Geology Exam 2
Describe: anticline, syncline, dome, basin.
- Anticline are like mountains (go up) - 2D Oldest beds in center If eroded on top, oldest beds would be in the middle and would get newer as you move away from the center - Synclines are u-shape (go down) - 2D If eroded on top, youngest beds would be in the middle and would get older as you move away from the center - Domes and basins - 3D Basin = bowl Dome = egg carton Tend to be much larger than anticlines/synclines
Know the types of body and surface waves. How do they differ?
- Body Waves - 2 Types 1. Compressional Wave (P-Wave) Particle motion = compression and dilation Particle motion is parallel to the direction of propagation Slinky - pushing & pulling motion 2. Shear Wave (S-Wave) Particle motion = transverse Particle motion is perpendicular to the direction of propagation (mostly vertical) Rope - up and down motion - Surface Waves - 2 Types - can't determine across the world 1. Rayleigh Wave Particle motion = elliptical motions in the vertical plane/parallel to the direction of propagation Spinning motion Amplitude decreases w depth Less move the further down you get (energy tapers off down) 2. Love Wave Particle motion = alternating transverse motions Snakes Particle motion is horizontal and perpendicular to the direction of propagation Amplitude decreases w depth P and S waves as body waves that arrive first - move through entirety of earth's surface - recorded at every seismic station besides S wave which can't move through water and Earth's core Surface waves cause ground to shake in localized areas
Describe some factors that dictate if magma rises through the crust or stalls in magma chambers.
- Density contrasts - solid mantle is much more dense than liquid magma - different densities throughout crust - Pressure from surrounding rock - Gas pressure
What are the 3 types of strain? In what settings will these types occur?
- Elastic (rubber band) No permanent deformation Most surface rocks behave elastically up to a point (limited) Buildup of elastic energy produces earthquakes - Plastic (silly putty) Permanent deformation Most metamorphic rocks High pressure, high temp, long time If apply quick stress, will break (rate of applied forces matter) - Brittle (twig) Permanent deformation through breaking Low pressure, low temp, short time
What other factors affect slope stability and how so (i.e. do they stabilize or destabilize slopes, why)?
- Fluids Abundant fluids reduces cohesion between particles Saturated sediments=less coherent Partially saturated sediments (damp but not saturated)=more coherent - Vegetation Roots can stabilize slopes, hold unconsolidated soil/sediment together Roots extract moisture from soil (reduce probability of saturation) But also add to weight of slopes (negative effect) - Subsurface geology Bedrock is the most stable subsurface geology, then sedimentary, then loose sediments
How do geologists monitor volcanoes and ultimately predict eruptions?
- Gas Monitor concentration and types - changes can tell us if eruption is imminent By plane over vent or on ground in a remote place (collect light) - Deformation Looking at surface bulging and deforming to see if magma is rising to fill a reservoir - Remote sensing Satellites to monitor deformation over wide regions, can see ash (can't see it with radar) Take temp w thermal imaging (helicopters) - Camera Can see gas emissions and changes in surface, small eruptions - Ground Vibration Monitoring Seismometers to sense vibrations and lahars (on banks of rivers) - can warn communities downstream Have to have some sense of surety that there's an imminent threat - can have a false eruption prediction - need to balance
Three ways the mantle melts and tectonic locations of each
- Increase in temperature. This can happen if new material is added to the upper mantle from the depth, for example via a mantle plume. (transform) - Decompression melting. This occurs when a rock rises adiabatically (without heat loss) to lower pressures. (divergent) - Addition of fluids (convergent)
What are some ways of mitigating volcanic hazards?
