Karst Landscapes
The international community has settled on karst,
the German name for Kras, a region in Slovenia partially extending into
Italy where it is called Carso and where the first scientific research of
a karst topography was made. Karst is theoretically possible in any rock
that is susceptible to solution but primarily denotes limestone terrains
(other possibilities being dolomite and evaporites). The extent to which
karst develops depends on a number of factors including the thickness, porosity
and permeability of the rock, and the climatic conditions.
One of the most spectacular types of karst is
found in the surrealistic landscape of S.E.China, pictured on many famous
Chinese works of art and known as Tower Karst.
One of the most famous outcrops of limestone
occurs along the south coast of Great Britain and forms the "White
Cliffs of Dover". Here the limestone is a very porous and permeable
chalk and consequently has little in the way of surface drainage.
A large part of Great Britain is underlain by
limestone. To the south and east of London lie the Cretaceous limestones
of the North and South Downs in a large anticline which disappears under
London in a large syncline to reappear at the surface in the Chilterns.
These are succeeded to the west by Jurassic oolitic limestones. Next comes
a band of Permian magnesian limestone. Finally, covering a large part of
northern England and extending into the Central Valley of Scotland is the
Carboniferous Limestones. Likewise in South Wales. Smaller but geologically
significant limestones are the Silurian aged Wenlock Limestone and Precambrian-aged
limestones of northern Scotland.
Limestone has long been of economic importance
as a building stone, as is attested to by the distribution of medieval rock
quaries illustrated in the diagram below. Basically there are two reasons
for this, firstly it is soft and easy to work with primitive tools and secondly
it is often pretty with enclosed fossils. For example, the highly fossiliferous
Purbeck "Marble" has been mined since Roman times.
The next image shows a cliff of the Lower Chalk
overlying the Upper Greensand.
The next image shows the northern edge of the
Chilterns forming the Dunstable Downs. It is not uncommon to find effifies
of animals and people carved into the white rock of the hillsides.
The next slide shows chalk being excavated near
Dunstable at the Totternhoe Quarry.
Moving north to Crummockdale we find the well-exposed
limestone pavement seen in the next image.
On closer view you can see how rainwater has
eaten into joints in the rock.
This is even more obvious when standing on top
of it. This is the so-called clint and grike landscape. The clints are the
upstanding blocks, the grikes the surrounding moats.
One of the most spectacularly developed examples
of such a landscape is found at Malham.
The next picture is taken looking back at the
people in the previous picture. A subterranean river can be seen emerging
from the base of the cliff. If you look real closely you can see climbers
on the cliff face.
One of the equally famous localities is nearby
Gapping Gill. Here a surface stream descends into the limestone.
The water falls 365 feet to the base of the
hole. During Spring break we would erect a winch over the hole and lower
people to the bottom.
An abandoned part of the Gaping Gill drainage
system was discovered in 1837 and opened up by blowing up a calcite dam
which blocked the entrance.
Immediately adjacent to the show cave is where
the water finally emerges after its underground journey.
Close by is Goredale Scar, a de-roofed underground river.
The remnants of the roof can be seen in the
next image taken in a direction of 180 degrees from the previous.
An enigma is seen in a nearby stream valley
with no water. Although we have seen that the porosity and permeability
of limestone generally precludes surface flow, such is not the case when
the ground is frozen, such as in the last Ice Age.
Leaving the cool, damp Yorkshire Moors, we cross
the Atlantic to the Blanchard Spring caverns of Arkansas. Here a similar
situation with water emerging from a cave.
Moving further west to the Texas/New Mexico
border we find a similar situation at Sitting Bull Falls. Here, water emerging
from a cave about halfway up the cliff has constructed mounds of tufa and
travertine.
Most spectacular is the highest point in Texas
at 8,749 feet, Guadalupe Peak, the edge of the Permian reef.
Further south, in Big Bend National Park we
have the Cretaceous limestones of the Sierra Del Carmen, here viewed from
Rio Grande village.
Also in Big Bend National Park we find the uplifted
Mesa de Anguila.
The next shows the exit from Santa Elena canyon
and the Terlingua river joining the Rio Grande. Note the flatness of the
Mesa surface.
Another view, the fault scarp is at the base of the cliff.
The Rio Grande has cut abut a thousand foot deep canyon through the Cretaceous
limestone.
Finally we move over to the warm, wet island
of Puerto Rico where the limestone has weathered into what is called Cockpit
karst, a subdued form of Tower karst.
An example of a karstic feature due to collapse
above a salt cavity is the Wink Sink, viewed in the next image from the
American Scientist.
Moving underground we see features specific
to limestone terrain, namely caves with stalagmites and stalactites. The
next image shows the entrance to one of the most famous, the Carlsbad Cavern
of New Mexico.
Nearby is the "New Cave", only recently
opened to the public and kept in "primitive" condition. One of
the highlights of it is "the skull".
Also within the New Cave is this enigmatic ribbon-like
stalagmite, partly submerged.
Moving back to Ingleborough show cave we have
the "beehive" and the "Sword of Damocles" stalactites.
Note the line around the wall indicating the former level of the lake inside
the cave before it was blasted. Note also, the cigarette.
More interesting is the area beyond that then
opened to the public. Here we see erosion along a vertical joint and a layer
of mud on the floor of the cave.
Lastly, we can see that the cave has widened
preferentially along the bedding planes in the limestone. You can just make
out the "curtains" hanging from the roof.
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