The Story Of The Forest Of Dean Area
There have been two parts to the posting "New Discoveries In The Forest Of Dean". Recently, I became aware of a project to extensively photograph every corner of Britain and Ireland and post the tens of thousands of photos. The site of this project is http://www.geograph.org.uk/. I have found the photos on the site to be immeasurably helpful in the study of natural history and I have decided to supplant the previous postings with this one, with links to photos included.
Here are map links. If you wish to follow along on a map, just enter in Lydbrook to start. http://www.maps.google.com/ and http://www.multimap.com/ The Forest of Dean is the western portion of Gloucestershire in England, along the border with Wales. Much of what we will be discussing is in the neighboring county of Herefordshire.
By the way, both of these map sites offer a download to make the map three-dimensional and I would like to assure readers that both downloads are perfectly safe.
I am so interested in the Forest of Dean simply because Lydbrook was where I entered the world. In terms of physical geography, the northern section of the forest is high ground divided up by several valleys. The hills representing the high ground are not material deposited by glaciers. Rather, the layers of rock representing the high ground are being cut up by glacial movement during the ice ages, leaving the valleys.
The high ground in the Forest of Dean could well have been land forced upward during the continental collision that I described in the posting "The Mysterious Geography Of Britain" earlier in this blog.
The wonderful thing about these photos is that they enable all readers, even the vast majority which would not be familiar with this area, to see how glaciers interact with land during ice ages. Similar examples can be found all over the approximately 30% of the world that was then covered by glaciers. The activity of glaciers in the Forest of Dean involves both primary glaciation, the movement of glaciers at the beginning of ice ages and secondary glaciation, the effects on the land when glaciers melt and break up at the end of an ice age.
There have been more than twenty ice ages. The last one began about 20,000 years ago and ended about 12,000 years ago.
SYMONDS YAT
Let's start our exploration of the Forest of Dean at a place called Symonds Yat. There are two slices into the rocky high ground here, which were created by the glaciers coming down from the Welsh Mountains during the ice ages. The glaciers which passed over the forest probably originated in the low area northwest of the city of Hereford, around Weobley and Kington, which is sorrounded on three sides by mountains. As I have documented on my geology blog, http://www.markmeekearth.blogspot.com/ glacial ice actually moves toward the southeast, rather than due south, because the eastward rotation of the earth imparts momentum to it.
It is very important to realize that it was not the main force of the glaciers which passed over the forest during the ice ages, but the somewhat lesser glaciers which came down out of the mountains. If it had been the main force of the glacier it is possible that all of the high ground in the Forest of Dean would be gone by now, but the Welsh Mountains formed a shield.
The main thrust of the glaciers from the northwest went between the gap between the Welsh Mountains and the Pennines at Liverpool. The glaciers carved away the ground as they proceeded along this route and the result is the Severn Vale. This is the broad low area around the Severn River. The Forest of Dean is on one side of the Severn Vale. The ice which passed over the forest joined the main flow of ice here.
Overlooking the village of Symonds Yat is the observation point on Yat Rock. If we look northwest from there, this is what we see:
Notice the Welsh Mountains in the distance, and the lowland in between. This is from where the glaciers came www.geograph.org.uk/photo/530746
We are looking northwest in these photos. The valley is the Wye Valley, named for the river which flows through it. The Wye flows southward from here and joins the Severn River at Chepstow.
In no way did this river carve the valleys through which it flows, the glaciers carved the valleys and the flow of the river found it's way through after the last ice age. The large loop in the Wye River on opposite sides of Yat Rock through Huntsham demonstrate how fast the water must have been flowing at the end of the ice age. It required this wide loop to make the 180 degree change of direction.
The formation of valleys like these through layers of rock do not necessarily happen during one ice age. A flow of water, whether from a permanent river or a flow of meltwater at the end of an ice age, will weaken the rock beneath it. Then when the next ice age arrives, the ice can push it's way into the weakened rock and the process is repeated over successive ice ages, until we have the finished valley.