- Mitigating Hazards - Warning Systems Lahar warning sirens, television and radio, broadcasts, emergency alert systems (signs) On river channels (at high risk for lahars) - Mitigating Hazards - Educate with Hazard Maps Show local geology - Mitigating Hazards - Alerts Advisory code: show what volcano is doing - for ex: exhibiting unrest due to change in gasses Aviation color code - put out for planes to see if air space is present around volcano (after Alaska event) - Mitigating Hazards - Plan & Practice Evacuation - Mitigating Hazards - Lahar Monitoring/Engineering Acoustic lahar flow monitors along river banks Japanese sabo ("sand protection") engineering to reduce risk from lahars Channelization of lahars by reinforcing natural or man-made pathways Impounding of lahar debris by dams and basins Removal of large boulders/trees by massive grates - Mitigating Hazards - Engineering for lava flows Earthen barriers can divert lava flows away from towns Lava will follow path of least resistance Works if lava is diverted down hill
3 ways of heat transfer
- Radiation Process of radioactive decay is still adding more heat to the Earth Losing heat to space - Conduction Rocks are poor conductors Transfer of heat by contact - Convection Mantle and outer core Temperature and density contrast (heat rises because lowers in density)
How do magmas evolve/differentiate/change composition? Be able to explain crystallization, magma mixing, and assimilation.
- Transition from liquid to solid (crystals) As magma cools, crystals nucleate - elements diffuse from other parts of magma to new locations Then pull in nearby atoms Process continues, crystal grows Crystals grow outward (like tree rings) Slower cooling means bigger crystals Evolution of magmas - differentiation Processes responsible for changing magma composition: - Magma crystallization - Magma mixing - Assimilation Magma Crystallization As magmas cool they form crystals These crystals settle out via gravity (denser than liquid magma) and the residual liquid has a different composition (less iron and magnesium) Aka fractional crystallization Magma Mixing Magmas from different sources may have different compositions These originally distinct magmas mix to create new magma (but sometimes incomplete mixing) Crystal Assimilation As magma rises through crust, can partially melt very small amounts of that crust Chunks of the wall rock may break off and fall into intruding magma - how we get xenoliths
Summarize in your own words for one another the factors that determine whether a slope is stable or unstable What two variables are the most important in classifying mass movements? Are landslides more or less frequent than you'd think in SoCal? Why?
-Angle or origin, fluids, vegetation, subsurface geology -Speed and type of material moved -More frequent than you'd think; wildfires burn of all the vegetation on the slopes, which destabilizes the slope
What are some reasons humans tend to live near volcanoes
-Fertile soil -Scenery -Recreation -Water resource -Fools!
Name and describe the various types of volcanic hazards. Know which are from effusive eruptions, which are from explosive eruptions, and which can occur without an eruption. Also know which present the greatest risk to human populations and ecosystems.
-Most significant hazards are lahars and PCDs (Pyroclastic Density Currents) - most occur with eruptions, but can occur w effusive styles or w/o eruptions - Lava flows: Effusive Hazards Basalt flows can travel fast More felsic compositions are much slower About 1 mph doesn't go far from source vent (higher silica = higher viscosity; pile up instead of spreading out) - rarely deaths directly by lava flows Lava flows can cause serious property damage Everything in path destroyed; can't rebuild in same spot; secondary effects (gas); changes in topography/ecology - Flood Basalts - Unique Effusive Hazards Fed by dikes/fissures eruptions Usually starts w hotspot Flow over wide areas Bring up gasses - changes climate - correlated with mass extinctions - Explosive Hazards - Localized Airfall Fire fountains can injure/kill people near the vent Fissures can catch people off guard, or ignore evacuations Volcanic bombs can be serious threat - not anticipated and can kill Gas builds up and causes it to explode - very localized - Explosive Hazards - Pyroclastic Flows Responsible for most volcanic deaths in 20th century Ground hugging, fast moving cloud containing hot gas, fine ash, pumice, and rock fragments - very hot Flows can reach very far from volcano Preceded by hurricane force winds with noxious gasses Kill by direct impact, burns, asphyxiation, inhalation of hot ash Bomb followed by collapse of material - Volcanic Ash Explosive/Effusive Hazards: Global Cooling Hazards that can occur without eruptions Debris avalanches/sector collapses (mass wasting) Needs turbulent air Tsunamis Moves large amount of water Earthquakes Ground fracturing as magma moves up through surface Lahars Crater lake eruption or failure - Volcanic gas emissions Volcanic gasses in order of abundance: H20, CO2, SO2, CO1, H2S, HCI, HF SO2 released into stratosphere causes global cooling (blocks sunlight) CO2 does the opposite, causes global warming (traps heat at surface) "Vog" (volcanic fog) = skin irritation, respiratory problems CO2 is usually very abundant
Understand how various volcanic landforms develop, including shield volcanoes, stratovolcanoes, lava domes, cinder cones, calderas (again picture the demo for this last). a. What controls these shapes/how do they form? b. Where does each tend to form (in what tectonic environments or locations)?
