SECTION K: Tectonic Processes and Landforms

Plate

Large, rigid slab of solid rocks

They move, either slide under or go together

Tectonics

Greek origins: to build

What is the theory of plate tectonics?

Considers the earths crust & upper mantle to be composed of several large, thin, relatively rigid plates that move relative to one another as they ride atop the hotter, more mobile material (asthenosphere)

Is this theory supported?

YES, by a wide range of evidence

When we talk about the plate tectonics we are referring to…

The lithosphere that float/ride on the hot sticky material in the asthenosphere

An important component of plate tectonics is..?

Continental drift

Continental drift?

Wegener’s theory of continental drift.

Proposes that continents were originally connected as 1 or 2 landmasses that have been broken up & drifted apart for several million years

What do we call these 1-2 landmasses that used to exist ?

Supercontinent PANGEA

Around 275 million years ago

Wegener’s theory is based on…

Matching :

Rocks & fossils

Mountain belts

Glacial evidence

Coastlines of S America and Africa

Did people accept Wegener’s theory ? Why?

NO

Because they thought the lithosphere was too rigid to move that much

And

Wegener didn’t know why/ couldnt explain how the continent could have moved that much

SO

The theory was rejected and he died on an expedition before ppl started accepting it

What are the 3 forms of evidence we have today for the plate tectonic theory?

1 — detailed map of the ocean floor

2 — plate boundaries

3 — sea floor spreading

—3A : Paleomagnetism

—3B : Ocean core sampling

Detailed map of the ocean floor was provided when and how?

After World War II

By bathymetric mapping, which provided evidence that led to development of theory of plate tectonics

In the 1950’s and 60s ____________ revealed?

Deep sea soundings via sonar revealed

Mid ocean ridges

Seamounts

Deep sea trenches

Mid-ocean ridges?

Areas in the oceanic crust where there’s new oceanic crust being created

Seamounts ?

Flat topped, old, eroded volcanoes that are underwater

Deep-sea trenches ?

Very deep in the ocean, maximum bottom of the ocean

The deepest one is Mariana’s trench

Plate boundaries contribute to…?

Evidence for plate tectonic theory (Wegener’s theory that was rejected)

What are plate boundaries ?

The boundary around each plate tectonic

Image of plates in relation to earthquakes (red dots)

Which plate boundaries have earthquakes ?

ALL PLATE BOUNDARIES including mid-ocean ridges

But some generate more earthquakes

The third evidence for plate tectonic theory?

Seafloor spreading !

Who/ when was the theory of sea floor spreading proposed? What is it supported by?

In 1960, Harry Hess proposed the idea of seafloor spreading which later developed into broader theory of plate tectonics

The theory is supported by two sets of evidence :

A — paleomagnetism

B — ocean core sampling / age of ocean floors

Paleomagnetism is

The first way to verify seafloor spreading:

Iron in cooled magma orients itself with the magnetic poles of earth

Provides a record of past magnetic fields

Magnetic field has changed orientation at least 170 times

Ocean core sampling

The second way to verify seafloor spreading:

Youngest crust & thinnest accumulation of sediments at mid-ocean ridges

Oldest crust & thickest accumulation of sediments near continents

What moves plate tectonics ?

Plate tectonics “float” on the asthenosphere but move by convection loops meaning they are driven by earths internal heat.

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

The model for tectonic plate movement consists of …

Seafloor spreading: oceanic ridges formed by currents of deep magma rising from the mantle which creates new crust on ridges

Subduction:

Older crust descends into earth (melted and recycled)

Which plate sinks during subduction ?

THE DENSER ONE

Plate boundaries overview (be able to draw this on paper)

Image:

When does plate divergence happen ?

Seafloor spreading (mid ocean ridges)

Rifting (rift valleys)

Types of plate convergence ?

Continent to ocean (subduction)

Ocean to ocean (subduction)

Continent to continent (minor subduction)

Where do transform plate margins occur ?

