Presentation on theme: "Volcanoes Carly Irving and Laura Cryan. What causes a volcano? Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing."— Presentation transcript:
What causes a volcano? Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Because it is lighter than the solid rock around it, magma rises and collects in magma chambers. The magma rises towards the surface because it is less dense than the surrounding rock (like a hot air balloon rising through the cooler air). If the magma reaches the surface it is called lava and lava accumulates to make a volcano
fluid or semi fluid material under the earth's surface from which lava and other igneous rock is formed by cooling Mouth of a Volcano Strata (Layers) Cross section of a Volcano
Cinder Cone A circular or oval cone made up of small fragments of lava from a single vent that have been blown into the air, cooled and fallen around the vent. These regularly throw out ash which builds flatter domes. Composite Volcano Found at destructive plate margins. A steep-sided volcano composed of many layers of volcanic rocks, usually made from high-viscosity (thick like honey) lava, ash and rock debris (broken pieces). Emits a stiff, rapidly solidifying lava which forms high, steep-sided cones. Shield Volcano Found along the rift valleys and ocean ridges of constructive plate margins. A volcano shaped like a bowl in the middle with long gentle slopes made by basaltic lava flows. Fissure Volcano There is no central crater at all. Instead, giant cracks open in the ground and expel vast quantities of lava that spread far and wide to form huge pools that can cover almost everything around. When these pools of lava cool and solidify, the surface remains mostly flat.
Different types of lava This kind of lava is called Pahoehoe (pa 'hoy hoy). It is smooth and runny (low viscosity) and moves fast! When cooled, it is ropey and shiny black. This kind of lava is called A 'A Lava. It is rough and jagged and very sharp. It is very, very thick and moves slowly. If A 'A lava is approaching you, you've got plenty of time to get out of the way.
Why do volcanoes erupt. Volcanoes grow by intrusion and extrusion. An intrusion is magma that moves up into a volcano and then it stops, never erupting. This way the volcano grows on the inside. An extrusion is an eruption. It can add layers of lava or ash. This way the volcano grows on the outside. Volcanoes erupt because of density and pressure. The lower density of the magma causes it to rise (like air bubbles in syrup). It will rise to the surface or to a depth that is determined by the density of the magma and the weight of the rocks above it. As the magma rises, bubbles start to form from the gas dissolved in the magma. The gas bubbles exert tremendous pressure. This pressure helps to bring the magma to the surface and forces it in the air, sometimes to great heights. Intrusion Extrusion
Why do volcanoes occur? Volcanoes occur when the earth's surface plate pull apart causing magma to rise to the surface. Volcanoes can also occur over hotspots and where one plate dives beneath another, forcing magma to rise to the surface. Plates diving under one another is known as subduction.
Divergent boundaries occur when plates are moving away from one another, thinning the crust and allowing heat and molten rock to reach the surface. This often occurs in the oceanic crust and results in sea-floor spreading, as the lava flows upward and cools. This figure shows how the mid-Atlantic Ridge is forming, as the plates move away from one another, creating numerous volcanoes along the boundary Examples : North America and Eurasian plate Divergent Boundaries/ Constructive
Convergent boundaries are the opposite. They occur when two plates collide. These type of boundaries occur between oceanic crust collisions, continental crust impact, as well as a meeting of oceanic with continental crust. The resulting structures are determined by the composition of the colliding plates. Examples Pacific plate and the Eurasian plate Convergent Boundaries / Destructive
Transform boundaries are when two plate plates slide past each other Example where this happens North America plate and the Pacific plate Transform Boundaries/ Conservative Transform Boundaries/ Conservative
Why do volcanoes occur where they do Volcanoes usually occur on the edge of plates, similar to where earthquakes occur. A lot of volcanoes occur in the Pacific ring of Fire. Volcanoes can also occur in the middle of plates, in hotspots, one such hotspots has formed the Hawaiian islands chains, As the earth rotated it passed over the hotspot and new islands were formed
Where are the earth's volcanoes ? This map shows the location of active, dormant, and extinct volcanoes throughout the world. Each individual volcano is shown as a single, red triangle. In many places in the world, there are so many volcanoes in a small area that they appear on this map as a cluster instead of individual triangles.
Case Study- Mt Pinatubo The Philippines is one of the poorest countries in South-East Asia and most effected by natural disasters. There are 17 active volcanoes in The Philippines. Since 1975, there have been twelve earthquakes and six volcanic eruptions. Over one million people were affected by floods in 2000. The Philippines has an average of 19 typhoons a year, causing flash floods and considerable damage to farmland and property. Between 1975-2000, there were 250 natural disasters causing 37,000 deaths.
