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What is the cause of earthquakes and volcanic activity?
the movements of tetonic plates.
What are plates?
Plates are the segments into which the crust of the earth is divided
How do tetonic plates move?
they are pushed together-an edge is created-convergent plate boundary
plates pull apart-divergent plate boundary
plates slide past each other-transform plate boundary
What plate boundaries form volcanoes?
convergent and divergent
What are the effects of volcanic activities?
ash fall
lava flows
Define a hazard
a risk of a threatening situation that occurs in the environment
Define a man-made hazard
is a hazard brought about due to man’s actions or neglect examples: leakage of radioactive emissions,oil spills
Define a natural hazard
an unpredictable threat that occurs in a climatic,physical,biotic environment
Define a natural disaster
the realization of a threat where harm and damage is done to humans,animals and their property
Define a climatic hazard
a hazard that originates in the atmosphere
What are the types of hazards?
Give examples of climatic hazards
Give examples of geophysical hazards
earthquake,volcanic eruptions,tsunami,floods,landslides
Define a geophysical hazard
one that originates due to occurrences on and below the land
Define a biotic hazard
hazards that are brought about by plants and/or animals or that affects plants and/or animals
Give examples of biotic hazards
epidemics,forest fires,plant diseases,pests
What are effects of volcanic eruptions?
pyroclastic flow-large masses of gas,ash and lava fragments which rush down the sides of the volcano
mudflows or lahars
volcanic bombs
Give solutions of volcanic eruptions
cannot be prevented
monitoring-active volcanoes and dormant ones can be monitored at scientific centres-signs that can be monitored are small earthquakes,bulges at the sides of the volcano and increase in sulphurous gases that are emitted
land use planning-before volcanic activity occurs,a parameter around the volcano can be designated as unsafe and either used for only certain activities or not used at all. In the event of a volcanic eruption,this area can be increased to create an exclusion zone
re-construction-after volcanic activity,the government can put things in place to allow the country to resume normal activity for example funds set up for natural disasters or aid given by other countries
education-through the use of media and educational institutions citizens can learn the proper behaviours before,during and after an eruption
What are the effects of earthquakes?
ground shaking and displacement-as the waves of the earthquake arrive at the surface of the earth,the ground moves.
collapse of buildings and infrastructure-ground shaking causes buildings to sway,move back or forth and lurch up and down. the movement also shatters windows and roofs collapse.
death and injuries-people are hit by flying or collapsing debris
shaking can cause the ground on steep slopes or the ground that has weak rock below it to slip away. landslides can destroy everything
fires-ground shaking can cause lamps stoves and candles to topple over
floods-bursting of dams
What are solutions to earthquakes?
planning-land use planning can encourage persons to build in safe areas
building design-use steel beams in contruction,attach buildings to their foundations with anchor bolts,strap large items to the wall
follow given building codes
education and preparation-have evacuation drills
What is the cause of an earthquake?
movements at plate boundaries cause faults to develop and faulting to occur. Due to faulting,movement begins but each fault block is held in place by friction. This causes pressure to build. Eventually,the faulting overcomes the friction and the pressure is released as energy which we feel as an earthquake.
Define the focus
the point below the earth’s surface where the most movement takes place and the most energy is released
Define the epicentre
the point on the surface of the earth which lies directly above the focus
Define foreshocks
small earthquakes felt before the major earthquake
Define aftershocks
smaller earthquakes felt after the major earthquake
How are earthquakes measured?
richter scale
mercalli scale
Define a drought
a condition whereby an area has less precipitation than normal over a few months or even years
What are the causes of drought?
climate change/global warming-increase in temperature causes a number of reactions among which are droughts
changes in the local landscape due to human activities (deforestation for example)-deforestation reduces the soil’s ability to transmit water to deeper levels of the ground and reduces evapotranspiration that could lead to local rainfall.
changes in the ocean temperatures brought on by El Nino which is an atmospheric phenomenon that causes the exchange of moisture between places west of the pacific and east of the pacific
Effects of drought?
crops fail because of no water for irrigation
livestock perish
creation of refugees/migrants
reduction of wildlife which affects biodiversitiy
increased soil erosion
Solutions of drought?
monitor water reserves and rainfall activity
reduce water loss-repair seepages and leaks in aged pipes and regulate water use and water meters
create water reserves
protect catchment areas
Define a flood.
