Magazine article Geographical

Coves & Cliffs Babbacombe: Our Series Showcasing the Royal Geographical Society (with IBG)'s Discovering Britain Walks Continues as Olivia Edward Takes a Stroll along the Coast near Torquay in Devon That Explores the Local Geology and the Coastal Processes That Have Shaped It

Magazine article Geographical

Coves & Cliffs Babbacombe: Our Series Showcasing the Royal Geographical Society (with IBG)'s Discovering Britain Walks Continues as Olivia Edward Takes a Stroll along the Coast near Torquay in Devon That Explores the Local Geology and the Coastal Processes That Have Shaped It

Article excerpt

If you look very carefully on Oddicombe Beach, you can catch a glimpse of a flash flood that took place around 300 million years ago. The beach sits within the English Riviera Global Geopark, self-taglined, as 'an epic adventure 400 million years in the making'.

Physical geographer and Royal Geographical Society (with IBG) Fellow Pat Wilson has designed a 75 kilometre trail that guides walkers through the geological dramas and highlights of the area. Along the way, walkers can see evidence of dramatic earth rqovements and previous eras when Britain was covered in tropical seas or smothered by a Sahara-like desert as our tiny piece of crust was pulled across the globe by the forces of plate tectonics. 'It's a journey through time,' says Wilson. 'Deep time.'

The telltale signs of the hundreds-of-millions-of-years old flash flood can be found in the tower that now holds up Babbacombe's restored 1920s cliff railway. To the untrained eye, the tower initially appears to be made of reddish breeze blocks but, in fact, it's breccia--a rock formed by small fragments of older rock being cemented together

'You can tell that this part was formed by a flash flood in a dry environment,' says Wilson as she traces her finger across a section of the rock's uneven surface, 'See how the contained rocks are sharp and angular? It shows that they were probably formed in a desert environment before they became caught up in the flood.' In contrast, water-based pebbles, smoothed down by years of wave action, would be rounded.

The slight angle at which they're lying--as if they've all just tumbled down a slope--is also a sign of a flood, as is their order, with the largest rock fragments lying at the bottom of these few layers of breccia. 'It shows that they were in fast flowing water,' says Wilson. 'The lighter stones would have been lifted and carried along, while the heavier ones would have moved more slowly and sunk to the bottom of the valley floor.'

ANCIENT STREAM

Once it has all been pointed out, the whole process becomes so obvious and vivid that I can almost see the ancient stream dragging these shards of rock down their dusty slope. It's all a sort of rocky detective game and Wilson has plenty more cases for us to solve. 'You've got to ask yourself, "Why is that landscape feature there?",' she says. 'Usually there's a reason and often that reason is geological.'

Before she's able to prove her points, she says, she needs to acquaint me with the main players. This can be done on the walk's first beach--Anstey's Cove--or elsewhere for those who don't fancy the (numerous) steps down. Most of the beaches have the area's main geological elements in pebble form: these are dolerite, Devonian limestone and black shale.

Dolerite is an igneous rock formed when magma forces its way up into the Earth's crust, cools, solidifies and is then exposed to erosion. 'Hold it in your hand and feel the weight,' says Wilson. It's black and iron-rich so weighs pleasingly more than other pebbles of the same size, a bit like holding a metal toy car compared to a plastic one.

Found alongside it is Devonian limestone, lighter and recognisable from the white circles found on its surface--the fossilised remains of small corals. Limestone was laid down when this area was covered in shallow tropical seas (when 'Britain' was about 20[degrees] south of the equator and the environment was similar to that of Australia's Great Barrier Reef today). Back then, the seas were teeming with life and Devonian limestone is largely the remnants of the millions of creatures that drifted to the bottom of these warm waters around 416 345 million years ago.

Finally, we have the black shales, flaky black rocks formed at the bottom of deep oceans. They're easily eroded but impermeable to water, unlike limestone, which allows liquid to seep through its fissures.

PREHISTORIC FINDS

Later, ex-lecturer Wilson tests my new knowledge by pointing to a spring and asking me to explain why it's gushing out of the middle of a cliff. …

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