Observation

This question was answered by very few candidates and most of those who attempted the question performed poorly.  The characteristics of rift valley are:

-           valley/depression produced by tensional forces
-           valley produced by compressional forces also
-           it has steep sides
-           width varies from 30 – 100 km
-           length varies and could be up to 7,200 km
-           usually very deep and could be up to 800 metres
-           usually consists of series of connected troughs
-           water collects in them to form rift valley lakes
-           it has parallel faults
-           the side blocks are uplifted
-           the floor may be flat
-           also called graben
-           examples include the Great Rift Valley of East Africa, River Rhine rift Valley, River Jordan rift valley
The mode of formation of rift valley goes thus:

• found in area of intense earth movement or crustal instability
• due to earth movement or tectonic activity, faults are developed in the earths crust
• this faults divide the earth crust into blocks
• tension or compressional force set in
• tensional forces tear the blocks apart from the central block
• central block sinks or subsides
• the sinken block forms a depression called rift valley
• compressional force can also form a rift valley
• due to compressional forces the two blocks on either side of the fault line ere pushed over the central block
• this results in the outer block over thrusting the central block
• this forces the central block to sink and form a depression known as rift valley.

            Characteristics of horst are:

• it is also called block mountain
• associated with rift valleys
• represents the uplifted portion of land
•  has steep sides
• has great heights
• the top may be flat or tilted
• also called block mountains
• examples include Ruwenzori Mts in East Africa, Vosges, Black Forests in France, etc

Mode of formation of horst goes thus:
-     caused by internal disturbance within the crust
-     caused by tensional or compressional forces
-     parallel vertical  faults develop in the crust
-     land is divided into blocks
-     subsidence may occur along fault lines forcing the flanking blocks to sink
-     the central block standing becomes a horst or block mountain
-     the flanking blocks may be forced up by compressional forces over the central block
-     the central block is held down as rift valley while upthrusted blocks forms horsts or block mountain