Volcanic Hazards PDF

Volcanic Hazards The structure of the Earth Types of volcanoes...

Volcanic Hazards The structure of the Earth Types of volcanoes Ash cloud Smal l pieces of pulverised rock and glass The Crust Varies in thickness (5-10k m beneath the Shield Made of basaltic rock and form gently sl opi ng cones from which are t hrown i nt o the atmosphere. ocean. Made up of serval large plates. layers of runny lava. Gas Sulphur dioxi de, water vapour and carbon Location: hot spots and constructive margins. dioxide come out of t he vol cano. Eruptions: gentle and predictable The Mantle Wi dest layer (2900km t hi ck). The heat and Lahar A volcanic mudflow which usually runs pressure means the rock is in a liquid stat e Composite Most common type found on land. Created by layers of ash down a valley side on the volcano. that is in a st ate of convection. and l ava. Pyroclastic A fast mov ing current of super-heated gas Location: Dest ructive margins flow and ash (1000 oC). They travel at 450mph. The Inner and Hottest section (5000 degrees). Mostly made Eruptions: explosi ve and unpredict able due t o the buil d of Volcanic A thick (viscous) l ava fragment that is outer Core of iron and nickel and i s 4x denser t han the pressure within the magma chamber. bomb ejected from the volcano. crust. Inner section i s solid whereas outer layer is liquid. Hotspots These happen away from any plate boundaries. They occur Managing Volcanic Eruptions Convection Currents because a plume of magma rises to eat into the plate above. Warning signs Monitoring techniques Where lava breaks through t o the surface, active volcanoes The Lit hosphere is di vided i nt o tectonic plat es which are moving can occur abov e t he hot spot. E.g. Hawaii. Smal l eart hquakes are caused as magma rises Seismometers are used t o detect earthquakes. due to convection currents in the asthenosphere. up. Case Study: Japanese tsunami 2011 Temperatures around t he vol cano ri se as Thermal imaging and satelli te cameras can be 1 Radi oactiv e decay of some of the elements in the core and activity increases. used to detect heat around a volcano. mantle generat e a lot of heat. Causes The earthquake happen ed at a destructive plate boundary, where the P acific plate subducts below the When a volcano i s cl ose to erupting it starts to Gas samples may be t aken and chemical North American plate.. release gases. sensors used to measure sul phur lev els. 2 When lower parts asthenosphere heat up they become less The 2011 Tōhoku earthquake and tsunami was caused by a 9.0-magnitude undersea earth quake off the Preparation dense and slowly rise. coas t of Japan that occurred on Friday, 11 March 2011.The epicentre was approximately 72 km (45 mi) eas t Creating an excl usion zone around the volcano. Being ready and able to evacuate residents. of Honshu. 3 As they move towards the top they cool down, become Hav ing an emergency supply of basic provisions, Trai ned emergency services and a good more dense and slowly sink. such as food communicat ion sy stem. Effects destructive tsunami waves of up to 37.9 Responses Tsunami warnings were issued and 4 These circular movements of semi-molten rock are metres that struck Japan minutes after the quake, evacuations ordered along Japan's Pacific coast Earthquake Management convection currents in some cases traveling up to 6 miles inland. Res idents within a 20 km (12 mi) radius of the 20,000 deaths, 2,500 missing Fukushima I Nuclear Power P lant were evacuated. PREDICTIN G 5 Convection currents create drag on the base of the tect oni c £ 189 billion damage People placed in temporary accommodation to plates and this causes them t o move. tackle homelessness. Methods include: Satellite surveying (tracks changes in the earth’s surface) Types of Plate Margins Laser reflector (surveys movement across fault lines) Causes of Earthquakes Radon gas sensor (radon gas is released when plates move so this Destructive Plate Margin Eart hquakes are caused when two plates become locked causing frict ion to build up. From this finds that) stress, the pressure will eventuall y be released, triggering t he plates t o move into a new Seismometer When the denser plat e subducts beneath the other, Water table level (water levels fluctuate before an earthquake). position. This mov ement causes energy in t he form of sei smic waves, to travel from the focus frict ion causes it to melt and become mol ten magma. The magma forces it s ways up t o the surface to form a towards and the epicentre. As a result, the crust vibrates t riggering an earthquake. Scientists also use seismic records to predict when the next event volcano. This margin i s also responsible for devastating will occur. The point directly above Depth of Earthquake earthquakes. the focus, where the PRO TECTION seismic waves reach first, Shallow Focus Deep Focus Constructive Plate Margin is called the EPICENTRE. You can’t stop earthquakes, so earthquake-prone regions follow -Usually smal l -Occur on Here two plates are moving apart causing new magma to SEISMIC WAVES (energy these three methodsto reduce potential damage: and common. destructive reach the surface t hrough the gap. Volcanoes formed waves) travel out from the -Seismi c waves margins. Building earthquake-resistant buildings along this crack cause a submarine mountai n range such focus. spread and -Damage i s Raising public awareness as t hose in the Mid At lantic Ridge. Improving earthquake prediction The point at which damage wide localised as Conservative Plate M argin pressure is released is area. sei smic waves called the FOCUS. travel vert icall y. A conservative plate boundary occurs where plates sli de Earthquake proof buildings ideas past each other in opposit e direct ions, or in t he same How do we measure earthquakes? direction but at different speeds. This is responsible for 1. Counter-wei ghts to the roof to 2. Roof made from reinforced earthquakes such as the ones t hat happening along the Mercalli Scale Richter Scale help balance any swaying. cement concrete. San Andreas Fault, USA. Measures how much damage is caused, Is a scientifi c measurement based on 3. Foundations made from 4. W indows fitted with shatter- Collision Zones based on observations, not scientific the energy released. reinforced steel pil lars, bai l-beari ngs proof gl ass to reduce breakage. instruments. Measured by seismometers using or rubber. Colli sion zones form when t wo continental plat es colli de. Base from ‘Instrument ’ and ‘Weak’ to measurement from 1 – 10 Neither plate is forced under the other, and so bot h are ‘Extreme’ and ‘Cataclysmic’. Logarit hmic – each point up the scale 5. Lightweight materials that cause 6. Ensure gas pipes have an forced up and form fold mountains. These zones are Limitations is that its subjecti ve due to i t is 10 times greater than the one minimal damage if fallen during an aut omatic shut off to prevent risk of responsible for shal low earthquakes in the Himalayas. being based on perception. before. earthquake. fire.