Geo 112 Second Exam
Seismic engineering
Designing and building structures to withstand earthquakes; making structure safe from the threats of EQs
Slumps as threats to property and an inconveniences more so that direct threats to life
Pretty Rocks slump in AK- developed from a minor maintenance concern to causing substantial road restrictions- temperature increase highest of all national parks since 1950- with the addition of heavy rainfall events -> permafrost thaws -> recent acceleration of many landslide in Denali build monitoring system to improve safety and help understand the movement and Plotter Kill- on cutbank of the stream; split tree; glaciated area- loose sediment, remote, not a major threat to anyone tree rings- become asymmetrical when a tree struggles to stay upright- to return to vertical trees add wood: conifers add downslope to push themselves up while deciduous trees add upsilon to pull themselves up
P-waves and S-waves -> interior of earth
Primary waves- arrive first; compressional body waves, travel through solids, liquids, and gases; travel up to the surface in an up and down motion -> initial upwards jolt of the EQ; velocity of P waves depends on material's density and how it changes volume and how it shears Secondary waves- arrive second; shear body waves- lateral shifting- side to side; travel through solids only (not outer core); travel up to the surface as sideways motion; velocity of S waves depends on materials density and how it shears surface waves arrive last and cause a lot of damage - all wiggly and crazy- snaky shaky
Volcano
a location where subsurface molten rocks breaks through the surface magma- molten rock beneath the surface lava- magma on the surface; molten rock on the surface of earth found on land and underwater
Magnitude
a measure of the EQs relative size based on ground motion -> ground motion deflect the needle of the seismograph and the amount of deflection and distance from EQ give magnitude 3 line chart- distance from earth quake, and amplitude -> where the line meets is magnitude (a bunch of different measures can lead to the same magnitude -> loss of energy from traveling through rocks? scales are logarithmic- each level is 10 times greater than the previous level EQ ground motion produced by a M8 is 10x ground motion of M7; M8 is 100x ground motion of M5; M8 is 1000x ground motion of M5
Angle of repose for loose sediment
fine sand- 35 deg coarse sand- 40 deg angular pebbles- 45 deg over those degrees, gravity can overcome friction, causing mass movements
Focus and epicenter
focus/hypocenter- the location (underground) where the EQ begins -> such as an underground rupture on a fault epicenter- the point on the Earth's surface directly above the focus
Volcanic gases as a hazard
gas as a major product of eruptions up to 9% of magma may be gas- H20, CO2, sulfur dioxide, hydrogen sulfide expanding gas caught in lava makes vesicles or holes -> pumice denser volcanic gases -> toxic -> present a suffocation or poisoning hazard these gases can displace air
Earthquakes and possible causes
ground shaking events -Causes *Motion on a fault. *Inflation of a magma chamber. *Volcanic eruption. *Meteorite impacts. *Underground nuclear detonations occur mainly when one body of rock is sliding past another (at a fault), gets stuck, then suddenly slips, releasing stored energy volcanic activity- movement of molten rock inside Earth or Eruption rebound of the lithosphere following deglaciation underground nuclear bomb tests
Pyroclastic flows vs. volcanic mudflows
mudflows have water but the other flows are more of an avalanche of hot ash and rock
Mass movements as natural hazards
naturally occurring events that also cause damage to life and property
how did ppl figure out the layers of Earth's interior?
observing the seismic waves that are recorded all over the surface of the earth from distant earthquakes. The seismic waves are reflected (bounced off) layers of different density, and they are refracted (bent) when they enter layers of different density.
