Physical Geology (Geol-201) Lecture Notes - Volcanoes and Igneous Rocks PDF

Physical Geology (Geol-201) Lec# 5-6. Volcanoes – Igneous Rocks Prof. A. Abdel-Rahman Department of Geology American University of Beirut (Lebanon) Introduction Types of Rocks: I. Igneous Rocks: form by crystallization (cooling and solidification of magma or lava (molten rock ma...

Physical Geology (Geol-201) Lec# 5-6. Volcanoes – Igneous Rocks Prof. A. Abdel-Rahman Department of Geology American University of Beirut (Lebanon) Introduction Types of Rocks: I. Igneous Rocks: form by crystallization (cooling and solidification of magma or lava (molten rock materials as volcanoes) II. Sedimentary rocks: form by depositions of small rock materials or precipitation of minerals as salt (halite) or carbonates (calcite) III. Metamorphic rocks: form by changes (high P & T) that affect pre-existing sedimentary or igneous rocks. The Rock Cycle (formation of Igneous rocks)  Igneous Rocks Magma = Hot molten rock material  Some Recent Volcanoes Popocatépetl: Mexican volcano's spectacular eruption caught on camera Mexico's Popocatépetl volcano erupted on Thursday with a dramatic show of lava & a cloud of ash and rocks that reached 3km into the sky. No-one was hurt. Popocatépetl is an active stratovolcano, 70km SE-Mexico City (the capital). Its name means "smokey mountain" in the indigenous Náhuatl language. Caught on camera, a time-lapse of the eruption shows its power. Published 10-January-2020. https://www.bbc.com/news/av/world-latin-america-51063189 Mount Etna: Mesmerising pictures of latest eruption. In Sicily, Italy, it is Europe's most active volcano. Erupted again in the early hours of Thursday morning 18-Feb-2021. Mount Etna has had spurts of activity recently. Catania International Airport was temporarily closed after Tuesday's eruption. https://www.bbc.com/news/av/world-europe-56109761 Time-lapse shows Indonesia's Mount Sinabung erupting. An Indonesian volcano erupted on Tuesday 2-March-2021, sending clouds of ash up to 5km into the sky. Located in North Sumatra, Mount Sinabung first erupted in 2010 after being inactive for centuries, and has seen an increase in its activity over the last year. There are no reported injuries but locals have been advised to stay 3km away from the crater. Video Website: https://www.bbc.com/news/av/world-asia-56253470 A. General Concepts Igneous rocks form by the crystallization (cooling and solidification) of hot molten rock materials magma or lava (when it reaches the surface). Magmas are hot viscous silicate melts containing (O, Si, K, Na, Ca, Mg, Fe, Al, Ti, Mn, P), and rich in gaseous content (CO2, SO2, H2O). High content of gasses can cause explosive eruptions. B. Two major groups of igneous rocks: 1. Intrusive or plutonic rocks produced when magma injected at same depth in the earths crust into the rocks of the crust; it cools and solidifies slowly. 2. Extrusive or volcanic rocks, when magma travels all the way up to earth’s surface through fissures and conduits, cools and solidifies fast. Extrusive (Volc.) versus Intrusive (plutonic) Rocks Textures: Extrusive (Volc.), Intrusive (plutonic): Glassy, Fine-grained, Coarse-grained, Porphyritic & Vesicular Textures.  C. Magma Categories Felsic Intermediate Mafic Ultramafic Rich in Si Rich in Mg, (>70%), K Composition Fe, Ca (low Richer in Mg Composition +Na but poor between felsic in Si: 45 to and Fe but in Fe & Mg and mafic 52%) poorer in Si Color light Intermediate dark Very dark Density low Intermediate high Very high Viscosity high Intermediate low Very low Lava type Rhyolite Andesite Basalt Picrite Types of lavas: Rhyolitic lavas (rich in Si, K & Na) Felsic, light colored, viscous lavas that erupts at relatively lower temperatures (600-800˚C). Rhyolitic lavas move ~10x slower than basaltic lava. (more viscous than basaltic lavas) Types of lavas: Andesitic lavas Intermediate in composition and physical properties between felsic (rhyolitic) and mafic (basaltic) lavas. They erupt at 800 -1000º C Types of lavas: Basaltic lavas (rich in Mg, Fe & Ca) Mafic in composition, dark colored, high density, low viscosity, erupt at high T (900 to 1400ºC. Moves ~10x faster than rhyolitic lava. (less viscous than rhyolitic lavas.  