This is a fine example of waterfall formation by the
differential weathering of the Upper Carboniferous Midgley Grit
(formerly the Woodhouse Grit) and softer underlying sandy shales.
The waterfall lies in a beautiful wooded amphitheatre where the
boundary of the grits and shales is clearly exposed and is
accessible. The gritstones contain interesting structures,
including sets of cross lamination and a sharp erosive base.
Goitstock Wood is recognised as having ecological importance.
Formation of Gritstone
Gritstone is a sedimentary rock composed of coarse sand grains
with inclusions of small pebbles. It is a coarser version of
sandstone.
As gritstone is a fluvial sedimentary rock it frequently shows
signs of cross-bedding or current bedding. It is quarried for
building material. British gritstone was used for millstones to
mill flour, grind wood into pulp for paper and grindstones to
sharpen blades.
The Millstone grit is a stratigraphic gritstone unit exposed in
the Peak District of north central England. It was laid down in the
late (upper) Paleozoic era, in the Carboniferous period, in deltaic
conditions.
Imagine a simple river flowing along bedrock, the harder rock
that lays underneath loose earth like soil and sand. It's moving
along pretty quickly and at a fairly steep incline. The bedrock
over which the water is flowing has varying degrees of density and
strength -- some layers are soft, while others are much harder.
When water flows over a layer of hard rock, it erodes the softer
rock beyond it. The bed of the river gets steeper as the water
carries the softer rock downstream, and eventually the flow of
water at this point becomes steep enough to be considered a
waterfall.
Water continues to fall against a back wall, which also
continues to wear away. Soon, the soft rock underneath the hard
rock falls back, and a plunge pool is created where the water
collects. Enough water moving over the hard rock will undercut it
and break it away, and big pieces of rock will collapse and fall
into the plunge pool, which makes it even bigger and deeper than
before. The soft rock below the hard rock is receding so much that
the hard rock becomes an overhang
Although the waterfalls we see today will be around for a long
time, they'll eventually recede and disappear. As hard rock is
slowly eroded by the constant flow of water, it falls into the
plunge pool and creates a large gorge. The waterfall is actually
retreating backwards. This happens very slowly -- just as it takes
thousands of years for a waterfall to form, it takes just as long
for it to disintegrate. Niagara Falls, for instance, is retreating
at the rate of 3.3 feet (one meter) per year.
Types of Waterfalls
You may have heard two other terms used to define a waterfall:
cascade and cataract. Although they both describe waterfalls, they
mean slightly different things. A cascade is the most common term
and usually describes a waterfall with any kind of irregular
surface underneath the water. It flows down in a fairly low volume,
and several stages can make up one large waterfall. A cataract, on
the other hand, is a waterfall with larger, more powerful volumes
of water and is typically accompanied by rapids.
Now that we've explained the terminology, let's examine some
different types of waterfalls. The most basic and recognizable type
of waterfall is the plunge waterfall. This happens simply when a
river spills out water over a ledge, and the water descends
vertically without coming into contact with any of the rock on the
way down -- it just crashes right into the plunge pool. This type
of waterfall would take longer to retreat, since the hard rock over
which the water is flowing is more resistant to erosion.
A block or,sheet waterfall is formed from a wide
river -- when the water spills over the edge, it looks like a big
sheet, especially if the flow isn't broken by any stray rocks
protruding from the back-wall. A block waterfall is usually wider
than it is high. Similar in nature is the curtain waterfall, which
is simply taller than it is wide, but still looks like a long
sheet.
Horsetail waterfalls are in constant or semi-constant
contact with rocks, which may erode faster than other types because
of constant runoff.
Punchbowl waterfall might descend into a small plunge pool,
but the plunge pool might quickly lead to another ledge where the
water descends as a plunge waterfall. These waterfalls are
generally called tiered. There are seemingly endless possibilities,
which is probably the biggest reason people look for and are
interested in new waterfalls.
To log this cache upload a photo of you/GPSr with the falls in
the background and E-Mail me the answers to the following
questions
1) Estimate the height of the falls.
2) From the information on the log page tell me what type of
Waterfall Goit Stock Falls is.
Any logs with no photo may be deleted