Презентація на тему «Volcanoes: Eruptions and Hazards»

content: Volcanoes: Eruptions and Hazards

content: What is a volcano?A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth's crust to the Earth's surface.The volcano includes the surrounding cone of erupted material.ventconemagma chamberconduit

content: What causes volcanoes?The Formation of MagmaMantle rock melts when the temperature increasesor the pressure decreases.

content: What causes volcanoes?Where Volcanoes FormTectonic Plate Boundaries!!!~75% world's active volcanoes in Ring of Fire

content: PlatesEarthquakesVolcanoesVolcanoes and Earthquakes are found on places where plates meet

content: What causes volcanoes?

content: What causes volcanoes?Hot Spots

content: How and why do volcanoes erupt?Hot, molten rock (magma) is buoyant (has a lower density than the surrounding rocks) and will rise up through the crust to erupt on the surface.Same principle as hot air rising, e.g. how a hot air balloon worksWhen magma reaches the surface it depends on how easily it flows (viscosity) and the amount of gas (H2O, CO2, S) it has in it as to how it erupts.

content: Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption!Think about shaking a carbonated drink and then releasing the cap.Small amounts of gas and (or) low viscosity (runny) magma will form an effusive eruptionWhere the magma just trickles out of the volcano (lava flow).How and why do volcanoes erupt?

content: The Composition of Magma Determines whether it is explosive or not!High contentMore likely to bettt!!!High t contentMore likely to be ttt!!!Why?Silica has a thick, stiff consistencyFlows slowlyTends to Harden in the volcano's ventwatersilicaEXPLOSIVEEXPLOSIVE

content: Pyroclastic materialRock fragments created by tt eruptionsmagma explodes from volcano and solidifies in the airexisting rock is shattered by powerful eruptionsVolcanic blocksVolcanic bombsLapilliVolcanic ashEXPLOSIVEWhat Erupts from a Volcano?

content: What Erupts from a Volcano?Lava can bethick or thin.Blocky lavaPahoehoeAaPillow lava

content: How do volcanoes affect the Earth?Flows and Falloutshot ash can flow really quicklyKnock down buildingsDam rivers (flooding/drought)Kill crops and livestockClimatic ChangesAsh & Gases can block sunlightDrop average global temperature noticeably

content: Types of VolcanoesShield volcanoCinder cone volcanoComposite volcano

content: Craters, Calderas, and Lava PlateauCraterFrom explosions of material out of the vent and the collapse of material back into ventCalderaMuch larger depression that forms when magma chamber empties and its roof collapsesLava PlateauForms when lava erupts from long cracks, or fissures, and spreads out evenly (thousands of km)

content: Explosive EruptionsMt. RedoubtExplosive volcanic eruptions can be catastrophicErupt 10's-1000's km3 of magmaSend ash clouds >25 km into the stratosphereHave severe environmental and climatic effectsHazardous!!!Above: Large eruption column and ash cloud from an explosive eruption at Mt Redoubt, Alaska

content: Three products from an explosive eruptionAsh fallPyroclastic flowPyroclastic surgeExplosive EruptionsPyroclastic flows on Montserrat, buried the capital city.

content: Direct measurements of pyroclastic flows are extremely dangerous!!!

content: Effusive EruptionsEffusive eruptions are characterised by outpourings of lava on to the ground.HawaiiCourtesy of www.swisseduc.ch

content: Pyroclastic flowLahars/Mud flowsPyroclastic fallLava flowNoxious GasEarthquakesVolcanic HazardsCourtesy of www.swisseduc.ch

content: Pyroclastic FlowFor example, eruption of Vesuvius in 79 AD destroyed the city of Pompeii

content: Pompeii (79AD)On August 24, 79AD Mount Vesuvius literally blew its top, erupting tonnes of molten ash, pumice and sulfuric gas miles into the atmosphere. Pyroclastic flows flowed over the city of Pompeii and surrounding areas.

content: Pompeii (79AD)Pyroclastic flows of poisonous gas and hot volcanic debris engulfed the cities of Pompeii, Herculaneum and Stabiae suffocating the inhabitants and burying the buildings.

content: Pompeii (79AD)The cities remained buried and undiscovered for almost 1700 years until excavation began in 1748. These excavations continue today and provide insight into life during the Roman Empire.

content: How do pyroclastic flows cause devastation?

content: Pyroclastic Flow - laharsHot volcanic activity can melt snow and iceMelt water picks up rock and debrisForms fast flowing, high energy torrentsDestroys all in its path

content: Pyroclastic FallAsh loadCollapses roofsBrings down power linesKills plantsContaminates water suppliesRespiratory hazard for humans and animals

content: Lava FlowIt is not just explosive volcanic activity that can be hazardous. Effusive (lava) activity is also dangerous.

content: Volcano MonitoringVolcano Observatories are set up on all active volcanoes that threaten the human population. These are designed to monitor and potentially to predict the eruptive behaviour of the volcano in question.

content: SeismicityDeformationGas Output(on volcano and remote sensing techniques)These three things are the most important precursors to an eruption.Volcano Monitoring

content: Gas samples are collected from fumaroles and active vents.Gas levels may also be monitored by remote sensing techniquesGas Monitoring

content: In Summary..Volcanoes are extremely hazardous.However, the volcano can be studied, monitored and understood.Each volcano is different, and offers a unique set of dangersPlans may be emplaced to help control potential damage.