2B — HIGH PRIORITY

Earthquake

A sudden release of energy in Earth’s crust that sends out seismic waves.

Focus

The point underground where the earthquake starts.

Epicenter

The point that is directly above the earth surface.

Difference between focus and epicenter

The focus is below ground; the epicenter is directly above it on the surface.

Richter scale

A base-10 logarithmic scale used to measure earthquake magnitude.

Moment Magnitude Scale

A better scale for very large earthquakes because it measures total energy more accurately.

Why the Richter scale is not linear

Each whole number increase means the seismic wave amplitude is 10 times greater.

Tsunami

A giant ocean wave usually caused by underwater earthquakes, volcanoes, or landslides.

Common causes of tsunamis

Earthquakes, volcanic eruptions, landslides, and sometimes meteor impacts.

Natural warning sign of a tsunami

The ocean may suddenly pull back from shore before the wave arrives.

DART system

A buoy system that helps detect and monitor tsunamis.

Volcano

An opening in Earth’s crust where lava, ash, and gases escape.

Where volcanoes commonly form

Mostly at convergent and divergent plate boundaries.

Magma

Molten rock below Earth’s surface.

Lava

Molten rock after it reaches Earth’s surface.

Pyroclastic flow

A fast, hot flow of ash, rock, and gas from a volcano.

Ring of Fire

A very active zone of earthquakes and volcanoes around the Pacific Ocean.

Composite volcano

A steep, explosive volcano with thick, slow-moving lava.

Shield volcano

A wide volcano with gentle slopes and faster-moving lava.

Cinder volcano

A small, steep, explosive volcano made mostly of cinders.

How composite and shield volcanoes differ

Composite volcanoes are steeper and more explosive; shield volcanoes are wider with faster lava.

Volcanic explosivity index (VEI)

A scale used to rate how explosive a volcanic eruption is.

Supervolcano

A volcano capable of an extremely huge eruption, usually VEI 8 or higher.

Caldera

A large depression formed when a volcano collapses after its magma chamber empties.

Hot spot

A place where hot mantle rises and forms volcanoes away from plate boundaries.

How Hawaii formed

The Pacific Plate moved over a hot spot, forming a chain of volcanoes.