Time and Tide

In The Hitchhikers Guide To The Galaxy, the character Slartibartfast designs planets, with a particular love of coastlines, and especially fjords, because they "give a continent a lovely baroque feel". I don't think he ever mentions 'rias' - a word I have not encountered for 55 years until doing a bit of reading about our day today

The estuary of the river Cleddau, south of here, is a spectacular waterway that extends 25km inland, with several branches - looking like a classic fjord. It is the site of the Milford Haven oil/gas terminal, where the water is deep enough to moor massive, ocean-going liquefied natural gas tankers for offloading, without any concern about the tides - which can rise and fall up to 7 metres here. 'Milford' is even an anglicisation of the Norse 'Melrfjordr' 

Closer to us, the only harbour within the 15km wide sweep of St Brides Bay is a much smaller flooded estuary - the river, and harbour town, of Solva. Here, the tide is much more significant: at low tide the harbour completely empties of sea water, leaving only the small river. Moored boats must be able to rest on their keel(s) and can only sail in and out when the tide returns

I've always referred to these valleys as 'fjords', but some (not all) of the things I've read call them 'rias'. Both are valleys that have been drowned by rising sea levels but, as far as I can work out, a fjord is a valley that has been scoured out by glaciers while a ria valley has not. Pembrokeshire was certainly under the ice sheets during the last glaciation, 10,000 years ago, but I think perhaps these valleys were gouged out by glacial meltwater, not the ice itself, which makes all the difference, apparently

This is a fence in Solva. Fjord or ria makes no difference, salt water is an electrolyte - it conducts electrons - which means it greatly assists the tranfer of electrons from iron to oxygen, creating the compound iron oxide, that we call rust. Salt water droplets blow up this steep-sided valley, land on the fence and chemistry takes its course - creating something that feels a little baroque