geo 100 exam 2

Convergent boundary

Plates move toward each other, causing subduction or mountain building.

Divergent boundary

Plates move apart, creating new crust at mid-ocean ridges or rift valleys.

Transform boundary

Plates slide past each other horizontally, causing earthquakes.

Five steps of an ocean’s life cycle

1) Continental Rifting 2) Narrow Sea Formation 3) Mature Ocean Basin 4) Subduction Begins 5) Ocean Closes and Mountain Building.

Continental rifting

A stage where continental crust splits apart to form a rift valley; divergent.

Narrow sea formation

A stage where rifting widens and fills with ocean water; divergent.

Mature ocean basin

A stage with a fully developed ocean and mid-ocean ridge; divergent.

Subduction begins

A stage where one oceanic plate sinks under another; convergent.

Ocean closes and mountain building

The final stage when continents collide and form mountains; convergent.

Midcontinent Rift type

Divergent boundary.

Age of Midcontinent Rift

About 1.1 billion years ago (Precambrian).

Reason Midcontinent Rift stopped

Rifting halted before oceanic crust formed, possibly due to mantle convection changes or plate stress.

Result if Midcontinent Rift continued

A new ocean basin would have split North America apart.

Volcano definition

An opening in Earth's crust where magma, gases, and ash erupt.

Lava definition

Molten rock that reaches Earth's surface.

Magma definition

Molten rock beneath Earth's surface.

Igneous rock formation

Forms when magma or lava cools and solidifies.

Viscosity definition

A fluid’s resistance to flow.

High viscosity fluids

Thick and slow-moving.

Low viscosity fluids

Runny and fast-flowing.

Effect of silicon on viscosity

Higher silicon content increases viscosity.

Effect of temperature on viscosity

Higher temperature lowers viscosity.

Relationship between gas and pressure in magma

High pressure keeps gases dissolved; when pressure drops, gases escape and cause explosions.

Viscosity and eruption violence

High-viscosity magma traps gases, causing more violent eruptions.

Volcanic ash formation

Formed from pulverized rock, glass, and crystals during eruptions.

Difference between volcanic and wood ash

Volcanic ash is tiny rock fragments; wood ash is burned plant material.

Shield volcano shape

Broad and gently sloping.

Shield volcano lava

Low viscosity and low in silicon.

Shield volcano danger level

Least dangerous volcano type.

Shield volcano locations

Found at oceanic hotspots and divergent boundaries.

Composite volcano shape

Steep and cone-shaped with layered deposits.

Composite volcano lava

Medium to high viscosity with moderate to high silicon content.

Composite volcano danger level

Moderately dangerous and explosive.

Composite volcano locations

Found at convergent boundaries.

Caldera volcano shape

Large crater formed by collapse after massive eruption.

Caldera volcano lava

Very high viscosity and rich in silicon.

Caldera volcano danger level

Extremely dangerous and catastrophic.

Caldera volcano locations

Found at continental hotspots.

Largest volcano type

Shield volcano (e.g., Mauna Loa).

Volcano danger ranking

Shield – least dangerous, Composite – moderate, Caldera – most dangerous.

Reasons people live near volcanoes

Fertile soil, geothermal energy, and economic opportunities.

Reason volcanic soil is fertile

Volcanic ash and weathered rock release nutrients.

Volcano prediction method: ground deformation

Monitoring changes in land shape due to magma movement.

Volcano prediction method: gas emissions

Measuring released gases like sulfur dioxide to indicate rising magma.

Volcano prediction method: seismic activity

Tracking small earthquakes signaling magma movement.

Likelihood of Yellowstone eruption in our lifetime

Very unlikely.

Past Yellowstone eruptions

Massive caldera-forming explosions that spread ash across North America.

Earthquake definition

Sudden release of energy caused by rocks breaking along faults.

Main cause of earthquakes

Movement along faults due to built-up stress.

Stress definition

The force applied to rocks.

Strain definition

The deformation of rocks due to stress.

Compression stress

Stress that squeezes rocks together.

Tension stress

Stress that pulls rocks apart.

Shear stress

Stress that causes rocks to slide past one another.

Brittle strain

Rocks break when stressed beyond their limit.

Ductile strain

Rocks bend or flow without breaking under stress.

Stress before an earthquake

Stress builds up along the fault.

Stress during an earthquake

Stress is released as rocks break and slip.

Stress after an earthquake

Stress drops as rocks settle into new positions.

Deep, powerful earthquakes

Occur in subduction zones.

Shallow, weak earthquakes

Occur near the surface or at divergent boundaries.

P-waves

Primary waves; fastest; compressional; travel through solids and liquids.

S-waves

Secondary waves; slower; shear motion; travel through solids only.

Surface waves

Slowest waves; travel along Earth's surface; cause the most damage.

Most dangerous seismic waves

Surface waves.

Determining earthquake location

Use arrival times of P and S waves at multiple stations to triangulate the epicenter.

Magnitude of an earthquake

Measurement of total energy released.

Intensity of an earthquake

Measurement of damage and effects felt at a location.

Earthquake prediction

Possible only as long-term probabilities, not exact predictions.

Tall buildings and seismic waves

Tall buildings resonate with long, slow waves.

Short buildings and seismic waves

Short buildings resonate with quick, fast waves.

Best building materials for quakes

Steel and wood, because they are flexible.

Liquefaction

When water-saturated soil behaves like a liquid during shaking.

Safety if trapped in quicksand

Move slowly, lean back, and float to reduce pressure on the sand.

Tsunami definition

Large ocean wave caused by underwater earthquakes, landslides, or eruptions.

Tsunami in deep water

Travels very fast with small height.

Tsunami in shallow water

Slows down and grows taller, becoming more destructive.