Section K: Tectonic Processes and Landforms

plate

large, rigid slab of solid rock

tectonics

greek origins: to build

what is the theory of tectonic plates

considers the earth’s crust and upper mantle to be composed of several large, thin, relatively rigid plates that move relative to one another as they ride atop hotter, more mobile material (asthenosphere)

what is wegener’s theory of continental drift

continents were originally connected as 1-2 large landmasses that have broken up and drifted apart over several million years

wegener’s theory was based on matching what

• rocks and fossils

• mountain belts

• glacial evidence

• coastlines of s. american and africa

what did wegener call his supercontinent

pangaea (275 million years ago)

why was wegener’s continental drift theory rejected

1. earth’s crust was believed to be too rigid to permit such large-scale motions

2. wegener did not offer a suitable mechanism that could displace such large masses for a long journey

What technological advancement after World War II helped develop the theory of plate tectonics?

Bathymetric mapping using sonar.

What three major ocean floor features were revealed by sonar mapping?

• mid ocean ridges

• seamounts

• deep sea trenches

what are mid ocean ridges

underwater mountain ranges formed by divergent plate boundaries where new oceanic crust is being formed

what are deep sea trenches

Long, narrow depressions in the ocean floor formed at subduction zones where one tectonic plate sinks beneath another

explain the figure

world wide seismographic network by 1960s.

• lines = plate boundaries

• red dots = earthquakes

all plate boundaries have earthquakes

what is seafloor spreading

The process where new oceanic crust forms at mid-ocean ridges and moves outward, pushing older crust away

What two types of evidence support the theory of seafloor spreading

• paleomagnetism

• ocean core sampling - age of ocean floors

what is paleomagetism

the study of Earth's past magnetic fields recorded in rocks

How does paleomagnetism provide evidence for plate tectonics

iron that has cooled in magma orients itself with the magnetic poles of earth which provides a record of past magnetic fields. the magnetic field has changed orientation at least 170 times

how does ocean core sampling provide evidence for plate tectonics

• the youngest crust and thinnest accumulation of sediments is located at the mid ocean ridges

• the oldest curst and thickest accumulation of sediments is located near continents

how do tectonic plates sit and how are they moved

• they float on the asthenosphere and are moved by convection loops driven by earth’s internal heat

• the mantle (magma) plumes from the mantle rise to the crust, spread horizontally and cool, moving segments of the crust

mantle plume

mostly stationary column of hot rock that extends from deep in mantle up to base of lithosphere

what are the two models for plate tectonic motion

1. seafloor spreading- oceanic ridges formed by currents of deep sea magma rising from mantle creating new crust on ridges

2. subduction - older, denser crust descends into earth (melted and recycled)

divergent plate boundary

• seafloor spreading

• rifting

• moving away (extension)

what are the three types of convergent boundaries

• continent to ocean (subduction)

• ocean to ocean (subduction)

• continent to continent (minor subduction)

convergence plate boundaries

plates coming together (compression)

transform plate boundaries

• on sea floor: offsets in mid ocean ridges

• on land: san andreas fault system

• move laterally and horizontally (shearing)

how does seafloor spreading occur (plate divergence)

• two plates move away from each other on the ocean floor due to magma upwelling (mantle plume) from asthenosphere

• the extrusion of magma creates ridge like features

constructive boundary

rock is created

what is rifting

• two continental plates move away from each other due to magma upwelling (magma plume) from asthenosphere

• may cause a gradual split in the landmasses (east african rift valley)

• produces distinct valley landscapes bordered by steep canyon walls

low land

area situated at a lower elevation than surrounding areas, with the potential for flooding

what does rifting cause

earthquakes, volcanic eruptions

what does rifting form

long mountain ranges separated by broad valleys

how do transform plate margins move

• slide horizontally past each other

  • plane of motion is along a nearly vertical break (or fault) that extends through much of the lithosphere

• san andreas fault system

  • transform plate boundary - n. american plate and pacific plate

what is a transform fault

mid atlantic ridge where the seafloor spreading creates transform faults

explain continent to ocean plate boundary

• denser oceanic plate subducts beneath buoyant continental plate

  • destructive boundary because rock is destroyed

  • subduction trenches form next to continents

    • the subducting plate pulls the rest down, causing movement (slab pull)

what are composite volcanoes (continent to ocean)

• magma rises, producing extrusive and intrusive igneous rocks

• continental volcanic arc (a line of volcanoes on land)

  • andes mountains (s. america) or cascades (n. america)

• both shallow and deep earthquakes (due to subduction)

explain ocean to ocean plate bondary

• both plates have similar densities (eventually denser plate subducts)

• features:

  • deep ocean trench

  • deep and shallow earthquakes

  • volcanic island arcs (aleutian island (alaska), japan, mariana islands (w. n. pacific)

• destructive boundary

explain continent to continent plate boundary

• 2 converging continental plates of similar density

  • minimal subduction occurs between mountains (himalayas)

• conservative boundary: rock is neither created nor destroyed

orogeny

a distinct period of mountain building

• compression (plate convergence) can create mountains

terrane

a piece of lithosphere that is ‘added’ to a continental plate

what is an earthquake

a sudden release of accumulated tectonic stress results in an instantaneous movement of the earth’s crust

• seismic waves radiate through the lithosphere

fault

crack in earth’s crust that results in the vertical and or horizontal displacement (movement) of one rock body relative to another

focus

the place in the lithosphere where the fault breaks

epicenter

point directly above the focus

• worst damage, strongest shocks

what are the two types of earthquake waves

body waves and surface waves

what are body waves and explain the two types

they move through the interior of the earth

• p waves (primary)

  • fastest moving waves (compress/relax)

• s waves (secondary)

