Zachary Murray Professor Webb Earth/Space Science Survey – 81121 Oct 4, 2020 EARTH & SPACE SCIENCE CHAPTER 7 – STUDY GUIDE TERMS Viscosity - easily flowing, gas is able to easily escape. The state of being thick and sticky, due to internal friction. Aa flows – type of balsamic lava flow that has a very rough, jagged, and extremely sharp surfaces. Pahoehoe flows – another type of balsamic lava flow that is very hot, and very free flowing. Its surfaces resemble wrinkly puppies and are very smooth. Can move at very slow rate. Lava tubes - are openings that are preserved as molten material flows. These allow for lava to flow great distances from its source. Pyroclastic material – are gases in magma that propel lava to great heights. Particles produced as gases expand and blow pulverized rock, lava, and glass fragments. Volcano – is a feature that is built of successive eruptions of lava or pyroclastic material or both from a central location. These events are separated by long periods of inactivity. Vent – The conduit ends at the surface opening. Crater – Located at the summit of most volcanoes is a funnel shaped depression. Caldera – A large volcanic crater formed by a major eruption. Parasitic cone – Cone shaped accumulation of volcanic material not part of the central vent of a volcano. Fumarole – The opening in or near a volcano, through which hot sulfurous gases emerge. Ring of Fire – Located around the Pacific Ocean. Consists of composite cones that erupt volatile-rich andesitic magma. Pyroclastic flow/Nuee ardente – Can often develop associated with the explosive eruption of composite cones; these consist of gas infused with hot ash & larger rock fragments that down the flanks of volcanoes; these are also referred to as a nuee ardente meaning glowing avalanche Lahar – Are volcanic mudflows that develop when volcanic debris (typically ash & dust) become saturated with water and rapidly move don slope; these usually follow stream valleys & gullies; they can form when large volumes of snow and ice melt during an eruption, or during heavy rainfall events (these develop when the volcano is not erupting) Fissure – Is the largest volume of volcanic material is extruded through fractures in the earth’s crust. Flood basalt – A low-viscosity basaltic lava which can cover a large geographic area. Happen when a fissure is on a continent. Volcanic neck – The rock of the volcanic pipe is typically more resistant to weathering than the surrounding pyroclastic material; this results in the pipe standing above the terrain long after the other material has been removed. Plutons – magma that is crystallized inside the Earth’s surface. Partial melting – is when the melting of igneous rock does not complete, when this occurs the liquid portion separates from the solid material and rises towards the earth’s surface due to density differences. Geothermal gradient – the change of temperature in the upper crust from 20 degrees Celsius to 30 degrees Celsius per kilometer. Decompression melting – Is when confining pressures drop enough. This can occur when a rock ascends due to convective upwelling moving the rock into zones of lower pressure. This melting generates magma along divergent boundaries and magma associated with hot spots. CONCEPTS 1.Describe the eruption of Mt. St. Helens in 1980 - This eruption was the largest human recorded volcanic eruption in North America. This blast blew out the entire north flank of the volcano, lowering the elevation of the volcano by more than 1350 feet. 59 lives were lost; trees were flattened within a 400km squared area; mudflows flowed 18 miles down the Toutle River; nearly 1 cubic kilometer of ash and debris were ejected. 2.Explain the factors that contribute to whether a volcano erupts quietly or violently - All magma contains a small percentage of water and other gases. These volatiles are held in solution by the pressure of the overlying material just as carbon dioxide is contained in a carbonated beverage. If volatile rich magma rises the reduction in pressure allows the dissolved gases to expand to form bubbles. 3.Discuss the characteristics of fluid basaltic magmas and viscous, silica-rich magmas - Very fluid basaltic magmas allow expanding gases to vent with relative ease. All these gases escape, they can produce lava fountains, these eruptions are generally quiescent. Highly-viscous, silica-rich magmas may produce explosives clouds of hot ash and transition into plumes termed eruption columns; when this magma ascends, the gas bubbles cannot escape easily and result in the magma expanding which adds more pressure to the volcano; this scenario can generate an explosive eruption in which magma is blown into tiny fragments to incredible heights; most explosive eruptions are followed by quiet extrusion of degassed lavas. 