The Formation of a Brook on Dartmoor
In my previous blog about the landscape of Dartmoor I described Sharp Tor (see Sharp Tor) and the sunrise over Sharp Tor was photographed from roughly the same spot as this image, which shows the valley between Sharp Tor and Carter Down with Row Brook forming and running down to meet River Dart, which is hidden in the valley below.
Dartmoor is originally the remaining part of a large volcano that erupted several hundred million years ago. When it now longer was active, the magma chamber deep underground began to cool and the lava in it turned to granite. Then over the millions of years the rock above was slowly worn away, and the granite of the magma chamber remains. Above the granite a layer of moorland, where once trees grew, but now it is mostly peat bogs, grass, moss, lichen and areas of standing water, due to the underlying granite being impermeable to the water.
One such little stream is Row Brook formed in the valley below, where I was photographing. The image above shows the valley with its watercourse. The water is mixed up with the moorland grass and peat bogs. The next image shows the same valley from the other side, from Sharp Tor an early morning half an hour after sunrise.
Row Brook is the shallow valley to the right in the image. The much deeper valley further away contains River Dart. Coming down into the valley I came to the old tree trunk that I used to frame Sharp Tor in my previous Landscape Post. Now I instead looked down towards the beginning of Row Brook.
All the rain that falls on Dartmoor is soaked up by the soil and bog, lichen and mosses and the water cannot penetrate further down than to the granite below, so in the wet season (which on Dartmoor means all year around!) the water just flows downstream underneath and sometimes above the grass and lichen, until it becomes a true stream and flows into the river.
I have tried to illustrate that with the following three images of water and moss and lichen. It is beautiful on a sunny day, but you still need sturdy walking boots to walk in these valleys.