Now let's look in the other direction from the top of Yat Rock, to the northeast: www.geograph.org.uk/photo/1617787
The elongated hill on the right is known as Coppet Hill (I have seen it spelled in different ways). Coppet Hill is aligned at a moderate angle to the direction of glacial movement from the northwest. The result is that it deflected the oncoming ice so that it broke through the limestone to the east side (right) of Yat Rock.
The elongated Coppet Hill also acted as a barrier so that it created a "glacial vacuum" behind it. Further east, the ice broke through the rock at yet another point at Kerne Bridge. The ice that came through there was diverted by the ice piled up against Ruardean Hill so that it was diverted into the "glacial vacuum" behind Coppet Hill.
This movement of ice eventually met that which had cut into the rock at the east side of Yat Rock. The result as seen today is the semi-circular valley around Coppet Hill and the area to the east of it, up to Kerne Bridge.
Here is the view, looking north, from the top of Coppet Hill. You can see the Kerne Bridge, over the Wye River, and Leys Hill on the other side of it. After Leys Hill, there is Chase Hill. The valley between Leys Hill and Chase Hill is at Coughton, which we will get to later. On the other side of Chase Hill is the town of Ross-on-Wye, which also has a valley that we will see. www.geograph.org.uk/photo/1187565
Here is a view of Coppet Hill from Leys Hill, to the east. The valley and the Wye River is between the hills: www.geograph.org.uk/photo/1309557
In this view, the mountains from where the glaciers came are in the distance. Coppet Hill is closer and the Wye River is in a hidden valley, carved by the glacier, before Coppet Hill: www.geograph.org.uk/photo/119223
Here is a view of the mountains in the distance from Ruardean, on Ruardean Hill south of Leys Hill: www.geograph.org.uk/photo/119217 A lot of glacial ice was pressed against Ruardean Hill during ice ages and when it melted, it formed Lodgegrove Brook, which runs east-west just north of Ruardean Hill.
LYDBROOK
Now, let's consider the long valley which extends southward from the village of Lydbrook. In fact, Lydbrook is built along the road along the bottom of the valley.
The two channels of ice described above, one beginning to the east of Yat Rock and the other beginning at Kerne Bridge, cutting their way through the rock, met at what is now the bottom of Lydbrook, where the Wye River now flows. The two channels of ice collided and diverted one another southward, cutting the valley through Lydbrook.
The peaceful serenity of Lydbrook along the Wye today belies the violence of the ice collision which formed it, the same goes for Symonds Yat. If you wonder how moving ice can cut such relatively neat channels through rock the reason, once again, is that a flow of water in times past will weaken the rock so that moving ice during a subsequent ice age will find the weak spots in the rock and force it's way through.
The valley through Lydbrook is dry today, but at the end of the ice ages it was a raging river of water from the melting glacier atop the area. It extends along New Road through Parkend and onward to the Severn. There are a number of entrances through which meltwater flowed into the Lydbrook Valley which are readily visible today. One is the valley around Speech House Road just east of Mile End and Broadwell, near Coleford. Deeper in the forest, water running into the Lydbrook Valley long ago formed a canyon at Wimberry Slade. There are more such channels to be seen on an ordnance map of the forest.
Here is where this great collision of ice took place at the bottom of Lydbrook, where the Wye River flows today: www.geograph.org.uk/photo/523362
This is another view of the Wye Valley, where the collision took place: www.geograph.org.uk/photo/1427622
These are views across the valley through Lydbrook. These are closest to the Wye River and the collision which diverted both channels of ice southward to form the Lydbrook Valley: www.geograph.org.uk/photo/1427688
Here is the valley through Lydbrook a bit further away from the Wye River, which is where the ice collision took place:
This photo is taken from across the Wye Valley from Lydbrook. You can see the Wye Valley in front of you and the Lydbrook Valley, with the houses in it, between the two hills in the distance. This makes it easier to imagine how the two channels of ice collided while forming the Wye Valley and, diverting each other southward, formed the Lydbrook Valley: www.geograph.org.uk/photo/355420
This valley continues southward to Parkend: www.geograph.org.uk/photo/1319028 and Lydney.
