-Volcanoes OUTLINE I. Volcanoes and Plate Tectonics II. Earth Structure III. How Magma Forms IV. Hawaiian Volcanoes The Nature of Volcanic Eruptions CONCEPTS 1. Specific magma compositions and thus volcanoes are associated with.
Download ReportTranscript -Volcanoes OUTLINE I. Volcanoes and Plate Tectonics II. Earth Structure III. How Magma Forms IV. Hawaiian Volcanoes The Nature of Volcanic Eruptions CONCEPTS 1. Specific magma compositions and thus volcanoes are associated with.
-Volcanoes OUTLINE I. Volcanoes and Plate Tectonics II. Earth Structure III. How Magma Forms IV. Hawaiian Volcanoes The Nature of Volcanic Eruptions CONCEPTS 1. Specific magma compositions and thus volcanoes are associated with specific tectonic environments 2. Chemical versus mechanical layering in the Earth 3. Partial melting 4. Subduction zone volcanism 5. Intraplate volcanism Volcanic gases billow behind those who have come to collect the offerings made by Hindus at the crater of Mount Bromo in East Java, Indonesia. Eldfell, Heimaey, Iceland Smoking craters of Mount Bromo (front) and Mount Semeru (back) on the Indonesian island of Java. Scientists have issued a high-alert warning for Mount Bromo after it showed signs of increased activity. The volcano, A man rides a donkey on a road covered with ash from an explosion of Shield Volcanoes of Hawaii Mahukona Loihi 32 kilometer miles Study Guide to Volcanoes •What causes volcanoes? •Are there different types of volcanoes? •What effects do volcanoes have? •Can we predict when a volcano is going to erupt? •Which volcano has killed the most people? •Do volcanoes do anything good? •Volcano facts Igneous Rock Names SiO2 content < 45% Volcanic Name 45-53% 53-70% >70% Basalt Andesite Rhyolite Plutonic Name Peridotite Gabbro Diorite Granite Description ultramafic mafic intermediate felsic Viscosity very low low intermediate high General Color very dark dark intermediate light Minerals olivine, pyroxene olivine, pyroxene, feldspar feldspar, amphibole feldspar, quartz, mica Occurrence mantle oceanic crust average continental upper continental crust crust Chemical Layering in the Earth 6371 km CRUST: oceanic ~10 km thick BASALT continental ~40 km thick ANDESITE MANTLE: ~3000 km thick PERIDOTITE SILICATES CORE: ~3300 km thick IRON outer core is liquid inner core is solid IRON Volcanoes Composite Cone Mt St Helens – USA Mount Fuji – Japan Crater Composite volcano is built up of alternate layers of LAVA and pyroclastic materials. They can explode with great violence. Pyroclastic Flow Ash layer Lava Layer Conelet Dyke Flank eruption Lava Flow Crust Nature of Volcanic Eruptions 1. Fluid basaltic lavas generally produce quiet eruptions (Hawaiian lava flows) 2. Highly viscous lavas (rhyolite or andesite) produce more explosive eruptions (Yellowstone & Mt. St. Helens hot ash explosions) Explosive eruptions at Kilauea are thought to be caused when water comes into contact with hot or molten rock (magma) and flashes into steam. In 1924, this happened after the level of the lava lake in Halema'uma'u Crater dropped below the water table. The walls of the crater then collapsed and blocked the opening down which the lava had drained, allowing steam pressure to build up and cause violent explosions. Many of Kilauea's pre-1924 explosive eruptions that produced significant ash deposits probably happened when the volcano's summit crater was so deep that its floor was below the water table, letting ground water seep in to form a lake. Whenever magma erupted into the lake water, violent explosions of steam and volcanic gases resulted, fragmenting the magma into tiny ash particles and driving fast-moving, extremely hot ash-laden steam clouds (pyroclastic surges) out of the crater. Composite volcanoes, sometimes known as strato volcanoes, are steep sided cones formed from layers of ash and [lava] flows. Composite volcanoes can rise over 8000 feet. Examples of composite volcanoes include Mount Fuji (Japan), Mount St Helens (USA) and Mount Pinatubo (Philippines). Shield Volcanoes Mauna Loa Hawaii –USA Shield Volcanoes are enormous features built up only from layers of lava. They produce lots of lava but they tent not to erupt violently. Layers of Lava Lava Flow 10,000m 250 kilometer Composite volcano to scale A Shield Volcano Shield Volcano K’ilaueau Volcano Materials extruded from a Hawaiian Volcano • Basaltic Lava Flows • Basaltic lavas are much more fluid • Types of basaltic flows – Pahoehoe lava (- twisted or ropey texture) – Aa lava (rough, jagged blocky texture) • Dissolved Gases • 1-6% of a magma by weight • Mainly water H2O vapor, carbon dioxide CO2 and sulfur dioxideSO2 Low-Viscosity Basaltic Lava A Pahoehoe lava flow Shield Shield volcanoes have gently sloping sides and are formed from layers of lava. Eruptions are typically non-explosive. Shield volcanoes produce