Biggest Earthquakes -> where?
occur mainly at plate boundaries -> largest EQs at subduction zones (convergent boundaries); big EQs also at transform boundaries
Permafrost
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3 triggers of slope failure
- Steepen: slopes more likely to fail if they are over steepened- if angle of repose is greater than 35 to 45 for the loose sediment; at steeper angles, gravity can overcome friction; cused by loading the top, citing part of the slope and filling it somewhere else, or undercutting the base - Weaken: reduce the strength of the slope by: adding water which adds weight and reduces friction; remove vegetation since roots help bind the soil together; or weather (break down minerals) which weakens rock - Shake: vibrations can loosen slope material- mainly caused by earthquakes, but also blasting with explosives, or traffic vibrations
Stahl and Arsenic contamination in Vietnam
- benefits of wells- access to water, decreased child mortality, but natural arsenic in GW- no immediate damage, colorless, odorless and tasteless -> effects compound over time- cancers, cardiovascular disease, diabetes, cognitive impariment - S-SE Asia- widespread in sediments and variable in ground water because microbes consume organic Carbon, releasing CO2- iron oxides in the soil -> release arsenic - changing environment may affect occurrence of arsenic -> improve understanding of hydrogeologic controls on arsenic mobilization- recharge pathway and arsenic mobilization, recharge source - Van Phuc- aquifer discharged into river but heavy pumping in Hanoi changed the GW flow -> depositional areas have more arsenic than non depositional area (erosion) which leaches over time -> very quick arsenic release once water enters into the bank, picks up the arsenic and iron very quickly -> ferrihydrite is the arsenic source, readily dissolves into the water yes the arsenic moved inland via the aquifer -> domestic wells, continued contamination of an already contaminated aquifer; recharge in depositional zone can contaminate inland aquifers reversal of GW flow changed arsenic concentrations- heavily pumped aquifers -> future contamination potential
What facilitated the discovery of sea-floor spreading
- facilitated by technological advances and sea-floor exploration during and after WW2 provided important clues - sonar maps of sea floors showed lots of topography -> 1) revealing a mountain range in the middle of every ocean basis (MOR) 2) deepest parts are along the edges of ocean basins (trenches) 3) lines of volcanoes rise from deep parts of sea floor (seamount chains) 4) mid ocean ridges offset by large fracture zones sea-floor discoveries - sea-floor sediment is thinnest in the center at ridges and gets thicker toward the margins of basins - oceanic crust is made entirely of basaltic rock - heat flow is highest along MOR - EQs are focused along trenches, ridges, and fracture zones by 1960 we had a modern view of ocean basins
Lava flow dangers
- generally easy to avoid - still threatens property, can't just stop it, and does not go away, leave massive trails of basalt - fast moving lava flows are dangerous to life
Nyiragongo, DR Congo
- lava is unusually low in silica - flank eruption from the side following an EQ - very hot, fast lava flows -> lava lake drained through fissures created by the EQ -> 60 km per hour, 2m of layers of lava - about 150 ppl died 2002 in the East African Rift
Landslides and other mass movements
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Guest lectures
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Plate tectonics and sea-floor spreading
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Volcanoes and Volcanic Hazards
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Earthquakes and tsunamis
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Why do rocks melt at D and C boundaries and hot spots? three different mechanisms
1) rocks melt at divergent boundaries (MORs and CRZs): where plates move apart, rocks melt because the pressure drops - MORs- new o-crust basalt is produced and the ocean basin grows outward- pillow basalts -CRZs- where ocean basins begin- the rigid lithosphere stretches and breaks and eventually volcanism begins forming ocean crust 2) rocks melt at convergent boundaries subduction zones: rocks are able to melt at lower temperatures if water is added; hot rock in the overriding plate melts when water is added from the downgoing plate; water released from minerals that get heated up; a line of volcanoes (arc) forms above the subducted plate 3) rocks melt above hot spots (mantle plumes)- stable plumes of hot rock rising from the lower mantle -> melt the base of the lithosphere like a blow torch
Classifying mass movements
1) type of materials- soil, mud, rock, snow 2) velocity- very slow to very fast 3) type of mass- chaotic cloud, slurry, coherent body 4) on land vs. underwater
Oso Mudslide in WA, US in 2014
43 killed, 49 homes destroyed, community buried, deadliest single landslide event in US history- 2014; many old landslides near by, landslides changing the meander of the river, causing erosion and then landslides on the other side- cycle repeats find different ages of active and historic slides in the area glacial situation- deep pile of fairly weak, relatively loose stuff/sediment -> trigger: changes in the stream, eating away at the toe of past slides, changing angle of the slope; lots of rain not long before
Pompeii and Herculaneum
79 AD, Vesuvius erupted covered Pompeii with ~ 3m of ash about 23 m of pyroclastic flow buried Herculaneum both remained buried for about 1500 years eruption produced pyroclastic debris and lahars- people and animals died in hot ash falls/flows; ash hardened around them, creating molds; volcanic mudflows buried people in H as they tried to escape
Wegner and Continental Drift
CD proposed in 1912- posits that continents were united as Pangea during the Mesozoic Era (Age of Dinosaurs) and have drifted apart since then
Layers of earth recognitions based on the composition and rigidity of material
Composition: - crust = rocky - mantle = rocky - outer core = metallic and molten - inner core = metalic and solid Rigidity: internal layering- layers differentiate - lithosphere = rigid crust + rigid uppermost part of the mantle - asthenosphere = denser and deformable (soft) upper mantle
Why do we think the core of Earth is made of metal?