  • slower moving

  • side to side and up and down shearing motion

what are surface waves

only travel across the surface. slower than s waves and arrive after s waves

what is the richter scale

related to the amplitude of seismic waves on a seismograph (logarithmic scale)

when you jump from a magnitude 6 to 7 earthquake, how much more energy is released

32x increase

when you jump from a magnitude 6 to 7 earthquake, what is the increase in wave amplitude

10x increase

moment magnitude

an accurate measurement of the energy released as a rock moves at a fault

the moment magnitude is calculated using

1. area ruptured along fault plane

2. slip (amount of movement or slippage along the fault)

3. rigidity of rocks near the focus

when is the richter scale more accurate and when is the moment magnitude more accurate

• richter for magnitude up to 7

• moment magnitude for >7

what are the four fault types

1. normal fault

2. reverse fault

3. overthrust fault

4. strike slip fault

what is a normal fault

• extension/tension

• vertical displacement

what is a overthrust fault

• collision, compression

• vertical and horizontal displacement

what is a reverse fault

• vertical displacement

what is a strike slip fault

• compression, shearing

• horizontal displacement

what is a fault zone

weakness in crust, cracks and movement

what is a fault scarp

steep cliff formed by faulting

what is a horst

an upthrown block that lies between two steeply inclined fault blocks

what is a graben

a downthrown block that lies between two steeply inclined fault blocks

tell me about the magnitude and damage from the 2011 great east japan earthquake

• 9.0 magnitude earthquake

• 33 feet tall tsunami destroyed costal towns and villages, carried ships inland, flattened homes

• damage to reactors at nuclear power plant, contaminating the area

ground shaking

shaking of ground decreases with increasing distance from epicenter. loose, unstable regolith, sediments and soil tend to amplify ground shaking

liquefaction

a phenomenon observed during an earthquake when water-saturated soil or sediments become soft or even fluid when ground shaking is strong

landslides

triggered by earthquakes

seiches

waves in lakes and reservoirs

tsunami

generated by underwater fault ruptures. barely perceptible in deep waters but build to heights up to 50 feet in shallow coastal waters

earthquake hazard warnings

ShakeAlert provides 10-60 second advance warning of the arrival of destructive seismic waves from a large earthquake on the u.s. west coast

precursors

warning signs of an impending earthquake such as foreshocks, water changes, radon gas, electrical conductivity changes, bulging ground surface, animal behaviour

what are volcanoes

a mountain or large hill containing a conduit that extends down into the upper mantle, through which magma, ash, and gases are periodically ejected

active volcanoes

have erupted in the last 10,000 years and could erupt again. (there’s hot, moving, mud pots, hydrothermal activity which means there’s magma heating stuff)

dormant volcanoes

not erupted for 10,000 years or more, but could awaken again

extinct volcanoes

have not erupted for tens of thousands of years and can never erupt again

extrusive volcanism

magma expelled while molten (lava)

intrusive volcanism

magma solidifies in shallow crust near surface

plutonic activity

magma solidifies far beneath surface

pyroclastic material

solid rock fragments, dust, ash, and lava bombs thrown in air by explosions

the ring of fire

• plate boundaries exist all around the pacific rim

• primarily subduction zones

• around 75% of all volcanoes lie in the ring of fire

high silica (felsic) eruptions

thick, sticky magma (high viscosity) and violent eruptions

• traps gasses, keeping it in the magma, building up pressure

• associated with composite volcanoes and lava domes (rhyolite)

intermediate silica content eruptions

intermediate viscosity magma (explosive eruption)

• composite volcanoes (andesite)

low silica (mafic) eruptions

thin, runny magma (low viscosity) and quiet, nonexplosive eruption

• associated with shield volcanoes (basalt)

• gasses escaping regularly so no pressure build up

what are cinder cone volcanoes

they are the smallest type of volcano, steep sided, consist of solidified magma fragments, rock debris, and ash (pyroclasts) that are ejected from a central vent, high erodible slopes

how are cinder cone volcanoes formed

they form very quickly following a single eruption, generally found near other volcanoes

what are composite/stratovolcanoes

they are intermediate-high silica level volcanoes with viscous lava that traps gases & builds up pressure, violent eruptions with alternating lava and pyroclastic layers, danger from pyroclastic flow

examples of composite/statovolcanoes

mt fuji, mt kilimanjaro, mt rainier, mt st helens

what is pyroclastic flow

they’re clouds (gas) of hot ash and dust that travel super fast (300km/h) down volcanoes, very low density so can travel across water

what are lava domes (plug domes)

small irregular shape, slow eruption of felsic lava (high silica) so magma is viscous and thick, viscosity leads to lava piling up around the vent - creating dome like shape

• most explosive volcano

what are shield volcanoes

have very fluid eruptions

• magma has low silica and low viscosity

• lava flows as rivers of molten rock with little/no pyroclastics

• very tall with shallow sloping sides

• mauna loa hawaii

what is a hotspot and how is it formed

• volcanoes found over a hot mantle plume in the asthenosphere

• mantle plume is stationary, and plate moves over it

• occurs under oceanic or continental crust

what is a seamount

extinct underwater volcano that does not reach the surface. high species diversity and biomass around sediments

what is a seamount chain

trail of islands and seamounts (submerged, eroded shield volcanoes) that developed over a stationary mantle plume (hotspot)

(hawaiian islands and emperor seamount chain)

what is a caldera

large bowl shaped depression formed by the collapse or explosion of a volcano

what are some volcanic hazards

• volcanic gases - h2o, co, co2, so2, hcl, hf

• lava flows - property damage

• eruption column

• pyroclastic density current

• lahar

what is lahar

volcanic mudflow from heavy rain and or snow melt during an eruption

• consistency of concrete when stationary