Tregynon Waterfall was originally formed due to ice. Today, Tregynon stream flows into Cwm Gwaun (the Gwaun Valley). During past ice ages, Cwm Gwaun was carved by water flowing at high pressure underneath large masses of ice. Following the peak of the last ice age, around 25,000 to 20,000 years ago, temperatures rose and the valley probably served as a route for large amounts of water from melting ice, called meltwater flows. These large meltwater flows expanded the valley as they carved the valley sides and floor. Smaller streams flowing into Cwm Gwaun were unable to deepen their valleys as quickly without the same volumes of water. Left as ‘hanging valleys’ high above, these smaller streams formed several waterfalls, including Tregynon Waterfall, as water dropped into the valley below. Tregynon is a particularly interesting example as today, the waterfall is located on the valley side, rather than at the valley head. Historic maps suggest that people made changes to the landscape further upstream of the valley head. This may mean that the waterfall was not always located exactly where it is now.
