unit 1 - plate tectonics

coastline fit

coastline fit

• close land fit between the coastlines of the continents

• coastlines fit together like puzzle pieces

• south america fits really well into africa

geological fit

• close geological correlation across landmasses

• shield and non-shield areas align, mountain ranges fit into mountain ranges

paleoclimatology

• study of past climates show that certain areas had the same climatological history that would only be possible had they been attached/in the same location

• some of the strongest evidence

paleoglaciation

• continental glaciation that correlated between land masses would have been impossible unless these continents were once united

fossil correlation

• fossil remains of pre-mesozoic life are uniform and correlate between the southern continents

• would be impossible for these plants and animals to have crossed the oceans as they are today

paleomagnetism

• within ocean basins where molten magma is extruded, there is evidence of plate movement as the magma shows signs of reversal of magnetic polarity over time

• in the ocean basin, the molten magma is thrusting through the earth, north is true north, but over time true north reverses

3 types of plate movement

• diverging, converging, and transforming

divergent/diverging plate boundaries

• moving away from each other

• forms new lithosphere and is the youngest land on earth

• creates mid-ocean ridges or rift zones (ex. east african rift valley)

• seafloor spreading can lead to mid-ocean ridges

converging plate boundaries

• moving together

• when 2 plates are moving towards each other, 1 plate will eventually be pushed down under the other plate due to variations in density

• 2 continental plates converge: may form mountains

• continental plate and oceanic plate converge: oceanic plate will subduct and create a trench

• 2 oceanic plates converge: process is longer, eventually one will begin to descend and be reclaimed by the mantle (may form a string of volcanic islands)

subduction zone

• where the lithospheric crust is being pushed under and reclaimed by the mantle (where the oldest rock material is found)

• occurs when an oceanic and continental plate meet

transforming plate boundaries

• occurs when 2 plates slide horizontally past each other

• surface area is neither created or destroyed

• known as a tear or strike-slip fault

• great friction between the 2 plates, and if they become locked massive earthquakes can occur when the pressure releases

types of faults

• normal, reverse (compression), strike-slip, horst, graben

normal fault

• plates move away from each other

• one goes up, one goes down

reverse (compression) fault

• plates converge, one goes up, one goes down

strike-slip fault

• transform boundary

horst fault

• block mountain, occurs under tension

• like a horse, you can mount it

graben fault

• rift valley, also created under tension

• looks like someone grabbed chunks out of it

types of rocks

• sedimentary, metamorphic, igneous

sedimentary rocks

• formed from layers of sand, silt, dead plants, and animal skeletons, mainly found in watery areas ex. sandstone

metamorphic rocks

• formed from other rocks that are changed by heat and pressure underground, found in mountainous regions ex. marble, quartz, slate

igneous rocks

• formed from melted rock deep inside the earth, found in volcanic regions ex. gabbro, basalt (in oceanic crust), granite, andesite (continental crust)

types of volcanoes

• cinder cone, shield cone, composite cone

cinder cone

• predominantly found on continents

• made up of acidic lava

• made of layers of cinder and ash

• compact/small in size

• highly violent and explosive

• associated with pyroclastic flows

• fast cooling = can cause clogged neck ex. Mt. Fuji

shield cone

• large and gentle sloping

• basic lava (basaltic lava) = wet like concrete

• do not violently erupt, instead ooze -> any accounts of violent eruption tend to be from steam as the lava comes in contact with the water

• cools very slowly and spreads over large areas

• predominantly found on ocean floors ex. Hawaiian Islands

composite cone

• most often formed over subduction zones (Pacific Ring of Fire)

• symmetrical formation with cake-like layers of lava and ash

• snow and ice-capped

• more moderately sloped than cinder cones

• tend to be larger in size

• sudden and violent eruptions ex. Pacific Ring of Fire

fissure

• juicy crack

• more associated w/ oceanic crust and occur when magma flows up through cracks in the crust and "erupts"

hotspot

• an area on the earth's mantle where magma rises up to melt through the crust, creating volcanoes or volcanic islands

types of eruptions

• lava flows, tephra flows, pyroclastic flows, mudflows

lava flows

• pour or ooze out of vents or cracks

• causes majority of harm to non-moveable objects (trees, cars)

• basaltic lava can travel vast distances vs. andesite lava that rarely goes past ~8 km.

• objects and terrain are either surrounded, buried or ignited

tephra flows

• made up of cinder and ash (super concentrated)

• majority of fragments fall back onto the slope, enlarging it

• alters climate

pyroclastic flows

• hot and dry rocks, gases and lava pieces

• fast-moving and dense <- 200m/s (like an avalanche in this sense)

• will burn anything in its path

• considered the most deadly of hazards (another name for the deadly gases and debris is nuees ardentes)

mudflows

• same consistency as cement

• happens when the steam, heat or lava from the volcano melt the snow-capped tops and ice, and that watery runoff mixes with ash, debris and dirt to create a mudflow

pros of volcanoes

• creates igneous rocks that can be used as building materials

• creates fertile soil

• a source of geothermal energy

• tourism! (slay)

cons of volcanoes

• destructive

• can cause lots of air pollution b/c of the ash (like Mt. St. Helens)

• can have many casualties if they erupt aggressively and without fair warning

• gas will kill you

caldera

• forms because the magma chamber empties/oozes out so fast that the volcanoes lose their structural integrity

• also forms because the explosion is so violent that the volcano blows its top off

batholith

• largest feature, looks like a giant pool of magma underground

laccolith

• 2nd largest feature

• found between layers

• usually dome-shaped but smaller

dike

• cuts through multiple layers (across)

sill

• stuck between layers

• cuts in between layers

earthquake

• when stress-deformed rocks break or release pressure by elastic rebound or sudden shift in position and severe shaking of the ground may occur

• lasts ~10-30 s

wave types

• body waves and surface waves

• primary waves, secondary waves, surface waves

primary wave

• aka compression wave

• a type of body wave (much smaller)

• travels by compressing and expanding the ground

• the fastest

• first to reach the earthquake recording stations

secondary wave

• aka shear wave

• second wave generated by quakes

• slower than the primary waves and travels in a side-to-side motion

surface wave

• more extreme + aggressive

• travels like ripples through calm water

• responsible for ground shaking which causes much of the damage during earthquakes

• includes love waves (move back + forth) and Rayleigh waves (rolling)

aftershocks

• smaller earthquake that follows a larger earthquake

• occurs in the same area of the crust/fault

focus

• the location where the fracture/shift occurs and the seismic waves originate

• depth varies but can be as deep as ~700km

epicentre

• located on the surface of the earth directly above the focus point

tsunami

• a series of waves caused by the displacement of water from an earthquake

magnitude

• a measure of the size/amplitude of the seismic waves generated by an earthquake

• recorded by seismographs

richter scale

• goes from 1 to 8.9

• each number is 10x stronger than the previous

• usually a tremor less than 3 will not be felt

• a 6.5 and above will cause extensive damage