geology exam 4 Flashcards
stratovolcano
a volcano built of alternate layers of lava and ash
pyroclastic flow
destructive mass of hot ash, lava fragments, and gases ejected explosively from volcano a downwards slope
lahar
a mudslide containing a mixture of ash and water
cinder cone
a steep, conial hill of loose pyroclastic fragments that have built around a volcanic vent
strike
refers to the trend of the feature on the surface, measured by the direction of a horizontal line drawn on the surface
dip
refers to how steeply the feature is tilted, measured downward from the horizontal. The maximum is 90 degrees.
fault
a structure in which the rocks on opposite sides of a fracture have been moved relative to one another
strike-slip fault
fault blocks moving horizontally, parallel to the strike of the fault
dip-slip fault
a break in the earth’s crust, across which older rocks are pushed above younger rocks (thrust fault)
normal fault
the hanging wall moves downward from the footwall
reverse fault
the hanging wall moves upward from the footwall
elastic strain
the ability of a material to resume its normal shape after distortion
ductile strain
the material changes permanently as a result of stress
brittle strain
a material that is hard but liable to break or shatter easily
displacement
occurs when a block of rock moves from one location to another
distortion
occurs when a body of rock undergoes a change in shape
rotation
occurs when a change in orientation has taken place
stress
a measure of how much deforming force has been applied to a rock
strain
a measure of how much a rock has changed in response to applied stress
elastic-rebound theory
when stress is applied to rocks, they first deform elastically. in this case, the stick bends. Stop the stress and the stick straightens out again
compressional stress
deforming forces squeeze a rock mass, acting directly opposite one another
tensional stress
deforming forces act directly opposite one another to pull an object apart
shear
deforming forces cause blocks of rock to slide past one another
lithostatic pressure
deforming forces are equal from all directions
anticline
a ridge-shaped fold of stratified rock in which the strata slope downward from the crust
syncline
a fold of stratified rock in which the strata slope is upward from the crust
seismic waves
a wave in the earth produced by an earthquake
body waves
solutions of the elastic equation of motion that propagate outward from a seismic source (S and P waves)
surface waves
travel more slowly through the earth’s material at the planet’s surface and are predominantly lower frequency than body waves (love and body wave)
P waves
the fastest body wave. It can travel through solids and liquids
S waves
slower and only travel through solids
wave
produced when a vibrating source periodically disturbs the first particle of a medium
focus
the place within the earth where the energy is released. Within the ground
stick
strain builds up during the quiet periods but friction between the blocks prevents motion
slip
increased stress overcomes the friction and the blocks move
stick-slip fault motion
fault block is not continuous. there is a short episode of movement followed by long quiet periods and then the fault blocks move again
Rayleigh waves
the only waves in which particle motion is circular rather than in a straight line
refraction
Snells Law/ waves bend back towards the surface when traveling through regions where the velocity increases with depth
modified Mercalli intensity scale
measures the amount of damage caused by the earthquake using roman numerals
Richters Magnitude Scale
measures the amount of energy released by an earthquake using Arabic numbers
relative age
statement that a rock is older or younger than another, relative to the other
numerical age
a statement of how many years old it is
uniformitarianism
the assertion that processes that make rocks today also made them in the ancient geologic past
original horizontality
layers of sediment are originally deposited horizontally under the action of gravity
superposition
rock layers are laid upon one another
inclusions
any material that is trapped inside a mineral during its formation
principles used to determine the relative age
uniformitarianism, original horizontality, superposition, inclusions, cross-cutting relationships, faunal and floral succession, graded bed, mud cracks, impressions
disconformity
an unconformity between parallel strata or lava flows, usually very irregular and often with inclusions
angular unconformity
an unconformity between non-parallel strata
nonconformity
an unconformity formed when stratified sedimentary rocks are deposited on eroded igneous or metamorphic rock
half-life
the amount of time it takes for one half of the remaining parent atoms to decay into their daughter products
constructive
forces that build landforms
destructive
forces of erosion that level landforms
slides
solid mass downhill landslides, rockslides
slumps
solid mass rotates and slides downhill
soil creep
the slow mass wasting process of soil on a slope, under the influence of gravity
talus
the pile of rocks that accumulates at the base of a cliff, chute, or slope
