Planet Earth Exam 3 Terms

Sagami Bay

An example of a place that has lithophaga (animals that eat rocks by boring into them), that live between high and low tide water line

Faults

The breakage of rock, causing them to be offset

Folds

Beds become twisted and bent by plate tectonics

Compression

A force that squeezes together and shortens a rock (convergent boundaries/subduction zones)
-Results in folding (plastic) and faulting (brittle)

Tension

Forces that stretch and pull apart a rock body (Divergent boundaries/mid-ocean ridges)
-Results in stretching/thinning (plastic) and faulting (brittle)

Shear stress

A force that pushes two sides of a body in opposite directions (transform boundaries/strike slips)
-Results in shearing (plastic) and faulting (brittle)

Strain

The reaction of rocks to stress

Elastic deformation

A change in the object under stress that disappears when the stress is removed. Reflects rock elasticity.

Brittle deformation:

The cracking and fracturing of a subject under stress. This is a permanent change. Happens at shallow depths and cold environments with low pressure

Plastic deformation:

A permanent deformation type. The bending of rock under increasing force. It requires great heat and pressure (like deep inside the earth)

Factors that affect the type of deformation

Temperature
Pressure
Strain rate (how fast)
Rock type

Formations

The basic lithological unit referring to a rock body that is differing from its over and underlying units and is mappable

Contour lines

A line on a map connecting points of equal elevation. You can use this to map the height above sea level

Strike

Bearing of a line defined by the intersection of a bedding plane and the horizontal

Dip

Acute angle between a bedding plane and the horizontal, measured perpendicular to strike

Types of dips

Anticlines: A fold of rocks where the beds dip away from the center. The oldest rocks are exposed.

Syncline: A fold of rocks where beds dip toward the center. The youngest rocks are exposed.

Types of folds

Plunging folds: The hinge line is not parallel to the ground

Symmetrical folds: Axial plane is vertical

Asymmetrical folds: Beds in one limb dip more steeply than those in the other

Overturned folds: Both limbs dip in the same direction but one limb has been tilted beyond vertical

Joint

a break in the rock with no movement

Fault

A break in the rock with movement

Strike-slip faults:

Shearing. Can be left-lateral or right-lateral faults depending on the way the rocks are skewed.

Dip slip

Normal (Hanging wall moves down. Tension. Divergent) or reverse (hanging wall moves up. Compression. Convergent.)

Can sometimes be thrust faults- a low-angle reverse fault

Where are the most active volcanos?

Mid-ocean ridges
Areas of compression: the pacific ocean
Subduction zones

Structure of volcanoes- Plumbing system

-Crater: The circular depression on top
-Vent: Where the lava comes out
-Pipe: Connects vent to magma chamber
-Magma chamber: Area of liquid rock below the surface

Caldera

A type of crater that is more than one km in diameter

Volcanic neck

Inner portion of a volcano that is resistant to erosion. Also referred to as its erosional remnant.

Cloud composition:

The convective region, umbrella region, and gas thrust region.

Materials extruded during an eruption

Lava, gases, pyroclastic materials (solid rock)

If the lava is hotter, has more dissolved gas, and has more silica...

It will have less viscosity and flow easier

Aa:

Type of lava. Blocky, more cooled, less dissolved gas

Pahoehoe

A hot, fast-moving type of lava that hardens to form smooth, ropelike coils

Lava that is more viscous will make volcanos erupt \_____ \________ because it cannot escape easily

More explosively

Fissure explosions

Have basaltic lava with low viscosity and flow long distances

Volcanic mudflow (Dangerous)

A mixture of water and pyroclastic material in a concrete-like slurry capable of moving up to 100 km/hour

Erupting column

Air is so hot inside the volcano that the materials inside are launched and spread as high as the stratosphere (mushroom cloud)

Pyroclastic flow (Very dangerous)

A mixture of hot gas, ash, and rocks moving at 150 km/hr that flows down a volcano

Shield volcanoes

Gently sloping mountains formed by thin, runny lava. Very wide and low.

