Separating Carningli from Foel Eryr and the rest of the Mynydd Preseli, Cwm Gwaun, the Gwaun valley, is an example of the network of large valleys that characterise this part of Wales. In Wales, the last ice age peaked around 25,000 to 20,000 years ago, but this was just the latest in a series of ice ages that covered large parts of the country. Scientists have suggested that during these ice ages, water flowing under high pressure beneath masses of ice was able to erode the underlying land surface, creating the valley network we see today. It is likely that these valleys would have provided routes for the water from melting glaciers following the end of the ice ages. These valleys may also have acted as ‘spillways’ from large glacial lakes that formed in the area. Many of the streams that flow through these valleys today are known as misfit streams, meaning they are much smaller than what you would expect given the size of the valleys they flow through. Cwm Gwaun itself is 500 metres wide and 70 metres deep in places. Some other valleys have no streams flowing through them at all.