On sea floor : offsets in mid-ocean ridges

On land : San Andreas fault system

No subduction

First type of plate divergence

Seafloor spreading :

Creates mid-ocean ridges

Two plates move away from eachother on the ocean floor due to magma upwelling (mantle plume) from asthenosphere

The extrusion of magma creates ridge-like features on the seafloor

Seafloor spreading is a ________ plate boundary.

Constructive.

Because new rock is being created

Second kind of plate divergence

Rifting:

When two continental plates move away from eachother due to magma magma upwelling (magma plume) from asthenosphere

May cause gradual split in the landmass e.g. East African rift valley

What does rifting produce?

Produces distinct valley landscapes bordered by steep canyon walls

Then, lowlands can fill with water, forming lakes (lake victoria)

Effects of rifting (3)

Elevates region

Causes earthquakes, volcanic eruptions

Forms long mountain ranges separated by broad valleys

Transform plate margins are..?

Boundaries where plates slide horizontally past eachother

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

Example of transform plate boundary?

The San Andreas Fault System

North American & pacific plate

California magnitude 6-7 usually San Andreas

What type of boundary is a transform plate margin ?

Conservative

Because there’s no rock being created

Transform fault

Mid-Atlantic ridge

Seafloor spreading creates transform faults

1906 earthquake ?

San Francisco earthquake

700 people died and 30$ billion in damage

From the San Andreas fault system

1989 earthquake ?

Loam prieta earthquake

Also caused by San Andreas fault system

62 ppl died and 6$ billion in damage

In the next thirty years California has a ____ chance of a large earthquake bigger than magnitude 6.7

72% chance

Three types of plate convergence ?

Oceanic to continental crust

Oceanic crust to oceanic crust

Continental to continental crust (minor or NO subduction)

Ocean to continent plate convergence

Denser oceanic plate (3.0g/cm3) subducts beneath buoyant continental plate (2.7g/cm3)

Destructive boundary because rock is destroyed (subduction)

Subduction trenches form next to continents

What is slab pull

The subducting plate pulls the rest down, causing movement

Ocean to continent convergent plate boundary can cause …

Composite volcanoes

Composite volcanoes

When magma rises, producing extrusive and intrusive igneous rocks

Continental volcanic arc

E.g. cascades (North America), Andes mountains (South America)

Created when a plate going down so theres stuff coming up onto land

Which earthquakes are caused by ocean to continent convergence plate boundaries ?

Both shallow and deep earthquakes (due to subduction)

Can be as deep as 600km below surface

Ocean-to-ocean convergent plate boundaries

Both plates have similar densities but the denser one subducts

Features of Ocean-to-ocean convergent plate boundaries

Deep ocean trench

Deep and shallow earthquakes

Volcanic island arcs:

e.g. Aleutian Islands (near Alaska), japan, and Mariana islands (western North Pacific )

Destructive boundary because rock is destroyed, associated with subduction

Continent to continent plate boundary

2 converging continental plates of similar density

Minimal subduction occurs because too buoyant so they crash and crumble

No subduction means no deep earthquakes

Mountains are created

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

The west coast mosaic of terranes

Summary of plate boundaries (photo)

Earthquakes are

A sudden release of accumulated tectonic stress results in an instantaneous movement of the earths crust

Seismic waves radiate through the lithosphere

Joint ?

A crack no movement

Fault ?

Crack in the earths crust that results in the vertical &/or horizontal displacement of one rock body relative to another

Focus ?

The placed in the lithosphere where the fault breaks

Epicentre ?

Point directly above the focus

On the surface, normally where the most damage happens

How do earthquake waves move?

Body waves : 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

AND

Surface waves : only travel across the surface, slower than S waves

Some side-to-side, rolling action, different ones move differently

What is one way to measure earthquake magnitude?

Richter scale

Richter scale is a measurement of ?

Measurement of energy released during an earthquake, compares relative “size” of earthquakes

Richter scale accuracy and development ?

