Learn: Geology midterm

Observation vs. Inference

An observation is direct data gathered via senses; an inference is an interpretation or conclusion drawn from observations

Hypothesis vs. Theory

A tentative explanation of how a system works based on a limited set of observations or experiments; a theory is a well-tested, broadly accepted scientific explanation.

The Doppler Effect

A shortening and lengthening of sound waves that we experience when an object moves toward us and then past us

The Doppler Effect & Redshift

Redshift occurs when an object moves away from the observer, stretching its light waves toward red and lowering their frequency and energy.

Edwin Hubble

Discovered that distant galaxies are moving away from Earth, and the farther away a galaxy is, the faster it is receding (Hubble's Law). His observations provided evidence for an expanding universe and supported the Big Bang theory.

Big Bang Theory

The universe began in a hot, dense state and has been expanding ever since.

How do we know what the interior of the Earth is made of?

1. Seismology (studying earthquake waves)

2. Meteorites (samples of material from the early solar system that survives passage through the atmosphere and hits the ground)

What are chondrites similar to?

The composition of the Solar System and Earth

What are iron meteorites similar to?

The composition of Earth's core (Fe-Ni alloy)

What are achondrites similar to?

Earth's crust and mantle

How old are Earth's oldest rocks?

3.8 billion years old

How old is the Earth?

4.6 billion years old

Body Waves vs. Surface waves

Body waves travel through Earth's interior (P and S waves); Surface waves travel along Earth's surface

P Waves (Primary waves)

P waves are compressional (fastest); travels through solids, liquids, and gases

S Waves (Secondary Waves)

S waves are shear (slower); cannot travel through liquids

Why do seismic waves refract?

Seismic waves change speed as they pass through different layers of Earth, causing them to bend or refract.

What is seismic tomography?

A tool that uses seismic waves to create images of Earth's interior by tracking how the waves travel through different materials.

What are the layers of the Earth & their properties?

1. Crust: Thin, solid, least dense layer

2. Mantle: Thick, solid rock that can slowly flow; denser than crust

3. Core: Mostly iron and nickel; outer core is liquid, inner core is solid

What is the Moho?

The boundary of the crust and mantle

What was Wegener's main evidence for continental drift?

- Continents fit together like puzzle pieces

- Matching fossils on continents now separated

- Matching rocks and mountain ranges

- Past climate evidence

Why was continental drift initially rejected?

Wegener couldn't explain how continents moved through the ocean floor. There was no known mechanism to drive continental movement.

What is Pangea?

A supercontinent where all of Earth's continents were joined together

What is Paleomagnetism?

studying the magnetic record preserved in rocks to learn about Earth's past; apparent polar weathering

How was the seafloor mapped?

Sonar mapped seafloor topography, while magnetometers detected magnetic patterns

What did Harry Hess propose?

Seafloor spreading—new oceanic crust forms at mid-ocean ridges and moves outward; age of crust is older the further it is from mid-ocean ridges

Lithosphere

• Cold

• Rigid

• Consists of crust and upper mantle

• 'Floats' on the asthenosphere

• Elastic: when it’s “bent” it returns back to its original shape

Asthenophere

• Hot

• Plastic rock that is near its melting point

• Deformation: when it’s “bent” it remains bent

How are Earth's plate boundaries marked?

The locations of earthquakes and volcanoes

Subduction Zones

A place where one tectonic plate goes underneath another plate into the mantle;

Increasing frequency of deep earthquakes into the overriding plate

What is the Wadati-Benioff zone?

A zone of earthquakes that follows a subducting tectonic plate as it sinks into the mantle.

What are the 3 types of plate boundaries?

1. Convergent

2. Divergent

3. Transform

Divergent Boundaries

• Plates move apart

• New crust form through volcanism

• Mid Ocean Ridges

• Earthquakes: Less powerful; shallow

• Volcanoes: Less explosive

Continental Rifting

Occurs at divergent boundaries, when a continental boundary begins to pull apart (ie: East Africa)

Convergent Boundaries

• Plates move towards each other

• Subduction occurs

• Mid ocean trenches

• Earthquakes: Powerful, Shallow AND Deep

• Volcanoes: Very Explosive

• Mountains

• 3 types of convergent plate boundaries (oceanic + continental, oceanic + oceanic, continental + continental)

Oceanic + Continental

• Oceanic plate (denser) sinks underneath the continental plate (less dense)

• Explosive Volcanoes

Oceanic + Oceanic

• Older & denser oceanic plate sinks underneath the newer & less dense oceanic plate

• Explosive volcanic oceanic arc

Continental + Continental

• Neither plate subducts because they are both relatively low-density

• They collide and crumple

• Forms mountains, no volcanoes

Transform Boundaries

• Plates slide past each other

• Earthquakes: shallow, can be strong

• Generally, no volcanoes

• Ex: San Andres Fault

Where does shallow and deep seismicity occur?

Shallow earthquakes occur at divergent and transform boundaries;

Shallow AND deep earthquakes occur at convergent boundaries

How are hot spots formed?

Forms when VERY HOT material (mantle plume) from deep inside the Earth rises towards the surface

What drives plate tectonics?

1. Slab Pull

2. Ridge Push

• Mantle convection also contributes (hot magma rises, while cooler magma sinks create convention and helps drive plate movement)

How do we measure plate movement?

GPS measures the velocity and direction of moving tectonic plates.

