FORM FIVE SELECTIONS 2021** FORM 5 JOINING INSTRUCTIONS
Get Help To Apply for University and Loans
Currents
These are drifts of water based on wind pattern, variations in
water temperature and salinity. True
ocean currents have little influence on the coastal processes and landform. The power of
the currents to erode at the coast is very limited, only responsible for
transporting sediments in suspension brought by waves and rivers into and out
of the lagoons and bays entrances. The currents influence distribution of
coastal ice, coral reefs or mangrove swamps.
Storms and tsunamis
Storms
caused by typhoon and hurricanes have the effect of rising sea surface and
generating waves that have the power to erode and destruct the coastal
infrastructures. Sometimes cause huge amount of sediments to
be deposited along the coastal plain accompanied with heavy floods.
Tsunamis
on the other hands are large sea waves generated by large earthquakes, submarine
volcanic eruptions, large landslides of the coastal cliff or meteorite impact,
etc. Tsunamis are common in areas with steep continental slopes and narrow
continental shelves that cause water to pile up into high waves.
Long-term sea level change
The worldwide
change in the average sea level is called Eustatic sea level change.
The changes in the
sea levels are caused by two many factors:
i)
Changes
in the volume of the ocean basins
ii)
Changes
in the volume of sea water
The changes in the ocean basin volumes are caused by:
i)
Sediment deposition caused by submarine
volcanic eruption or other sources
ii)
Trench formation- Separation between two
continents
iii)
Subsidence of the oceanic crust
iv)
Uplift of mid-ocean ridges
v)
Increase/decrease in the length of the
ridge system.
The changes in the
ocean basin volumes happened in Cretaceous (140-65 Ma) when the sea level was
raised over 300m due to rapid ridge spread (Schlüter, 1997). It caused widespread flooding of the
continents and formation of shallow seas. The phenomenon is called
transgression of the sea (seawater moved onto the land). In Tanzania, the
shoreline reached near Chalinze at place called Msolwa. In tertiary, there was
a decline in sea level that caused ocean to retreat. This retreat of the sea is
called regression of the sea.
The changes in the
volume of seawater are mainly due to advance es and retreats of polar ice
sheets. It is related with global changes in temperature. These days the
melting of ice is related with global warming.
Short-term variation is due to density variation associated with inflow
of fresh water and changes in water temperature.
Coastal erosion
Causes of coastal
erosion
There are a number of factors contributing to erosion at the coastal
area. According to Hails (1977), these factors can be categorized as follows:
1) Beach mining for
placer deposits and aggregates. Placer deposits at the coast consist of mainly minerals
such as diamond, zircon, rutile, ilmenite and Monazite.
Mining activities cause loss of sand
from frontal dunes and beach ridges.
2) Reclamation
schemes: Changes in coastal
configuration, interruption of natural processes often causing new patterns in
sediment transport.
3)
Storms and tsunamis:
Strong waves associated with tropical storms and submarine earthquakes.
4)
Increased recreational needs
in response to population pressures. These accelerate deterioration
and destruction of vegetation on dunal areas and promoting erosion by wind and
wave action.
5)
Wave action particularly in
sections with vertical cliffs and those affected with littoral drift.
6)
Deforestation, fires and
overgrazing of sheep and cattle.
.jpg)
0 Comments