John Rodgers, President of the Cumbrian Geological Society guided Mid Wales Geology Club in the Lake District on a memorable weekend in 2016, and now has visited us at Plas Dolerw, Newtown to deliver a fascinating evening lecture in May 2017. John holidayed some years ago, driving through Death Valley in eastern California. This is a newly created landscape, with modern geomorphological features, one of the hottest places on the planet – average July daytime temperature 115ºF (46ºC), devoid of vegetation, a far cry one might think from the paradise which is the Vale of Eden in his home county of Cumbria. But you would be wrong to think that, as he amply demonstrated. He showed a strong similarity between the landscape features of Death Valley and those of Eden Valley, with one major difference: Death Valley is a new landscape still in formation, but the rocks of Eden Valley were created 250 million years ago when England was a hot, dry, unvegetated desert lying within the supercontinent of Pangaea. Since then Eden Valley has been covered and finally uplifted and eroded to reveal many aspects of its ancient depositional environment; it is an ‘exhumed landscape’.
John took us through many of the similarities between the two valleys: Death Valley as it is now, and Eden Valley revealed as it was long ago. Both valleys have mountains either side, with a faulted graben between, creating an arid valley floor, dry for long periods but with flash floods producing alluvial fans spreading from the mountainsides onto the valley floors. Imbrication (stacking alignment of the stones) reveals the flow directions. And even the differences brought about at a colder time by different snowfall on opposite valley sides can be discerned. On both valley floors magnificent wind-blown, crescent-shaped barchan sand dunes appeared, so characteristic of sandy deserts. As global sea levels began to rise, high evaporation from salt water lakes (playa lakes) led to salt deposits, and then to gypsum; dessication cracks can also be seen. The famous geological principle ‘the present is the key to the past’ enables us to interpret the relict structures of the beautiful Eden Valley in the context of those processes seen in action today, and in the geologically recent past, in the hell-hole which is Death Valley.