Litho: Granite

Question 1

What are the characteristics of granite? (3)

Answer 1

Chemical composition
Rock texture
Rock structure

Question 2

What is the chemical composition of granite? What is the weathering process called?

Answer 2

feldspar + water -> KOH (carbonated and removed in solution)+ aluminium silicic acid (kaolinite clay and silicic acid also removed in solution)

Hydrolysis, esp in humid climates

Question 3

What is the rock texture of granite?

Answer 3

Phaneritic (coarse textured) with large crystals

Question 4

What is the rock structure of granite?

Answer 4

High in secondary permeability due to presence of joints:

• shrinkage joints (contract during cooling)
• sheet joints (stresses set up during pressure release)

Block disintegration -> spheroidal weathering -> core stones

Question 5

What landforms can be found in the humid tropics?

Answer 5

Deep layers of regolith known as saprolite (ruxton and berry)

Question 6

What landforms can be found in the seasonally humid tropics?

Answer 6

Tors and Inselbergs

Ruware, bornhardt, blocky Inselbergs, castlekopies

Question 7

What type of rock is granite?

Answer 7

Intrusive igneous rock formed from the solidification of granitic magma. It forms granitic plutonic features such as batholiths.

Question 8

How are deep weathered regolith formed?

Answer 8

The gradual decomposition of granite from the surface downwards will produce 4 identifiable zones, each older and more advanced than that lying beneath it. Until bsw is reached.
(From 1-4)
Residual debris, Gruss and a few corestones, mainly corestones, partially weathered rock

Question 9

How does landform development in the seasonally humid tropics differ from the humid tropics?

Answer 9

Regolith here is less thick as chemical weathering is slower due to lower levels of overall precipitation and rate of regolith removal is higher due to absence of dense vegetation.

Question 10

What are tors?

Answer 10

Small hills or heaps of boulders, usually about 4-20m high rising abruptly from surrounding gentle ground surface eg. Zimbabwe tors (also found in temperate areas)

Question 11

What are inselbergs?

Answer 11

Steep-sided, isolated hills that rise abruptly above the surrounding plane

Question 12

describe ruwares

Answer 12

Smooth convex surfaces, low and domed shaped. Insipient inselbergs formed in the early stage of development.

Question 13

Describe bornhardts

Answer 13

Characterised by great heights (>300m) and near vertical or overhanging sides. The rounded summit and thick rock sheets are caused by massive sheet jointing produced by pressure release.

Question 14

Describe blocky inselbergs

Answer 14

They develop where rectangle jointing is dominant

Question 15

Describe castle koppies

Answer 15

Formed when inselbergs are subjected to prolonged sub-aerial weathering and collapse. They look like low, irregular hills.

Question 16

What is the theory of etchplanation?

Answer 16

rate of weathering vs rate of regolith removal

Question 17

What are etchplains?

Answer 17

Land surfaces subjects to deep weathering, followed by partial or complete removal of the regolith cover

Question 18

Describe the process of etchplanation

Answer 18

A pluvial period (humid) is associated with dominant weathering which concentrates where joints of high density are. High rainfall, temps, and dense vegetation promotes hydrolysis of granite at joints, leading to selective weathering. An interpluvial period reduces the rate of weathering, causes vegetation to degenerate and allows more effective surface wash to strip the unprotected regolith. BSW is undulating due to diff rates of weathering

Question 19

How are deep weathered regolith formed?

Answer 19

The gradual decomposition of granite from the surface downwards will produce 4 identifiable zones, each older and more advanced than that lying beneath it. Until bsw is reached.
(From 1-4)
Residual debris, Gruss and a few corestones, mainly corestones, partially weathered rock

Question 20

How does landform development in the seasonally humid tropics differ from the humid tropics?

Answer 20

Regolith here is less thick as chemical weathering is slower due to lower levels of overall precipitation and rate of regolith removal is higher due to absence of dense vegetation.

Question 21

What are tors?

Answer 21

Small hills or heaps of boulders, usually about 4-20m high rising abruptly from surrounding gentle ground surface eg. Zimbabwe tors (also found in temperate areas)

Question 22

What are inselbergs?

Answer 22

Steep-sided, isolated hills that rise abruptly above the surrounding plane

Question 23

describe ruwares

Answer 23

Smooth convex surfaces, low and domed shaped. Insipient inselbergs formed in the early stage of development.

Question 24

Describe bornhardts

Answer 24

Characterised by great heights (>300m) and near vertical or overhanging sides. The rounded summit and thick rock sheets are caused by massive sheet jointing produced by pressure release.

Question 25

Describe blocky inselbergs

Answer 25

They develop where rectangle jointing is dominant

Question 26

Describe castle koppies

Answer 26

Formed when inselbergs are subjected to prolonged sub-aerial weathering and collapse. They look like low, irregular hills.

Question 27

What is the theory of etchplanation?

Answer 27

rate of weathering vs rate of regolith removal

Question 28

What are etchplains?

Answer 28

Land surfaces subjects to deep weathering, followed by partial or complete removal of the regolith cover

Question 29

Describe the process of etchplanation

Answer 29

A pluvial period (humid) is associated with dominant weathering which concentrates where joints of high density are. High rainfall, temps, and dense vegetation promotes hydrolysis of granite at joints, leading to selective weathering. An interpluvial period reduces the rate of weathering, causes vegetation to degenerate and allows more effective surface wash to strip the unprotected regolith. BSW is undulating due to diff rates of weathering