Water Based - Geology
Richards Mountain Pages
If there is one thing that Britain has in abundance its water. The rain erodes the mountains, the rivers
sculpt the valleys and the sea scrapes away at the coast. The background to this page is taken from a
patch of scanned in Portland limestone that has been polished into a pebble by the waves of Portland Bill.
One thing you won't find any of in Britain are geysers. The one shown dramatically to the left here
is Strokkur in Iceland. Geysers like these slowly build up a ceramic crust where the dissolved minerals
settle out as the water cools on the ground.
Waterfalls
Waterfalls are one of the most obvious forces for sculpting the landscape. They occur where a stream or
river travelling over tough rock comes across some weaker rock that it can dissolve. The weaker rock gets
eaten away to form a waterfall - hence why waterfalls tend to nestle in hollows. Waterfalls do not change
much of the country, as they only affect a small part of any landscape. There are plenty of excellant
examples all over the hillier parts of Britain, and the odd example in the South.
Scree Fans
In the mountainous corners of the country (Scottish Highlands, Lake District, Snowdonia and to a
lesser extent the Brecon Beacons), you'll find plenty of fans of scree flanking the sides of mountains.
These piles of loose rock were formed by the action of water creeping into cracks in the rock and freezing.
As it does so it expands and levers off a chunk of rock. Over an enormous amount of time the debris forms
a pile of scree. examples.
Rias
Have you ever wondered about the broad inlets of sea around Plymouth and the South West? They seem to be
a bit big for estuaries when you look at the size of the rivers that drain into them. They happen to be
fine examples of Ria's. These are river valleys that have become drowned by rising sea levels or sinking
land. Expect a few more if global warming catches on!
Wave Action
Chesil Beach is one of the most impressive examples of the action of waves on the coast line. A stretch of beach extends
in a neat curve from Abbotsbury, to Portland. The tide here has pushed the bigger stones to the Portland end. For the best view
go to Tout Quarry on Portland.
Further to the East, another example of wave action is Lulworth Cove. Here a gap in the harder rocks as let the sea in
to erode soft rocks behind. The end result is a circular cove with a narrow entrance.
Other examples of what the tide can do can be found all along the coast.
Calmer Waters
If you walk along a sandy beach or lake shore you'll probably find ripples in the sediment causes by the water. In rare
cases these can get preserved under a fresh layer of sediment. Over time the sediments harden and you get stunning layers
of stone ripples like the example here found on Orkney. Look carefully and you'll see that different layers have
different ripple patterns, often at contrasting angles to the neigbouring layers. Preserved in these layers is quite a
record - you just need to understand the different patterns.
Meanders
There are meanders on many of Britains rivers, but the best examples can be found where the landscape is open
enough to appreciate them. at opposite ends of the country, two particularly good examples are:
- Water Of Nevis - above the gorge in Glen Nevis, the river is much slower moving. Although the bends aren't
particulary impressive, the effect of scouring by the Falls of Steall is. On the inside of the bend the water is
often not even ankle deep. On the outside your head would be underwater if you stood on the bottom!
- Cuckmere River - the only river in the South East that hasn't been developed, it winds all over the wide
valley South of Alfriston.
The mechanics of meanders is rather interesting. As soon as a bend starts to form, the water moves faster on the outside
of the bend, whilst that on the inside slows down. This causes the outside to erode, and deposits to form on the inside.
The meander gradually grows more bendy, until the river makes an 'Omega' shape and eventually meets itself. This shortcuts
the meander. Sediments eventually block off the two ends, and an Oxbow lake is left behind. You can see how
meanders are created and broken in fast motion by watching a thin trickle of water down a vertical glass sheet - but you
need to get the flow rate just right.
Braided Rivers
The river Dee West of Braemar is the best example I've seen of a braided river. If you visit in Summer, when the river sits lazily
in the valley, you can see the huge banks of shingle left behind when the river was last in spate. The summer course splits around
islands of this stuff, whilst the spring course barges straight through.
Limestone Pavement
Particularly around Ingleborough in Yorkshire, but also on Hutton Roof Crags, and many other peaks, you can find
limestone pavements. Originally a flat slab of rock, acidic rain water slowly dissolves channels, gouging out grooves
over thousands of years. The smaller
grooves support various ferns and other delicate plants. The deeper ones can swallow the unwary walker.
The technical terms to look up are clints and grikes.
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