D. Classification of Igneous Rocks Chemical Composition Textures Mineralogy SiO2 (wt. %) (Main Minerals) Plutonic Volcanic Peridotite Picrite Olivine, Pyroxene, < 45% Ultramafic Dunite Garnet 45 -- 52% Mafic (Mg+Fe Ca-plagioclase, olivine, Gabbro Basalt pyroxene rich) Ca-Na plagioclase, Diorite Andesite Hornblend 52 -- 66% Intermediate K-feldspar, alkali Syenite Trachyte Amphibole Quartz, K-feldspar, Na- > 66% Felsic (Si+K+Na Granodiorite Dacite plagioclase, Biotite ± rich) Granite Rhyolite Muscovite E. Textures of Igneous Rocks Texture refers to the shape and size of the mineral grains and the relationship between them. 1. Aphanitic texture: fine-grained textures in volcanic rocks. Minerals are difficult to identify. 2. Glassy texture: due to very rapid cooling of lava. They are typically amorphous. Obsidian is an example. 3. Vesicular texture: (like Swiss cheese); rock contains cavities caused by gas in a lava. Examples include: Scoria or highly vesicular basalt and Pumice (in more viscous lavas so more void space) 4. Porphyritic texture: occurs in rocks containing two generations of crystals; Phenocryst (large crystals formed during magma ascent) occurring within a groundmass of fine grained crystals that have crystallized at the surface. 5. Pyroclastic Texture: flattened pumice clasts, glass shards and rock fragments welded by ash or tuffaceous volcanic materials (found in pyroclastic rocks or ignimbrites). 6. Phaneritic texture: coarse-grained textures in plutonic rocks where crystals can be seen with the naked eye.  Some Textures in hand samples Dacite Porphyry Andesite Porphyry Aphanetic (fine-grained) Basalt Phaneritic (coarse-grained) Diorite Glassy Obsidian Vesicular Rhyolite (Pumice) Vesicular Basalt (Scoria)  Volcanic Breccia Glassy texture (in Obsidian) Reasons Obsidian is black despite being Si-rich felsic rock Reasons are that the amorphous nature of volcanic glass, the surrounding volcanic & atmospheric gasses during its fast cooling, some very small percentage of impurities (like reddish- brown Obsidian having dusty iron oxide impurities), & possibly other (yet to be known) reasons give Obsidian such apparent black or reddish-brown colors (although it is for sure a very Silica-rich rock. If you cut a very thin slice of it (by a rock saw), you will see it is transparent with a greyish tinge (or shade) and not deep-black color as that of Basaltic rocks. F. Types of Lava: Lava types vary according to the chemical composition, gas content and the temperature of lavas. Accordingly, several types of lava occur: 1. Basaltic Lava: These are mafic (Mg+Fe rich), dark colored, fluid (low silica) lavas that erupt at high temperatures (1000-1400˚C). Several types occur: a. Flood Basalts: highly fluid (low viscosity, high density) basaltic lava erupting on a flat terrain and spreading out in thin sheets as a flood of lava. The successive lava flows often pile up into huge basaltic plateaus. b. Aa (ah-ah) lava: these are jagged blocks of lava due to gas escape. As lava cools while moving slowly, a thin skin is formed which then slowly breaks into rough sharp blocks and angular boulders that ride on the massive viscous interior. c. Pahoehoe lava: ropy structures that form when the highly fluid (low viscosity) lavas spread into sheets and a thin glassy elastic skin harden on its surface which is then twisted into coiled folds or ropes. d. Pillow lavas: ellipsoidal masses (blocks) of lava that form during an underwater (submarine) volcanic eruption. Pyroclastic flows form via sub-areal eruptions 2. Rhyolitic Lava: These are typically felsic, light colored, viscous (Si+K+Na rich) lavas that erupts at relatively lower temperatures (800-1000˚C). Rhyolitic lavas (due to their Si-rich viscous nature) move ~10x slower than basaltic lava. 3. Andesltic Lava: These are intermediate in composition and physical properties between felsic and mafic lavas. Ropy (pahoehoe) basaltic lava flows low viscosity ropy lava Lava flow features (surfaces); Ropy (pahoehoe) & aa lavas. a Figure (a). Ropy surface of a pahoehoe flow, 1996 flows, Kalapana area, Hawaii. Low viscosity ropy lava High viscosity aa lava b Figure (b) Ropy surface of a pahoehoe flow, and aa flow surface meet in the 1974 flows from Mauna Ulu, Hawaii. b  Aa (ah-ah) lava Skin breaking into angular pieces above viscous interior Advancing aa lava flows during an eruption in Hawaii 3m The transition between aa & pahoehoe is controlled by two Factors: viscosity & strain rate Types of lavas Basaltic lavas: Pillow lava: are Ellipsoidal blocks of lava that form during an underwater volcanic eruption. Sub-marine eruption Spectacular Columnar joints G. Crystallization (of Igneous Rocks): It is the cooling, solidification or crystallization of hot magma or lava, in which unordered, randomly distributed ions begin to be arranged in an orderly pattern. When melt is consumed, it solidifies into interlocking crystals. Slow cooling gives large crystals, quenching gives fine-grains or glass. - Magma contains 10 abundant Elements (O, Si, Al, Fe, Mg, Ca, Na, K, Mn, Ti, H, P & gases such as vapor water, CO2 and S2). As magma cools, the most abundant O & Si join to form the (SiO4)4- tetrahedral. With progressive cooling, the tetrahedra polymerize to form more complex structures of various silicate minerals that crystallize at various T & P conditions. The Rate of cooling, composition of magma & volatile content all influence the crystallization process. With cooling of magma, Bowen (1945) noted that: 1. Certain minerals crystallize first (simple Si-structures) as Olivine, then at successively lower temperature others begin to crystallize as the composition of melt changes (at ~ 50% crystals Mg, Fe, Ca depleted, Si, Na, K enriched), 2. If a crystallizing mineral remains in the melt it reacts with melt to produce the next mineral in the sequence. 3. With decreasing T, more complex silicate mineral structures form. - Bowen’s Reaction series (discontinuous reaction series): Olivine (first to form), will react with the remaining melt to form pyroxene, the amphibole, biotite (discontinuous as each mineral has different crystal structure). - The other branch (continuous series; all framework silicates) shows the earliest formed Ca-Plagioclase that reacts with the Na-rich melt to give Na-plagioclase. - At late stage of crystallization K-feldspar (orthoclase), muscovite and quartz form. - Discontinuous Reaction series Continuous Reaction series High T (1,200-1000˚C) Rock Type High T (1,200-1000˚C) - Olivine Ultramafic Rocks - Pyroxene Mafic R. Ca-Plagioclase - Amphibole Intermed. R. Ca-Na-Plagioclase - Biotite Felsic R. Na-Plagioclase K-Feldspar Muscovite Quartz Low T (700-650˚C) Low T (700-650˚C) Bowen’s Reaction Series H. Diversity of Igneous Rocks Magmatic Differentiation is a process by which uniform parent magma may lead to rocks of a variety of compositions. 1. Fractional Crystallization: the separation of a cooling magma into components by the successive formation and removal of crystals at progressively lower temperatures (see Bowen’s Reaction Series). 2. Different degrees of partial melting of same mantle or crustal source rock or different source rocks will produce different magma compositions which eventually crystallize to give different rocks 3. Magma mixing: mixing of two or more magma results in a 3rd magma composition that is intermediate between the 2 magma types. 4. Assimilation of host (country) rocks results in the change of the chemical composition of the melt, which eventually gives different rocks. I. Origin and Types of Magmas Controlling factors on the melting of rocks include the water content & the confining pressure. More water lowers the melting point of any mineral, while increasing pressure lead to increasing melting points. Partial melting produces melt with high silica contents. 