natural disasters exam #2 study guide - fall '22

the fire triangle

fuel, oxygen, heat

drought

a period of drier-than-normal conditions that results in water-related problems

drought-related problems

- soils dry out
- plants can die
- streamflows decline
- water levels in lakes and reservoirs fall
- depth to water in wells increases

factors that contribute to drought

- ocean temperatures
- changes in the jet stream
- changes in the local landscape

fire factors

- fuel moisture
- relative humidity
- wind

protections against fire

- buffer zones
- better roof materials
- better windows and doors
- sprinkler systems

buffer zones

keeps the fire away from the buildings

better roof materials

- roofs cannot be made of flammable materials (especially wood)
- instead they're made of tile, metal, etc.

better windows and doors

- add fire ratings to help keep fire from entering a building

sprinkler systems

installing sprinkler systems on roofs to help stop a fire/keep a fire from spreading to the roof

secondary fire impacts

- debris flow
- hydrophobic soil
- impacts of water balance (P = R + Et + G)

wildfires

unplanned fires that burn in natural areas

natural causes of wildfires

lightning, meteors, and coal seam fire

human causes of wildfires (90% of wildfires caused by this)

- Burning waste
- Unextinguished campfires
- Target shooting
- Fireworks
- Powerlines
- Cigarettes
- Arson
- Vehicles- flat tires, dragging chains, exhaust systems
- Children playing with matches

orographic effect

the precipitation that occurs when moist air rises up the side of a mountain

climate change

change in earth's operating conditions

factors involved in climate change dynamics

temperature change, change in precipitation, sea level rise

global temperature projection

there's an overall projection for larger increased temperatures in the arctic

global precipitation projection

some places projected to get less rain, some are projected to get more

causes of sea level rise

thermal expansion, melting of land ice (glaciers and ice caps)

health impacts of climate change

- increase in weather-related mortality (heat strokes)
- increase, re-emergence, and spread of infectious diseases (malaria)
- increase of air quality-respiratory illnesses (asthma)
- increase in radiation damage (skin and eye cancers)

ozone hole

allows more UV radiation to reach the earth's surface

the carbon cycle

the flow of carbon between the atmosphere, rocks, oceans, and biosphere

five different set of theories are blamed for climate change:

1.) astronomical
2.) atmospheric changes
3.) geophysical
4.) land/water changes
5.) glaciological

plate tectonics

- plate tectonics states that the outermost layer of the Earth (the lithosphere) is composed of thin plates that slide around-our continents move!
- a unifying theory that explains how the Earth works, and why hazards occur where they do on the Earth's surface
- scientists learned about plate tectonics by observing the distribution of fossils, the properties and distributions of different rock types, and the locations of geologic hazards

earthquakes

a release of energy when rocks stuck and straining against each other finally break or slip by each other along a fault

how earthquakes occur

- the rocks on earth's crust are relatively cold and brittle
- if we stress cold, brittle rocks, they get strained/deformed
- when this strain is released quickly, it causes earthquakes

the Tohoku earthquake

huge 9.0 magnitude earthquake on the east coast of Japan; very destructive

continental drift

the hypothesis that continents are mobile

Wegner's 5 main lines of supporting evidence for continental drift:

1.) "fit" of continents
2.) location of glaciations
3.) fossil organisms
4.) rock type and structural similarities
5.) paleoclimates persevered in rocks

"fit" of continents

Wegener noted that continents seem to fit together; could not be coincidental

location of glaciations

- Permian (225 mya) glacial deposits are found on four continents
- the glacial material in Africa and India are now near the equator
- with a restored Pangea, permian glacial deposits fit together in the region that used to occupy the south polar ice cap

fossil organisms

- identical fossils found on widely separated landmasses
- these organisms could not have crossed an ocean

rock type and structural similarities

mountain ranges with identical rock types and ages are present on opposite sides of the Atlantic

paleoclimates persevered in rocks

aligning Pangea in this position at the South Pole allowed Wegner to also accurately predict the locations of deserts and more tropical environments; the environments he predicted match the climate belts on Earth today

mid-oceanic rift zone

an area where the earth is pushing itself apart

characteristics of a mid-oceanic rift zone

- ridges on both sides
- shallow earthquakes
- volcanos
- normal faults

sea-floor spreading

- upwelling mantle erupts at the mid-ocean ridges
- new crust moves away from ridges, gathering sediment
- at trenches, the sea-floor dives back into the mantle
- provided a potential mechanism for continental drift

earth's interior layers

crust, mantle, outer core, inner core

convection cell

the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which results in a transfer of heat

continental crust

granitic, underlies the continents, less dense, lighter in color, mixture of different rock types

oceanic crust

basaltic, underlies the ocean basins, more dense, darker in color, from the mantle

lithosphere

the outermost 100-150 km of earth; nonflowing, rigid, brittle material that moves as plates

asthenosphere

upper mantle below the lithosphere; flows as a soft solid

plate boundaries

locations on the earth where tectonic plates meet and interact with each other

types of plate boundaries

divergent, convergent, transform

divergent boundary

plates are moving apart

convergent boundaries

plates are coming together

transform boundaries

plates are sliding by each other

divergent boundary characteristics

ridges on both sides, shallow earthquakes, volcanoes, and normal faults

convergent boundary characteristics

trenches, shallow to deep earthquakes, volcanoes, and thrust faults on the overriding plate

transform boundary characteristics

shallow earthquakes, no volcanoes, plate material is neither created nor destroyed

types of convergent boundaries

oceanic-continental, oceanic-oceanic, continental-continental

plate collision

- subduction consumes ocean basins
- ocean closure ends in continental collision
- example: himalaya

hot spots

- hot spots perforates to overriding plate
- volcano builds above sea level
- plate motion pulls volcano off plume
- example: Hawaii-Emperor seamount chain

volcano

a vent where molten rock can come out of the earth

Where does magma come from?

