Friday, 31 August 2018

Land and Sea

Visitors to Torbay, where I lived in the 1950s and 1960s, crowded to the beaches when the tide was out, but had to retreat further and further up the sands as the tide was coming in. Then, many left the beach area to go in search of ice cream, sea food, chips and dougnuts - and to play in the amusement arcades.

As a child, I realised that the tidal cycle varied from day to day and also through each month. It was only later that I uderstood that this was the effect of the gravitational pull of the sun and moon on the World’s oceans and that tides were the result of “bulges” and “troughs” in these huge masses of water, reaching their highest when the sun and moon were in alignment in what are termed spring tides. Waves would crash against the shore when the wind was blowing a gale from the east during spring tides and I loved going to the seafront during these storms to watch the cascades of spray – such a contrast to lying on the sand on a warm summer day. After these storms, there would be sand, stones, shells and all manner of flotsam washed on to the promenade behind the sea wall that marked the limit of the blue on a map...

Occasionally, there have been catastrophic breaches in sea defences, as occurred along the coast with the dramatic collapse of the village of Hallsands in Start Bay at the beginning of the Twentieth Century (see above). It was a fishing village, with a sea wall, and was also protected by underwater shingle banks offshore. These shingles were considered very suitable for building purposes and they were dredged, resulting in Hallsands losing a key defence against the effect of storms. The remains of the village provide sombre evidence of the power of the sea as an erosive force and, as a child, I found that looking down on the remains adjacent to the cliff brought a sense of fear and awe. This dramatic location was used in Michael Winner’s film The System [1] for a scene where the characters played by Oliver Reed and Jane Merrow had a romantic liaison – the forbidding atmosphere of the place providing a metaphor for what was to happen in their future relationship.

More recently, there has been serious erosion to the north of Torbay, with the breakthrough of the sea wall at Dawlish and the subsequent undercutting of the main railway line to South Devon and Cornwall. Brunel is widely recognised as a brilliant engineer, but his vision was sometimes unchecked. Certainly, his building of a railway line between sandstone cliffs and the sea was a recipe for trouble and so it has proved on many occasions. The sandstone cliffs of Dawlish (I use the term sandstone to include breccias, where large mineral fragments are embedded in a sandy matrix) are pitted and sculpted by the action of winds and rain and this gives us a clue to another form of coastal erosion; that from landward. Any visitor to the “Jurassic Coast” in southern England is familiar with regular rock falls, as are those who walk under chalk cliffs. They also occur in sandstone areas. There is a good example of such a fall just to the north of Torbay, between Oddicombe and Petitor. This is how the great writer Philip Henry Gosse describes this part of the coast in the 1860s [2]:

Along the margin of a cliff, now steep and sheer, now breaking into an uneven but variously verdant slope, we begin our march, ever and anon pausing to gaze on the smiling scene below. The descent we are just leaving behind, half-covered with the gorse and guelder-rose, is Oddicombe, whose white crescent beach lies below, bounded by the limestone promontory of Petit Tor, which divides the huge precipices of red sandstone close at hand from the bluff coast of the same formation that stretches away to the northward; its ruddy cliffs and bold headlands – Watcombe, The Ness at the mouth of the Teign, the perforated rocks and needles near Dawlish – gradually fading into blue as the coast-line trends away to the eastward, and is lost to the aching gaze somewhere about the boundary of the county.

It is a lovely scene..

Gosse lived in St Marychurch, Torquay, and he made extensive collections of marine organisms between Oddicombe and Petitor, but the sandstone outcrop is different in profile to the one with which he was so familiar. Recent cliff falls have strewn the beach below with masses of rubble (see below), including the remains of houses built on the cliff top to give fine views. Sandstone is a porous rock and consists of mineral grains eroded from older rocks that have become cemented with new mineral deposits and then compressed. In some areas deep within the Earth’s crust, porous sandstone strata provide reservoirs containing oil that we extract after drilling: a similar feature to the aquifers contained within chalk, from which we extract water using boreholes. Needless to say, sandstone that becomes saturated with water, and that is fractured, produces slides like those seen repeatedly at Oddicombe. If you wish to know more of these events, the website of Ian West and Nikolett Csorvasi [3] has many excellent illustrations of the Oddicombe cliffs over time and is well worth browsing.

The original sand that formed the rock may come from deserts, or from sediments at the bottom of seas or lakes. This takes us to the idea of time scales. The coastline of Torbay, so obviously composed to the observer of bands of limestone, sandstone, slates and shales [3], would have looked very different just a few thousand years ago, although the underlying rocks were, of course, always present. Sea level is higher now that it was then and we know that coastal forests have been flooded [4]; remains becoming visible during contemporary low spring tides. If we could see pictures from that time, we would still recognise headlands, although these would be inland and have rather different profiles to the ones we see today. If we go further back in time everything is changed markedly, with the island of Great Britain joined to continental Europe. Before that, Great Britain was part of a huge land mass on a tectonic plate moving around the surface of the Earth, supported on the Earth's magma core.

The Oddicombe cliff falls are easy to recall as they continue and there have been major collapses in the last ten years. We know of the destruction of Hallsands village from contemporary records, and we know of the Torbay forests from the evidence of their remains, although some find it difficult to believe. Events that occurred a million, tens of millions, hundreds of millions and thousands of millions of years ago are quite beyond our understanding. We are sure they occurred, but we cannot comprehend geological time scales. We never will.

[2] Philip Henry Gosse (1865) Land and Sea. London, James Nisbet & Co.

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