Natural Hazards

• Natural hazards are natural events which post risk of damage to property and potential loss of life. Examples include: earthquakes, tsunamis hurricanes, tornadoes, land-slides, extreme rainfall and lightning.
• Hazard risk is the chance or probability of being affected by a natural event. Factors which affect hazard risk are

  1. ability to cope,
  2. vulnerability and
  3. nature of the hazard
• There are two types of crust, oceanic and continental. The earths crust is divided into sections known as tectonic plates
• The point at which two tectonic plates meet is known as a plate boundary or plate margin.
• Whilst convection currents do occur in the mantle, research shows that the key drivers of plate movement are slab push (as a plate subducts pulling the plate with it) and ridge push (as new land is created at ocean ridges gravity causes the higher part of the plate to push away). Slab pull is believed to be the major driving force
• Earthquakes and volcanoes tend to occur in long narrow bands, often following the edges of continents. The largest band is found along the Pacific Ocean (Pacific Ring of fire). Earthquakes & volcanoes are often also found in the middle of oceans e.g. the Atlantic
• Some volcanoes are found in isolated clusters e.g Hawaiian islands in the middle of the Pacific plate (due to a hotspot). Earthquakes also occur without volcanoes, for examples throughout Central Asia, particularly around the Himalayas.
• Two tectonic plates move towards each other at a DESTRUCTIVE boundary
• Where oceanic crust meets continental crust, the denser oceanic crust will be subducted, forming an ocean trench. As it sinks it magma is formed at depth. This hot magma rises & where it reaches the surface erupts as a volcano.
• The friction and pressure that builds up during the collision of the plates and subduction of the oceanic crust can also result in earthquakes at a destructive boundary when the energy is released as the rocks along the fault line shift.
• The type and shape of volcano differs with type of magma. Shield volcanoes are formed where there is more free flowing lava, giving rise to frequent, gentle eruptions. Thick and sticky lava eruptions are less frequent and more explosive forming composite volcanoes
• Winds are large scale movements of air caused by differences in air pressure. Winds are where air molecules move from areas of high to low pressure. The greater the pressure difference - the stronger the wind.
• Air pressure is the force exerted on the surface by the air above. Where air is RISING there is LOW PRESSURE, where air is sinking towards the ground there is HIGH PRESSURE
• At the equator, air is heated strong by the concentrated energy from the sun. This warm air rises creating an area of low pressure at the equator
• At the poles, cold, dense air, sinks creating high pressure. This high pressure is then drawn back towards the equator as surface winds
• The earth's winds are part of the global atmospheric circulation which has three 'cells' of air movement in each hemisphere - the Hadley Cell, Ferrel Cell and Polar Cell.
• As the earth rotates, winds are deflected to the right in the northern hemisphere and in the southern hemisphere they are deflected to the left.
• At the equator, where tropical rainforests are found, the intense heating results in low-pressure and with the sun directly overhead temperatures are high. The rising, warm air, cools and condenses resulting in high rainfall in these areas
• Most deserts are around 30o north or south of the equator, here sinking air and high pressure results in few clouds & little rain. Lack of clouds means intense heating in the day, but temperatures drop at night due to a lack of clouds to keep heat in.
• The UK is located at around 55oN close to the border of the cold air moving down from the south and the warm air moving up from the north giving rise to a low pressure zone.
• Tropical storms are areas of very low atmospheric pressure which generally form between the tropics 5-20o N/S of the equator where ocean temperatures are higher As warm, moist air reaches high altitudes, powerful winds spiral around a calm central point ('eye of the storm') - the warm air cools and condenses forming heavy rainfall and thunderstorms.
• Tropical storms are given different names depending on their location. HURRICANES in the Atlantic and E Pacific Ocean; TYPHOONS in the North Pacific ocean and CYCLONES in the South Pacific and Indian Oceans
• Tropical storms require certain conditions to form

  (i) they form over areas of deep warm water (at least 709m deep and 27oC+); (ii) between 5-20o N/S equator (not enough spin from the earth's rotation at the equator itself)

  (iii) areas of low wind shear, wind needs to stay relatively constant with height - a high wind sheer will tear storm clouds apart;

  (iv) form in tropical regions - areas of intense low pressure
• Tropical storms spin anti-clockwise in the northern hemisphere and clockwise in the southern hemisphere due to the CORIOLIS EFFECT
• As temperatures warm with climate change more oceans may reach the necessary 27oC with more places experiencing tropical storms we are also likely to see an increase in the intensity of storms as higher temperatures fuel stronger and more damaging storms
• As temperatures warm with climate change more oceans may reach the necessary 27oC with more places experiencing tropical storms we are also likely to see an increase in the intensity of storms as higher temperatures fuel stronger and more damaging storms
• Tropical storms are measured on the Saffir-Simpson wind scale - the higher the category, the higher the intensity of the tropical storm, with categories varying from 1-5 with 5 the most damaging
• Primary effects of hurricanes include structural damage, extensive flooding and storm surges.

  Secondary effects include possible triggering of landslides, contaminated water supplies, costs of damage
• Responses to Tropical Storms include immediate responses to try and minimise loss of life and long-term responses which involve restoring the area and also planning ahead to try and reduce the effects of future tropical storms.
• We can monitor for potential development of tropical storms, through the use of satellites, which can identify high altitude rain clouds and also through aircraft which fly through tropical storms to collect air pressure, rainfall and windspeed data
• Data from satellites and aircraft is put into prediction models which can enable "Hurricane Watch" warnings to be issued to encourage people to take action, such as boarding up windows and evacuation.
• Protection measures for tropical storms, include reinforcing windows and doors, bringing in outdoor furniture, installing emergency generators, building of cyclone shelters and the use of sea walls to help protect from storm surges
• Planning for Tropical Storms can involve training emergency services, educating people e.g. National Hurricane Preparedness Week, emergency kits held in homes & looking at longer term planning ensuring new developments are not in places at risk
• The UK has seen more extreme weather, e.g. with more intense, prolonged winter rainfall events (e.g. 2013-14) as well as higher maximum temperatures and longer warm spells / heatwaves (e.g. summer 2022) with temperature over 40oC measured for the first time
• The world's climate has changed significantly over time with shifts between cold periods known as glacials and warm periods known as inter-glacials over the last 2.6 million years (Quaternary). We are currently in an interglacial period known as the Holocene
• We use proxy data (natural recorders of changing climate) to reconstruct how temperatures have changed, including tree-rings, ice-cores, pollen analysis and sea-bed sediments
• We also have changes such as retreating glaciers, changes in sea level and changes in the timing of bird migration / tree and plant flowering which are also indicators of changes in climate
• Long-term changes in the earth's climate can be explained by internal factors (those outside of the earth's atmosphere) internal factors (related to the ocean, land and atmosphere)
• External factors affecting climate change include changes in the earth's orbit around the sun (orbital geometry) and changes in solar output
• The earth's orbit around the sun changes from circular to more elliptical over 100,000 year period, the earths angle of tilt also changes and the earth 'wobbles' on its axis. Collectively these orbital variations affect the distribution of solar energy