A flood is a body of water that temporarily covers land that is usually dry and considered useful to man when dry.
What are the causes of floods?
1)Heavy or prolonged rainfall-intense rainfall,that is, a large volume of rain falls in a short space of time or rain falls continuously over several hours or even days,rainwater will not be able to penetrate into the soil either because the drops are too large or the soil is saturated with water.
2)Deforestation-trees break the large drops of intense rainfall into smaller drops which can penetrate into the soil(interception.) So if no trees are there,the water will simply flow over the surface.
3)Solid waste in waterways-litter of various types clog waterways and cause the water level in rivers etc. to rise quickly whenever rain falls.
4)Impermeable surfaces/hard surfaces-some soils do not allow water to pass through so after heavy rainfall,flooding will result.Also man-made impermeable surfaces such as paved roads and concrete yards also prevent water from penetrating into the soil.
5)Coastal flooding-the movement of waves beyond the high tide level.It happens because of a tsunami or a storm surge caused by hurricanes.
Why are urban areas prone to flash flooding?
Because of the man made impermeable surfaces such as concrete yards and paved roads which prevent water from penetrating into the soil.
What are the effects of floods?
loss of crops-prices of food crops will rise
roads are blocked
spread of diseases-cholera,malaria,dengue,leptospirosis
loss of life
loss of property
homes are flooded
polluted portable water
What are the solutions to floods?
build a dam
dredge the river(widen and deepen the river)
raise height of river bank
remove/stop solid waste
landzoning-avoid building near rivers and coastlines
Define a tsunami.
A series of long,high sea waves brought about by earthquakes,volcanic activity that occurs underwater or landslides
What are the causes of tsunamis?
underwater volcanoes,earthquakes or landslides.
all tsunamis are caused because of a bulge caused by:
the power of the volcanic eruption
the displacement of water in a landslide
underwater plate movement
all these movements trigger giant waves and these waves travel at speeds up to 500 km/hr.They travel in a circular motion,outwards in all directions from where they originate.
What are the effects of tsunamis?
death-deadly currents sweep people away,causing them to drown
trees are uprooted and animals drown
buildings,infrastructure and personal property are destroyed
destruction of homes,buildings and infrastructure near the coast
risk of disease created by stagnant and contaminated water
What are the solutions/mitigation for Tsunamis?
countries within and surrounding major oceans can network together to create Tsunami Warning Systems e.g. Pacific Tsunami Warning System
create alarm systems to warn persons who are near the coast,to head for higher ground.
encourage development away from coast,in areas prone to tsunamis.
countries can educate their population about measures to take when a tsunami is approaching-if the sea suddenly recedes,run for higher ground etc.
What is a tornado?
A tornado is a rapidly rotating column of air that forms under a thundercloud.It is sometimes called a twister. Tornado winds exceed 480 km/h
What are the causes of tornadoes?
Thunderstorms that lead to tornadoes form when warm moist air and a cold front meets:before the thunderstorm,a horizontal rotating column of air forms.The rising air that helps to form the thunderstorm changes the rotating column from horizontal to vertical.Eventually,the entire thundercloud gets caught up in this rotating column.The lower base if the cloud eventually touches the ground and a tornado is formed.
What are the effects of tornadoes?
destruction of homes and property
entire fields of crops can be lost
animals are killed
people are killed and/or injured
What are solutions for tornadoes?
things can be done to prevent damage/minimise damage:
build bunkers or basements in your home
ensure that people/objects are tied down severely
insure(insurance)property/properties against disasters
families can create emergency plans
Define a hurricane.
an intense low pressure weather system(500-1500 km wide) with bands of strong winds (over 119 km/h)that spiral around a central area called the eye
What is the difference among a hurricane,typhoon and a cyclone?