-Pahoehoe lava: ropey lava (video from Hawaii ex) Forms in less viscous rocks Forms ropey texture as top cools and bunches while warm lava underneath flows out -A'a lava: slightly cooler and more viscous Also effusive and occurs in basalt, but the lavas it occurs in are a bit more viscous Thickens and piles up more bc the stuff in it is more viscous Forms separate bits called "clinkers" and it's these jagged pieces of material Remember video: clinkers fall Much slower due to increased viscosity! More sporadic instead of steady flow -Effusive basalts=shield volcanoes Shield Volcanoes form when eruptions are dominated by low viscosity lava flows -Largest volcano in the solar system Shield volcanoes are the only volcanoes we see elsewhere in the solar system! Olympus Mons is a shield volcano on Mars 81,100 feet (more than 3X the size of Mt. Everest) -Fire fountains: driven by gas expansion in low viscosity basalt magma Create lava flows -Cinder cones: steep sided and relatively small accumulations of tephra (pyroclasts) from fire fountain style eruptions Explosive Felsic Magmas=Stratovolcano -Steep sided volcano formed from alternating layers of pyroclastic fall/flow and viscous lava flow or domes Aka "composite" -Form from andesite and rhyolite magma -Very common in subduction zones Makes sense when considering process of melting to to addition of water Effusive Felsic Magmas=Lava Domes -Steep-sided dome or spine shaped feature -High viscosity lava, low in volatile content -Usually caused by a single eruption (could last for years) -Erupts effusively and very slowly, but the dome can collapse Calderas: Crater Lake, OR and Lake Toba, Sumatra -When a large volume of magma erupts, the ground can collapse to form a caldera -Calderas often mark very large eruption of felsic magma
What are the 7 principles of stratigraphy (rules for determining relative ages)? Be able to describe each, and use them to determine relative ages of co-existing rocks and features within.
1. Original horizontality: sediments are 1st laid down horizontally - can be folded by tectonics or pushed vertically onto their side out of og position 2. Superposition: younger sediments overlie older sediments 3. Cross-cutting relationships: a feature that cuts across another must be the younger of the 2 Dike: vertical and planar magma intrusion - magma is injected into deposit Sill: horizontal and planar magma intrusion Fracture forms that cuts across dike - fracture will now be the youngest If fault forms in same orientation as dike, won't know age at all because they don't cut across each other (just would know it is younger than the beds) 4. Inclusions: if any igneous rock contains fragments of other rock, fragments are older 5. Lateral continuity: sediments are laid down in sheets, so if horizontal layer is observed on opposite sides of canyon, can assume they were once a continuous bed 6. Unconformities: gaps in the geologic record Evidence of uplift and erosion Unconformities exist where geologic record is incomplete Sometimes represented in figures as irregular line 7. Fossil succession: bio stratigraphy Uses fossils of extinct creatures to determine sequence of time Can compare beds that are not located in same place
How do we determine whether a tsunami was generated before it comes ashore?
Amplitude increases - DART buoys (detect tsunamis in deep ocean water)
Know the difference between effusive and explosive eruptions.
An eruption dominated by the outpouring of lava onto the ground is often referred to as an effusive eruption (as opposed to the violent fragmentation of magma by explosive eruptions) Effusive: gentle flows (think Hawaii) Explosive: bellows out (think mt st helens) Gasses are important in determining eruption type! - dictated by viscosity and gas content
Know the 3 main types of unconformities, and the difference between them
Angular: deformed sedimentary rocks under horizontal sedimentary rocks - bottom layers aren't in original position but top layers are Disconformity: missing time (sedimentary bed or beds) in horizontal sedimentary sequence Nonconformity: igneous or metamorphic rocks under horizontal seds
Describe: anticline, syncline, dome, basin.
