Paper 1: Living with the physical environment

The Challenge of Natural Hazards (1.1)

Natural Hazards (1.1.1) Definition: extreme natural events that can cause loss of life, extreme damage to property and disrupt human activities. Natural hazards can either happen in a certain area (e.g. tornadoes), or anywhere in the world (e.g. flooding). Some hazards need climatic/tectonic conditions to occur (e.g. tropical storms or volcanic eruptions). Human activities can influence how often certain natural hazards occur and how severe they are. Tectonic hazards: occur when the Earth's crust moves; e.g. when plates move, friction can cause them to become stuck. Tension builds until the plates release, leading to an earthquake. e.g. earthquakes, tsunamis, volcanoes, mountain avalanches  Climatic hazards: occur when a region has certain weather conditions; e.g. heavy rainfall can lead to flooding e.g. flooding, tornadoes, tropical storms (hurricanes), droughts Hazards can have economical, social and environmental consequences. For each hazard event, the risks or probability of a particular consequence occurring can vary greatly, depending on certain factors. in a developing country, the death toll tends to be high but the short-term economic costs are often relatively low, whereas in a developed country the death toll tends to be low but the short-term economic costs can be extremely high long term (more complex): developing countries can be slower to repair damage to roads and buildings → reduction in tourists and therefore a long term loss of valuable income  hazard risks are increasing due to population growth, urbanisation, pressure on marginal land and changes to the natural environment  marginal land: land that's difficult to develop and yields little profit urbanisation: growth in the urban population, usually resulting in the extension of towns and cities

Plate Margins (1.1.2) The Earth is made up of 4 layers: inner core: in the centre (5150km below surface), the hottest part of the Earth, solid - made up of iron and nickel, temperatures of up to 500°C outer core: liquid + can flow, depth from 2900-5150km, made up of iron and nickel, produces magnetism on earth, unknown temp. mantle: upper part - solid, lower down - semi-molten (magma) + behaves like plasticine, composed mainly of silicate rocks, rich in iron and magnesium, thickest section - a depth of 2900km, temp. up to 5000°C → produces convection currents, movements powered by heat from core, makes up ½ of the earth's mass crust: outer layer, relatively thin (although varying thickness), 5-10km thick undersea, 5-90km thick on land, divided into plates that move very slowly - either continental/oceanic, temp, of 1600°C Plate Tectonics Theory: Heat rising and falling inside the mantle creates convection currents generated by radioactive decay in the core. Magma rises and pushes against the underside of the plates, moving them. Cooler magma sinks back to the core. Converging plates = plates move towards each other   Diverging plates = plates move away apart Oceanic crust = found underneath oceans, denser than continental crust + can be subducted, destroyed by plate movement Continental crust  = found underneath land masses and continents, lighter, (generally) older than continental crust, less often destroyed - plates moving in opposite directions form a constructive boundary - plates moving towards each other form either a destructive/collision boundary    - oceanic crust goes under continental crust, leaving a deep oceanic trench - plates sliding by each other form a conservative boundary Destructive Plate Margins Usually involves an oceanic + continental plate Plates move towards each other (converges) → causing earthquakes Oceanic plate (denser) is forced beneath continental plate into the mantle ← subduction As the oceanic plate subducts, changes in pressure cause part of the plate to melt  Pressurised magma escapes through weaknesses in the crust and reaches the surface through a composite volcano Subductions zones are associated with destructive volcanic eruptions (when plates melt + magma escapes to surface) and powerful earthquakes (plates slipping past each other) The extra magma created causes pressure to build up. Oceanic + oceanic: subduction leads to oceanic trench; build up pressure leads to underwater volcanoes bursting through oceanic plate; lava cools and creates new land called island arcs e.g. Pacific ring of fire Collision Plate Boundary Two continental plates move towards each other (converges) As they converge, they crumple up, creating fold mountain ranges It crumples since neither plate is 'heavy' enough to subduct into mantle Associated with earthquakes. Conservative Margins Two plates move past each other - either in the same/opposite direction, most often at different speeds Friction builds up as plates move past each other - can eventually be released as an earthquake Only associated with earthquake activity (friction causes plates to stick, pressure builds up, then plates slip violently along a fault causing ground to ripple and shake). Earthquakes can be very destructive as they occur near the surface. No crust is created/destroyed, so no landforms are created. On oceanic crust, this can displace a lot of water. On continental crust, fault lines can occur where the ground is cracked by the movement. e.g. San Andreas fault, Western USA Constructive Margins Two oceanic plates move away from each other (diverge) As plates diverge, pressure is released in mantle → magma rises to the surface in a less explosive underwater volcano Magma (called lava once reached surface) cools, solidifies and forms new land (crust) ← sea floor spreading Two continental plates diverge, causing any land in the middle of the separation to be forced apart ← creates rift valley Volcanoes form where the magma rises Eventually, the gap will most likely fill with water and separate completely from the main island Associated with minor earthquakes and volcanic activity.   Earthquakes are found on all types of plate margins, but volcanoes only occur at constructive and destructive margins. a lot of volcanoes occur in the 'ring of fire' → a group of volcanoes that are located along the plate margin of the Pacific plate  