Cinder cones

-Short-lived volcanos
-Typically ~300 meters, small with steep sides
-Formed from pyroclastics

Stratovolcanos (composite volcanos)

-Alternating pyroclastic layers and lava flows
-Lava made of andesite
-Found in the ring of fire and the Mediterranean

Focus

spot inside the earth where the rocks first fail

Epicenter

point on the surface above the focus

Faulting terms

Fault slip: The distance that the fault moved

Fault trace: being able to see how far plates have moved

Fault scarp: Vertical movement during an earthquake

Types of shocks

Foreshocks: Smaller earthquakes that precede a major earthquake

Aftershocks: Smaller earthquakes that follow a major earthquake

Elastic rebound theory

Tectonic forces will slowly deform rocks until the forces holding the rocks together are overcome and the stored energy is released

Body waves

Travel through the Earth's interior

P-waves

Primary or push-pull waves. These are the fastest waves, they travel at 6km per second. They change in volume and can travel through liquids and solids.

S-waves

Shear or secondary waves. 2nd the fastest waves, traveling at 3.5 km per second. They can change in shape, but cannot travel through liquids.

Surfaces waves

Travel along the Earth's surface
These have the greatest amplitude and cause the most damage
Can have rolling or side-to-side motion

Three ways to measure an earthquake:

1. Measuring the amount of damage caused
2. Measuring the size of the seismic waves
3. Measuring the amount of energy released

Modified Mercalli intensity scales

Measuring the effects of the earthquake on both people and buildings

Problems: It depends on how much civilization is around the area and what the structures are built on.

Magnitude scales

Measurements based on how much the ground shakes
- Richter scale: putting a number to how large the waves received are
Size is logarithmic: Increase 1 unit\= 10 times greater shaking

Problems: Big earthquakes get saturated and you cannot measure all the energy released

Moment magnitude

Based on the amount of energy released
Determined based on what has failed by looking at:
1. The strength of the rocks
2. The area of the rocks that broke
3. The distance that rocks moved

How can we examine the earth's interior?

Looking at how seismic waves move through the interior of the earth with seismographs

How many seismographs are needed to determine the direction of an earthquake?

3

Order of wave arrivals at a seismograph:

P, S, then surface

Travel-time curves

Give us the distance from the seismograph to the epicenter through determination not calculation.

How can you tell the distance to the epicenter?

The difference in time between the arrival of the p and s wave will be longer depending on how far away you are from the epicenter

Seismic wave velocities \_________ with depth in the earth

increase

When seismic waves pass from a layer with certain seismic properties to another with entirely different ones, two things occur

1. Reflection: Some waves bounce off of the next layer
2. Refraction: Waves travel into the next layer but are bent

From faster to slower velocities...

Waves bend down

From slower to faster velocities...

Waves bend up

Seismic line

Give us a kind of x-ray of the earth
Shows us all the surfaces where seismic waves change direction

The low-velocity zone

Where all seismic wave velocities are low (this is between 100-200km down). This is because, at this part of the mantle (the asthenosphere), the rock is much weaker and more plastic.

The transition zone

The middle portion of the mantle, from 400 to 670 km deep, in which there are several jumps in seismic velocity.

How thick are the lithosphere and continents under the ocean?

Lithosphere - 125km thick
Continents - 200km thick

Continents elevation

840m

Ocean elevation

4km/4,000m

P-wave shadow zone

P waves dying out from 105 degrees to 140 degrees because the P waves bend at the liquid core.

How do we know that the outer core of the Earth is liquid?

S waves cannot move through it.

S-wave shadow zone

Those areas more than 103 degrees from an earthquake focus where no S-waves are recorded.

Lithosphere

The uppermost mantle and the crust

Seven Major Plates

North American, South American, Pacific, African, Eurasian, Australian-Indian, Antarctic

How fast do plates move?