Anticline: mountain thing (oldest in middle) - dome Syncline: u-shape (oldest on the sides) - basin
What processes create tsunamis?
Anything that moves a large amount of water very rapidly Can be earthquakes, landslides, meteor impacts, volcanic eruptions near the coast
Describe the relative size of EQs that can occur in each tectonic setting.
Area of breakage is limited to brittle crust - the more crust that breaks, the more energy released Lithosphere = crust and upper mantle Oceanic lithosphere very thin - not very big earthquakes at mid-ocean ridges Divergent: small thickness (smallest earthquakes) Transform: medium thickness lithosphere (moderate earthquakes) Convergent: subducted lithosphere (huge earthquakes) The strongest not because deepest but because area that ruptures is large Rocks are poor conductors - not heating up fast enough to become ductile
What is an isotope? parent/daughter
Atoms of the same element that have different numbers of neutrons. Unstable isotope = parent Stable isotope (product) = daughter May take multiple episodes of decay to become stable
Be familiar with the case examples of notorious earthquakes we discussed in class. I do not expect rote memorization of the EQ locations and dates that I discussed in class. Instead, I might give you the name and date of and EQ and ask a question about a unique aspect of it. For example, the 1811-12 New Madrid EQs illustrate how a failed rift in the mid-continent can cause some particularly troublesome intra-plate earthquakes. The 1986 Loma Prieta EQ demonstrated that dumping EQ debris (from the 1906 San Francisco EQ) into water poses a liquefaction hazard. Be able to relate these different case studies to important concepts from the lesson, for further example, why the intensity might be different in entirely different regions that experience similar magnitude earthquakes.
Cascadia Subduction Zone - 1700 Oral histories of Indigenous populations New Madrid, MO Felt across entire eastern region of the country (rock is way different from San Fran's - different geology that allows propagation) - fault system from breakup of Pangaea (failed rift) - San Fran liquefaction - built on landfill
What is a tsunami?
Comes from Japanese words "tsu" (harbor) and "nami" (waves) A series of waves created by the rapid displacement of water Not a tidal wave - Tidal wave is due to normal course of high and low tides Tsunamis have nothing to do with tides! The two can look similar tho
What are the 3 types of stress? In which plate tectonic environment can you find each type?
Compression (convergent) Tension (divergent) Shear (transform) Shallow levels (crust): rocks fracture - fault - one block will move up to make area smaller Tension will form regular fracture until magma rises to surface Then slide past each other Deeper levels: rocks flow (very ductile) - will squish Will stretch out and elongate to oval shape Bend things being sheared (deforming but not breaking)
How can we mitigate tsunami hazards? How can we prepare?
Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys Detect tsunamis in deep ocean water Allow warning for distantly generated tsunamis (no warning for local tsunamis) Expanded DART program in Pacific and Atlantic oceans -Other mitigation techniques Inundation mapping Don't build on waterfront! Tsunami Barriers Education of local communities on hazard, evacuation, emergency planning
What is intensity? How is it measured? Is intensity the same at all locations? Why or why not?
Describes amount of ground shaking, damage in a particular area Depends on where the observation was made (distance, subsurface geology) Measure on a scale of I to XI (1 to 12) Each earthquake has many intensities
Be able to describe the difference between dip slip and strike slip faults, and their subtypes (dip slip - normal, reverse/thrust; strike slip - left and right lateral).
Dip slip (fault plane is dipping at various angles) Reverse: hanging wall moves up - compression stresses Thrust: just a low angle for reverse fault Normal: hanging wall moves down (blocks of rock taking up more space) - extensional forces Strike slip Left-lateral and Moving to left from where you're standing Right-lateral Moving to right from where you're standing Two kinds name by sense of motion Our evidence for recognizing faults Fault scarp: if movement was recent enough, top part would still be sticking out above or below the fault plane (whatever part that projects beyond flat surface) Offset sedimentary layers Slickenlines: if you have a fault scarp, you will see grooves in surface Fault breccia: ground up, angular rocks within the field (in between 2 planes)
Know the processes/factors that can change shear stress and can trigger mass wasting (connect these to the controls on slope stability).
