1.
A volcano that has erupted within recorded history.
2.
Magma with a medium silica content that erupts more violently than basaltic magma; named after the Andes mountain range.
3.
The plasticlike layer of Earth's upper mantle on which the rigid lithospheric plates float and move.
4.
Fluid magma that is low in silica and produces quiet, non-explosive volcanic eruptions.
5.
The largest type of intrusive igneous rock body, formed when massive magma bodies cool slowly underground over hundreds of kilometers.
6.
A large, bowl-shaped depression formed when the top of a volcano collapses into its partially emptied magma chamber after an eruption.
7.
A steep-sided, loosely packed volcano formed when tephra falls to the ground during explosive eruptions.
8.
A volcano built by alternating explosive and quiet eruptions that produce alternating layers of tephra and lava.
9.
A squeezing force that pushes rocks together, causing them to fold, fault, or form reverse faults.
10.
Alfred Wegener's hypothesis that all continents were once connected in a single supercontinent that broke apart and drifted to their current positions.
11.
The cycle of heating, rising, cooling, and sinking of material caused by differences in temperature and density inside Earth's mantle.
12.
The steep, bowl-shaped area around a volcano's central vent.
13.
A plate boundary where two tectonic plates pull apart or move away from each other.
14.
Vibrations or shaking produced when rocks break along a fault surface after reaching their elastic limit.
15.
The point on Earth's surface directly above an earthquake's underground focus.
16.
A surface or crack along which rocks move when they exceed their elastic limit and break.
17.
A large crack in Earth's surface through which fluid lava flows to form flood basalts.
18.
The underground point where earthquake energy is first released in the form of seismic waves.
19.
The remains, imprints, or traces of prehistoric organisms preserved in rock.
20.
Thick, silica-rich magma that traps gases under high pressure, resulting in violent, explosive volcanic eruptions.
21.
An unusually hot area deep between Earth's core and mantle where rising heat melts rock and forces magma upward through the crust, independent of plate boundaries.
22.
Molten rock that has reached Earth's surface through a vent or fissure.
23.
A process occurring during severe earthquake shaking where wet, saturated soil acts more like a liquid, causing buildings to sink and collapse.
24.
The rigid, solid outer layer of Earth made up of the crust and solid upper mantle, broken into tectonic plates.
25.
Molten, liquid rock beneath Earth's surface.
26.
A sensitive instrument used by scientists to record and measure the direction and strength of magnetic fields in ocean floor rocks.
27.
The measure of energy released during an earthquake, recorded by seismographs and measured on the Richter scale.
28.
An underwater chain of volcanic mountains and rift valleys stretching along ocean floors where new seafloor is generated.
29.
A scale that describes earthquake intensity based on structural damage and human observation at a specific location.
30.
The boundary between Earth's crust and upper mantle where seismic waves abruptly change speed due to density changes.
31.
A break in rock caused by tension pulling forces, where the rock above the fault surface moves downward relative to the rock below.
32.
A deep underwater trench formed at subduction zones where an ocean plate bends and sinks into the mantle.
33.
The single, ancient supercontinent composed of all Earth's landmasses joined together about 200 million years ago.
34.
A large, rigid section of Earth's lithosphere that floats and moves around on the asthenosphere.
35.
The unifying theory that Earth's crust and rigid upper mantle are broken into plates that move around on a plasticlike layer of the mantle.
36.
The fastest type of seismic wave that compresses and stretches rock particles in the same direction the wave travels.
37.
A rapid, high-temperature avalanche of scorching gas, ash, and volcanic rock fragments rushing down the sides of an erupting volcano.
38.
A break in rock caused by compression forces, where the rock above the fault surface moves upward and over the rock below.
39.
A magnitude scale based on seismogram line height used to describe the total energy released by an earthquake.
40.
A deep valley or gap that forms on land or along mid-ocean ridges where tectonic forces pull Earth's crust apart.
41.
A type of seismic wave that moves rock particles at right angles to the direction the wave is traveling; cannot pass through liquids.
42.
Harry Hess's theory that magma is forced up at mid-ocean ridges, creating new seafloor and pushing older ocean crust sideways.
43.
A wave of energy generated by an earthquake that travels outward from the focus through Earth or along its surface.
44.
An instrument equipped with a drum and hanging mass used to detect, register, and record seismic waves.
45.
An area on Earth's surface where no direct seismic waves are detected because S-waves are stopped by the liquid outer core and P-waves are bent.
46.
A broad, gently sloping volcano built by quiet, non-explosive eruptions of fluid basaltic lava.
47.
A break in rock caused by shear forces where rocks slide past each other horizontally with little vertical movement.
48.
The area at a convergent plate boundary where a denser oceanic plate sinks beneath a less dense plate into the mantle.
49.
The slowest moving seismic wave that causes ground particles to roll and sway back and forth, responsible for most structural earthquake damage.
50.
A pulling force that stretches Earth's crust in opposite directions, causing normal faults and rift valleys.
51.
A plate boundary where two tectonic plates slide horizontally past one another in opposite directions or in the same direction at different speeds.
52.
A massive seismic sea wave produced by underwater faulting or earthquakes on the ocean floor.
53.
An opening in Earth's crust through which magma, gases, ash, and lava escape onto the surface.
54.
The solid, resistant igneous core left standing after the softer outer cone of an extinct volcano erodes away.
55.
An opening in Earth's surface that erupts sulfurous gases, ash, and lava, constructing volcanic landforms over time.
