Geography & History Notes | KCSE, NECTA, ZIMSEC & GCSE

  The tide is a periodic rise and fall in the level of the ocean and other large water bodies. Tides occur when the moon and to some extent the sun exert a gravitational pull on the water bodies on the earth. A lunar day is time taken by the earth to complete one rotation with respect to the moon (24 hrs 52 min) Lunar month is time taken by the moon to complete one revolution around the earth (27.3 days) The moon is always ahead of the earth by 52 minutes due to its revolution e.g. if Nairobi is opposite the moon at 6 pm the following day the high tide will be at 6.52 pm. The tidal range is the difference between the highest level reached by high tide and the lowest level reached by low tide. Types of tides Spring Tides In which the highest and lowest tides occur. Occurs when the sun, moon, and the earth are in a line (syzygy position) and pulling in the same plane causing pulling force to be greatest. Neap Tides In which high tide is lower than normal and low tide is higher than ...

  An ocean current is a continuous, directed movement of the seawater generated by a number of forces acting upon the water, including wind , the Coriolis effect, breaking waves, cabbeling and temperature and salinity differences. depth contours, shoreline configuration, and interaction with other currents influence a current's direction and strength. ocean currents are primarily horizontal water movements. Warm ocean currents are ocean currents that move warm water from the equator. Warm current has warm water therefore they are less dense than cold water. Warm ocean currents have influenced the climate or environmental conditions of the areas adjacent to them in the following ways; They lead to warm conditions, i.e. they tend to warm or raise the temperature of the adjacent area, this is because the winds which blow over them are warmed up and as they blow onshore they bring in warm conditions e.g. the North Atlantic drift raises the temperatures of the coasts of Portugal, Franc...

  Cold ocean currents are ocean currents with waters of low temperature, i.e. the waters are cold. In Africa the main cold ocean currents include; the cold Benguella current and the cold canary current. Elsewhere examples include the Californian current, cold Peruvian current, the North equatorial current, East Greenland Current, and the West Australian current. The following are Characteristics of cold ocean currents They are characterized by low temperatures, i.e. they have low waters.  They tend to flow from high latitude regions to regions of low latitude, i.e. they flow equator wards from regions of cold conditions.   They generally flow on the western side of the continental landmasses. This is true in the lower latitude regions.   In the mid and high latitude regions, they tend to flow on the eastern sides of the continents e.g. the Labrador Current, the Oya siwo current.   They tend to characterized by high density/low salinity.  ...

  An ocean current can be defined as a horizontal movement of seawater in the ocean . Ocean currents are driven by the circulation of wind above surface waters, interacting with evaporation, sinking of water at high latitudes , and the Coriolis force generated by the earth's rotation.  The nature of ocean currents has influenced human activities in the coastal regions. Effects of warm ocean currents: The resultant high rainfall experienced has encouraged crop cultivation or rain fed- agriculture .This is common along the east African coast and West African coast where a number of crops are grown, e.g. cloves , sisal, and sugarcane along the East African coast. Along the West African coast crops like cocoa are grown in Ghana . The high rainfall experienced encourages the growth of forests and people may be involved in forestry activities, e.g. in Gabon , forestry activities such as lumbering are practiced. On the east African coast lumbering is also carried out in the...

  Coral reef is the mass of corals build-up by the accumulation of skeletons of coral polyps and other marine organisms. Coral is a limestone rock made up of the skeletons of the tiny marine organisms ie coral polyps. The polyps usually live in closely peached colonies of thousands and their skeletons are made up of calcium carbonate. When the polyps die, their skeletons and shells accumulate at the bottom of the sea and they are eventually compressed together with time by their own weight, consolidated and cemented together to build a coral reef. other organisms such as echinoderms and calcareous algae help to cement the space between the skeletons. The following are 3 types of coral reefs. Fringing reefs this is the platform of corals attached to the coastline and extending seaward for a distance of a few hundred meters. The surface of the reef is highly irregular with many broken corals and many large hollows resulting from selective solution; however, ...