Earthquakes Anything that reduces gravitational forces or increases shear stress can trigger movement Addition of water Increases pore pressure between grains, reduces cohesion Acts a lubricant between grains Adds weight Can cause granular material to flow Slope structure Subsurface geology Bedding planes Each layer is in individual bed and if contact between them is weak landslides are more likely Weak or fractured Changes in slope structure Undercutting (coastal cliffs) Road cut (increase shear forces) Removal of vegetation If plants are removed, reduces cohesion, less means to hold soil together - don't have deep roots Deforestation contributes to landsliding
What are some ways that we can mitigate landslide hazards?
Fencing Tunnels - strong rock (landslides will occur over top of the tunnels) Retaining walls - concrete blocks built into hillside - keep houses/road from tumbling Drainage ditches - water gets funneled in and goes away instead of infiltrating hillside
Define focus/hypocenter, epicenter, fault, and be able to locate them on a diagram.
Focus or hypocenter: the place within the earth where the earthquake initiates Epicenter: the point on the Earth's surface directly above the focus (map view of focus) Fault: fracture along which slip occurs
Know the main types of mass wasting - type of material involved, type of movement, relative speeds, and differences between the types.
From fastest to slowest: Rock fall §Avalanche §Landslide (or debris slide) §Debris flow (aka mudflow, lahar) §Slump §Creep -Rock falls "Fall" is the movement style, "rock" is the material moving" Free-fall from vertical cliff Forms talus pile at base Often results from freeze and thaw weathering Can also have different style of movement of same material Rock avalanche, rock flow Yosemite Happy Isles Rockfall, 1996 80,000 tons of rock fell >1700 ft in freefall Impacted at 250 mph Air blast leveled 10 acres of trees -Avalanches Style of movement where solid material is mixed with turbulent air Can be different material/compositions Snow avalanche Ice avalanche Debris avalanche Rock avalanche Can move very fast (up to 200 mph) -Landslides Coherent rock moves on plane of weakness (failure surface, slide plane) May occur at a boundary between rock types or within weak rock Move up to 180 mph Example: earthquake lake, near Yellowstone Can be composed of various materials Rock slide (composed of rock) Debris slide (composed of rock ,soil, ground cover) Think of landslide Italy video; moves as coherent mass -Debris flows Flows are a style of movement that is facilitated by the addition of water Debris flows specifically are a wet slurry of soil, volcanic ash, rocks, ground cover, other stuff Lots of rain OR at volcanoes/volcanic eruption Also called mudflows, lahars (the latter specifically at volcanoes) Lahars largely create it through glacial ice at volcanoes; triggered by rain -Slump/rotational slides Style: a coherent mass that moves in a "rotational" fashion (see yellow arrows below) Moves slowly (minutes to days) -Creep Slowest form of mass movement; a few cm per year Freeze-thaw cycles cause motion of surface layers Too slow to watch but effects are visible at surface (curved tree-trunks, tilted fences, destroyed retaining walls)
Describe each of the hazards associated with earthquakes, emphasizing how/why each process occurs.
Ground shaking Falling buildings/structure failure Landslides (later) - in areas of steep topography w erosion and loose soil Fires Liquefaction (unconsolidated, wet sediments) Tsunamis (later) - giant waves under ocean Earthquake Effects - Ground Shaking Damage depends on: Proximity to hypocenter Magnitude of the EQ Local geology Building quality Earthquake Effects - Structural Failure Collapse of freeways, building columns Infrastructure needs to be built w certain reinforcements - building codes Mitigation for structure failures: Uniform Building Code (UBC) Small quakes - no damage Moderate quakes - repairable damage Large quakes - should protect lives/not collapse (may need to be demolished) Earthquake Effects - Fires Things that trigger them: power lines Why they are hard to put out: water lines are also broken Secondary hazard associated with breaking of electrical wires, power lines, gas and water lines Liquefaction Some types of rock withstand shaking better than others Unconsolidated materials (sand/silt/clay) saturated w water will flow when shaken Behaves as fluid Can't support structures Loose sediments with water get compacted > loose layer of water below building > building sinks Lessons from San Fran disaster Know local geology Don't build on landfill in EQ territory Earthquakes don't kill people, it's the secondary hazards (structural failure - buildings falling, etc)
What are the 2 main parts of a fault? Be able to label them.