Stress vs. Strain

Stress is the force applied to rock;

Strain is the change in shape that a rock experiences in response to an applied stress

What are the 3 types of stress?

1. Compression = squeezing; shortens & thickens

2. Tension = pulling apart; stretches & thins

3. Shear = sliding past; does neither

What are the hanging wall and footwall?

Hanging wall is above the fault;

footwall is below the fault

What are the 3 types of faults?

1. Normal: result of tension stress, divergent boundaries, hanging wall moves down

2. Reverse: result of compressive stress, convergent boundaries, hanging wall moves up

3. Strike-slip: result of shearing stress, past horizontally

What are the 2 types of strike-slip faults

1. Right-lateral strike-slip fault: the other side appears to move to your right

2. Left-lateral strike-slip fault: the other side appears to move to your left.

Displacement

Amount of movement along a fault

The Earthquake cycle

The buildup and release of elastic strain

Hypocenter

Location where fault slip occurs (underground)

Epicenter

The point on Earth's surface directly above the hypocenter

How do you locate an earthquake?

Use at least 3 seismograms to triangulate the earthquake's location

How is earthquake size measured?

1. Magnitude (energy released)

2. Intensity (ground shaking)

Richter Scale

A logarithmic scale measuring earthquake magnitude

(ie: a 7.0 is 10× stronger than a 6.0)

Intensity of ground shaking is related to

-Energy released

- Distance from the hypocenter

- Type of bedrock

Where do 95% of earthquakes occur?

Plate Boundaries; earthquakes can also occur within continents along old fault

New Madrid, MO earthquakes

Three magnitude 8.0-8.3 earthquakes struck the New Madrid area, causing major ground movement and making the Mississippi River temporarily flow backward

Charleston 1886 earthquake

A magnitude 7.3 earthquake that caused intense shaking, killed about 60 people, and was felt as far as Maine

Primary sesimic hazards

1. Ground shaking

2. Fault movement

Secondary sesimic hazards

1. Liquefaction

2. Landslides

3. Ground Subsidence

4. Tsunamis

5. Fire

What is a mineral?

1. Naturally occurring

2. Solid

3. Definite chemical composition

4. Orderly arrangement of atoms (crystalline structure)

5. Generally Organic

Ionic vs. Covalent bonds

Ionic: electrons are transferred; Covalent: electrons are shared.

Graphite vs. Diamond

Their carbon atoms have different structures/bonding, giving them different properties

What is the common building block of minerals in the crust?

Silicate Tetrahedra; results in strong minerals, relatively resistant to weathering

What happens when acid is added to calcite?

Releases CO2, limestone terranes can turn into sinkholes

Intrusive vs. Extrusive Igneous Rocks

Extrusive rocks cool at the Earth's surface, while Intrusive rocks cool at depth below the Earth's surface

What is decompression melting?

Mantle rock rises and pressure decreases, causing it to melt

Three Melting Processes

1. Decompression melting: changing pressure (liquid → gas)

2. Flux melting: changing composition (solid → liquid)

3. Heat transfer: changing temperature (solid → liquid)

Igneous Rock Classification

Classified based on composition (mafic, intermediate, felsic) and texture (crystal size).

Mafic

Low silica, high iron and magnesium; forms at high temperatures

Intermediate

Between mafic and felsic in composition and silica content

Felsic

High silica, low iron and magnesium; forms at lower temperatures

What is the relationship between viscosity of a melt and its composition?

More silica = higher viscosity (thicker);

less silica = lower viscosity (runny)

What is the relationship of igneous rock texture (i.e. crystal size) and cooling history?

Slow cooling → large crystals;

Rapid cooling → small crystals

Why do civilians live in volcanic areas?

Volcanic areas have fertile soils, which support agriculture

Three products of volcanoes

1. Gases

2. Pyroclastic Debris

3. Lava Flows

What are lahars?

Water-rich pyroclastic flows

Volcanic architecture

1. Crater: a bowl-shaped depression atop a volcano

2. Caldera: a gigantic volcanic depression (very large)

What are the 3 types of volcanoes

1. Shield (largest; most common)

2. Cinder (smallest)

3. Stratovolcanoes (AKA composite volcanoes & intermediate size)

Why are stratovolcanoes so explosive?

Water and other volatiles from subduction zones

At what geologic settings do we find volcanoes?

Subduction Zones

Effects of volcanoes on civilization

- Tsunamis

- Volcanic ash

- Pyroclastic flows

- Volcanic gases

- Climate Change

How can volcanic ash affect air traffic?

Volcanic ash can damage aircraft engines and disrupt air travel

How can citizens mitigate volcanic risks?

- Understand the past

- Date old eruptions

- Determine recurrence interval

What is recurrence interval?

The average time between volcanic eruptions at a volcano

Volcanic hazard maps

Shows areas at risk from volcanic hazards, helping with planning and evacuation

How are volcanic hazards monitored and communicated?

Monitored through GPS/InSAR, seismicity, gas emissions, and satellites;

Risks are communicated to the public and policymakers

Physical vs. Chemical Weathering

Physical weathering breaks rock into smaller pieces (doesn't change composition);

Chemical weathering changes the minerals in rock

What are the 3 major controls on weathering?

1. Rock Type

2. Climate

3. Time

What are the 3 types of chemical weathering?

1. Dissolution

2. Hydrolysis

3. Oxidation.

What are examples of physical weathering?

- Frost Wedging

- Thermal Expansion

- Exfoliation

- Biological Activity