1. Basaltic magma Form by partial melting of Asthenosphere, Peridotite produces basalt magma that rises as it is lighter than surrounding. The 10-km thick Oceanic crust is made up of basaltic rocks. 2. Andesitic magma (Fractionation, partial melting of oceanic basaltic crust in a subduction zone; occur in Andes mountain). 3. Granitic (Rhyolitic) magma form by fractionation of mafic magma, by melting of continental crustal rocks, or by melting of sediments in subduction zones. Occur in continental crust. J. Intrusive Rock-Forms (Mode of occurrence) Emplacement of hot molten magma into intermediate or high levels of the Earth’s crust may be associated with partial melting of the surrounding “host or country rocks”, near contacts (wall rocks). This process is called assimilation, & the remnants of these partially melted host rocks are called xenoliths. The magma could be in the form of major or minor intrusions. These are of several types: 1. Batholith: Very large igneous masses (> 60 km2 width or diameter) bounded by steep walls) that cuts across host rocks and has no apparent floor as it extends to great depths. They formed by Mountain-building processes and are intermediate to felsic in composition. Examples include the Cordillera of North America (Sierra Nevada batholith, and the coastal batholith of Peru). 2. Pluton: A large igneous intrusive body similar to batholith, but smaller size (less than 60 km2 in area) that cuts across the host rocks. 3. Laccolith: Mushroom-shaped body of relatively small size (several km in diameter), with the roof was arched or lifted by pressure of incoming magma. 4. Phacolith: Similar intrusive body with both curved roof and floor. 5. Dikes: Dikes are wall-like vertical masses characterized by parallel sides. These vary in width from few centimeters to many meters and may extend for tens of kilometers. They could also occur in swarms (groups). They are discordant, and cut across surrounding rocks. These emplaced along fissures, cracks and fault planes during extensional or tension-induced tectonics. 6. Sills: Concordant horizontal sheets of igneous rocks that lie parallel to bedding planes of sedimentary (or igneous) host rocks, frequently showing columnar structures. 7. Lopolith: Funnel-shaped, large igneous rock body. 8. Layered Intrusions: Large sheets of igneous rocks, much thicker than sills. All intrusions are exposed due to uplift and the erosion of the cover. Uplift & weathering lead to the exposure of the intrusive igneous rock bodies on the surface of the Earth. Laccolith Sill Lopolith Pluton Dikes Batholith  Mode of occurrence – Intrusive Igneous rock bodies or structures Laccolith Dike Lopolith Sill Dike Pluton  Mode of emplacement of intrusive rock bodies Figure 4-20. Schematic block diagram of some intrusive bodies. Pluton Sill Pluton Dike Batholith  Pyroclasts and gases +Gases will escape to the atmosphere → Pipe Central vent eruption→ volcanoes Side vent...accumulating on Lava flows the surface to form a volcano. Lavas erupt through a central vent and side vents,... Temperature Pressure...rises in a pipelike Magma channel through the chamber lithosphere to form a crustal magma chamber. Lithosphere Magma, originates in the asthenosphere...  a. Laccolith b. Lopolith Figure 4-26. Shapes of two concordant plutons. a. Laccolith with flat floor & arched roof. b. Lopolith intruded into a structural basin. The scale is not the same for these two plutons, a lopolith is generally much larger.  