Hanging wall (on top) Footwall (underneath) These terms came from mining (hanging lanterns and where they stand)
What should you do in the event of a tsunami warning?
If you are at the beach or near the ocean, and you: • Feel the earth shake for 15 seconds or longer, or • See the water retreating, or • Hear a loud roar from the ocean MOVE immediately to higher ground - DO NOT WAIT for a tsunami warning § Do not return until "all clear" is issued by competent authorities (it could be up to 12 hours) § The upper floors of high multi-story concrete hotels in low-lying coastal areas can provide a safe place during tsunami, if you cannot move quickly to higher ground. § If you are at sea, and tsunami warning has been issued for your area, do not return to port.
Why was the 2004 Indian Ocean tsunami so deadly? What about the 2011 Tohoku EQ in Japan?
Japan Big, subduction zone earthquake w lots of shaking Intense infrastructural damage Tsunami impacts infrastructure Tsunami walls were lower than the overriding tsunami Nuclear reactors melted down Indian Ocean 9.0 magnitude earthquake displaced huge amount of water - pressure built up within tectonic plates for a long time 11 countries no tsunami warning systems - no communication
What is the difference between joints and faults? What stresses can form joints?
Joint: crack where rock pulled apart Fault: rocks have slipped past each other Stresses that can form joints: burial and tectonic forces (being extended or compressed), cooling and contraction, unloading
Why are lahars typically the most deadly and damaging type of volcanic hazard?
Large lahars can crush, abrade, bury, or carry away almost anything in their paths. - like rivers of concrete
Why do we measure seismic waves at 3 stations (triangulate) to determine earthquake location?
Locating earthquake source/Epicenter using triangulation between 3 seismic stations, epicenter is where all 3 circles can intersect
Understand how different compositions (mafic/basalt and felsic/rhyolite) erupt either effusively or explosively; refer to the table of volatile content versus viscosity on the last lesson slide.
Low viscosity (mafic/basalt): low volatiles - effusive, products = lava flows high volatiles - explosive, products = fire fountains High viscosity (felsic/rhyolite): low volatiles - effusive, products = lava domes high volatiles - explosive, products = stratavolcanoes/calderas
What causes explosive eruptions? What controls the magnitude of those explosions?
Magma viscosity dictates ease of degassing Ease of degassing dictates explosive potential of eruption -Near the surface, all that dissolved gas is converted into bubbles - a lot of gas = explosive - At high pressure, gas can be dissolved in magmas Explosiveness of eruption dictates whether lavas or pyroclasts are produced cooler, more viscous magmas (such as andesite) reach the surface. Dissolved gases cannot escape as easily, so pressure may build up until gas explosions blast rock and lava fragments into the air!
What is the angle of repose? How does it relate to slope stability?
Maximum angle at which loose material remains stable Angular grain pieces build up to steeper slopes Slopes fail when - angle of slope > A.O.R This angle is different for different materials
What is magnitude? What variables affect magnitude?
Physical representation of earthquake size Wave amplitude, duration, energy release Logarithmic: each magnitude unit is 10x larger than the previous unit The larger the fault area that slips, the larger the magnitude also strength of rock, amount of movement, proximity to fault and depth
What mitigation techniques help minimize earthquake hazards and how?
Predict earthquakes and evacuate Long term fault patterns, foreshocks, animal behavior NOT GOOD AT THIS Design buildings to withstand them - a few ways to do so Shear walls (reinforce across vertical columns) Fasten furniture Reinforce concrete and masonry Bolt houses to the foundation
What is pressure/stress? How is it different from a force?
Pressure is a force acting over an area (psi = pounds/square inch) In geology, we call pressure stress Confining pressure: same amount of stress from all directions Differential stress: different amounts of stress from different directions Stress (pressure) = force over a given area
Be able to discuss some of the important eras and periods of the geologic time scale (the periods/events described in class). When did they begin/end and why? What life existed?