Earthquakes (1.1.3) As plates don't perfectly fit into each other, they don't move in fluid motions so plates can become stuck due to friction between plates. When plates are stuck, the convection currents continue to push, building up pressure. It builds so much that it cannot be sustained and plates eventually give up. All of this pressure is released in a sudden movement, causing a jolting motion in the plates which is responsible for seismic movement spreading throughout the ground in the form of seismic waves (or shock waves).  Focus: the point underground where the earthquake originates from. Epicentre: area above ground that is directly above the focus. Found along all boundaries, but the Ring of Fire accounts for 90% of the world's earthquakes. Seismicity is measured using the Richter scale ← measure of the strength of the seismic waves. The Mercalli Scale is also used as a rate of the destruction caused. It has a definite end at 12 (XII), but is subjective as it's dependent on human development being present rather than the strength of seismic waves.    The magnitude of an earthquke is dependent on its focus. Conservative boundaries have the shallowest earthquakes → close to    the epicentre + stronger seismic waves.    Destructive boundaries usually have deeper focuses → seismic waves are spread over a larger area before they reach the    epicentre. Earthquakes are frequent around the world and occur every day at boundaries. Hundreds of smaller magnitude earthquakes that cannot be felt by humans occur every day, whereas the larger earthquakes are less frequent.  Earthquakes follow no pattern and are random so there is irregularity between events. Hazards Caused By Seismic Events shockwaves (seismic waves) - the further away from the focus, the weaker the shockwaves tsunamis when an oceanic crust is jolted during an earthquake, all of the water above the plate is displaced. The water travels fast but with a low amplitude (height). As it gets closer to the coast, the sea level decreases so there is friction between the sea bed and the waves → waves slow down and gain height, creating a wall of water (average 10ft high, can reach 100ft) liquefaction - when soil is saturated, the vibrations of an earthquake causes it to act like a liquid → soil gets weaker and more likely to subside (sink) when it has a large weight on it landslides and avalanches - movement in soil or snow will cause it to become unstable Environmental Seismic Hazards - earthquakes can cause fault lines which destroy the environment (primary effects) - liquefaction - radioactive materials and other dangerous substances leaked from power plants (secondary effects) - saltwater from tsunamis flood freshwater ecosystems - soil salinisation  Economical Seismic Hazards - businesses destroyed (primary effects) - economic decline as businesses are destroyed (tax breaks etc.) (secondary effects) - high cost of rebuilding and insurance payout - sources of income lost Social Seismic Hazards - buildings collapse, killing/injuring people and trapping them  - gas pipes rupture, starting fires which can kill - water supplies are contaminated as piped burst, spreading disease and causing floods - tsunamis which lead to damaging flooding Political Seismic Hazards - government buildings destroyed -political unrest from food/water shortages - borrowing money from international aid - can be international chaos and 'lawlessness' (e.g. looting) 