Density calculations show that Earth's core is metal. Seismic waves show that the inner core is solid and the outer core is liquid. Metallic meteorites and the magnetic field are also clues about the makeup of the core Iron, nickel, and other heavy metals like gold, are what makes up the core of the earth because they are the heaviest of the metals and so sank toward the center of the earth
Example of each type of plate boundary
Divergent Boundaries- MORs, mid-atlantic ridge, Iceland on top of an MOR Convergent- Himalayas; any trench along many continents, Marianas trench south of Japan Transform- San Andreas Fault
Seismicity
EQ activity -> the frequency, intensity, and distribution of earthquakes in a given area movement on a fault can cause seismicity -> along an existing fault or a brand new one
Body wave and Surface wave
EQ energy travels in the form of waves body- travel through the interior of the Earth surface- travel along the Earth's surface
Wegner's evidence for Continental Drift (5); his failure to convince ppl
Evidence: 1) fit of continents- appear to fit together across the Atlantic Ocean 2) glacial erosion and deposition- straitiaons indicate ice flow from SE Africa; ancient glacial deposits found in polar and non-polar regions 3) equatorial deposits- ancient coal swamps and coral reefs found in non-tropical regions; sand dunes and evaporites (salt deposits) are found in non-subtropical regions 4) fossil distribution- fossils of two land dwelling reptiles, a freshwater reptile, and a seed fern are found on several continents; could not have cross oceans by themselves 5) matching rocks- same rock formations found in South America and Africa; Appalachians and Europe his evidence was strong but most scientists rejects his hypothesis -> largely because he could not explain why continents moved
Volcanic crater lakes and mass suffocation
Lake Nyos, Cameroon, Western Africa deep lake in a volcanic crater part of a hot spot chain- from ocean onto land CO2 burped from the lake and displaced oxygen trigger unknown but landslide expected -> upturn the water CO2 heavier than air -> blanketed the ground -> suffocated almost 2000 ppl and 3500 head of cattle CO2 held at the cool bottom but something disturbed the lake and stirred it up -> releasing lots of CO2 prevention -> Degas the lake to prevent CO2 buildup
Source of energy driving movement of tectonic plates
Plate tectonics driven by convection- lower mantle heated by outer core, warm matter rises to MOR -> in trenches, O-crust subducts and sinks and melts -> cycle repeats plate tectonics is driven by convection in the mantle the force pulling on downing plates is slab pull the force pushing plates apart- ridge push
how does sea-floor spreading explain MOR with high heat flow, yong and thin rock in the muddle and edges of the basin being old, cold and thick
SFS explains the age of oceanic crust age increases away from MOR; ages are mirror images across the MOR; oldest at continental margins, youngest in the center of ocean basins thicker bc it gets pushed out
Pyroclastic flow
The expulsion of ash, cinders, bombs, and gases during an explosive volcanic eruption glowing avalanches of hot ash -> very dangerous move downslope at speeds over 100 kph -> even faster with a thin layer of air trapped beneath
Arrival time
The time in which P or S waves arrives at a seismic station; when the EQ wave first arrives at a seismic station allows us to locate the epicenter -> P waves travel faster than S waves; the farther the waves travel, the farther S waves lag behind P waves (bigger delay) using graph- shows how fast P and S waves travel -> use time it took for the waves to arrive to determine the distance between the epicenter and seismograph -> use that to make a circle with that distance as the radius -> consult with other seismograph-havers -> find where the circles over lap to determine the location where the EQ occurred
Controlling the upper and lower boundaries of a permafrost layer