BICKNOR
The collision between channels of glacial ice in what is now the Wye Valley, and which diverted each other's force southward to cut the Lydbrook Valley, was not quite so neat and simple. The proportion of ice coming through each end varied. For a time, the ice of the combined channel actually went in a different direction, and not through the Lydbrook Valley.
In the photo above, the ice also formed a much smaller and incomplete valley to the right (west) of the Lydbrook Valley. This is what we could call the Bicknor Valley because it is near the village of that name.
By the way, there is two villages named Bicknor. One is Welsh Bicknor, and the other is English Bicknor. Here, I am referring to English Bicknor. Welsh Bicknor is across the Wye River from Lydbrook. Both of these villages are actually in England. The reason that they are so-named is that a lot of Welsh Labourers (laborers) lived in one of the villages, so it became known as Welsh Bicknor.
Here are some photos of the valley at Bicknor. It forms a V with the origin of the Lydbrook Valley, pointing at their common origin. A small brook now flows through this valley. The Bicknor Valley was never completed down to the Severn Vale and it shows what the Lydbrook Valley must have looked like at an earlier stage of it's development:
By the way, look at how rounded are the Welsh Mountains in the distance. That means that the mountains are very old. One of my theories is that these mountains were once high enough to block the weather and that is why there is so much coal in Wales today. You can see "Coal Made Really Simple" on my geology blog.
THE WYE VALLEY
Let's go back to the scene at Symonds Yat: www.geograph.org.uk/photo/784049 and consider the Wye Valley from this point southward, until it joins the Severn River.
There are two places in this stretch of the Wye Valley where a branch river formerly joined the main river until changes in water flow after the end of the ice age caused the upstream section of the main river to either run dry or to become a very minor flow and the former branch to become the main river.
The first such instance is at Garnew, west of Symonds Yat. The former upstream of the river is completely dry and what was once merely a branch flowing into the main river has become that river.
The second is at Monmouth. The Monnow River was once the main river. It was a glacial route from just north of the Black Mountains.
At Redbrook, we have an example of a dead end glacial channel off the main Wye Valley. The ice cutting this channel turned around and headed back northward.
The ice covering the area around Coleford was maybe one or two kilometres thick and when it melted, it released a temendous amount of water. This meltwater carved drainage channels in the rock as it made it's way to the Wye Valley, which we can see today.
Two obvious drainage channels are at St. Briavels and Bigsweir. Two drainage channels nearly opposite each other at Brockweir and Tintern created an opposing flow, forming the loop in the Wye River that is there today.
The Coleford area was a basin of water collection. A large drainage river flowed from here to Newland. The basin at Coleford also drained into the Lydbrook Valley through what is now the valley around Speech House Road. From the woods to the north of Staunton, I see that two gorges have formed as channels by which meltwater flowed into the Wye Valley.
Look at the basin that Coleford is built in and the slopes of the basin within the town: www.geograph.org.uk/photo/765926
Here are scenes of the Wye Valley, and valleys that once drained water and ice into it, at various points from Symonds Yat southward to union with the Severn River. The first two photos are of former drainage valleys which emptied into the Wye Valley and, the rest are of the Wye Valley itself:
www.geograph.org.uk/photo/707629
www.geograph.org.uk/photo/474580
www.geograph.org.uk/photo/1786549
www.geograph.org.uk/photo/11219
www.geograph.org.uk/photo/1499407
www.geograph.org.uk/photo/1402615
www.geograph.org.uk/photo/474580
www.geograph.org.uk/photo/1786549
www.geograph.org.uk/photo/11219
www.geograph.org.uk/photo/1499407
www.geograph.org.uk/photo/1402615
ROSS-ON-WYE
Moving northward, there is another valley which served as a mighty river at the end of the ice ages to drain meltwater, but which is dry today. The valley through the town of Ross-on-Wye has similarities to the one through Lydbrook. It was formed when glacial ice found a weak spot in the rock from a previous flow of water over that rock. The glacier was probably also diverted by ice piled against Leys Hill and Chase Hill. If there were a source of water where the Severn Vale is now located, this would be a major river flowing through Mitcheldean and Longhope.
