1. Volcanoes

2. What are Volcanoes? A volcano is a rupture of the Earth's crust which allows hotlava, poisonous gases and ash to escape from the magmachambers below the surface. Volcanoes occur because the Earth's crust is separated into 17rigid tectonic plates that float around on a hotter andsofter mantle below. This is why volcanoes are generally found around placeswhere the plates converge and diverge. For example, asthe plates move apart, a fissure opens in the ground,allowing lava to pour out onto the surface. This is called afissure volcano. Scientist who study volcanoes are call Volcanologists. 3. Volcano Phases Volcanoes can be in one of three phases: Active, Dormant,and Extinct. Active volcanoes are ones that have erupted in the pas10,000 years, and that are likely to erupt again. Anexample is Mt. Saint Helens in U.S.A. Dormant volcanoes are ones that have not erupted in thepast 10,000 years, but still have the possibility, thoughunlikely. An example is Mt. Rainier in the U.S.A. Extinct volcanoes are ones that nobody think will eruptever again. An example is Mt. Ashitaka in Japan. 4. Types of Volcanoes There are four types of Volcanoes: Fissure Volcanoes, Cinder Cone Volcanoes, Shield Volcanoes, Composite Volcanoes, 5. Fissure Volcanoes Fissure volcanoes are cracks in the ground that are onlya few metres wide but can be several kilometres inlength. Fissure volcanoes are not usually explosive. Instead, thelava seeps out of the gaps in the surface of the crust. 6. Shield Volcanoes Shield volcanoes are almost entirely made up out of fluidlava flows. Vent after vent flows out through the volcano from thecentre vent. This builds a broad, gentle sloping cone of a flat, domeshape, similar to a warriors shield. 7. Composite Volcanoes Composite volcanoes are some of the grandest on theworld. They are typically large, steep, symmetrical cones builtof alternating flows of lava ash and cinders. Most have a crater at the summit which contains acentral vent or a clustered group of vents. 8. Cinder Cone Volcanoes Cinder cone volcanoes are formed large globs of lavabeing launched from a single vent. As the gas-charged chambers explodes, lava getslaunched into the air only to fall back down aroundthe main vent as cinders in an oval or circular cone. Most have a bowl-shaped crater in the centre. 9. What Causes Volcanoes? Volcanic activity frequently occurs on the boundaries oftectonic plates as the pressure within causes themagma below to rise up and explode or escape to thesurface. 10. The Ring of Fire! The Ring of Fire is a string of volcanoes that runs aroundthe edge of the Pacific Ocean. The Ring of Fire is quite a circle, more like 40,000kilometre long horseshoe. A string of 452 volcanoes stretches from the southern tipof South America, up along the coast of NorthAmerica, across the Bering Strait, down throughJapan, and into New Zealand. 11. Measuring Volcanic Eruptions Volcanic eruptions are measured using the Volcanic Explosivity Index(VEI) Since the size and force of eruptions vary, Volcanologists take anumber of factors into account when measuring volcaniceruptions, such as: Volume of material ejected, height of the eruptive column,duration etc. Each eruption is given a rating of 0-8. 0 being non-explosive andharmless, and 8 being Run for your lives the planet is melting! Each point on the scale is 10 times more powerful than the onebefore. This makes the most devastating eruptions that we knowof thousands of times more powerful than the eruption that tookoff the top 400m of Mt. St Helens almost a quarter of a centuryago. 12. VEI 13. Earthquakes 14. What are Earthquakes? An earthquake is the result of a suddenrelease of energy in the crust thatcreates seismic waves. The seismicity of an area refers to thefrequency, size, and type of earthquakeexperienced over a period of time. 15. What cause Earthquakes? The Earth's crust is made up of several tectonic plates.These plates are always moving around on the mantle. Because these plates are moving, they constantly grindagainst one another and get stuck. When the rest of the plate moves far enough, one of thetwo plates fault, which releases large amounts ofenergy that was stored up by the tension. This causes an earthquake. 16. Focus and Epicentre The focus of an earthquake is where it begins, this iswhere the plate slips on a fault line, usually at theplate edges. The Epicentre is the point directly above the Focus onthe surface of the earth. This area will suffer from themost direct damage. 17. Seismic Waves Seismic waves are the waves of energy caused by thebreaking of rock during an earthquake. The main two types of waves are body waves and surfacewaves. Body waves occur in two types, primary waves (P) andsecondary waves (S). Surface waves occur after the body waves as lowerfrequencies which are responsibly for most of the damageand destruction on land. Surface waves have two types, Love waves and Rayleighwaves. 18. Wave Types 19. Measuring Earthquakes The vibrations earthquakes produce aredetected, recorded and measured byinstruments called Seismographs. The line made by a seismograph iscalled a seismogram and shows thechanging intensity of the earthquakeby responding to motion of theground below the instrument. From the data expressed inseismograms, scientists the time,the epicentre, the focal depth, thetype of faulting of an earthquakeand how much energy was released. 20. The Richter Scale 21. The Modified Mercalli Scale