Ceunant Mawr (which translates as the waterfall of the great ravine) is probably one of the most impressive waterfalls in Wales on the course of Afon Arddu (River) and plunges in two stages into the gorge below.
View From Below The Falls
Only 15 minutes from the High Street of Llanberis. This can be spectacular after rain.
Start at the junction of the High Street and Church Lane (See Waypoint), between the Parish Church and the garage.
Follow Church Lane around a curve until the Snowdon Railway viaduct is in sight. 100m before reaching it turn right on a tarmac track by a cattle grid.
After a few yards take a narrow unsurfaced path to the left, skirting the house garden to reach a concrete path that runs up the side of the Afon Hwch. Five minutes easy walking brings you to the falls. A view from above is also possible.(This is the coordinates given) For this follow the tarmac track uphill from the cattle grid. Where this meets the railway a gate allows you to cross the track (Take care!) to get a view of the falls.
View From Above The Falls
Formation of Waterfalls
Waterfalls are most commonly formed when a river is young.
At these times the channel is often narrow and deep. When the river courses over resistant bedrock, erosion happens slowly, while downstream the erosion occurs more rapidly.
As the watercourse increases its velocity at the edge of the waterfall, it plucks material from the riverbed. Whirlpools created in the turbulence as well as sand and stones carried by the watercourse increase the erosion capacity.
This causes the waterfall to carve deeper into the bed and to recede upstream. Often over time, the waterfall will recede back to form a canyon or gorge downstream as it recedes upstream, and it will carve deeper into the ridge above it.
The rate of retreat for a waterfall can be as high as one and half meters per year.
Image used under GNU Free Documentation License
Often, the rock stratum just below the more resistant shelf will be of a softer type, meaning that undercutting due to splashback will occur here to form a shallow cave-like formation known as a rock shelter under and behind the waterfall. Eventually, the outcropping, more resistant cap rock will collapse under pressure to add blocks of rock to the base of the waterfall. These blocks of rock are then broken down into smaller boulders by attrition as they collide with each other, and they also erode the base of the waterfall by abrasion, creating a deep plunge pool or gorge.
Streams become wider and shallower just above waterfalls due to flowing over the rock shelf, and there is usually a deep area just below the waterfall because of the kinetic energy of the water hitting the bottom. Waterfalls normally form in a rocky area due to erosion. After a long period of being fully formed, the water falling off the ledge will retreat, causing a horizontal pit parallel to the waterfall wall. Eventually, as the pit grows deeper, the waterfall collapses to be replaced by a steeply sloping stretch of river bed. In addition to gradual processes such as erosion, earth movement caused by earthquakes or mudslides or volcanoes can cause a differential in land heights which interfere with the natural course of a water flow, and result in waterfalls.
The Geology of Snowdonia
The complex and diverse geology of Snowdonia has done much to shape the present landscape as land and sea have changed place more than once. Great mountain ranges have been pushed up out of the oceans only to be slowly eroded away, their debris carried by the rivers and laid on the sea bed to form the substance of future mountains.
Volcanic rocks have produced distinctive features on Snowdon, Cadair Idris, the Glyderau, the Carneddau and Arenig. A distinguishing feature of the rocks of Snowdonia is that some are ancient. The fossil shell fragments on the summit of Snowdon are a memory of life on the seabed over 500 million years ago. The oldest physical feature of Snowdonia is probably the ‘Harlech Dome’ created in the Cambrian era before the volcanoes erupted. Snowdon and Cadair Idris form the northern and southern extents of the dome respectively. What we now know as the Rhinogydd stand at the centre, on what was the original ‘uplift’ of sedimentary rocks, composed of muds and sands, but later altered by the volcanic activity to become the slates and grits of today.
In recent geological terms, Ice Age activity has done much to shape the landscape. The glaciers that were at their peak 18,000 years ago in Snowdonia scoured out great U-shaped valleys including Llanberis and Nant Gwynant in the north and Tal-y-Llyn in the south. The same period also formed rocky ‘cwms’ or corries, hanging tributary valleys many of which have breath-taking waterfalls cascading over them, whilst the characteristic pinnacled knife edge ridges or arêtes like Crib Goch are found where two ‘cwms’ formed on either side of a mountain.
Other Geological features to look out for such as
volcanic rocks, sedimentary rocks including intrusive rhyolite, dolerite, granite, gritstone, mudstone, slate, siltstone & sandstone
carved rockfaces & ridges
prominent shaped peaks
rounded elevated mounds
geological layers of rocks
loose rocks & boulders
glacial mountain lakes
deep glacial valleys
volcanic rock, tuffs+ plugs
magma flow banding
ruins of mineral mines
slate quarries & slag heaps
To log this earthcache, please email via my profile with the answers to the following questions
1:Estimate the height of the second section on the falls
You may find this website helpful
2:What is the surrounding rock made from and how is it created?
Also adding a photo to your log would be great but this is now optional and not a requirement for logging the cache.