Types of volcanoes Shield volcanoes Cinder-cone volcanoes Stratovolc. (or Composite) Volcanoes Calderas Diatremes (volcanic neck), Kimberlite lavas that usually contain Diamond Volcanic domes (cinder-cones) K. Major types of volcanoes 1. Shield volcanoes: Are made up of broad and gently sloping cones constructed of solidified lava flows. Lava flows spread widely & thinly (low viscosity) flowing from a central vent. The slopes are between 2° & 10° producing a volcano in the shape of flattened dome or shield. Eruptions are non-violent as lavas are fairly less viscous (basaltic lava) that sometimes erupt along fractures or fissures (Fissure eruptions). Great volume of lava erupt. Example: Island of Hawaii which is a series of shield volcanoes. 2. Cinder cone volcanoes (Tephra cones): Are volcanoes constructed of loose rock, fragments ejected from central vent and accumulated near the vent. Volcanoe flanks are symmetrical & have high slopes of 30° Pyroclastic flows or ejecta (fragments) due to explosive eruption include dust, ash, bombs (large lens-shaped fragments from molten blobs ejected into air become solidified forming pyroclastics), consisting of felsic (rhyolitic–dacitic) compositions & are characterized by high gas content. 3. Composite volcanoes or stratovolcanoes: Constructed of alternating layers of pyroclastics (tephra) and lava flows. Slopes are inclined by 10° & 30°. Pyroclastic layers build up steep slopes near the vent; lava flows partially flatten the cone. These volcanoes build up over a long time. Eruptions are intermittent (thousands of years in active alternating active years). Mostly intermediate compositions: andesites and dacites (Ex: Mount St.-Helens, Washington (1) Shield volcano Types of volcanoes Slope 2° to 10° Mafic compositions Basaltic mafic lava flows (2) Cinder cone volcano Pyroclastic felsic flows Slope 30° Felsic compositions (3) Stratovolcano Intermediate compositions Slope 10° to 30° Pyroclastic flows Lava flows & Lava flows Emil Muench/Photo Researchers Pyroclastic flows 10/10/2024 40 (1) Shield volcano Tend to be very large & broad as great volume of lava erupted. Tend to be less eruptive therefore pose less threat to human beings (2) Cinder Cone volcano They have a well-developed central vent & symmetrical flanks. The flanks have slopes of 30° (2) Cinder Cone Volc.: Cerro Negro Volcano of Nicaragua (South Amer.) is an example (3) Composite volcano or Stratovolcano Concave shape composite volcano Consists of layers (strata) of lava flows & pyroclastic debris They erupt viscous, gaseous lava, & pyroclasts which make these volcanoes very explosive & highly dangerous Eruptions are intermittent Alternating Lava flows & pyroclastic flows. Slopes are inclined by 10° & 30°. (3) Composite (or Strato-) volcano → Slopes are inclined by 10° to 30°. Common in subduction zones → Mostly intermediate compositions: andesites & dacites. e.g., Mount fuji (Japan), Vesuvius (Italy), Ex-strato volcano: Mount St-Helen (Washington ST.) (3) Stratovolcano → Mt St. Helens before May, 1980 eruption Emil Muench/Photo Researchers 10/10/2024 46 4. Caldera complexes: The evolution (3-stages) of Caldera formation: a). Emplacement of magma at shallow depth. The crystallization of intrusive rocks increases volatile (gas) contents in the remaining melt lead to pressure build up, that may rupture roof host rocks. Mount St.-Helen before 1980 eruption was caldera volcano b). Explosive eruptions of volcanic materials due to pressure of volcanic gasses that rupture cap or roof rocks forming pyroclastic material (such as glass shards, volcanic dust or ash, tuff, volc. bombs) forming pyroclastic flows. Some lava flows may also erupt in successive pulses (“ejecta”). c). Caldera collapse due to the weight of the volcanic pile, on empty magma chamber (negative space) left after magma eruption. Most of the (circular) lakes (e.g. Crater Lake, Oregon) occupy calderas that are later filled with rain and groundwater (typically of a diameter of 10 to 15 km).  4. Caldera complexes Caldera: structures & field relationships Figure 4-9. Development of the Crater Lake caldera. Crater Lake National Park & Vicinity, Oregon. (4) Caldera collapse forming a Crater lake  Two more types of volcanoes 5. Diatreme (volcanic neck): Example; Shiprock, New Mexico. Kimberlite lavas that may contain Diamond typically occur as pipes or diatremes. 