Upper limit- controlled by seasonal temperature variations- active layer that thaws and re-freezes annually permafrost- the layer that stays frozen all year round- for at least two consecutive years low limit- dictated by geothermal heat, temperature increases with depth, so at a certain depth, the soil is not frozen
Fault
a fracture in rock along which movement occurs normal fault: diverging plates -> spread and slip downwards reverse/thrust fault: converging plates -> force pushing them together causes one plate to slide up above the other strike-slip fault: transform plate -> rocks slide past each other along the fault plane a plate boundary is a large scale fault
Creep
a graduate downslope movement of regolith (soil and loose rocks on top of bedrock) caused by: - gravity, plus an assiting factor- usually - freeze-thaw cycles: ice lifts particles, gravity makes them fall- downslope - wet-dry cycles: wet clay-rich soils expand, contract when dry, moving downhill bc gravity quite common- signs include: sagging foundation, cracked walls, tilted power poles or gravestones, curving J-shaped tree trunks
Landslides
a relatively fast sudden movement of rock and debris down a non-vertical slop debris may travel on a cushion of compressed air- only making things worse, faster- like an air-hockey table move along a weak failure surface- change in sediment layer, different degree of hydration glacial sediments particularly prone to landsliding since the bottom layer are usually low permeability- water travels down lubricateing that surface making landslides more likely
Failure surface
a weak surface that forms the base of a landslide, the bottom limit above which was a mass movement
Using lag times to determine EQ location
allows us to locate the epicenter -> P waves travel faster than S waves; the farther the waves travel, the farther S waves lag behind P waves (bigger delay) using graph- shows how fast P and S waves travel -> use time it took for the waves to arrive to determine the distance between the epicenter and seismograph -> use that to make a circle with that distance as the radius -> consult with other seismograph-havers -> find where the circles over lap to determine the location where the EQ occurred
seismograph and seismogram
an instrument that measures and records details of earthquakes, such as force and duration -> records ground motion caused by earthquakes in the form of a seismogram -> pen dangles and spinning paper drum bolted to the ground spins, so the drum moves and the pen stays stationary showing the seismic activity/the ground moving up and down
Convergent Plate Boundaries
areas were two plates meet at a subduction zone and the more dense plate slides under the less dense plate -> density rule! oceanic crust is iron-rich basalt (dense); average continental rock is granite (less dense) trench forms where two plates converge and one subducts friction between the two plates pulls the sea floor down at the trench volcanoes form when rock partially melts at the base of the overriding plate- age. determines how far into the overriding plate the Vs pop up - older and colder reaches certain depth faster so Vs are closer to the trench - younger and warmer rock subducts more gradually so Vs are farther into the overriding plate Volcanic arc: explosive Vs form when an oceanic plate subducts beneath a silica-rich continual plate; water released from minerals as they heat up -> volcano collision of two continental plates produces high mountain ranges because neither plate is dense enough to fully subduct -> these collisions occur after all the oceanic part of a mixed plate has been subducted -> Himalayas from the collision of the Indian and Eurasian continental plates producing the Tibetan Plateau and they continue to rise
Divergent Plate Boundaries
areas where two plates move apart- new oceanic crust is formed- sea-floor spreading; new crust is hot - it sinks as it cools and contracts becoming denser and moves away from the ridge at divergent boundaries plates separate, rock melts because pressure drops, new sea floor forms, new sea floor spreads apart, ocean basin grows outward, continents ride along passively, accumulating new material around their edges over time
