The Admiralty Chart of the Solway Firth marks several areas of ‘Changeable Depths’ – areas where the sea-bed moves around, sometimes forming channels, sometimes large sand-waves and shoals. But the Solway’s geological story has always been of changeable depths and malleable margins, as glaciers formed and melted, and sea-levels changed relative to the land.
You can see marks of earlier changes on the shores and estuarine banks of the rivers that feed into the Firth:
Clay is often associated with the peat on the shores: grey and slippery. But there is also red clay in other places too – as used to make the loom-stones and fishing-weights.
Clay has been a necessary building material around the Upper Solway, mixed with straw as the basis for building clay dabbins houses. For What’s a clay dabbin, see here.
More recent changes along the edges of coast are the result of industry, especially the former iron-works and steel-making on the Cumbrian side. The molten slag was poured onto the shores where it formed platforms and low cliffs; bubbly ‘floating stones’ and blue and moss-green slag pebbles are found washed up on many beaches. (For more on this see The Volcanoes of Workington here ).
For ships heading up the Solway, the changeable depths are a problem and especially in the days of sail, many ships were wrecked on the sandbanks. These days hydrographical surveyors check the topography and bathymetry of the seabed using advanced scanners and computer programmes to measure changes. Buoys mark the passage between Workington – where ships for Silloth take on a pilot – and Silloth. For more on this see Piloting a ship to Silloth here. Ports such as Silloth, Workington and Maryport Marina are constantly at risk of silting up and need dredging or flushing out: there’s a video of a hydrographic survey (from a drone, in April 2020) of the Port Of Workington and the mouth of the R Derwent here.