Plate Boundaries
What type of plate boundary creates a subduction zone?
Convergent
Which seismic wave arrives first at a seismograph station?
P-waves
What tectonic plates are involved in the Cascadia Subduction Zone?
The Juan de Fuca Plate and the North American Plate.
What evidence do scientists use to study Earth’s interior?
Seismic waves from earthquakes.
In a subduction zone diagram, which plate sinks beneath the other plate?
The denser oceanic plate.
Why do Earth processes like mountain building happen so slowly compared to human lifetimes?
Tectonic plates move extremely slowly over millions of years.
What caused the massive floods from Glacial Lake Missoula?
An ice dam broke and released enormous amounts of water
What surface feature commonly forms where one plate subducts beneath another?
Deep ocean trench
Which seismic wave cannot travel through liquids?
S waves
What is the main reason the Cascadia Subduction Zone is dangerous?
Stress can build for centuries and release in a massive earthquake.
What does the S-wave shadow zone prove about Earth’s outer core?
The outer core is liquid.
What natural disaster is most commonly triggered by large undersea subduction zone earthquakes?
Tsunamis
Why can scientists use earthquakes almost like an “X-ray” of Earth?
Seismic waves change speed and direction depending on the material they travel through
What U.S. region was heavily shaped by the Missoula Floods?
Eastern Washington / the Channeled Scablands
What type of plate boundary creates rift valleys?
Divergent
What happens to seismic waves when they move into material with a different density?
They refract (bend) and change speed.
Name two major hazards caused by a Cascadia Megaquake.
Strong ground shaking, tsunamis, landslides, coastal subsidence, infrastructure damage.
Why can P-waves travel through the outer core while S-waves cannot?
P-waves can travel through liquids, but S-waves only travel through solids.
Why might scientists and emergency planners focus heavily on earthquake preparedness in the Pacific Northwest even though major Cascadia earthquakes are rare?
Because the impacts would be catastrophic and affect millions of people despite the long time between events
Explain how the movement of tectonic plates can reshape Earth’s surface over millions of years.
Plate motion can create mountains, trenches, volcanoes, and new ocean crust over geologic time.
Why are the Missoula Floods considered evidence that Earth’s surface can change rapidly?
The floods carved huge landforms in a relatively short amount of time.
Compare convergent and transform boundaries by describing the motion and a landform or hazard associated with each.
Convergent boundaries collide and create mountains/trenches; transform boundaries slide past and create earthquakes.
Why do scientists track both P-wave and S-wave behavior after earthquakes?
Comparing them reveals differences in Earth’s internal layers and states of matter.
Why might coastal areas suddenly sink during a Cascadia Megaquake?
The overriding plate can suddenly drop when built-up stress is released.
How does the bending of P-waves help scientists identify Earth’s inner layers?
Changes in wave speed and direction reveal density boundaries between layers.
Imagine two cities are the same distance from a megaquake. One experiences far greater destruction. Give one scientific reason why the damage levels could differ.
Differences in soil type, building construction, elevation, tsunami exposure, or local geology can greatly change earthquake impacts
Why is the Cascadia Subduction Zone considered evidence that Earth is constantly changing?
It demonstrates active plate motion, crust recycling, earthquakes, and long-term surface change.
How are the Missoula Floods and the Cascadia Megaquake similar?
Both are caused by natural Earth processes and can dramatically reshape landscapes and impact large regions
A scientist discovers a region with volcanic mountains, deep trenches, and frequent large earthquakes. What type of boundary is most likely present and why?
A convergent subduction boundary because those features form where oceanic crust sinks beneath another plate.
A seismic station detects P-waves but no S-waves from an earthquake. What can scientists infer about the material the waves passed through?
The waves passed through a liquid layer because S-waves cannot travel through liquids.
Explain why a Cascadia Megaquake could affect areas far beyond the Pacific Northwest coastline.
Tsunamis can cross oceans, infrastructure networks are interconnected, and economic impacts spread nationally and globally.
Explain how seismic wave evidence supports the conclusion that Earth has BOTH a liquid outer core and a solid inner core.
S-waves stopping proves the outer core is liquid, while refracted P-waves speeding up and bending differently indicate a dense solid inner core.
Design a subduction zone diagram: what labels and features MUST be included to accurately explain how megaquakes occur?
Oceanic plate, continental plate, trench, mantle, stress buildup zone, arrows of movement, earthquake locations, and tsunami generation area.
Earth processes operate on massive spatial and temporal scales. Use the Cascadia Subduction Zone as evidence to defend this statement.
Plates move only centimeters per year, but over millions of years they build stress, recycle crust, create mountains, and produce catastrophic earthquakes affecting enormous regions.
Scientists once rejected the idea of the Missoula Floods because the floods seemed too catastrophic to be realistic. What evidence eventually convinced scientists the floods actually occurred?
Giant ripple marks, massive gravel deposits, dry waterfalls, and the carved Scablands provided physical evidence of enormous floods.