Transform Plate Boundaries
areas where two plates slide past each other; sometimes the plates stick then slip, causing EQs strike-slip faults san Andreas faule is a transform boundary separating two plates (absolute motion different from relative motion along this fault
Hawaiin Islands and Canary Islands
both sets of islands consist of hot spot volcanoes tectonic plate moves and the hot spot stays in the same play -> over time a row of volcanoes forms younger islands/volcanoes are down motion of the way the plate is going; often heading in the direction of the higher age -> bc the hot spot does not move but the plate does record changes in plate direction
Thawing permafrost and geologic and environmental hazards
caused by global warming but also could lead to the acceleration of global warming organic matter buried and frozen in the permafrost -> frozen for 1000s of years; thaws -> exposed to microbes that can break down the carbon materials, releasing CO2 or methane into the atmosphere -> GH gas effect -> accelerated global warming permafrost carbon feedback cycle, released much faster that it was taken in- there is like lots of frozen carbon in there also newly unfrozen microbes could make humans and animals very sick- ancient bacteria and viruses; there is also radioactive, toxic mining water, hazardous chemicals and extremophile microbes in there can reveal some cools stuff tho
Yellowstone National Park
continental hot spot! several ancient volcanic calderas -> lots of volcanism evidence there mineral springs, geysers, boiling mud YS hot spot- calderas, magma chamber and EQs
Reducing EQ risks
cross bracing to reinforce the struuture base isolators that allow the ground to shake and the building an move freely- not relying on the ground for all the support -> not built directly on the ground retrofit soft-story buildings: strengthen existing walls (brace, plywood, anchor to foundation); add new shear walls (built to resists sideways motion); add steel frame in soft areas of the building external skeletons to reinforce and redirect the waves metal jackets for concrete highway supports early warning systems send out signal when P waves hit (before S and surface waves); phone apps EQ preparedness- annual shake out, learn what to do
Magnetic stripes in the sea-floor and confirming sea-floor spreading; Positive and negative marine magnetic anomalies and how these stripes form
discovered magnetic variations in o-crust confirmed by spreading we know the present orientation and strength of the mag field, but has reversed many times in Earth's history (poles switch); the orientation of the field is recorded by iron minerals in lava flows- even at MORs sea floor has alternating stripes of normal and reversed polarity - recorded by lava extruded at MORs form linear belts that are parallel to and symmetric across ridges (locks in the magnetic signal once the lava crystalizes positive when normal, negative if polarity is reversed
Mass movement definition
downslope movements of geologic materials (rock, regolith, snow) under the influence of gravity and over a wide range of speeds
Tectonic plates
earths rigid outer layer is broken into tectonic plates that move tectonics- the study of the processes that move and deform Earth's crust EQ and volcanoes concentrated along plate boundaries made of lithosphere -> work because the Earth is layered made of rigid lithosphere (rigid crust and rigid upper mantle)
Pyroclastic debris
ejected by explosive volcanoes -> fragmented or molten material that is blasted or sprayed out of a volcano and lands in solid form ash as a breathing hazard- inhaling glass blocks and bombs as impact hazards- falling rocks/molten rock
Nevado del Ruiz, Armero, Columbia, 1985 deadly volcanic mudflow
eruption of volcano melted about 10% of snow and ice on top; water and ash combined to make a lagar that grew during travel, reaching up to 60 mph; buried the town of armero below and over 23k people died
