Francis Hickenbottom's Nature Notes: 19th August, 2011.

Francis Hickenbottom’s Nature Notes.

19th August 2011

I visited the Yorkshire coastal town of Filey for a couple of days earlier in the week. Whilst my daughter played on the sands, I couldn’t resist sketching the steep cliffs of Carr Naze, which can be seen at the northern end of the beach.

The cliffs are made of a thick layer of boulder clay which sits on top of a band of harder rocks - a layer of sandstone on top of a layer of oolitic limestone. The sandstone and limestone were formed in the jurassic period and are packed with fossils, whilst the boulder clay was carried to the area and deposited by glaciers during the last ice age . A wide variety of erratic rocks from as far away as Scotland and Scandinavia come out of the boulder clay and it releases a range of fossils.

An interesting feature of the cliffs is a band of sedimentation which can be seen in the sketch. This is a sandy layer deposited during a period when the glacier retreated and a lake was formed before the ice advanced again. This layer has been found by sand martins and clusters of nest-holes can be seen in the cliff-face.

Sand martins can always be seen flying back and forth along the cliff-tops during the summer months and on the day on which I sketched the cliffs a group of sand martins were whizzing around above the sand in a sheltered corner of the beach close to the cliffs. At one time, they were flying all around me and looked as though they were feeding on the many flies which live on and around the material which is left on the strand-line.

The cliffs of Carr Naze always remind me of those which I saw during a visit to Bolivia about ten years ago. The capital city of Bolivia, La Paz, sits in a basin and is surrounded by steep, deeply eroded cliffs of boulder clay. Two of the sketches on this page show typical views of the cliffs from the streets of the city.

Like the cliffs of Carr Naze, the Bolivian cliffs are deeply eroded, producing steep faces, gullies, fluting, arretes and pinnacles. In both Bolivia and Filey, some of the faces and ridges look alarmingly steep and give the impression that they could collapse without warning.

The final sketch on this page was made during a lunch-stop as we trekked in area of the Val de los Animos. My main objective in making the sketch was to take my mind off my hunger.

The trek was our first during our visit to Bolivia and the teenagers who had been given the task of buying and packing the provisions for the seventeen members of the group had slipped up, leaving us seriously short of carbohydrates. I sketched the surrounding cliffs whilst the others tried to divide a bar of chocolate into seventeen equal parts.

The spires of mud and clay to be seen in the area were especially interesting because many of them were topped with capping stones. It was clear that the presence of a flat stone would dramatically reduce the rate of erosion of the material beneath it, resulting in the formation of a spire. I don’t know the appropriate technical terms for these structures and this process, if there are any, but I can say that the pinnacles would have provided classic images for a geology textbook.

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