as being the lowest in the Yoredale Series.  The Great Scar Limestone (Forming the familiar Malham Cove and Gordale Scar) can't be too far below us here!  

Another view of the Cauldron Falls, showing the cliffs of Gayle Limestone and the undercutting of the shale/sandstone beds.  

Beneath the overhang we have an interesting sandwich ....

Thinly bedded sandstones and shales that seperate the Gayle Limestone (top) from the Hawes Limestone beneath my feet. 

Regardless of any geology - the Cauldron Falls are there to be enjoyed.  Turner loved them!

Nearby lie the most famous falls in the Dales at Aysgarth.  These are the beautiful Upper Falls - best seen after heavy rain. This time the steps were formed in one kind of limestone - in this case the Gayle Limestone - when shale beds in between the limestone were cut back by the swirling water so the the limestone wedges above collapsed to to form the steps.  Hope that makes sense!  This is the major 'step' left by the Wensleydale glacier.

Here, the Ure falls over a major step caused by collapse of a block of limestone caused by undercutting of shale beneath; a splendid sight.

The Middle Falls at Aysgarth tumble over steps between the Gayle and Hawes limestones ...

While finally - at the Lower Force ...

The Ure cascades spectacularly over the same Hawes Limestone we stood on at The Cauldron Falls.  We reach the very base of the Yoredale Series.  Hundreds of thousands of years from now this will be a great gorge worn down so that the hidden Great Scar Limestone beneath forms the valley sides.  But we'll all be dead - so forget that!

Further west along the dale at Askrigg, we meet the beautiful Mill Gill Force.  We are also in the higher layers of Yoredale limetones.  In this case, the beck tumbles over Hardraw Scar Limestone, over sandstone and into a shale plunge pool.  The complete cycle of three rocks in the sequence - formed by sea, river and thick mud  - is called a cyclothem.  This is one of the very best examples in Yorkshire.

Mill Gill certainly deserves a visit along the well-marked path behind Askrigg church.  In flood, it is one amazing wall of sound! 

Wensleydale abounds in stunning views.  Here the stepped Yoredale Series is seen well below the legendary hill of Addlebrough.

In close up - it's an impressive sight - and one that beckons you to climb it!

Wensleydale does have its gentle side - as this view of the glaciated dale shows.

It also has its aggression - as any trip behind the Green Dragon pub at Hardraw quickly reveals ...

Here Hardraw Beck falls as the highest surface waterfall in England - Hardraw Force -  nearly 100 feet over a single cyclothem of Hardraw Scar Limestone, sandstone and shale.  The people to the right of the fall are standing on the soft shale bed.

The overhang of Hardraw Scar Limestone is well seen here, with the sandstone gradually becoming shale at the plunge pool.  This is a wonderful place, no matter what the water conditions.

Classic view of Hardraw Force: worth every penny of the entrance fee.  It lies on private land.

In winter, without the leaf cover - the rainbow in the spray is worth the trip alone.  I was lucky today.

Paint the whole world with a rainbow!

The classic 'cyclothem' of limestone, sandstone and shale.  You couldn't see it better!

And to finish the day - a visit to the stunning Cotter Force, just outside Hawes.  This follows the same cyclothem as Hardraw Force, but the beds are closer together so we get an impressive series of steps in the river bed.

The steps in the beds of shale are well seen.  This is a place that has to be seen.  Watch out for kingfishers!

And that concludes our tour for now.  Later in the year we'll complete our Wensleydale Waterworks survey with a visit to two more classic waterfalls that lie in this enchanting dale.

For more information on geology - please visit my Dales Rocks website  for the Yorkshire Dales National Park.  

Stephen x

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