4.What are the concentrations of gases that are incorporated into magma? - The gases emitted are water vapor (70%), carbon dioxide (15%), Nitrogen (5%), and smaller amounts of chlorine, hydrogen, and Orgon. 5.Describe the classification of pyroclastic material - there are 4 classifications of pyroclastic material. Ash & dust which is produced when lava contains so many gas bubbles that it resembles a froth, producing very fine glassy fragments. Lapilli is another classification which are pyro clasts the size of small beads or a walnut (2-64mm). Blocks are particles larger than lapilli (larger than 64mm or 2.5in) made of hardened lava. Lastly there are bombs which are the same size as blocks (64mm or 2.5in) but they are made of incandescent lava. Some pyroclastic are classified by their texture and composition such as scoria and pumice. Scoria is vesicular ejecta with a basaltic composition (size range of lapilli). Pumice is vesicular rock with a andesitic or felsic composition. 6.Differentiate between shield volcanoes, cinder cones, and composite cones Including characteristics and examples of each - Shield volcanoes are generated from the accumulation of fluid basaltic lava; these exhibit a broad, slightly domed structure, most have grown from the ocean sea floor to form islands (contains very small amounts of pyroclastic material eruption is generally quiet). Cinder cones (also called scoria cones) are built from ejected lava fragments; pyroclastic material size ranges from fine ash to bombs(over a meter in diameter); most abundant type of the major volcanic types(smallest of the volcanic types); relatively steep sloped; possess large, deep craters relative to their small size; most are produced from a single short-lived eruption. Composite cones (also known as stratovolcanoes) most are located in a narrow zone that surround the Pacific Ocean; very large, symmetrical structure composed of lava & pyroclastic deposits; may generate explosive eruptions or erupt quietly; tend to have very complex development histories due to their explosive nature. 7.Explain the three ways in which calderas form. - crater lake caldera is when there is an explosive eruption of a volcano and then an inward collapse over time filling with water and snow. Shield volcano calderas release magma at different times, causing a smaller caldera with a different shape. Resurgent caldera is formed from there being many spots in an area where magma chambers are collapsing, these are the largest. 8.Describe the characteristics of dikes, sills, laccolites, batholiths, and stocks - Dikes are sheet-like (lobular) bodies produces when magma is injected into fractures that cut across rock layers (discordant). Sills are tabular plutons formed when magma is injected along sedimentary bedding surfaces (concordant). Laccolites form in the same manner as sills (concordant) however these result from more viscous magma. Batholiths are intrusive bodies (massive) with a surface exposure of more than 100 km (discordant). Stocks are smaller intrusive bodies; these may actually be batholith but have not been fully exposed. 9.How can sills be distinguished from buried lava flows? -Upper portions of lava flows usually contain voids produced by entrapped gas bubbles and only the rocks below show evidence of metamorphism. Fragments of the overlying rock wall rock occur in sills and metamorphic zones exist above below sills. 10.Describe the role of heat, pressure, and volatiles in the development of magma - The role of heat is responsible for Geothermal gradient and another source of energy to melt crystal rocks comes from rising basaltic magma. The role of pressure is melting (which is accompanied by an increase in volume) occur at higher temperatures at depth because greater confining pressure; when confining pressures drop enough decompression melting occurs. The role of volatiles is water content plays a major factor in determining the temperature at which a rock will melt; water is an important factor in magma generation along subduction zones. 11.What are the three general groups of volcanic activity throughout the Earth? - divergent plate boundaries, convergent plate boundaries, and intraplate activity. 12. Explain the formation of volcanoes along convergent plate boundaries, divergent Plate boundaries, and areas not associated with plate boundaries. - convergent plate boundaries formation of volcanoes or more wedge shaped. Diverging plates are mostly associated with decompression melting and associated with the midocean ridge. Intraplate activity is not associated with plate boundaries and are formed from “hot spots”.