Harry Hess' sea-floor spreading hypothesis
hypothesis presented in 1959 1) molten rock rises beneath MOR 2) cools to form new sea floor (becomes denser) 3) new crust moves away from the ridge (pulled up when warm -> gravity pulls it down - sea-floor spreading) 4) sinks at trenches and is consumed back into the mantle 5) contents ride along passively like floating corks lava rises and crystallizes in the center of the MOR then splits in half and moves to each side as new lava rises in the center
Iceland is special
lies on the MOR above a mantle plume (hot-spot volcanism) west Iceland on the NA plate and E. Iceland is on the Eurasian plate and are separating at about 2 cm/yr many Icelandic volcanoes are glaciated; ash plumes; fissure eruptions
Orting, WA and handling lahars
living with lagar hazards- Mt. Rainier as a source of lahars for millennia lagar evacuation map, sirens, drills -> preparedness different cases- like flood intervals river facilitate the flow into the city, danger in the valley
Volcanic ash as a hazard
magma contains dissolved gases -> confining pressure decreases as magma rises -> gases come out of solution, has pressure builds -> sticky silica-rich magma plugs vent -> gases build up enough pressure to blast past the plug -> creating ash or frozen shards of silica glass and larger fragments -> lava eruption follows tiny shards of glass -> there are also bigger categories
Contiental rift zones
over time- land rifts as the land begins to pull apart -> breaks and stretches -> volcanism can begin -> forming a MOR (to be)/ocean floor is formed -> continues to spread -> forms ocean basin today- East African Rift, pulling apart and volcanoes in the rift zone- triple junction; Kilimanjaro past- the Atlantic Ocean began as a CRZ about 200 million years ago
Engineering related hazards associated with EQs
pancaking- when buildings are made of concrete and each floor is a slab of concrete proper on a lip around the edge -> EQ and the interim caused by the movement of the ground -> floors just fall straight down when the sides give out soft story collapse- like Southern CA- the bottom floor is much less rigid than the floors above- garages and empty space vs. more internal walls above -> makes this floor more likely to collapse in an EQ- twisting and buckling -> can be retrofit for reinforcement swaying and toppling- buildings of different heights sway in response to different wave frequencies (tall most affected by low frequencies) (short most affected by high frequencies) [surfacce waves=lower frequency than body waves, cause more destruction; deeper EQ -> less impact from surface waves] buildings sway too much -> collide and cause lots of destruction rupture of concrete highway supports- succumb to the shearing motion- collapse under lateral motion
MacManus-Spencer and PFAS Contamination
per and polyfluoroalkyl substances- oil and water repellency; carbon fluorine bonds- super strong and nothing can degrade them but also persistent, bioaccumulative and toxic; in 98% of Americans- cancer, liver toxicity, neonatal toxicity, lipid metabolism disruption legacy PFAS- been out there for a while being phased out -> replaced with something new that are somewhat less bad if the point source is in an area, the watershed is more likely to be contaminated hopsack falls, NY and the Saint-Gobain Performance Plastics- ground water super contimanted- free bottled water and carbon filters- superfund site found across the US- plastic manufacturers, airports, WWTPs (from residential homes- teflon and other plastics) field sampling to help understand it unanswered questions - how long will they remain in water, soil, and continue to impact ground water - will replacement PFAS bioacumulate- environment and organisms - how can we deal with what's already there and precent further contamination changing lifetime levels- slow to adapt, and they are also non-regulatory for the most part, govt slow to act
What is permafrost? Where is it found?