decompression melting, heat transfer melting, flux melting

decompression melting

if you remove the pressure (crustal thinning or venting), it is easier to melt material (less force/area holding it together

heat transfer melting

hot mantle rock or magma melts overlying continental rocks; occurs in continental hot spots and along subduction arcs

flux melting

if you add volatiles (water, carbon dioxide) to mantle rock, then it melts easier; occurs is subduction zones

viscosity

a liquid's resistance to flow; the more resistant it is, the more viscous is it

lava flows

- lava is magma that reaches the surface
- it can be thin and runny or thick and sticky
- flow style depends on viscosity

basaltic lava flows

- mafic (basaltic) magma is very hot, has low silica content and therefore low viscosity
- these type of flows are thin and have low explosivity
- they generally come from melted mantle with little contact with continental rocks.

two types of lava deposits:

1.) pahoehoe
2.) a'a

pahoehoe

"smooth" and "ropey" lava deposits from smaller, slower flows

a'a

rubbly" and "sharp" lava deposits from larger, faster flows

volcano types

shield, cinder cone, composite (aka stratovolcanoes)

shield volcanoes

- broad, slightly domed-shaped
- made by lateral flow os low-viscosity basaltic lava
- have a low slope and over large geographic areas
- example: Mauna Loa in Hawaii

cinder cones

- the smallest type of volcano
- built of ejected little spheres of lava piled up at a vent

magma source

- the source of the melt dictates the initial composition:
- mantle source - ultramafic and mafic magmas
- crustal source - intermediate, felsic magmas

assimilation

magma melts the country rock it passes through, incorporating it into the magma

fractional crystallization

process in which different minerals crystallize from magma at different temperatures, removing elements from magma

felsic lava flows

- higher silica makes felsic magma viscous
- thick flows and explosive eruptions (unlike basalt, they do not flow rapidly)

rhyolitic lava flows

- rhyolite, with the highest amount of silica, is the most viscous magma
- produce lava domes and explosive eruptions
- rhyolitic lava rarely flows
- plus the vent as a lava dome - builds up pressure

Stratovolcanoes (composite volcanoes)

- large, cone-shaped volcano
- composed of alternating layers of lava and tephra
- often symmetric; can be odd shapes from landslides, etc
- examples: Mt. Fuji, Mt. Rainier, Mt. Vesuvius

volcanic hazards

- noxious gases
- tsunamis
- pyroclastic flows
- lahars
- earthquakes
- landslides

krakatoa was a...

composite volcano

earthquakes caused by volcanic eruptions may also trigger...

tsunamis or seismic sea waves

explosive pyroclastic debris

- created when intermediate and felsic magmas erupt explosively
- produces and ejects a large quantity of volcanic ash and other materials

pyroclastic flows

high-speed gravity driven avalanches of hot ash, rock fragments, and gas that move down the sides of a volcano during explosive eruptions

ignimbrite or welded tuff

deposits of ash from volcanic eruptions

lahar

volcanic ash that is readily moved by water within a debris flow; are often deadly; have the consistency of wet cement

holocene eruptions

kalama eruptions; goat rock eruptions

caldera

gigantic volcanic depressions that are formed from massive eruptions after a volcano collapses

Mt. Rainier

stratovolcano; magma here is a product of flux melting

Yellowstone mantle plume

- the mantle plume melts the upper mantle, forming basaltic magma
- partial melting and assimilation produce rhyolitic magmas

Yellowstone eruption warning signs

massive earthquakes, ash and steam coming from the volcano, etc.

warning signs of Pinatubo

- geologic evidence of ash flows and carbon dating
- small eruptions of steam and ash occurred
- lots of earthquakes
- lots of sulfur dioxide emitted from the vents, then shut off
- dome growth

level 4 warning

- Level 1: activity
- Level 2: increasing activity (earthquakes and steam eruption)
- Level 3: eruption in 2 weeks
- Level 4: eruption in 2 days

where do most earthquakes occur?

along plate boundaries

what causes an earthquake?

* earth movements along faults
- volcanic activity
- landslides
- explosions
- fracking

stress

a force acting on a body over a unit area

strain

due to the external stress, the body may undergo deformation; this deformation per unity length is the strain

tensile stresses

pulling apart

compressive stresses

pushing together

bending stresses

when you bend an object, you are applying compressional stress on the inside of the bend and torsional stress of the outside of the object bend

shear stresses

when an object experiences stresses working in opposite directions; sliding along each other

elastic rebound theory

theory that rocks that are strained past a certain point will fracture and spring back to their original shape

fault initiation

- tectonic forces add stress to unbroken rocks
- rock deforms slightly (elastic strain)
- rock cracks
- cracks grow to point of failure
- earthquake energy released

fault motion

- faults move in jumps
- once motion starts, it quickly stops due to friction
- eventually, strain will build up again, causing failure
- this behavior is termed stick-slip behavior