Volcanoes (1.1.4) Volcanoes occur on constructive and destructive plate boundaries where plates melt and magma erupts through a plate. Alternatively, they may occur on hotspots too.  Volcanoes form when magma (molten rock from beneath the Earth's crust) reaches the surface. The magma erupts to form lava. Hotspots: areas of volcanic activity where hot magma plumes from the mantle rise and burn through weaker parts of the crust, (possibly) creating volcanoes and islands. The plume stays in place as the plate continues to move, sometimes causing a chain of islands (e.g. Hawaii). Structure Of Volcanoes magma chamber - where the molten rock is stored beneath the ground main vent - channel through which magma travels to reach the Earth's surface secondary vent - some magma may escape through the side of the volcano, particularly if the main vent becomes blocked crater - found at the top of the volcano, where the magma erupts from Volcanic Effects Ash from large volcanoes has been known to affect global climates geothermal energy (heat within the Earth used to generate electricity) can be generated in areas where magma lies close to the surface → good for increasing renewable energy usage ash ejected by volcano acts as a good fertiliser for soils  volcanoes attract many tourists volcanoes are dangerous - can kill people and damage property economic activity can suffer as it's hard for businesses to operate post-eruption habitats and landscapes are damaged by lava flows Explosivity Of Volcanoes If a volcano has been dormant for a long time, it would be more explosive as there has been a long build-up of pressure. In contrast, if a volcano erupts frequently, it will be less explosive as there wouldn't be as much pressure (e.g. volcanoes in Hawaii). Volcanoes are more explosive where the Earth's crust is weaker and thinner or where there are more fractures. Volcanoes that contain basaltic magma are more explosive as it as a low viscosity (than rhyolitic magma). Basaltic magma also contains less gas so there is less pressure. The more magma, the more explosive the volcano can be. The bigger the volcano, the bigger the eruption, the less frequent the eruption. Earthquakes can trigger volcanoes. Volcanoes happen more on a destructive margin: the plate that's being subducted melts (oceanic), feeding into the magma chamber. More magma in the magma chamber = increased pressure more build-up of pressure at destructive margins in contrast, no pressure at conservative margins, because the crust isn't being destroyed/weakened so the molten magma can't reach the surface Volcanic Hazards lava flows - silica makes lava viscous and slow, which is common in explosive eruptions viscosity: resistance to flow  lahars (mudflows) - caused by various reasons, usually by melting ice at high latitudes  glacial floods - when temperatures are high from magma, glaciers or ice sheets at high temperatures quickly melt and a large amount of water is discharged tephra - any type of rock that is ejected by a volcano toxic gases - released during some eruptions, even CO₂ can be toxic as it can replace oxygen since it's heavier acid rain - caused when gases like sulfur dioxide are released into the atmosphere pyroclastic flows - clouds of burning hot ash and gas that collapses down a volcano at high speeds (average speed of 60mph but can reach 430mph) volcanic bombs - large blocks of hot rocks thrown from a volcano Environmental Volcanic Hazards - ecosystems damaged through various volcanic hazards (primary effects) - wildlife killed - water acidified from acid rain (secondary effects) - volcanic gases contribute to greenhouse effect (global warming) Economic Volcanic Hazards - businesses and industries destroyed/disrupted (primary effects) - jobs lost (secondary effects) - profit from tourism industry Social Volcanic Hazards - people killed (primary effects) - homes destroyed from lava/pyroclastic flows - fires can start putting lives at risk (secondary effects) - mudflows/floods - trauma - homelessness Political Volcanic Hazards - government buildings and other important areas destroyed/disrupted (primary effects) - conflicts concerning government response, food shortages, insurance etc. (secondary effects) The magnitude of volcanoes is measured using the Volcanic Explosivity Index (VEI) - the more powerful, the more explosive.   Volcanoes are classed as either active, dormant or extinct. Usually, a higher frequency eruption means they are effusive, whereas low frequency means they are explosive (due to build up and pressure). effusive = calmer, lower magnitude eruptions explosive = intense high magnitude eruptions Volcanic eruptions are normally regular, in the sense that the eruptions on each type of boundary are similar (e.g. eruptions on destructive boundaries will regularly be explosive). The regularity of eruptions can help estimate when eruptions will take place (i.e. every 10 years). Seismic activity, gases releasing, elevation etc. can all indicate an imminent eruption, but there are no definite predictions to a volcanic eruption.