fast flowing fluid [lava] that can flow for many miles. Examples of shield volcanoes include the Hawaiian volcanoes. Although these eruptions destroy property, death or injury to humans rarely occurs. Dome (Acid Lava Cones) Acid [lava] is much thicker than [lava] which flows from shield volcanoes. Dome volcanoes have much steeper sides than shield volcanoes. This is because the lava is thick and sticky. It cannot flow very far before it cools and hardens. Cinder Cones, Tuff Cones Diamond Head Koko Head Paracutin - Mexico The volcano is built up of layers of pyroclastic materials. When it erupts it is normally with great explosive force. Volcanic Bombs 300m Pipe Layers of Ash and Cinder What are active, dormant and extinct volcanoes? Volcanoes are found in three states - extinct, dormant and active. An extinct volcano will never erupt again. A dormant volcano has not erupted in 2000 years. An active volcano has erupted recently and is likely to erupt again. Where are volcanoes located? Volcanoes are found along destructive (subducting) (diagram) plate boundaries, constructive (divergent) (diagram) plate boundaries and at hot spots in the earth's surface. What is the Ring of Fire? The 'Ring of Fire' (map) is a volcanic chain surrounding the Pacific Ocean. It is formed along a destructive (subducting) plate boundary. The BBC News Web Site contains an excellent article on the 'Ring of Fire' What are lahars and pyroclastic flows? The most destructive aspect of volcanoes are lahars and pyroclasic flows. Lahars are volcanic mudflows created when water (from rain or meltwater from glaciers) and ash mix. This deadly combination can have devestating results on the surrounding area. When lahars settle they can be metres thick and as hard as cement. Lahars can occur long after a volcanic eruption. Pyroclastic flows are avalanches containing hot volcanic gases, ash and volcanic bombs. On steep volcanoes pyroclastic flows can reach speeds of over 100 miles per hour. Why do people live close to volcanoes? Volcanoes have a wide range of effects on humans. These can be problematic or beneficial. It is usually the destructive nature of volcanoes which is more widely documented. However, many people rely on volcanoes for their everyday survival. Today, many millions of people live close to volcanoes for this very reason. People live close to volcanoes because Geothermal energy can be harnessed by using the steam from underground which has been heated by the Earth's magma. This steam is used to drive turbines in geothermal power stations to produce electricity for domestic and industrial use. Countries such as Iceland and New Zealand use this method of generating electricity. Volcanoes attract millions of visitors around the world every year. Apart from the volcano itself, hot springs and geysers can also bring in the tourists. This creates many jobs for people in the tourism industry. This includes work in hotels, restaurants and gift shops. Often locals are also employed as tour guides. [Lava] from deep within the earth contains minerals which can be mined once the lava has cooled. These include gold, silver, diamonds, copper and zinc, depending on their mineral composition. Often, mining towns develop around volcanoes. Volcanic areas often contain some of the most mineral rich soils in the world. This is ideal for farming. [Lava] and material from [pyroclastic flows] are weathered to form nutrient rich soil which can be cultivated to produce healthy crops and rich harvests. Geothermal energy "makes economic sense Can we predict when a volcano is going to erupt? Scientists who specialize in volcanoes are called volcanologists. They are getting better at predicting volcanoes. The most reliable method is listening to the 'rumbles' inside a grumbling mountain. Earthquake tremors and ground level changes are monitored for the active lava dome buildup. They also look at the changes in the gases which come out of volcanic mountains, the angle of the slopes, and bizarrely, the behavior of animals in the area. Animals often seem to be able to 'detect' when an eruption is coming, and they become agitated and worried http://volcanoes.usgs.gov/ash/index.html Igneous Rocks What are They? • Fire Rocks • Formed underground by trapped, cooled magma • Formed above ground when volcanoes erupt and magma cools The role of water Pillow Lavas Assimilation and magmatic differentiation Convection- heat transfer which takes place by hot, lower density material rising and cool, higher density material sinking Decompression melting At a Mid-Ocean Ridge Plate Boundaries 1. Divergent: Mid-ocean ridges where hot material rises to make new ocean floor-BASALT 2. Convergent: Subduction zones where cold material dives back into the mantle- ANDESITE 3. Conservative: Transform boundary where 2 plates slide by each other