Unit 3 - Geological Processes

inner core

solid, composed of mostly iron and nickel, it reaches ~ 5000°C with tremendous pressure

outer core

liquid, convection forms the Earth's magnetic field

mantle

composed of hot, dense rock that flows like hot asphalt due large temperature changes in the mantle that create convection currents (deep hot rock rises while cooler rocks sink)

crust

very thin, 5-30km thick, generally composed of granite (continents) and basalt (oceans) that make up the tectonic plates that move

lithosphere

the Earth’s outer layer, includes the crust and uppermost layer of mantle

asthenosphere

layer between the lithosphere and the lower mantle, movement due to convection currents drives plate tectonics

boundaries

areas where tectonic plates meet

divergent boundaries

regions where two tectonic plates are moving away from each other, cracks between plates fill with magma from the asthenosphere to form new crust

rift valley

divergent boundaries on continental crust form a long narrow depression

convergent boundaries

two plates move towards each other and collide, the denser plate bends and descends below the other in a process called subduction.

subduction zone

lithosphere is being subducted or pushed down into the mantle

oceanic-continental convergence

as the oceanic rock gets pushed down, forming a deep trench, it begins to melt and build up pressure, leading to a volcanic arc at the edge of the continental plate

volcanic arc

string of mountains/volcanoes formed by an oceanic plate subducting under and uplifting a continental plate

oceanic-oceanic convergence

one plate gets pushed under the other (forming a deep trench), the heat produced near the subduction zone melts the rock of the overlying plate, causing magma to form and rise to produce volcanic formations

volcanic island arc

chain of volcanic islands in the ocean formed by one oceanic plate subducting under and uplifting another

continental-continental convergence

continental plates collide but neither subducts, they crumple, fold and uplift occurs

transform boundaries

when tectonic plates slides past each other crust is neither created nor destroyed, rather it is only deformed

strain

rocks resisting movement and bending

stress

the force exerted on rocks, causing them to bend

elastic rebound

vibrations from an earthquake deforming the land around it

focus

the exact location within the crust where an earthquake occurs

epicentre

the point on the surface above where an earthquake is first felt

fault

a crack in a tectonic plate

aftershock

smaller vibrations following an earthquake, can often cause more damage than the quake itself

foreshock

smaller vibrations preceding a large earthquake

what defines an earthquake

the orientation and magnitude of the stress and the type of rock material

tension

stress that lengthens the material

compression

stress that squeezes the material

shear stress

stress that twists the material

hanging wall

the steep, overhanging side of a fault

foot wall

the inclined side of a fault

reverse fault

caused by compression, hanging wall rises

normal fault

caused by tension, hanging wall sinks

strike-slip fault

caused by shear stress, both walls move horizontally

fault creep

sections of a fault moving slowly over a period of time

stick-slip motion

sections stick, build up pressure, and then shift suddenly producing an earthquake

seismograph

device that records vibrations from earthquakes

seismogram

traces recorded of earthquakes

P-waves

travel through solid and liquid rock with a compressing motion

S-waves

travel only through solid rock with a side-to-side motion

surface waves

travel along the surface of the earth up and down and sideways, arrive last and are most destructive

2 uses of seismic waves

data regarding earthquakes, data regarding the composition of Earth's interior

refraction

what happens to P-waves when they travel across boundaries

S-wave shadow

area on the opposite side of the Earth from a quake where S-waves are not detected, revealed an inner liquid core that completely blocked these waves

richter scale

logarithmic scale to categorize earthquakes based on wave size and distance from epicenter

moment magnitude scale

more accurate scale to categorize earthquakes based on a wide variety of factors

modified mercalli scale

scale that categorizes earthquakes based on the amount of damage to society and the amount of humanitarian aid needed

Wadati-Benioff zone

zone along a subducting plate where most earthquakes occur

liquifaction

during an earthquake, ground already saturated with water becomes unstable and turns into a mobile fluid that can no longer support structures

tsunami

massive sea waves caused by underwater earthquakes or landslides

Indonesia tsunami

December 26, 2004, a 9.0 magnitude earthquake off the coast of Sumatra forms a massive wave that kills over 230,000 people and devastates southeast Asia

