Question

1.  
   1. Differentiate between weathering and mass wasting.   
   2. Explain two ways in which plants cause weathering. 
2. Describe each of the following physical weathering processes.
   1. Crystal growth     
   2. Block disintegration.    
3. Explain how the following factors influence weathering.
   1. Rock texture.   
   2. Topography     
4. The diagram below represents a landscape affected by mass wasting. Use it to answer questions (i) and (iii).
            
   1. Name the type of mass wasting shown above.  
   2. State three conditions which may influence the occurrence of the mass wasting above.
   3. State three negative effects of the above form of mass wasting on the human environment.  

Answer 1

1.  
   1. Weathering is the mechanical breakdown/chemical decay of rocks at or near the earth's surface in situ while mass wasting is the movement of rock and soil down slope under the influence of gravity.
   2.  
      • When plants cause mechanical weathering, their roots grow into rocks and crack them. It can also happen in streets or sidewalks.
      • When plants cause chemical weathering, there roots release acid or other chemicals, onto rocks, which then forms cracks, and breaks apart.
2.  
   1. Crystal growth
      • It occurs in areas that experience large diurnal range of temperatures such as in deserts.
      • During the dry season, the moisture /water in the rocks underground is forced up by capillarity action onto the surface of the earth where it evaporates.
      • Salts contained in the moisture are precipitated and deposited in the cracks to form crystals
      • Contained precipitation cause accumulation of the salts.
      • The crystals grow and exert pressure on the rocks mainly on the cracks.
      • The resultant stress causes the rocks to disintegrate.
   2. Block disintegration
      • It occurs in areas that experience large diurnal range of temperatures such as deserts.
      • It occurs on rocks with joints and bedding platforms
      • During the day, the rock is heated intensely by solar insolation leading to expansion mainly along the joints.
      • During the night, rapid cooling occurs as the temperatures fall leading to contraction of the rock.
      • This causes stress in the rock leading to development of cracks along the joints.
      • When the process occurs over a long period of time the joints/cracks are enlarged
      • The rock eventually breaks/ separates along the joints into smaller blocks called rock blocks.
3.  
   1. Rock texture
      • Fine textured rocks are weathered faster. This is because the tiny particles have a large surface area around the individual particles allowing chemical weathering to occur.
      • Coarse grained rocks are weathered slowly. This is because the large grains have a smaller surface area for chemical weathering to occur.
   2. Topography
      • On steep slopes, the weathered rock materials are washed away quickly. This exposes the underlying rock surface to weathering leading to faster weathering process.
      • On gently sloping/flat areas, weathering occurs slowly. This is because the weathered rock material cover the underlying unweathered rock.
4.  
   1. Landslide/ rock slump/slumping.
   2.  
      • The extent of saturation/ amount of precipitation
      • Angle of slope/gradient of the land
      • Nature of the materials on a slope
      • Tectonic movements/earthquakes/volcanic eruption
      • Human activities such as mining/quarrying/underground nuclear tests
   3.  
      • Loss of human lives
      • Loss of property/destruction of property
      • Disruption of transport and communication lines/ may block rods and railway lines
      • Causes stress/fear.