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Geological Processes

FLUVIAL LANDSCAPES (2)

3) Map: Fluvial3

a. In this map there is a visible difference in elevation between the east and west

portions: the fist is almost completely flat area with plenty vegetation, marshes

and many bendy rivers, the second is a mountainous zone with lesser green area

and a few, non-winding, rivers. This difference in elevation is indicated by the

contour lines, far apart in the flat zone (with a contour interval of 5 ft) and close

together in the mountainous area (with a contour interval of 20 ft). This

remarkable difference is probably due to faulting activity that caused

discontinuity in the rock leading then to a fracture and a significant

displacement.

b.Where do you find deltas in this map?

c.

Why?

d.

What is the flow direction of Lawrence Creek? Explain your answer.

4) Map: Fluvial4

a.What is the cause for the semi-circular features observed in this map (of which

one major example is observed in the central western portion)?

b.

Do you expect the geology and rocks in this map to be younger or older than

those in the eastern portion of Map Fluvial3?

5) Maps: Fluvial3; Fluvial4

a.

Write a brief summary of the geological history of this area based on your

interpretation of the features observed in these maps. (Make sure you know

where the areas in these selection maps are relative to each other

geographically). Remember that geological history is 4-dimensional, in as you

also have to think in terms of how areas change in time. Feel free to include

diagrams or figures to i llustrate your geological reconstruction.

6) Map: Karst

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a. In the section C of this map we can observe a stream appearing in surface and

then disappearing several meters ahead in a sinkhole. This is a peculiar feature

of karst topography: the landscape is shaped by the dissolution of the layers of

bedrock; usually carbonate rock like limestone or dolomite. This creates a vast

system of underground drainage and caves. Usually there is little or no water on

the surface of this type of environments but we can find occasional rivers, which

are underground streams emerging onto the surface between layers of rock, asthe one identified in this map.

b. Another peculiar feature of karst topography that can be found on surface re

sinkholes, also called dolines. These elements are very much distinctive of this

type of landscape but sometimes might not be preset because the soluble rock is

mantled (for example by glacial debris) or confined by superimposed non-

soluble rock strata. The dolines are represented on the map by tiny looping

contour lines indicating depressions, which are subsequently filled with water.

The agent of erosion that initially created the depression is water from acid

rains.

c. By analysing the two surface features on this map we can see the role of

karsification in the landscape. Erosion by mildly acidic rainwater on weakly

soluble bedrock like limestone acts in particular along the fractures and

weakness points of the rock. Over time, the fractures became bigger as water

keeps on dissolving the bedrock and eventually creates underground rivers. The

calcium carbonate in the rocks that are being dissolved and the penetrating

water can forms many features below and above surface, such as flutes, clints,

grikes, sinkholes, cenotes, foibe, disappearing streams and reappearing springs,

limestone pavements, karst towers, karst aquifers and many caves.

d. The Jenolan caves are a very important example of karst topography that can

be found in the N.S.W. area. The limestone has been dissolved by the acid rainsand has created vast underground cambers where the formation of spectacular

stalactites and stalagmites took place. Other similar examples are caves found in

Northern Territory and in South Australia.

e. The Jenolan caves are probably the worlds oldest dated cave system. By

measuring the ratio of radioactive potassium and trapped argon gas, scientist

where able to determine the age of the clay in the cave: it is approximately 340

million years old. In other Australian territories the formation of the limestone

and creation of caves goes back to about 200 million years.