A hurricane is given for these systems that originate in the Atlantic Ocean.
A typhoon originates in the Indian Ocean
A cyclone originates in the Pacific Ocean
What are the conditions that favour the formation of a hurricane?
warm temperatures of at least 26 degrees Celcius
a large source of moisture such as the ocean
spiraling winds which usually occur more than 10 degrees North and South latitude-this is because spiraling winds are a result of the Coriolis force which is formed when the earth spins on its axis
divergent outflow in the upper atmosphere(10 km above)
What are the stages in the formation of a hurricane?
1)tropical disturbance-an area with heavy and sustained thunderstorm activity-can be caused by the Inter tropical convergence zone or a tropical wave-begins off the coast
2)Tropical depression-weather disturbance intensifies,inflow of warm air from ocean surface,weak spiralling pattern develops, pressure drops, wind speeds 62 km/h
3) tropical storm-winds become organized, strong circular movement gives rise to an eye, lower pressure, wind speeds increase 63-118 km/h, the system gets a name
4) hurricane-eye of hurricane is visible in satellite imagery, low pressure, wind speeds greater than 119 km/hr, growth and intensification is measured using a saffir
5) death-lose power as they approach higher latitudes because the temperature is lower, lose power as they move over large continents because it needs moisture,
Effects of hurricanes?
Trees are blown over
Flooding caused by heavy rainfall destroy crops
Flooding Also leaves large scale soil erosion
Houses are damaged or destroyed
Power lines are brought down
Roads are blocked
People are killed
the economy suffers as sources of income such as agriculture and tourism are affected
tourism is challenged because of the damage to hotels
Solutions for hurricanes?
individuals should know what to do before,during and after a hurricane
government responses-meteorological offices can track hurricanes so that they can provide better information to the public
educate pupils in school and adults via the media about the dangers of hurricanes and ways to reduce damage
ODPM-national agencies can collaberate with other agencies to coordinate disaster response activities
Define a landslide
A down slope movement of a large mass of soil and rocks under the influence of gravity
What are the natural causes of landslides?
torrential rainfall-when a large amount of water finds its way into the sil and the rocks on the slope,it gets in between the soil particles and rock spaces,loosening the bonds that hold them together and cause them to be more easily moved by gravity
slopes that have permeable rocks resting on impermeable rock-permeable rock allows water to pass through it,impermeable rock does not allow water to pass through it. When rain falls,the water sinks through the permeable rock but remains as a layer above the impermeable rocks. The makes the top of the rock slippery and the soil slides down the slope.
seismic activity-the shaking that results from earthquakes helps to loosen the bonds between soil and rock particles,allowing them to be pulled down by gravity.
What are the man-made causes of landslides?
cutting a road into hillsides-this increases the slope angle and leaves part of the slope unsupported so it is easily brought down by earthquakes and rainfall
constructing buildings and infrastructure on slopes-this places an additional weight on the slope making it vulnerable to natural triggers of landslides
leaking pipes and sewers-this can cause the soil to become heavier(water gives additional weight) and gravity overcomes the forces holding the soil/rock together
quarrying-loosens rocks and soil particles making them vulnerable to the force of gravity.
the removal of vegetation can also increase the likelihood of landslides.
What are the effects of landslides?
people die as stones and soil cover them
damage to homes and property as the land beneath a house gives away,it collapses and is destroyed. debris can also destroy it
roads are blocked cutting communities off one another
rivers are dammed and it can eventually lead to flooding
valuable top soil is lost,hindering agricultural activity
removal of vegetation/forest cover
What are the solutions for landslides?
landslide hazard mapping-areas should be tested for landslide vulnerability and major developments should be prohibited in areas that are high risk landslide zones
build restraining structures such as retaining walls
steep slopes can be graded into gentler ones
repair any leaking pipes and sewage mains
Categories: Geography