On a map or the satellite imagery, it is easy to see that there is a major bend in the Wye River at Ross-on-Wye. This is because we have a situation similar to that at Monmouth and Garnew. This valley through the town was actually the main river following the ice age and the flow from Hereford was only a branch joining it. But as the volume of water from melting glaciers reduced, this became a dry valley, as it is today.
The glacial thrust which formed the valley at Ross-on-Wye came north of Chase Hill and was then deflected southward toward Drybrook and Mitcheldean by May Hill, the route is now followed by Rudhall Brook. There is a nearby valley extending south from the village of Coughton from glacial thrusts between Howle Hill and Chase Hill and this glacial route in successive ice ages seems to join the one that went through Ross-on-Wye on it's way to Drybrook.
Remember the view from the top of Coppet Hill, looking eastward. You see a closer hill and a further hill. The valley at Coughton is between the two and the valley at Ross-on-Wye is on the other side of the further hill. The buildings of Ross-on-Wye are visible: www.geograph.org.uk/photo/1187565
Here is a view of Chase Hill from Bridstow, across the Wye River from Ross-on-Wye: www.geograph.org.uk/photo/996598
In this photo, the two hills which affected the flow of ice which formed the valley through Ross-on-Wye can be seen from Bridstow. Chase Hill is the closer one and May Hill, with the famous clump of trees on the top representing the highest elevation in the Forest of Dean, is the further hill: www.geograph.org.uk/photo/996593
Here are views in the valley at Coughton: www.geograph.org.uk/photo/1128524 www.geograph.org.uk/photo/478727
The photo web site does not have any useful views of the valley in the town of Ross-on-Wye, but if you would like to have a look at it, you can go to my photo blog of Europe. Just go down to the "Town of Ross-on-Wye" and you will see the slope of this glacial valley. http://www.markmeekphotos.blogspot.com/
So, the glacial valley through Ross-on-Wye starts as one valley before it splits. The valley through Lydbrook started as two valleys, but ended up as one. The Wye Valley, from Symonds Yat southward, is one throughout.
DRYBROOK
The glacial movement from Ross-on-Wye continues to Drybrook. The resulting Drybrook Valley is parallel to that of Lydbrook, it continues southward past Cinderford, through Soudley and ultimately, Blakeney into the Severn Vale. On the other side of Plump Hill from the Drybrook Valley are parallel drainage valleys through Mitcheldean and Longhope.
On my photo blog of Europe, http://www.markmeekphotos.blogspot.com/, the third photo from the top is taken in the direction in which the glaciers would have came to carve the Drybrook Valley. The photo is taken looking northwest and is the same photo on the cover of my book "The Theory Of Primes". Notice the U-shape to the ground that is characteristic of glacial movement.
Here are views of the Drybrook Valley:
While driving through the area on the main road, the A4136, the valleys through Lydbrook and Drybrook can be seen as dips in the road level. Here is the one representing the Drybrook Valley at the Nailbridge traffic light: www.geograph.org.uk/photo/1124521
A similar dip can also be seen in the A4136 as one passes Lydbrook. I would like to point out that there is another dip in the A4136 at Brierley, between Lydbrook and Drybrook. This is yet another glacial valley similar to the other two, except that it is far less developed at this point. If there are further ice ages, there will be a valley at Brierley similar to Lydbrook or Drybrook. Here is the dip in the road at Brierley: www.geograph.org.uk/photo/555202
GLACIAL IMPACT CRATERS
Now, still at Drybrook, let's go on to another phenomenon. A glacial impact crater is a land form which I discovered and documented several in the area of Niagara Falls. They are described in detail on my Niagara blog.
Basically, a glacial impact crater is formed when glacial ice is pressed up against a hill or escarpment during an ice age. When the ice age ends, the ice begins to melt. The glacial ice might be one or two kilometers thick so that it will be warmer at the bottom than at the top. As the ice melts faster near the bottom, the glacier becomes top heavy and may also fracture laterally.