6. Dome Volcanoes (cinder cones): These are characterized by viscous & thick slowly flowing lava, which oozes like toothpaste from a tube & piles up close to volcanic vent rather than spreading freely. They also tend to be relatively small in area & build-up peaks (height of hundreds of meters), as some cinder cones). Mount St.-Helen after 1980 eruption became dome volcano. (5) Diatreme (volcanic neck) Shiprock, New Mexico (6) Dome volcano (cinder cones) They are characterized by viscous & thick slowly flowing lava (like toothpaste from a tube) piles up close to the volcanic vent rather than spreading freely and are typically Felsic (Si-rich lavas). Tend to be relatively small in area and build up peaks up to several hundreds of meters of height. Domes plug the vent and trap gases beneath them → pressure can increase until explosion occurs→ Pyroclastic flows/ Ejecta. Mount St.-Helen after 1980 eruption became dome volcano. Examples of some volcanic Craters Figure 4-6. a. Maar: Hole-in-the- (a) Maar Ground, Oregon. b. Tuff ring: Diamond Head, Oahu, Hawaii. c. Scoria cone, a Surtsey, Iceland, 1996. b Tuff ring (b) (c) Scoria cone c c L. The Global Pattern of Volcanism Magma originates at depths where temperature is high enough and pressure is low enough so the rock can be totally or partially molten. The majority of magmas are generated in the upper mantle, at depths between 50 and 250 km. Typically, magmas are generated in three plate-tectonic settings: (1) Spreading zone volcanism (Divergence): Sea floor is broken up by rifts; pressure is released leading to partial melting of asthenospheric materials. Basaltic magma is generated, and erupts to form ocean-ridges as Mid-Atlantic ridge. (2) Subduction zone volcanism (Convergenc): (a) Volcanism at ocean-continent convergence: Source is a mixture of basaltic volcanism rising from mantle and remelted subducted ocean slab along with continental crustal materials. Large quantities of Andesitic lava in continental arcs are produced. Andes Mountains in South America is an example. (b) Volcanism at ocean-ocean convergence: Subducted plate melts leading to extrusion of basalt in island arcs. Example: Japan island arc, Phillipine Sea, Aleutian island arc & Mariana island arc that form part of the ring of fire. (3) Intraplate volcanism (Hotspot): Occur far from plate boundaries, caused by Hot Spots; jet or plumes of hot solids material rise from deep within the mantle (or core-mantle boundary), reaches low pressure of shallow depths, begins to melt, magma penetrates the lithosphere and erupts at the surface; example: Hawaiian Islands in middle of Pacific plate. Volcanism & Lithosphere: Plate tectonics & Global Pattern of Volcanism Hot Spots Convergence volcanism Divergence volcanism Hot Spot volc. Convergence volcanism  2 1 3 4 Global Pattern of Volcanism Hot Spots Divergence Mantle Plume: narrow jet of Convergence rising mantle (deep mantle) 57 Volcanism & Lithosphere: Plate tectonics, Pattern of Volcanism (1) Divergence - Spreading zone volcanism (Oceanic & Continental Rifting) (1) Divergence - Spreading zone volcanism Divergence: Oceanic Spreading (Rifting)  Decompression melting at Mid Oceanic ridge: Hot mantle rises, decompresses, and melts. Pillow lava Newer, thinner sediments Older, thicker sediments Sheeted dikes Oceanic in basalt crust Gabbro Moho Mantle Peridotite layer Spreading center  Iceland Volcano (20-March-2021) Iceland volcano: Lava-spewing Fagradalsfjall 'subsiding' (1) Divergence: Continental Rifting (Example: the East African Rift) (2) Subduction zone (Convergence) Volcanism (Oceanic-Oceanic & Oceanic-Continental) Subduction zone Volcanism (Oceanic - Oceanic) Convergence: Oceanic - Oceanic Oceanic-Oceanic Subduction: Mt.Pinatubo, Philippines Wikipedia Subduction zone