Quatemary Period: homo erectus (1.3 Ma) Conozoic Era: 80% of all species died (65 Ma) - end of dinosaurs Mesozoic: 95% marine species died (250 Ma) - Pangaea Paleozoic: marine life explosion - trilobites (544 Ma) Precambrian: not much life - vast majority of Earth's history - from formation to 544 Ma Changes are often due to climate change (impact from meteorite that impacts atmosphere or huge volcanic eruptions)
Difference between relative and absolute dating
Relative: age of something relative to other things (no number; very qualitative) Absolute: age in absolute number (radioactive decay - measure daughter isotopes)
Three ways rocks can melt
Rocks directly in contact with magma reservoirs - not much melt - least common way - rocks are poor conductors Decompression/depressurization Divergent plate boundaries (mid-ocean ridges) Hot spots - deep in mantle Add some antifreeze (flux melting) By adding water to mantle rocks, the melting temp gets lowered (like antifreeze or salt on the roads) Occurs in subduction zones (water driven off into overlying rocks - no changing temp or pressure) - lots of water and therefore very explosive
Define seismology, seismograph, and seismogram. Very generally, how does a seismometer work?
Seismic Monitoring Seismic waves are detected in the field by seismometers, devices that generate electric signals as they move (converting vibrations due to seismic waves into electrical signals) Seismographs record these signals Seismology The study of earthquake waves (dates back almost 2000 years to the Chinese) Seismographs are the instruments that record seismic waves (now mostly computers)
What can cause lahars?
Snow, water, ash mix to the consistency of wet cement, forming flow mass wasting Overall the most lethal volcanic hazard May occur without eruption Can be created by Pyroclastic flows melting glaciers/snow (most common) Lava flows onto glaciers or snow (rare) Heavy rainfall on loose ash
What term do geologists use for the result of stress on a rock? How is it different from stress?
Strain - rocks respond to stress by deforming Stress is pressure/force and strain is the resulting deformation
What is stratigraphy? What is a stratigraphic column/section? What is a sedimentary bed?
Stratigraphy is part of relative dating. It is the study of Earth history as preserved in sedimentary layers - know about local climate, was water present or not, evolution of life (fossils). A bed is a single layer of sediment. A stratigraphic section is when different beds form when sedimentary conditions (depositional environments) change and representing the vertical location of the rocks.
What is an earthquake? How are they generated?
Strictly speaking, ground shaking Technical definition: earthquake is the vibration of Earth, produced by the rapid release of energy Energy released radiates in ALL directions from source, also called the focus Energy travels in the form of waves Sensitive instruments around the world can record the event Process Forces in earth cause stress Stresses accumulate as elastic deformation until Rocks can't withstand stress and breaks along weak zones = faults
Why is volcanic ash such a major hazard to people, buildings, and airplanes?
Tiny fragments of volcanic glass = inhalation hazard Hot enough to burn skin or lungs Prolonged exposure = silicosis (shortness of breath, cough) Causes roof collapse If mining, higher risk of collapse Ash dispersed great distances = effects large area (darkness, clogs waste and water systems, inundates roads, ruins crops, causes lahars) Volcanic lightning is a thing Aviation hazards Large explosive eruptions can send ash far Cannot be seen at night (or by radar) Ash is abrasive = damage to windows and moving wing parts Ash particles have lower melting point than combustion engine, glass melts and sticks to turbines and they shut down High economic impacts
Know the general magnitude of such tsunami physical properties as wavelength, velocity, and amplitude in open ocean vs. near shore. How long does it take for tsunamis to cross oceans?