2-10 cm per year

The four basic concepts of plate tectonics

1. The outer portion of the Earth is composed of rigid plates
2. The plates move
3. Plates deform at their edges
4. Interiors are quiet

Thickness of components of the Earth

Continental crust \= 40-65 km
Continental lithosphere \= 200 km
Oceanic crust \= 5-8 km
Oceanic lithosphere \= 125 km

Most large-scale geological activity happens at:

Plate boundaries

Craton

A portion of a continental plate that has been relatively undisturbed since the Precambrian era

Shield

Exposed part of the craton.

Platform

Covered part of the craton

The east coast of the US is a...

Passive margin (not a plate boundary. No activity)

Hawaii is over

A mantle plume (hot spot)

Hawaiian islands are younger to the

Southeast

Benioff zone

Topographic image of the subduction zone beneath Japan. He found that as you get farther away from the trench, the deeper earthquakes become

Ophiolite

Slice of ocean floor that was lifted up onto a continent

What do we get at continent-continent collisions?

Mountain ranges (plates scrunch up because one cannot go under the other)

Convective drag

Mantle convection currents carry lithospheric plates along the top
Think: Conveyor belt in two directions

Ridge Push

The mid-ocean ridge is higher than the adjacent abyssal plain. The sea floor slides away and down from the ridge axis (the highest point)

Slab pull*

As plates move away from the hot ocean ridge, they cool off and become denser. Eventually it gets pulled down into the mantle due to its own weight.

Divergent boundaries (Spreading centers, the mid-ocean ridge)

Stretching stress, basaltic magma, shallow earthquakes
-Creation of new ocean floor
-Tension features: Graben, volcanism, ridges (expanded, hot crust)

Grabens:

A block that has dropped downward between two normal faults

Convergent boundaries (subduction zone)

Compressive stress, granitic, magma, intermediate-depth earthquakes
-Creates trenches where plates are destroyed

Transform boundary

Shearing stress and shallow earthquakes

Layers of the ocean crust

1. Oceanic sediments: Mud and skeletons (0.5 km thick)

2. Pillow basalts/lavas: meter-wide blocks of basalt. Forms from lava erupting underwater (0.5km thick)

3. Sheeted dikes: Basalt that rises into cracks in rocks (1.5 km thick)

4. Gabbro: Same chemical composition as basalt but with larger crystals (cools slower) (4-5km thick)

Continental rifting

Hot spots can hit the bottoms of continents and crack them, creating three armed rifts

Physiographic provinces

A region with similar geological history, meaning that there is similar terrain throughout it.

NJ has the crossover of these provinces:

The Highlands (from the Precambrian era)

The valley and ridge (From the Cambrian and Devonian)

Piedmont or Newark Basin (from the Triassic and Jurassic)

Coastal Plain (from the Cretaceous and upper Mesozoic)

What are the two supercontinent events that formed the provinces?

Pangea and Rodinia

The order of events in New Jersey's rock formations

1. Rodinia creates the highlands province
2. NJ becomes a passive margin, collecting sediment after Rodinia rifts apart
3. NJ becomes active again during the assembly of Pangea creating the Valley and Ridge province
4. Pangea rifts apart to make Piedmont (Newark Basin)
5. Passive margin again: coastal plain province

Which province is described:
- The oldest rocks in NJ (1.3 billion to 750 million years old)
- Very deformed rocks with complicated patterns
- Resistant to weathering
- No sedimentary rocks: only igneous and metamorphic
- 50% granite, 45% gneiss

The Highlands

Which province is described:
-Folded and faulted paleozoic sedimentary rocks
-Alternating belts of erosion-resistant sandstone and easily eroded shale and limestone
-Contains broad valleys (shale and limestone) and steep ridges (sandstone)

Valley and ridge

Which province is described:
- A kind of rift basin or half-graben formed by the break up of Pangea
- Formed 225-185 million years ago
- It was filled with water that collected sediment (sandstone-black shales-red siltstones-basalt)
-Regular changes from black shales to red silts due to Milankovitch cycles

The Newark Basin