6. a) Briefly define the following geologic terms with respect to streams. 18 ma
ID: 293266 • Letter: 6
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6. a) Briefly define the following geologic terms with respect to streams. 18 marks) (i) stream competence (ii) point bar (ii) water gap (iv) base level Describe the fongitudinal profile of a typical stream from its head to its mouth. (6 marks) b) c) Fill in the blanks in the following passage. (6 marksh A stream is only a small component of a much larger regional system or network of streams called a_. These regional networks are separated from each other by an imaginary line called a (i) Networks of streams can form particular patterns, often in response to the kinds of rocks on which the streams develop or the structural geology of the rocks underneath. A common pattern is known as a_ lii pattern, in which tributaries form a system of irregular branches. A iv) pattern often develops on volcanic cones or domes. If the bedrock contains many joints and faults, apattern often develops. If the bedrock consists of alternating layers of resistant and less- resistant strata of rock, a(vi)_pattern can form.Explanation / Answer
6.a. i. Stream competence : The maximum size of rock particle transported by a particular flow of a stream is called stream competence. Stream has lower competence and with velocity it increases. Typically, a competent rock is more viscous than an incompetent rock, more prone to fracture and maintains its thickness on deformation.
ii. Point bar : This is found in meandering river system and found on the convex side of the meanders. They grow by individual increments outwards into the meandering curves. Point bars consist of sands and fine gravel. This shows fining upward sequence.
iii. Water gap : Water gap is created where a river or stream cuts through a mountain ridge.
iv. Base level : A theoretical plane surface underlying a land mass, denoting the depth below which erosion would be unable to occur. Sea level provides a base level on a regional scale. Local base level may be provided by the junction between a tributary and the main river.
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