Velocity is dependent on water depth In deep water tsunami travels at ~1000 kph (>600 mph=speed of a jet plane) Wave slows in shallow water (30-50 kph, or 18-30 mph) As it slows, water piles up behind the wave, increasing amplitude (wave height) -Tsunami in deep ocean Velocity here is proportional to the square root of water depth Long wavelength, small wave height (like regular waves), high velocity Not so dangerous to be here during tsunami -Tsunami in shallow water Velocity slows, all of the water in long wavelength piles up to form high waves Waves may break offshore or form a bore -How widespread are the impacts? Can hit all of the coastlines around that ocean -Landslide tsunamis Anything that moves water rapidly can generate a tsunami Submarine landslides among the most devastating Seward, AK 1964
What types of earthquakes cause tsunamis? Which do not?
Very large (>M7) Quakes that displace water Reverse/thrust and normal faults can both generate tsunamis Strike-slip faulting doesn't generate tsunamis Quakes that trigger landslides
Define viscosity. Understand the controls on viscosity. Recall our blowing bubbles demo!
Viscosity: a measure of a fluid's resistance to flow More viscous=less flowy (scale on slides) Magmas have a wide range of viscosity due to temperature, composition (esp SiO2 and water content), and crystals and bubbles (solid and gas volume) - Higher temperature=lower viscosity - More Si bonds=less able to flow High viscosity is silicon-rich liquid (ex rhyolite) Low viscosity is lower silicon liquid (ex basalt) - Higher crystal content=higher viscosity Crystals interfere with each other=resists flow
What is the P-S interval? Why is it important in locating an epicenter?
Waves arrive at different times because velocities differ Timing between is called the P-S interval - used to estimate distance from seismometer to epicenter
What is the geologic time scale? How was it devised?
a record of the life forms and geologic events in Earth's history based on the rock record developed after scientists observed changes in the fossils going from oldest to youngest sedimentary rocks. They used relative dating to divide Earth's past in several chunks of time when similar organisms were on Earth
Define shear stress. How does it affect slope stability?
component of gravity that pulls things down slope If the shear stress is greater than forces holding the slope in place (gravity), failure will occur
What is mass wasting?
downslope motion of rock, soil, dust and other debris under the influence of gravity
What is a force? How are weight and mass different? 3 stresses
force = mass*acceleration (usually gravity) Force is a push or pull expressed as amount of acceleration experienced by a mass Your weight = your mass *force of gravity (9.8 m/s2) Pressure is a force acting over an area Compression (convergent) Tension (divergent) Shear (transform)
What are some reasons magmatism is important to society and or/why we should study volcanic eruptions? What is magma?
importance: mineral/ore deposits, geothermal energy, eruptions/fertile soil, created oceans, crust generation, volcanic hazards What is magma? Molten rock, xenoliths, gasses (volatiles), mineral crystals Where does magma come from? Mantle melting - ascending to crust and changing before erupting
Understand the following terms: solidus, geothermal gradient.
solidus is the highest temperature at which an alloy is completely solid - where melting begins geothermal gradient: Temp increases with depth = geotherm Varies with location in Earth Temp goes down as pressure does Rate of T increase is lower in mantle and core (conduction in core vs convection in mantle) Importance: pressure and temperature dictate if a rock is solid or liquid
radiometric dating? What is the basis for this type of dating
the process of measuring the absolute age of geologic material by measuring the concentrations of radioactive isotopes and their decay products. Based on principles of radioactive decay
How do we define half life? Why is it important?
the time for 50% of parent atoms to decay After each half-life, half of the remaining parent isotopes have decayed Measure the amount of parent and daughter isotopes of a system present in the rock today The ratio of parent to daughter tells you how old it is the more unstable, the shorter the half life exponential decay
How can eruptions lead to global cooling?
throws out a tremendous number of particles and other gases. These will effectively shield us enough from the Sun to lead to a short-lived global cooling period Fine ash may stay in stratosphere for weeks, gasses for years Produce H20 and CO2, but SO2 is usually most important SO2 enters atmosphere and turns to sulfuric acid (aerosol) Strongly absorbs/reflects the sun's radiation = changes in climate Cooling for as long as aerosols stay in stratosphere (1-4 years) Atmospheric ash can reduce sunlight Temperature after super eruptions - decades, hundreds, thousands of years - temperature drops
Why does the water sometimes recede before a tsunami comes ashore?
transfer of energy from the seafloor to the ocean, causing waves on the surface to radiate outward in all direction