Volcanism. Oceanic-Continental Subduction zone volcanism: Vesuvius & Etna (Italy) Oceanic-Continental) Note: best example of Oceanic-Continental is The Andes Mountain Geology.com Subduction zone volcanism: Mt. Etna (Sicily, Italy) (6) Dome volcano: Mount Saint Helen (Subduction) hudsonvalleygeologist (3) Hotspot (Intraplate Volcanism) Oceanic- & Continental Hotspot volcanism  (3) Hotspot (Intraplate) Volcanism Mantle Plume: narrow jet of rising mantle materials (rising from the deep mantle) and erupt within a tectonic plate & not along plate boundaries. Example Hawaii islands (hotspot volcanism in an oceanic environment), and Columbia River Flood basalt (in Oregon & Washington States, NW-USA) is an example of (hotspot volcanism in a continental environment). (3) Hotspot Volcanism: magmatic geosystems Hot-spot volcano Mantle plume (hot spot) Mantle Hot spots (3) Hotspot volcanism. Oceanic: Hawaii-Empror Chain Fig02-05 N Hotspot – Oceanic Environment Observations: 1. Chain of volcanic island extending northwest then N, 2. Intra plate feature (not at plate boundary) 3. The pacific plate is moving northwest over the Hawaiian hot spot (3) Hotspot (Oceanic) The Hawaii islands (3) Hotspot volcanism, Oceanic: Emperor–Hawaii Seamounts chain: B 2060 km A Distance from A to B= 2060 km Time elapsed between A and B= 64.7-42.4= 22.3 Ma V= d/t = (2060*106) /(22.3*106) =~ 92 mm/a Rate of the pacific plate is calculated to be about 10 cm/a  (3) Hotspot volcanism (Continental) Flood basalts: Columbia Plateau, Washington State These are vast outpouring of basalt from fissures (fissure eruptions; shield volcanoes): forming plateaus in continental areas or along the seafloor spreading ridges. The flows formed range from 5m to 3000m thick. An example is the Columbia River basalt Plateau (composed of successive basaltic layers),formed as a result of intense and continuous volcanic activity. These develop into shield volcanoes Map of flood basalts: Columbia Plateau, Washington & Oregon (3) Hotspot (Continental) Hotspot (Continental) Flood basalts: Columbia River Plateau, Washington (3) Hotspot (Continental) Shield volcano Types of volcanic hazards & effect on living beings 1. Rapidly moving pyroclastic flows (Nuées Ardentes) or lava flows→ fatalities/ burning of vegatation and fauna (animals). 2. Poisonous gases (CO, SO2…), have adverse effect from irritation to suffocation. E.g., Vesuvio, Etna (Italy) etc. 3. Lahars or Volcanic Mudflow: Heat leads to melting of snow. Rain and melt water from snow can loosen pyroclasts piled on steep slopes inducing deadly Mudflow. 4. Giant Sea Waves or Tsunamis: form after the occurrence of submarine volcanism, waves may reach 20m high. 5. Thick ash could cover agricultural land (kill crops) and livestock (kill animals, people could die from famine). Types of Volcanic Hazards: Generation & emission of gases Volcanism & Atmosphere Types of Volcanic Hazards: interaction with atmosphere, gases Gases are mostly responsible for the intense explosive eruptions occurring in volcanoes. The most abundant gases typically released into the atmosphere from volcanic systems are water vapor (H2O), carbon dioxide (CO2) and sulfur dioxide (SO2). Volcanoes also release smaller amounts of others gases, including: hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCl), hydrogen fluoride (HF), and helium (He). Gases travel with the prevailing wind direction e.g., Hawaiian Fog: when sulfur dioxide and other gases reacts with air moisture & oxygen → result in aerosols which reflect sunlight & are made visible→ fog-like masses Volcanic Hazards – (April (1993) Lascar volcano eruption, Chile. Lascar volcano eruptive products are typical medium-to-high potassium calk-alkaline, dominated by two pyroxene andesites and dacites, and more subordinated horblende andesites and dacites, and clinopyroxene-olivine basaltic andesites. Gardeweg et al (2011) suggest that magma mixing/mingling is a crucial process in Lascar volcano END