FINAL QUESTIONS1) What is a metamorphic rock? What agents are used in the formation ofmetamorphic rocks? What is confining pressure and differential stress A metamorphic rock is a rocked formed from the transition of one rock into another by temperatures and/or pressures unlike those in which it formed. The agents of metamorphism: Heat - the most important agent, recrystallization results in new stable minerals, two sources of heat: contact metamorphism - heat from magma, an increase in temperature with depth due to geothermal gradient Pressure (stress) - increases with depth, confining pressure applies forces equally in all directions which doesn't change the rock's shape, rocks may also be subjected to differential stress, which is unequal in different directions which does change its shape Chemically Active fluid - mainly water with volatile components, enhances migration of ions, aids in recrystallization of existing minerals, can cause significant change in chemical composition of the rock (metasomatism) Protolith (parent rock) - most metamorphic rocks have same overall chemical composition as the parent rock, mineral makeup determines the degree to which each metamorphic agent will cause change2) What are the different types of metamorphism? Be able to explain them. Whichtype produces the most metamorphic rocks? What is an aureole? Hydrothermal metamorphism - chemical alterations caused when hot, ion-rich fluids (hydrothermal solutions) circulate through fissures and cracks that develop in rock, most widespread along the axis of the mid-ocean ridge system Regional metamorphism - Occurs during mountain building, produces the greatest volume of metamorphic rock, rock usually display zones of contact and/or hydrothermal metamorphism Contact or thermal metamorphism - occurs due to a rise in temperature when magma invades a host rock, a zone of alteration called an aureole forms in the rock surrounding the magma, most easily recognized when it occurs at the surface or in a near-surface environment3) What is foliated and nonfoliated? What rocks did we discuss in lecture arefoliated and which are nonfoliated? What are the different textures? What aretheir orders by increasing grain size and metamorphic grade? Be able to identifyschist and gneiss. Foliation is any planar arrangement of mineral grains or structural features within a rock Foliated textures: Rock or slaty cleavage - closely spaced planar surfaces along which rocks split, where rocks can be easily split into thin tabular sheets (slate) Phyllite texture - a wavy foliation of fine grained platy minerals (muscovite and chlorite) that exhibit a somewhat metallic (silvery) luster, wrinkled form (phyllite) Schistosity - platy minerals are discernible with the unaided eye and exhibit a planar or layered structure, parallel alignment of platy and/or elongated minerals (schist) Gneissic texture - during higher grades of metamorphism, ion migration results in the segregation of minerals, gneissic rocks exhibit a distinctive banded appearence, compositional banding (gneiss) Other texture - porphyroblastic texture (large grains called porphyroblasts are surrounded by a fine-grained matrix of other minerals) Foliated rocks - slate (very fine grained, excellent rock cleavage, generated from low-grade metamorphism), phyllite (platy minerals not large enough to be identified with unaided eye, glossy sheen and wavy surfaces, exhibits rock cleavage), schist (medium to coarse grained, platy minerals predominate), Gneiss (medium to coarse grained, banded appearance, high-grade metamorphism) Nonfoiliated Textures - metamorphic rocks that lack foliation and have equal crystal size due to equal pressure on all sides (marble and quartzite)4) What are the parent rocks of marble and quartzite? What main mineral inmarble? Marble: coarse and crystalline, parent rock limestone or dolostone, composed essentially of calcite or dolomite crystals Quartzite: Formed from a parent rock of quartz-rich sandstone, quartz grains are fused together5) What is mass wasting? What is the difference between mass wasting anderosion? Mass wasting refers to the downslope movement of rock, regolith, and soil under the direct influence of gravity, a geologic process that often follows weathering, mass wasting and running water produce stream valleys Erosion refers to processes that move material to another site under the influence of transporting agents such as, water, ice, or wind whereas Mass Wasting refers to material that falls under influence of gravity with little or no transporting agent, processes range considerably in rate6) What are the different factors that attribute to mass wasting? What is the angleof repose? For mass wasting to occur there must be a slope angle, Most rapid events occur in areas of rugged geologically young mountains, As a landscape ages less dramatic downslope movements occur Gravity is the controlling force Important triggers include: Saturation of the material with water, diminishes particle cohesion, water adds weight Oversteepening of slopes - stable slope angle (angle of repose) is different for various materials, oversteepened slopes are unstable Removal of anchoring vegetation Ground vibrations from earthquakes - may cause expensive property damage, can cause liquefaction - water saturated surface material behave as fluid-like masses that flow Landslides without triggers - slope materials weaken overtime, random events that are unpredictable7) What are the different types of mass wasting? Be able to describe them. Whatare some indicators that certain mass wasting types occurred? Example is howdo you know that soil creeping is occurring? Each event classified by the material involved: debris, mud, earth, rock Also classified by type of motion: fall (free-falling pieces), slide (material moves along a surface as a coherent