Geography Term 1

Driving force of plate movement

Convection current:
1. Mantle near the core heats up and rises
2. Mantle near the crust cools down, becomes denser, and sinks back down
3. Mantle is heated again near the core and rises, the process repeats
4. Converging currents pull plates tgt and diverging ones pull plates apart

Slab pull:
1. When 2 plates collide, the denser plate bends and slides under the other plate. (subduction)
2. The seafloor sinks under the mantle, pulling the plate behind it due to its weight. Gravity plays a major role in driving plate movement

Process of earthquake

1. When plates move, pressure is built up along the plate boundaries

2. Pressure becomes too large and plates can no longer withstand

3. The plate displaces and fractures suddenly

4. A large amount of energy is released in all directions in the form of seismic waves at the point of the fracture ( focus)

5. Violent shaking of the Earth’s crust is resulted

How hazards affect people’s lives (earthquakes)

Earthquake:

• People suffer from deaths and injuries due to collapsing buildings and emergency response

• Landslides and damaged infrastructure/ buildings causes road closure, disrupting traffic and transport

• Fires due to broken gas pipes

• Power blackouts due to broken power lines

• Tsunami due to earthquake on seafloor

• Floods due to collapsing dam

How hazards affect people’s lives (volcanic eruptions)

• People and lifestock → injuries and death due to ash and dust

• Damaged crops → farmers lose money/ food become expensive due to shortage

• Lava flow damaging settlements and roads: economic problems, loss of property, loss of lives

• Dust and ash clouds: poor air quality → disrupt traffic and health hazard/ jams plane engine and causes aviation hazards, disrupting flights

Why would people live in hazardous zones

• Money: tourist attraction, big city with high living standards and econ/job opportunities, poverty + strict migration laws

• People: optimistic and underestimate risk, believe gov has enough tech and money to cope, family/ social ties, used to lifestyle and culture → can’t adapt to a new place

• Resources: useful minerals, heat and steam generate geothermal power, fertile soil from volcanic ash, gentle slopes suitable for farming and settlement

Measures for natural hazards (preventative)

1. Warning and monitoring systems: seismometers to detect earthquake, issue early warnings (allow time for ppl to take actions to prepare for the hazard)

2. Building design: shock-proof to withstand vigorous shaking (ensure safety bc most deaths are caused by collapsing buildings)

3. Education: gov educating public on how to respond to natural hazards, annual evacuation drills (increase rescue efficiency bc ppl are more likely to save themselves and familiar with evacuation routes)

4. Land-use zoning: hazard-prone areas for greenbelt or recreation, building codes to prevent illegal buildings and restrict height and density, ban power plants and dangerous factories, temporary shelters in schools, sports ground and park for emergency evacuation (reduce damages and vulnerable population)

Measures for natural hazards (remedial)

1. Emergency assistance: temporary shelters with emergency supplies like water, food and blankets, efficient rescue through training and emergency medical assistance, coordinate rescue efforts and manage relief supplies (meet basic needs of survivors)

2. Rehabilitation: restore damaged buildings and infrastructure, counselling services, accept donations from MDCs (live normal lives)

Factors affecting natural hazards

• Nature of the hazard: time of occurrence, magnitude, depth of focus, frequency and regularity of the hazard

• Demographic characteristics: population density, population age

• Development: economic (funding for preventative measures and emergency responses), education (awareness and medical personnel)

• Government efficiency: government effectiveness (corruption, coordination), law enforcement

Landslide measures

• Remove water: spread cement and install weepholes, install surface drainage channels (remove excess water, reduce water in slope, prevent water seepage, decrease stress)

• Physical support: soil nails and retaining walls (anchor slopes, provide physical support, increase strength)

• Regular inspection and maintenance through laws: decrease stress and increase strength

• Others: educate public on importance of slope safety, issue early warnings and roadside warning signs, clear squatter areas and careful planning on the use of slopes

• Remedial: provide emergency services

Landslide factors

Natural factors:

• Heavy rainfall: increases stress and weight, decrease strength, water in spaces between soil particles will decrease cohesion

• Hilly relief: over 60% of hk slopes are larger than 60 degrees, steeper = more stress

• Granite rocks: joints allow water to seep into the rock, easily weathered by hot and wet climate

Man-made factors:

• Urban development: cutting and filling of the slope for land development steepens it or remove sideways support, man-made slopes built in early years are poorly designed

• Lack of proper or regular maintenance: rainwater seep through cracks easily, increasing weight