Developed in 1935 by Charles richter

Only accurate to about 7 magnitude

What type of scale is the Richter scale?

Logarithmic scale : 0-9

Related to the amplitude of seismic waves on a seismograph

Each whole number represents →

around 32x increase in energy released

10x increase in wave amplitude

Another way to measure earthquakes

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

How is moment magnitude calculated ?

Area ruptured along the fault plane

Slip (amount of movement or slippage along the fault)

Rigidity (which is a studied, known value) of rocks near the focus

More accurate above 7.0 earthquakes

What type of relationship does magnitude and frequency have

Inverse relationship

Types of earthquake faults

Normal fault

Reverse fault

Strike-slip fault

Overthrust fault

Normal fault

Tension / extension : blocks of land moving away from eachother

Verticale displacement

Reverse fault

Collision / compression : land pushing together

Vertical displacement

Strike-slip fault

Shearing (side-by-side) displacement is horizontal : no tsunamis at strike-slip because tsunamis need vertical displacement

Overthrust fault

Compression: vertical and horizontal displacement, often associated with subduction

Fault zone

Weakness in crust

Fault scarp

Steep cliff formed by faulting

Horst

“Horstin’ it up!”

An upthrown block that lies between two steeply inclined fault blocks

Graben

“Graben it down”

A downthrown block that lies between two steeply-inclined fault blocks

Example of Graben in Canada ?

Ottawa-Bonnechere Graben has two faults, pulling apart, causing the land to sink in the middle

Causes earthquakes

What earthquake related disaster happened in 2011?

Great east japan earthquake

9.0 magnitude earthquake, most powerful ever recorded in japan

Tsunami 33 feet high

Hit Sendai (10m)

Damage from 2011 japan earthquake ?

Destroyed coastal towns and villages, carried ships inland, flattened thousands of homes, then washed tons of debris and vehicles back out to sea

Damage to the reactors at TEPCO’s Fukushima Daiichi Nuclear Power Plant

Contaminated a wide area that still forced around 100,000 residents to evacuate

Around 16,000 died

What’s a volcano?

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

BUT Yellowstone hasn’t erupted in 600 000 years but the magma is still hot and moving so it might again

What indicated activeness ?

Magma or hydrothermal properties

Dormant volcanoes ?

Not erupted in the last 10,000 years or more but could erupt 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 the surface

Plutonic activity ?

Magma solidifies beneath the surface

Pyroclastic material ?

Solid material that comes out volcano

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

The ring of fire is also called ?

Circum-Pacific Belt / Andesite line

What is 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

Something high silica is called …

Felsic

Low silica is called …

Mafic

Result of high silica eruptions ?

Thick sticky (high viscosity) and violent eruption

Associated with composite volcanoes and lava domes (rhyolite)

Blow themselves up and collapse because highly explosive because bubbles of gas are trapped in thick magma and pressure builds up

Intermediate silica eruptions ?

Intermediate viscosity magma, explosive eruptions traps quite a bit of gas but not as much that it blows itself up

Composite volcanoes (andesite)

Low silica eruptions ?

Mafic eruptions

Thin runny magma (low viscosity), quiet, non-explosive eruptions

Associated with shield volcanos (basalt)

Know this chart:

Types of explosive volcano ?

Cinder cone volcano

Composite / stratovolcanos (synonyms)

Cinder cone volcanoes

Form very quickly following a single eruption

Generally found near other volcanoes

Steep sided

Consist of solidified fragments, rock debris, and ash (pyroclasts) that are ejected from a central vent

Highly erodible slopes (erode over a shorter amount of time)

Composite / stratovolcanoes

Very violent eruptions

Made of alternate levels of high silica levels (andesite lava)

Lava is viscous : it cools and hardens before spreading far

The viscous lava traps gases & builds up pressure

Alternates lava & pyroclastic layers

Danger from pyroclastic flow

Which type are found in the ring of fire ?

Composite / stratovolcanoes