mass), flow (material moves as a chaotic mixture) Also by the velocity of the movement: fast, slow Slump - movement of a mass of rock or unconsolidated material as a unit along a curved surface, occurs along oversteepened slopes Rockslide - blocks of bedrock slide down a slope, generally very fast and destructive Debris flow (mudflow) - consists of soil and regolith with a large amount of water, often confined to channels, serious hazard in dry areas with heavy rains, debris flows composed of mostly volcanic materials on the flanks of volcanoes are called lahars Earthflow - form on hillsides in humid regions, water saturates the soil, commonly involve materials rich in clay and silt. Creep - gradual movement of soil and regolith downhill, aided by the alternate expansion and contraction of the surface material Solifluction - promoted by a dense clay hardpan or impermeable bedrock layer, common in regions underlain by permafrost (alternate freezing and thawing), can occur on gentle slopes8) What is a scarp? A scarp is a line of cliffs produced by faulting or erosion, especially from wave activity and erosion9) Which mass wasting process has the slowest rate of movement? The fastest? Rockslides are the fastest mass wasting process, Creep is the slowest10)What is an earthquake? What is the epicenter, focus, fault, and seismic waves? An Earthquake is the vibration of Earth produced by the rapid release of energy, energy released radiates in all directions from its source (the focus), energy is in the form of waves, sensitive instruments around the world record the event Focus - the place within the Earth where earthquake waves originate Epicenter - location on the surface directly above the focus Fault - movements that produce earthquakes are usually associated with large fractures in Earth's crust called faults, most of the motion along faults can be explained by the plate tectonics theory Seismic waves are the form that the energy that the earthquakes release takes11)What is elastic rebound theory? Who first proposed this? What earthquake wasthe studied to create this theory? Mechanism for earthquakes was first explained by H.F. Reid Rocks on both sides of an existing fault are deformed by tectonic forces, rocks bend and store elastic energy, frictional resistance holding the rocks together is overcome Slippage at the weakest point (the focus) occurs, vibrations (earthquakes) occur as the deformed rock "springs back" to its original shape (elastic rebound). Earthquakes most often occur along existing faults whenever the frictional forces on the fault surfaces are overcome. The 1906 San Francisco earthquake was studied to create this theory12)What is aftershocks? Foreshocks? Aftershocks are adjustments that follow a major earthquake that often generate smaller earthquakes Small earthquakes, called foreshocks, often precede a major earthquake by days or, in some cases, by as much as several years13)What is a seismograph? What is a seismogram? A seismograph is an instrument that records seismic waves, it records the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape More than one type of seismograph is needed to record both vertical and horizontal ground motion Records obtained from the seismograph are called seismograms14)What are the different types of seismic waves? Be able to compare and contrastthem? Which are the fastest? Which can travel through liquids? Which are theslowest? Which are the most destructive? What is liquefaction? Types of seismic waves: Surface waves - travel along outer part of Earth, complex motion, cause greatest destruction, waves exhibit greatest amplitude and slowest velocity, waves have the greatest periods (time intervals between crests), most destructive and the slowest Body waves - travel through Earth's interior, two types based on mode of travel: Primary (P) waves - push-pull (compress and expand) motion, changing the volume of the intervening material, travel through solids, liquids, and gases, P waves are the fastest waves Secondary (S) waves - shaking motion at right angles to their direction of travel, travel only through solids, slower velocity than P waves, slightly greater amplitude than P waves Liquefaction of the ground - unconsolidated materials saturated with water turn into a mobile fluid15)What factors do we study to determine the amount of destruction that earthquakecan cause? Amount of structural damage attributable to earthquake vibrations depends on intensity, duration of the vibrations, nature of the material upon which the structure rests, design of the structure Ground shaking - regions within 20 to 50 km of the epicenter will experience about the same intensity of ground shaking, destruction varies considerably mainly due to the nature of the ground on which the structures are built16)How does one determine the distance between a seismological recording stationand the earthquake source? How does one find the epicenter? Locating the epicenter of an earthquake: Three recording stations are needed to locate an epicenter, each station determines the time interval between the arrival of the first P wave and the first S wave at their location, a travel-time graph is used to determine each stations distance to the epicenter A circle with a radius equal to the distance to the epicenter is drawn around each station, the point where all three circles intersect is the earthquake epicenter17)What is the Richter Scale? Be able to describe how we find it. What is theMercalli Scale? How is different than the Richter Scale? Two measurements describe the size of the Earthquake: Intensity (a measure of the degree of earthquake shaking at a given locale based on the amount of damage), magnitude (estimates the amount of energy released at the source of the earthquake) Modified Mercalli Intensity Scale was developed using California