It is a hot and sunny August Sunday; the beach is crowded; there is no “roke” at Roker today. The golden sand is firm, warm and enticing; grains sparkle in the sunlight (all of this might need some imagination). This beach has been a source of fun and entertainment for over a century. People are at their leisure – sitting, walking, and playing, children are digging holes and building sand castles, kites are flying – Roker Beach is buzzing; it is alive with activity and fun. It is a paradise for sand castle builders. Yet how many of the people enjoying the sea air and the noise of the waves breaking have ever asked themselves the simple question – “where does the sand come from”? First, take a close look at the beach, especially close to Roker Pier on its northern side and at the foot of the sea wall where they have been tossed up by waves. It isn’t all made of sand – there are lots of pebbles and cobbles. Many of these coarse fragments are a creamy, buff colour. They have been eroded from the local cliffs which can be seen at, for instance, Roker Ravine. The rocks here are bedded limestones of the Magnesian Limestone. They are of Upper Permian age and are about 240 million years old. The limestones contain not only calcium carbonate but also calcium magnesium carbonate – or dolomite. They were originally formed beneath the waters of the western side of what geologists call the Zechstein Sea (Zechstein is a German term for “tough stone”). Its warm waters, then located close to the equator, teemed with marine life and extended from the east coast of northern England right across northern Europe and into Poland. At the top of the cliffs, above the light-coloured rocks and often obscured by vegetation, is a brown, stony soil called till. This was laid down by ice when this area experienced the freezing conditions of the last Ice Age, around two million years ago.
But today these cliffs and the Lower Promenade from Roker towards Parson’s Rocks and Whitburn are protected by a sturdy sea wall that dates back to Victorian times. This prevents the sea from eroding the local rocks but, in so doing, depletes the natural supply of particles to the beach. Coastal erosion is often given a bad press but, quite simply, if there were no erosion there would be no beach and therefore no pleasure! There are other pebbles too – much darker in colour. These have probably come from far away, some transported by ice but others as ships’ ballast and then dumped. Pieces of brick and masonry are also present; these are the remains of long-gone industries. Together with the exotic ballast fragments they are a reminder of just how important nearby Sunderland once was as a port. Forty years ago you could also have picked up pieces of coal from the beach, when the mining industry was still active; but today these have all been either collected for burning or washed away by coastal currents. Much of the finer sand grains are derived from glacial deposits and have been carried here from far afield when the North Sea was covered by ice.
The magnificent, elegantly curving Roker Pier, with its lighthouse at the end, is an icon. It was badly damaged by the “Beast from the East” in February 2018 but the granite blocks that make up this mighty triumph of engineering have withstood repeated attacks from the sea since it was built between 1885 and 1903. Why are there so many pebbles, cobbles and a build-up of sand against the pier? This is because the dominant direction of transport of sediment in the area is from north to south along the beach face; the so-called longshore drift. Though it was not intended to do so, the pier acts as a barrier to this movement and the sand, pebbles and cobbles build up against it.
North of the pier, at the back of the beach below the sea wall are some low rocky outcrops of limestone. If you look carefully at these you can see shapes like spheres a few centimetres in diameter and cavities from which spheres have been eroded out. This is a rare and unusual rock, world-famous, and, because the spheres – or concretions to give them their proper name – resemble cannon balls, it is known as the Cannonball Limestone. The concretions grew progressively over hundreds of thousands of years around individual nuclei, pebbles or bits of shell, as a result of complex chemical reactions involving salt and other minerals on the floor of the warm, shallow, tropical Zechstein Sea.
First there is a mountain; ……….. Or was there?
