focus
the point beneath earth's surface where rock moves, which causes an earthquake
epicenter
the point on the earth's surface directly above the focus
P wave
a type of seismic wave that travels through Earth's interior and compresses and expands
S wave
a type of seismic wave that travels through Earth's interior and moves side to side as well as up and down
vent
the opening in a volcano through which magma and gases escape
shield volcano
a gently sloping mountain made of lava released from nonexplosive eruptions
cinder cone
a steeply sloped volcano made of pyroclastic material from explosive eruptions
composite volcano
a tall, cone-shaped mountain made of alternating layers of lava and pyroclastic material
squall line
a row of severe thunderstorms
tornado
a rapidly rotating column of air that extends from a cumulonimbus cloud and touches the ground
Fujita scale
a scale used to rate tornado intensity
tropical cyclone
a rotating storm system originating over warm waters with winds that exceed 119 kph (74 mph)
hurricane
a tropical cyclone forming in the Atlantic and eastern and central Pacific Oceans
storm surge
a wall of water that moves ashore when a hurricane strikes land