buildings as its standard, the drawback of intensity scales is that destruction may not be a true measure of the earthquakes actual severity Richter magnitude - concept introduced by Charles Richter in 1935 Richter scale - based on the amplitude of the largest seismic wave recorded, accounts for the decrease in wave amplitude with increased distance Largest magnitude recorded on a Wood-Anderson seismograph was 8.9, magnitudes less than 2.0 not felt by humans, each unit of Richter magnitude increase corresponds to a tenfold increase in wave amplitude and a 32-fold energy increase18)What is Tsunami? Tsunamis, or seismic sea waves - destructive waves that are often inappropriately called "tidal waves", result from vertical displacement along a fault located on the ocean floor or a large undersea landslide triggered by an earthquake In the open ocean height is usually less than 1 meter, in shallower coastal waters the water piles up to heights that occasionally exceed 30 meters, can be very destructive19)What are the different layers of the earth? Physical and compositional? Three principal compositional layers: Crust - comparatively thin outer skin that ranges from 3 km at the oceanic ridges to 70 km Mantle - a solid rocky (silica-rich) shell that extends to a depth of about 2900 km Core - an iron-rich sphere having a radius of 3486 km, solid rock, very hot Layers defined by physical properties: Lithosphere (sphere of rock) - Earth's outermost layer, consists of the crust and uppermost mantle, relatively cool and rigid shell, averages about 100 km in thickness but may be 250 km or more thick beneath the older portions of the continents Aesthenosphere (weak sphere) - beneath the lithosphere in the upper mantle to a depth of about 600 km, small amount of melting in the upper portion mechanically detaches the lithosphere from the layer below allowing the lithosphere to move independently of the aesthenosphere Lower mantle - rigid layer between the depths of 660 km and 2900 km, rocks are very hot and capable of very gradual flow Outer Core - composed mostly of iron-nickel alloy, liquid layer, 2270 km thick, convective flow within generates Earth's magnetic field Inner Core - sphere with a radius of 3486 km, material is stronger than the outer core, behaves like a solid20)How do we determine what the different layers of the earth are? What do we useto study these layers? Which layer is thinnest? Largest? The rather abrupt change in seismic-wave velocities that occur at particular depths helped seismologists conclude that Earth must be composed of distinct shells. Layers are defined by composition and physical properties. Because of density sorting during an early period of partial melting, Earth's interior is not homogeneous With increasing depth, Earth's interior is characterized by gradual increases in temperature, pressure, and density The crust is the thinnest layer. The mantle is the largest layer of the earth.21)What is the lithosphere defined as? The asthenosphere? The lithosphere is the Earth's outermost layer consisting of the crust and uppermost mantle. It has a relatively cool, rigid shell. The aesthenosphere is beneath the lithosphere in the upper mantle to a depth of about 600 km. A small amount of melting in the upper portion mechanically detaches the lithosphere from the layer below allowing the lithosphere to move independently of the aesthenosphere. 22)What is the difference between the continental and oceanic crust? Continental crust is lighter with Granitic rocks Oceanic crust is denser and composed primarily of basalt23)What is groundwater? How much of the worlds water is freshwater? How muchis salt water? What are the three highest percentages of Earths freshwater? Groundwater is water found in the pores of soil and sediment, plus narrow fractures in bedrock. Groundwater is the largest reservoir of fresh water that is readily available to humans. Freshwater is 2.5% of the world's water Saltwater is 97.5% of the world's water The three highest percentages of Earth's freshwater are ice sheets and glaciers, groundwater, and lakes and reservoirs.24)What is the water table? What is the aerated zone? The saturated zone? Whatis the capillary fringe? What is porosity? The zone of saturation happens when water is not held as soil moisture percolates downward and then reaches a zone where all of the open spaces in sediment and rock are completely filled with water (water within pores is called groundwater) The water table is the upper limit of the zone of saturation. (Depth is highly variable, shape is usually a subdued replica of the geography; gaining streams and losing streams) The zone of aeration is the area above the water table, includes the capillary fringe and the belt of soil moisture, water cannot be pumped by wells. Capillary fringe extends upward from the water table, groundwater is held by surface tension in tiny passages between grains of soil or sediment Porosity is the percentage of total volume of rock or sediment that consists of pore spaces; it determines how much groundwater can be stored, variations can be considerable over short distances25)What can excessive groundwater withdrawal cause? In many places the water available to recharge an aquifer falls significantly short of the amount being withdrawn Subsidence - ground sinks when water is pumped from wells faster than natural recharge processes can replace it (San Joaquin Valley of California) Sinking a well can lead to groundwater pollution and contamination problems26)What is losing stream and gaining stream? Compare and contrast. Gaining streams gain water from the inflow of groundwater through the streambed Losing streams lose water to the groundwater system by outflow through the streambed Interactions - a combination of the above, a stream gains in some sections and loses in other areas