Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 4: Part 2 Volcanoes and Other Igneous Activity PowerPoint Presentation Stan Hatfield . SW Illinois College PowerPoint Presentation Ken Pinzke. .Southwestern SW Illinois College Stan Hatfield Illinois College Ken Pinzke . Southwestern Illinoisof College Charles Henderson . University Calgary Charles Henderson . University of Calgary Tark Hamilton . Camosun College Copyright (c) 2005 Pearson Education Canada, Inc. 4-1 Volcanic Structures and Eruptive Styles A size comparison of the three types of volcanoes Copyright (c) 2005 Pearson Education Canada Inc. 4-2 Volcanic Structures and Eruptive Styles Types of Volcanoes • Composite cone (Stratovolcano) – Most are located adjacent to the Pacific Ocean (e.g., Fujiyama, Pinatubo, Mt. St. Helens, El Chichon, Mt Hudson) – Monte Vesuvio destroyed Pompeii & Herculaneum – Large, classic-shaped volcano (> hundreds of metres high & > several kilometres wide at base) – Composed of interbedded lava flows & pyroclastics Copyright (c) 2005 Pearson Education Canada Inc. 4-3 Living in the Shadow of a Composite Cone Eruption of Vesuvius in AD 79 Victims of Pompeii & Herculaneum Casts of several victims theInc. AD 79 eruption of Mount Vesuvius. Copyright (c) 2005 Pearson Educationof Canada 4-4 Volcanic Structures and Eruptive Styles Living in the Shadow of a Composite Cone – The Lost Continent of Atlantis and Santorini Ammoudi Beach, >60 m ash covers ruins Thera blew(c)1627 BCE & destroyed Crete. Santorini was rebuilt in the caldera. Copyright 2005 Pearson Education Canada Inc. 4-5 Volcanic Structures and Eruptive Styles Nueé Ardente: A Deadly Pyroclastic Flow also called a Welded Ash Flow or Welded Tuff – Most violent type of activity (e.g., Mount Vesuvius 79 AD, Mt. Pelee 1902 and Mount St. Helens 1980) – A nueé ardente: (glowing avalanche cloud at night) – Fiery pyroclastic flow made of hot gases infused with ash and other debris – Move down the slopes of a volcano at speeds up to 200 km per hour – Unlike other ash falls, this one fuses as it collapses – May also produce a lahar, which is a volcanic mudflow Copyright (c) 2005 Pearson Education Canada Inc. 4-6 Volcanic Structures and Eruptive Styles A nueé ardente on Mt. St. Helens 1980 & Pinatubo 1991 Copyright (c) 2005 Pearson Education Canada Inc. 4-7 Calderas • Steep-walled collapse depressions at the summit (Crater Lake is an example) • Size exceeds 1 km in diameter • Hawaiian-Type Calderas • Yellowstone-Type Calderas Kilauea Caldera Copyright (c) 2005 Pearson Education Canada Inc. 4-8 Mt. Mazama – Crater Lake Caldera Sequence events formed Copyrightof (c) 2005 Pearsonthat Education Canada Inc.the caldera at Crater Lake, Oregon 4-9 Fissure Eruptions and Lava Plateaus • Fluid basaltic lava extruded from crustal fractures called fissures • CRB: Columbia River Plateau; ~12.5 Ma flood basalts also occur in the Chilcotin, S-central BC • Several Massive Extinction Events – Bio-Geological Period Boundaries coincide with Flood Basalts – Deccan Traps, Siberian Traps, Karoo SA, Parana CRB Chilcotin Roza Member Frenchman Springs Chasm Provincial Park Copyright (c) 2005 Pearson Education Canada Inc. 4-10 Other Volcanic Landforms Lava Domes • Bulbous mass of slowly extruded, congealed lava • Most are associated with late stages of an explosive eruption of gas-rich magma • These are slow but dangerous and can spawn block & ash flows Volcanic pipes and necks • Pipes are short conduits that connect a magma chamber to the surface • Often they remain as buttes after the pyroclastics & cone erode away Copyright (c) 2005 Pearson Education Canada Inc. 4-11 Other Volcanic Landforms: Lava Domes A lava dome forms on Mt. St. Helens following the eruption. Copyright (c) 2005 Pearson Education Canada Inc. 4-12 Other Volcanic Landforms Volcanic pipes and necks continued • Volcanic necks (e.g., Shiprock, New Mexico) are resistant vents left standing after erosion has removed the volcanic cone since ~27 Ma • Tow Hill, Graham Island is a ~5 Ma volcanic neck Copyright (c) 2005 Pearson Education Canada Inc. 4-13 Intrusive Igneous Activity Nature of Intrusions • Orientation with respect to the host (surrounding) rock – Discordant – cuts across sedimentary rock units, or other existing structures – Concordant – parallel to sedimentary rock units Copyright (c) 2005 Pearson Education Canada Inc. 4-14 Intrusive Igneous Activity Most magma is emplaced at depth in the Earth • An underground igneous body, once cooled and solidified, is called a pluton • There is lots more inside than surface to the crust! Nature of Intrusions • Shape – Tabular (sheetlike: ~horizontal, sill, laccolith) both concordant to strata – Tabular (sheetlike: ~vertical to inclined, dyke) cross cutting as planes, cones, rings – Massive (irregular mass: pluton) cross cutting – Cylindrical: Plugs, Pipes, Buttes when eroded Copyright (c) 2005 Pearson Education Canada Inc. 4-15 Shallow Intrusive Igneous Activity Laccolith concordant Caldera Dyke cross cutting Butte Stock < 1 km3 1<Pluton<10 10<Batholith<100 Some intrusive igneous structures. Copyright (c) 2005 Pearson Education Canada Inc. 4-16 Intrusive Igneous Activity Nature of Intrusions • Dyke – a tabular, discordant pluton – Forms in brittle rocks or from fast intrusion ~km/sec • Sill – a tabular, concordant pluton (e.g., Palisades Sill in New York/Jersey ~205 Ma opening of Atlantic, rifting of Pangea) – Forms in ductile rocks, pliable sediments, easier to inflate than to intrude higher, buoyancy or gas lost • Laccolith – Shonkin Sag, Montana – Similar to a sill but domed convex up – Lens or mushroom-shaped mass – Arches overlying strata upward Copyright (c) 2005 Pearson Education Canada Inc. 4-17 Intrusive Igneous Activity A dark-coloured sill made of gabbro in the NWT 4-18 . Copyright (c) 2005 Pearson Education Canada Inc. Intrusive Igneous Activity Nature of Intrusions • Batholith – Largest intrusive body – Surface exposure of 100+ square kilometres (smaller bodies are termed stocks or plugs) – Frequently form the cores of collisional mountains Exfoliation Sheet Joints Tensional cooling structures In coarse grained granites Little Rock Texas Copyright (c) 2005 Pearson Education Canada Inc. 4-19 Intrusive Igneous Activity Mesozoic Granitic batholiths that occur along the western margin of N. America Copyright (c) 2005 Pearson Education Canada Inc. 4-20 Intrusive Igneous Activity Emplacement of Batholiths • Magma at depth is much less dense than the surrounding rock – Increased temperature and pressure causes solid rock to deform plastically – The more buoyant magma pushes aside the host rock and forcibly rises in the Earth as it deforms the “plastic” host rock Copyright (c) 2005 Pearson Education Canada Inc. 4-21 Intrusive Igneous Activity Emplacement of Batholiths • At shallower depths, the host rock is cooler and exhibits brittle deformation – Movement of magma here is accomplished by fractures in the host rock and stoping – Inclusions in the host rock or xenoliths are evidence supporting the movement of magma through solid rock – We saw some of these as deformed mafic clasts or enclaves in the lighter coloured granitic rocks of the Devonian Tyee Stock at Finlayson Point Copyright (c) 2005 Pearson Education Canada Inc. 4-22 Plate Tectonics and Igneous Activity Global distribution of igneous activity is not random • Most volcanoes are located within or near ocean basins • Basaltic rocks are common in both oceanic and continental settings, whereas granitic rocks are rarely found in the oceans Copyright (c) 2005 Pearson Education Canada Inc. 4-23 Plate Tectonics and Igneous Activity Location of some of Earth’s major volcanoes.4-24 Copyright (c) 2005 Pearson