Case Study- Mt Pinatubo The country forms part of the "Ring of Fire" where the plates that make up the earth's crust are colliding around the rim of the Pacific Ocean. Mt Pinatubo is an active ash volcano located on the island of Luzon in the Philippines. Up until June 15, 1991, Mt. Pinatubo was inactive for about 600 years and was approximately 5725 ft above sea level. In June and July, 1991, Mt Pinatubo erupted throwing ash 50, 000 miles into the atmosphere and all over the island. At least 550 people died because of the eruption.
Pinatubo environmental impacts For months volcanic materials remained suspended in the atmosphere, where the winds dispersed them to envelope the earth, reaching as far as Russia and North America. 250,000 acres of land lost.
Pinatubo economic impacts Pinatubo has created new money-making opportunities in tourism with approximately 1000 visitors a day more than 650,000 people lost their livelihood because their place of work was destroyed. Hundreds of millions of dollars in private properties and infrastructure lay in ruins which would require several years to rebuild and vast sums of money. Many houses and buildings collapsed from the weight of accumulated ash deposits.
Pinatubo economic impacts jets that encountered the ash and sustained about $100 million in damage. Infrastructure closed commercial and industrial activities suspended
Pinatubo social impact 500,000 people living in the shadow of the volcano are still affected today by this natural disaster.
Pinatubo demographic impact At least 550 people died, 184 injuries and 23 people missing. (some reports state up to 847 deaths)
Mt St Helens Mt. St. Helens, a peak in the Pacific Northwest's Cascade mountain range.
Mt. St Helens May 18, 1980, was the most destructive in the history of the United States, in terms of its social, economical, demographic and environmental impacts. After over 100 years of dormancy the eruption of Mt. St Helens was started by an earthquake, with a magnitude of 5 on the Richter Scale. The surface of the northern side moved downhill and pressurised magma was able to explode outwards through the weakened area. Trees were pushed flat and air and debris moved so fast that it overtook the people trying to escape. Ice and snow on the mountain was converted into superheated steam which combined with ash to produce fast flowing mudflows that heated the Toutle River below to 90 degrees C.
Mt. St Helens environmental impacts Many tens of thousands of acres of prime forest were damaged. Wildlife in the area suffered heavily. The Washington State Department of Game estimated that in the most affected areas by the eruption almost 7000 animals (mainly deer, elk and bear) perished. Most animals below ground or water level when the disaster struck were able to survive. Downwind of the volcano, in areas of thick ash accumulation, crops such as wheat, apples and potatoes were destroyed. Many crops survived that were blanketed by only a thin layer of ash. Effects of ash fall on the water quality of streams, lakes and rivers were short lived and minor.
Mt. St Helens environmental impacts The eruption brought environmental benefits too. Crusting of ash on crops on ash helped to retain soil moisture through summer, which led to higher than normal production of crops such as wheat. In the long term, ash will provide chemical nutrients that will benefit the soil.
Mt. St Helens economic impacts More than 185 miles of highways and roads and 15 miles of railways destroyed or heavily damaged. All buildings and manmade structures in the vicinity of Spirit Lake were buried and more than 200 houses and cabins destroyed. Over a thousand commercial flights were cancelled following airport closures. Tourism dealt a crippling blow, with convention, visits and meetings cancelled. In the short term devastating, perhaps though now visitors have a new reason to visit A overall total of £1.2bn damage calculated
Mt St Helens social impacts Unemployment rose ten fold many people made homeless Farmers loss of income due to crops destroyed Several months on people reported stress and emotional problems
Mt. St Helens demographic impacts 57 people lost their lives
How do people cope and perceive with volcanoes? Although volcanoes are deadly and can cause much destruction, people still continue to live in their shadows. An example is Mt Vesuvius in Italy, where over 3 million people continue to live in the Bay Of Naples even though a serious eruption of the magnitude of 79AD ( which wiped out Pompeii and hercalaneum) is due very soon.
Is there a way to prevent or manage a Volcano There really isn’t any way to prevent a volcano from erupting as the forces involved are too big and complex to understand or fight, this means that to minimise the damage what we need to do is try and predict when a volcano will erupt, and what the effects will be. What they are doing in Japan is to monitor their volcanoes very carefully to try and understand WHEN they are going to erupt. In some places they are also building concrete dams across gullies and valleys on volcanoes. These dams are meant to catch the material from the volcanic flows so that they are not as damaging to the lower flanks where people live. The best plan of action is still to just evacuate the areas that we think will be affected (plus some more area for safety), and wait for the eruption to run its course