permanently frozen ground (over 2 years)- ice acts like cement to bond soil, rocks, and vegetation together; found in cold climates or high latitudes of areas of high altitudes, where the ground does not thaw completely even in summer can be continuous or discontinues- big parcels or small little pockets- talk is an ear of unfrozen ground surrounded by permafrost
Landscape features that indicate permafrost presence
pingos- ice cored hills, ice accumulates underground pushing up the surface, forming a hill with an ice core patterned ground- stone/sorted circles: ice dense grows in autumn as active layer thaws and refreezes daily -> uneven surface; water migrates to lens, causing it to grow, pushing stones up above it, gaps filled by smaller sediments, larger stones roll down the uneven ground, finer sediments left in the middle
Reducing volcanic hazards
preparedness indirect effects- starvation from loss of crops and homes
Head scarp and toe
scarp- step or cliff that marks the break-away point of the mass that is moving head scarp is the highest up point that broke away toe- where the slump mass collects, where the mass movement collects- at the bottoms
Lahars and their dangers
pyroclastic debris + water = volcanic mudflow (lahar) -> major hazard slurries of ash-rich debris and water (melted ice, lake) flow rapidly down volcanic sloped (60mph) denser than water -> can carry much heavier objects- rocks, boulders -> hits with more force then sets out like concrete when the water drains out Mt. Pinatubo Philippines 1991 eruption- lahars more devastating than the actual eruption
Signs of slope failure- past and future- that are observables
recognizing big and old landslides can be challenging studying prehistoric landslides can help assess modern risk -> surveying the soil development, taking sediment cores, and studying the level of cosmic ray exposure of rocks and sediments findings- wet periods, not deglaciation, triggered landslides
Tsunamis
result when a large amount of seawater is displaced rapidly- EQ, volcanic eruption, landslide typical: big EQ raises or lowers the sea floor; giant mound of water forms on sea surface; surface feature collapses into waves bc of gravity; waves race away from the epicenter (over 700 km/hr); if wave starts 130km from shore, arrives in ~ 15 min plate locking most generated at subduction zones- where the plates meet buildup of energy- bc two plates get stuck (locked area) buckling of the overriding plate- slow distortion and increase of energy slip and release of stored energy- stuck area ruptures, releasing energy as an EQ rebound of overriding plate- ground moves bc of the EQ -> causes displacement of water -> waves spread -> tsunami when tsunami waves reach shore, their height increases can cross oceans and surprise and even kill people far away
Slumping
semi-coherent slip of regolith along a curved sliding surface
Making of silica in lava
silica-poor lava: partially melting silica-poor oceanic crust (hot spots) silica-rich lava: partially melting silica-rich continental lithosphere; only gets silica from this crust- mix-ins lava cools quickly above ground so volcanic rocks have tiny crystals - basalt- cooled quickly above ground; hard to see individual minerals - granite- cooled slowly under ground; easy to see individual materials
Probable effect of climate change and global warming on permafrost
slow degradation of permafrost worldwide -> serious consequences; arctic summers getting warmer and longer, active layer gets deeper and deeper -> can't fully refreeze if it gets to deep, permafrost recedes ice acts as cement -> melts and causes the soil to lose its structure and weaken weakened coastlines more vulnerable to erosion infrastructure- shifting and settling of the ground- not as solid as it was-m under ground homes, property, roads, bridges increased risk of rockfalls and landslides bc soil is now much looser, can liquefy, leading to slumps loss of permafrost under bodies of water can cause them to drain into permeable ground now that it isn't blocked by ice -> loss of lakes and wetlands thawed permafrost is organic and carbon-rich -> can ignite
Mudflows, lahars, and debris flows
slurries of water and mud (+/- rocks); the speed depends on the slope and water content lahars are volcanic mudflows- water and volcanic ash/debris wildfire -> heavy rain -> mudslide
Avalanches
snow or debris mixed with air that travel down slopes at high velocity loose snow avalanche- starts from one point and expands/accumulates downhill slab avalanche- a whole slab breaks off and moves as a unit along a surface can be caused by humans- loose, fresh snow on top of refrozen, hard crust -> avalanche danger- slab can break loose under own weigh or by human activity on the slab
Preventing and discouraging slopes from failing; How to prevent damage and injury from slope failure and remediation methods
