HAZARDS

• At constructive plate margins eruptions are small with lots of lava flow. Eruptions are basaltic lava, with low viscosity and higher temperature. less viscous, basaltic magma allows gas to escape easily, preventing the build-up of pressure.
• At destructive plate margins eruptions are explosive due to magma forcing its way to the surface, we get acidic lava and high gas content with high viscosity and low temperature. More viscous, acidic magma prevents gas from escaping and leads to a greater build-up of pressure. 
• TEPHRA - solid material of varying sizes ejected by volcano ash to volcanic bombs,
• • ASH FALLOUT - large quantities of ash carried by the wind and deposited on the ground, travels many km, causes respiratory problems, injuries and damage to to habitat.
  • E.g. the 2010 Eyjafjallajökull eruption in Iceland produced an ash cloud that disrupted air travel in Europe for several weeks
• PYROCASTIC FLOW - (NUEE ARDENTE) - super heated mixture of gas and tephra that flows at speeds of 700km/hour, destroys everything in its path.

  • E.g. when Fuego volcano erupted in Guatemala in 2018, pyroclastic flows destroyed several nearby towns
• LAVA FLOW - lava flows at different speeds depending on the slope, temp and viscosity, most move slowly without causing direct damage to humans but severe damage to nature and infrastructure. 2021 eruption of Mount Nyiragongo in the Democratic Republic of Congo
• VOLCANIC GASES- eruptions release large quantities of gases such as sulphur dioxide and carbon dioxide which are very dangerous to humans respiratory health and wildlife. Kilauea in Hawaii (USA) releases large amounts of sulphur dioxide leading to air quality alerts and health warnings for residents
• LAHARS- mudflow that occurs when tephra mixes with water from rainwater or melted snow, fast flowing destroying everything in their path. Lahars that occurred when Mount Pinatubo erupted in the Philippines in 1991 caused extensive damage and disruption
• • JOKUPHLAUPS - floods caused by a sudden release of water and rocks when glacial ice is melted by the eruption
  • The 2010 eruption of Eyjafjallajökull triggered a jökulhlaup which destroyed several bridges and roads
• ACID RAIN - when sulphur dioxide emitted during the eruption reacts with water vapour in the atmosphere to form sulphuric acid, can damage crops, aquatic systems.
• HOT SPOTS - form around the core of the earth where radioactive decay is concentrated, extreme heat causes magma plumes which are upwellings of superheated rock that rise from deep within the earths mantle, they can break through the middle of the tectonic plate to reach surface causing volcanic activity and earthquakes far away from plate margins.
• ISLAND CHAINS - hot spots and magma plumes can lead to the creation of Island Chains such as Hawaii, Magma plume is stationary so when the tectonic plate moves over it a volcano chain is formed, volcanoes are active above the plate boundary but go extinct as the plate moves away.
• FOLD MOUNTAIN - when continental plate is compressed and deformed and folding due to pressure, long relative narrow belt of mountains with parallel ridge and valleys e.g. Himalayas
• DEEP SEA TRENCH - long narrow depression in the ocean floor adjacent to land areas associated with island arcs, denser heavier plate subducted under lighter less dense continental plate e.g - Peru and French
• OCEAN RIDGE - divergent plates under the ocean, as plate move apart magma rises up to fill the gap and this accumulates over time to become taller and wider e.g.. MID ATLANTIC RIDGE.
• RIFT VALLEY- Divergent plates are beneath the land, as plates move apart the crust streches and fractures, areas of crust drop down between faults and create a valley e.g.. EAST AFRICAN RIFT VALLEY
• Mt Merapi?

  • Mount Merapi
  • Location - Java, Indonesia
  • Date 25th October -30th November 2010
  • Magnitude - VEI 4
  • Plate boundary Destructive plate boundary where the Indo-Australian plate is subducting below the Eurasian plate
  • Type of volcano  composite
• PRIMARY SOCIAL IMPACTS - 353 deaths, damage to over 19,000 homes, 1000 hectares of crops destroyed, displacement of 350,000 people and injuries and illness due to sulphur dioxide in air.
• PRIMARY ECONOMIC IMPACTS - Economic loss of £450 million due to impact on farming and tourism, over 30 bridges were damaged, disruption of trade and economic activity over 2500 flights cancelled.
• PRIMARY ENVIRONMENTAL IMPACTS - Destruction of biodiversity and habitat, over 200 hectares of forest were damaged, poor air and water quality.
• PRIMARY POLITICAL IMPACTS - Social unrest, looting and political instability.
• SECONDARY SOCIAL IMPACTS - Disruption to peoples mental health; nearly half the people effected suffered from mental health issues, disruption to healthcare and education and disruption to religious and traditional practices.
• SECONDARY ECONOMIC IMPACTS - food prices increased due to damage to livestock and crops, slower economic growth due to damage to business and disruption of tourism; domestic tourism fell by 30% and international tourism fell by 70%.
• SECONDARY ENVIRONMENTAL IMPACTS - Acid rain and long term pollution of rivers and land.
• SECONDARY POLITICAL IMPACTS - some residents claimed hat the compensation scheme was inadequate and unfair.
• MT MERAPI SHORT TERM RESPONSES - over 350,000 people evacuated, over 200 temporary shelters set up, police and military deployed to maintain order and distribution of aid by Indonesian red cross.
• LONG TERM RESPONSES TO MT MERAPI - financial assistance provided to people to rebuild their houses, 16,000 new homes built by gov. to help people, new volcano monitoring centre created to alert people in high risk areas, evacuation plans improved.
• How earthquakes occur

  1. Tectonic plates move due to convection currents and processes like slab pull and ridge push

  2. Plates get stuck and become locked together due to friction

  3. Rocks deform and leads to a build-up of stress and pressure

  4. Strength of the rock is exceeded, it fractures (breaks)

  5. Energy is released in a process known as elastic rebound
• Focus


  The point where the rocks fracture
• Seismic waves

  1. Travel outward from the focus towards the Earth's surface

  2. Causing the ground to shake
• Epicentre


  The point on the Earth's surface directly above the focus
• P WAVES - body wave , fastest , reach surface first , travel through liquids and solids and they're the least damaging.
• S WAVE - body wave , slower than p waves , only travel through solids , cause a sideways motion , more damaging.
• LOVE WAVE - L WAVE - Surface wave , slowest and causes side to side motion, larger and energy focused on surface, most damaging.
• LIQUEFACTION - shaking of the ground causes loose or saturated soils to loose their strength, they solid particles will start to act like a liquid and won't be able to withstand any pressure of infrastructure or buildings and they will sink e.g 2011 CHRISTCHURCH EARTHQUAKE. most often observed in loose saturated sandy soil.
• LANDSLIDE - downward movement of soil and rock on a slope, can be triggered by intense shaking during an earthquake, greater risk if soil is looser, steeper or shaking lasts longer e.g 2008 Sichuan Earthquake - China ---> 60,000 landslides.
• TSUNAMIS - Earthquake beneath the sea bed, sea bed jolts, eater is displaced and forced upwards creating a wave, wavs slow when near land and wavelength becomes compressed and this leads to an increase in wave height e.g 2011 Tohoku earthquake -- > Tsunami