Japan tsunami

March 11, 2011, a massive earthquake off the east coast of Japan causes a massive wave that kills over 15,000 people

other issues with earthquakes

landslides, ground subsidence (dropping), fires

volcanoes

all processes involving the discharge of magma, hot fluids, and gases

which areas produce the most volcanoes

subduction zones

volcanism at convergent plate margins

magma is generated in the subduction zone by the partial melting of the oceanic crust, it rises through the upper plate, mixing with minerals, rock and sediment from the overlying plate, if it makes it to the surface it is extruded through composite volcanoes usually in mountain belts (volcanic arc)

tephra

combination of gas, rock, and magma that is released violently during volcanic eruptions

pyroclastic flows

columns of tephra and hot ash that race down the sides of mountains and kill everything in their paths

volcanoes at oceanic-oceanic convergent boundaries

less violent explosions due to high viscosity, low silica content in basaltic magma,produces island arcs

pillow lava

when basaltic lava reaches the ocean

volcanism at divergent plate margins

basaltic magma (dark mafic rock) is generated by the partial melting of the asthenosphere and is nonexplosive, extruded largely as pillow lava

volcano hot spots

volcanic chains form when a tectonic plate moves over a mantle plume or hot spot that leaks magma onto the surface, forming islands such as Hawai'i

flood basalt

when magma extrudes from a hot spot into cracks in a plate

magma chamber

underground pool of magma beneath a volcano

conduit

path that magma follows from the chamber to the surface

vent

region where magma from underground reaches the surface

crater

land depression formed by magma erupting up from underground, usually less than 1km in diameter

caldera

a very large crater formed from a massive volcanic eruption, can often collapse and fill with water to form a lake

mafic eruption

50% silica, high in Fe and Mg, low viscosity, gas escapes easily, mild eruption

intermediate eruption

60% silica, moderate Fe and Mg content, moderate viscosity, some gas is trapped, moderate eruption

felsic eruption

70% silica, low Fe and Mg, high viscosity, lots of gas is trapped, violent eruption

pluton

an intrusive volcanic feature

batholith

extra large pluton, common in mountain chains

laccolith

magma that intrudes layers of rock and uplifts the rock above

sill

layer of magma intrusion parallel to other bedrock layers

dike

jagged magma intrusion cutting through bedrock

cinder cone volcano

small cone-shaped mound formed from layers of volcanic ash

shield volcano

large, flat volcano with runny lava that forms thin layers into a dome shape

composite volcano

most common type of volcano, forms from alternating lava flows and tephra eruptions, lava is trapped easily leading to violent eruptions

weathering

changes to the appearance and composition of rocks on the Earth's surface

3 types of weathering

biological, chemical, mechanical

4 agents of mechanical weathering

ice, wind, running water, gravity

joints

curved cracks that form parallel to the rocks surface from a release of pressure on the rock

exfoliation

when joints form on the surface of a rock and the rock breaks into curved sheets that peel away

ice wedging

water seeps into a crack in a rock and freezes, expanding the crack, this process repeats and the crack grows bigger until the rock splits

abrasion

rocks collide with each other through gravity, running water, or wind, and break or wear each other down

chemical weathering

chemical reactions take place between the rock and CO2, acids, water, or oxygen, changing the chemical and physical appearance of the rock

hydrolysis

when minerals react with water to form new minerals and compounds

4KAlSi 3 O 8 + 4H+ 2H 2 O = 4K + Al 4 Si 4 O 10 OH 8 + 8SiO 2.

equation of hydrolysis of feldspar

hydrolysis of feldspar forms

kaolin clay, acids, quartz

leaching

when minerals affected from hydrolysis dissolve in water and seep into underlying rock layers

carbonation

CO2 dissolved in water produces carbonic acid, which reacts with minerals to form a new product

underground caverns are formed by

calcite in limestone reacting with carbonic acid, forming calcium bicarbonate which wears away easily

oxidation

when metals in rock combine with oxygen to produce metal oxides

acid precipitation

ordinary rainwater combines with nitrogen dioxide and sulfur trioxide to form sulfuric and nitric acids which greatly accelerate chemical weathering

examples of biological weathering

plant roots, animal digging, cellular respiration producing CO2--> carbonic acid

factors affecting rate of weathering

climate, amount of exposure, rock composition, topography

how does climate affect weathering

warm, rainy climates with lush vegetation increase the rate of weathering

how does rock composition affect weathering

sedimentary rocks weather much faster than metamorphic or igneous rocks

rocks containing ________ weather faster than rocks containing ________

calcite, quartz