stabilizing unstable ground - increased vegetation- roots help stabilize the potential failure plane - lowering level of reservoirs help dry and strengthen potential failure planes - terrace steps to help remove loads from the slope and catch debris- more for steep, loosely consolidated walls - creating new and diverted channels away from cliffs to prevent undercutting - retaining walls and nets to trap debris (highways); different types: stream valley- allow water to flow but block debris; diversion- direct debris in different direction; shelter- allows debris to flow over, preventing damage - rock bolts- physical bolts to strengthen jointed or fractured rocks - just remove the entire hill slope
Rate of movement of tectonic plates
tectonic plates move about as fast as fingernails grow- a cm or two per year; but over millions of years it absolutely adds up
Lava chemistry
the chemistry of lava affects the type of eruption and the shape of the volcano key factor silica (SiO2) content -> silica is sticky the higher the silica content, the higher the viscosity (resistance to flow) low silica, higher temps, thin and runny (like Hawaiian islands- basalt everywhere) intermediate, sticker lava, higher viscosity, explosive eruptions, lots of airborne particles high silica, lower temps, thick, higher viscosity, slow eruptions, builds domes, some explosively affects the shape of the volcano: - low silica -> runny lava -> flows rapidly -> travels far before cooling -> thin layers of lava -> gentle slopes and non-explosive eruptions (shield volcanoes) ex: Hawaii, Galapagos - intermediate silica -> sticky lava + ash -> lava flows more slowly -> cools before traveling far -> thick layers of lava -> steep slopes and explosive eruptions -> layering of crystalized lava and pyroclastic debris (ash) -> composite volcanoes or stratovolcanoes- Mt. Fuji and Ngauruhoe (NZ), Mayon Philippines high silica, high viscosity lavas form domes
Nevado Husacaran in Peru 1970
the highest peak in Peru, M 7.7 earthquake triggered a massive landslide of rock and ice that reach a nearby town- Yungay- less than two minutes after the EQ, Yungay and Ranranhirca sat a the base of Huascaran- towns were crowded for the market that day R-town was in direct path of the landslide Yungay seemed protected but the slide went airborne over a ridge and proceeded to the the town squarely; most survivors were at the cemetery on the hill, 18k ppl died, many still buried
Ring of fire
the line of volcanoes around the Pacific marking the location of subduction zones
Active layer of permafrost
the thin layer that thaws each summer and re-freezes every winter, 30-200cm; mainly in the Arctic
Ice wedges and ice wedge polygons
top of wedge marks the bottom of the active layer; develop over time as freezing ground contracts and cracks in the winter -> then the open cracks fill with melt water in the spring (freezes in the permafrost forming an ice vein, creating a cycle with layers that keep spreading the crack over time polygons are 3D features that outline the cracks- show where ice wedges are -> intersect to form polygons; cracks and ice wedges intersect to form polygons on the surface
Contiental Crust vs. Oceanic Crust
two diff. compositions of crust continental- less dense; thicker (~35-40km); average rock type = granite (low in iron, magnesium), silica oceanic- more dense; thinner (~6-10km); rock type = all basalt (high in iron, magnesium) on top of the mantle which is even denser rocks, most of it is partially molten like warm asphalt
2004 Sumatra-Andaman Islands
undersea mega thrust EQ- M9.1-9.3 caused by a rupture in the fault between the Indian and the Burma plate (India subjecting under); causes massive tsunamis- hit Indonesia, Thailand, and East coast of Africa ~230,000 dead and incalculable damage one of the deadliest natural disasters in recorded history
2011 Japanese tsunami
undersea megatrhust EQ off the Eastern coast of Japan- most powerful in Japan's recorded history recurrence of a much earlier earthquake -> same mechanism pacific plate subducting under -> build up of energy -> slips and ruptures -> movement of ground -> tsunamis as high as 100ft- wave breaker/tsunami walls overcome by the waves; channeled the waves made them bigger ~20k dead, lots of damage, nuclear disaster
Rockfalls
very cohesive mass + gravity _> rock free-falls from a cliff talus- the pile of broken rock that accumulates at the base of a rocky cliff -> warning sign of more rock falls
Volcanic arc (and trenches)
volcanoes form when rock partially melts at the base of the overriding plate- age. determines how far into the overriding plate the Vs pop up - older and colder reaches certain depth faster so Vs are closer to the trench - younger and warmer rock subducts more gradually so Vs are farther into the overriding plate Volcanic arc: explosive Vs form when an oceanic plate subducts beneath a silica-rich continual plate; water released from minerals as they heat up -> volcano can be oceanic like the Aleutian Islands in AK or continental like the Cascades in the PNW trenches and volcanic arcs linked together- arc always on the overriding plate
Pyroclastic deposits
whether or not it sticks together depends on how hot the ash was: - tephra - unconsolidated loose ash -> cooler ash - tuff - lithified and stuck together -> hotter ash
Examples of catastrophic slope failure
~ what happened, causes, and warning signs