The result is a vast slab of ice weighing millions of tons falling from a height of a kilometer or more and leaving a very distinctive crater in the ground.
Not only is Drybrook a valley, it is also a glacial impact crater. During the last ice age, ice moving along the main glacial route through the Severn Vale pressed up against Plump Hill in Mitcheldean. When the ice age ended, such a vast slab of ice crashed into the ground near the Drybrook Valley.
The result is what we now call Harrow Hill. The hill slopes downward in the direction in which the slab was moving in the same way as all of the other glacial impact craters.
Here is a view from the top of Plump Hill, looking out over the Severn Vale: www.geograph.org.uk/photo/268007 Notice the drainage valley at Mitcheldean in the foreground, which I mentioned earlier.
Here are views of Plump Hill from below: www.geograph.org.uk/photo/739896
Look at the slope of Harrow Hill at Drybrook: www.geograph.org.uk/photo/1355254
On my photo blog, I took two photos of Harrow Hill from across the Drybrook Valley at Ruardean Hill which clearly show the flat slope of the hill characteristic of glacial impact craters, they are the eighth and ninth photos from the top http://www.markmeekphotos.blogspot.com/
As such slabs of ice melt, they tend to leave culverts through which the water flowed away as the slab melted. Bridge Road on Harrow Hill is built in the low-lying culvert through which the meltwater drained away into the Drybrook Valley: www.geograph.org.uk/photo/1355263
CINDERFORD
Now that we are familiar with glacial impact craters, let's move on from Drybrook to Cinderford. The same process happened here. Ice from the main glacial route through the Severn Vale pressed up against Littledean Hill. At the end of the ice age, a vast slab of ice crashed to the ground on what is today the landscape of Cinderford. It is flattened and sloping, just as is Harrow Hill.
Here is the view from the top of Cinderford, looking east over the Severn Vale. The centre (center) of London is about 150 km in this direction. The high ground on the other side is the Cotswold Escarpment: www.geograph.org.uk/photo/1459070
Now if we go a short distance and look in the opposite direction, we find ourselves looking at the slope formed by the vast ice slab which crashed down: www.geograph.org.uk/photo/1459193
Here are other views of the slope of Cinderford created by the glacial impact crater, notice the similarity to Harrow Hill: www.geograph.org.uk/photo/1039189
Cinderford actually has two slopes, another one sloping down off the one caused by the impact crater. The lower, secondary slope is actually the side of the Drybrook Valley through which torrents of water flowed at the end of the last ice age. You can see in this view that the Cinderford area actually forms a bowl with Ruardean Hill in the distance. The lower part of this bowl was filled with water from the melting ice, which flowed out through Soudley and down to Blakeney. See the bowl: www.geograph.org.uk/photo/854797
Here is another view that conveys a sense of the bowl from the bottom: www.geograph.org.uk/photo/759954
These scenes are of the secondary slope in Cinderford, sloping down from the main slope, created by the impact crater, to the slope created by the flow of meltwater out through Soudley:
In this photo, at the centre of Cinderford, you can see the secondary slope angling downward off the main slope: www.geograph.org.uk/photo/132426
This is a photo taken closer to Soudley, where the water that went past Cinderford flowed out on it's way to the Severn Vale: www.geograph.org.uk/photo/1605897
This flow ended up at Blakeney, closer to the Severn River. Here is a view of the valley there: www.geograph.org.uk/photo/533100
The main flat slope of Cinderford, shaped by the impact crater can be seen in the fifth and sixth photos from the top on my photo blog, http://www.markmeekphotos.blogspot.com/ Cinderford is the town in the distance in these views taken from Drybrook. If you look closely, you can even see the gap in the distant hills over to the right where the water ultimately flowed out at Soudley.
U-SHAPE
I would just like to show a couple of more scenes of that U-shape that moving glaciers tend to leave on the ground. This U-shape to the ground is to be seen all over the Forest of Dean, looking northwest from Yat Rock, looking northwest from Drybrook and at the bottom of Lydbrook. Here are more such scenes which I noticed:
posted by Mark Meek @ 11:42 AM
0 Comments:
Post a Comment
<< Home