Education Canada Inc. Plate Tectonics and Igneous Activity Igneous Activity at Convergent Plate Boundaries • Subduction zones – – – – Occur in conjunction with deep oceanic trenches Descending plate partially melts Magma slowly moves upward Rising magma can form either – A volcanic island arc (island arc) if in the ocean – A continental volcanic arc if subducted under continental lithosphere Copyright (c) 2005 Pearson Education Canada Inc. 4-25 Plate Tectonics and Igneous Activity • Subduction zones – Associated with the Pacific Ocean Basin – Region around the margin is known as the “Ring of Fire” – Most of the world’s explosive volcanoes are found here – Stratocones & Calderas both occur in this setting Copyright (c) 2005 Pearson Education Canada Inc. 4-26 Plate Tectonics and Igneous Activity Igneous Activity at Divergent Plate Boundaries • Spreading centres – The greatest volume of volcanic rock is produced along the oceanic ridge system – Mechanism of spreading – Thermal bulge on top of Mantle from upwards convection – Lithosphere pulls apart and slides downhill to both sides – Less pressure on underlying rocks, mantle upwells to fill in – Results in partial melting of mantle (decompression melting) – Large quantities of basaltic magma are produced – The process lasts 10’s to 100’s of Ma – Older ideas like “Ridge Push” clash with the extensional setting Copyright (c) 2005 Pearson Education Canada Inc. 4-27 Plate Tectonics and Igneous Activity Intraplate Igneous Activity • Activity within a tectonic plate • Associated with mass of hotter than normal mantle called mantle plumes • Form localized volcanic regions in the overriding plate called a hot spot – Produces basaltic magma sources in oceanic crust (e.g., Hawaii and Canary Islands) – Vast outpouring of mafic lava creating large basalt plateaus like Columbia Plateau and Deccan Plateau in India (latter may have affected climate in Upper Cretaceous) Copyright (c) 2005 Pearson Education Canada Inc. 4-28 Plate Tectonics and Igneous Activity Hotspot Decompression Hawaii, Iceland Island Arc, flux Japan, Aleutians Continental Arc, flux Andes, Coast Ranges Three zones of volcanism with central volcanoes4-29 Copyright (c) 2005 Pearson Education Canada Inc. Plate Tectonics and Igneous Activity Mid Atlantic Ridge Deccan Traps K/T Flood Basalts Plume Head East African Rift Three zones ofPearson extensional volcanism from decompression. Copyright (c) 2005 Education Canada Inc. 4-30 Plate Tectonics and Igneous Activity Large Igneous Provinces (LIPS) also form Oceanic Plateaux: Caribbean, Ontong Java, Kerguelen Model of a mantle plume and associated hot-spot volcanism . Copyright (c) 2005 Pearson Education Canada Inc. 4-31 Can Volcanoes Change Earth’s Climate? Explosive eruptions emit huge quantities of gases and fine-grained debris into the atmosphere which filter out and reflect a portion of the incoming solar radiation In Troposphere Months-Years, Stratosphere >> Examples of volcanism affecting climate • Did Deccan Traps 65 Ma end Cretaceous Hothouse • Mount Tambora & Indonesia – 1815 (caldera) • Krakatau, Indonesia – 1883 (caldera) • Mount Pinatubo, Philippines – 1991 (stratocone) Copyright (c) 2005 Pearson Education Canada Inc. 4-32 Can Volcanoes Change Earth’s Climate? Eruptions can emit great quantities of sulphur dioxide gases, which combine with water to form sulphuric acid particles called aerosols; they reflect solar radiation back to space. The answer is Yes. They are regarded as an explanation for some aspects of Earth’s climatic variability. When aerosols penetrate the stratosphere with its rapid jet stream the entire heat balance in the atmosphere can shift, changing the rest of atmospheric convection. Copyright (c) 2005 Pearson Education Canada Inc. 4-33 End of Part 2 of Chapter 4 Volcanism Copyright (c) 2005 Pearson Education Canada Inc. 4-34