Unit 8: Earthquakes and Volcanoes 2025 - Pavlik (H)

Amplitude

Height of a wave

body waves

waves that travel through the interior of the earth

Cape Ann Earthquake

Happened in 1775, had a magnitude of 6.2, and its epicenter was right off Gloucester. Largest quake in colonized Boston history

divergent

type of boundary that produces shallow earthquakes, less pressure being released, causes more damage at the surface

DUCK, COVER, and HOLD ON

how do you survive an earthquake?

Earthquake

shaking of Earth's crust due to a release of energy

elastic rebound

states that as plates move past each other, friction causes them to stick together, strain builds up causing the plates to first bend, and then break. The earthquake occurs at the moment the plates break and slide past each other. ; idea created by H.F. Reid

epicenter

location along the surface directly above the focus of an earthquake

fault

a crack in the earth along which movement occurs

Fire

ground shaking can break gas lines causing _____. water lines can also break making it hard to stop the _____. Devastated the city in the 1906 San Francisco earthquake

focus

location of an earthquake, within the earth, where the waves originate

ground shaking

as plates move past one another, energy is release as waves causing

H. F. Reid

Proposed the elastic rebound theory

Inge Lehmann

Discovered the boundary between the outer and inner core of Earth.

intensity

amount of damage done to an area by an earthquake

landslides

caused when an earthquake destabilizes an already weak slope.

liquefaction

saturated material turns fluid, turning ground into a liquid like pudding, underground objects may float to the surface, soil needs to be saturated, water forces itself into rocks pushing them up. Causes Buildings sink and fall over

Love and Rayleigh

the two types of surface waves

magnitude

calculations that use data provided by seismic records to estimate the amount of energy released at the source of the earthquake concept introduced by Charles Richter in 1935 (not the scale but what does it measure)

Modified Mercalli

Earthquake scale that measure intensity, roman numeral

Mohorovicic discontinuity

aka Moho; boundary that separates the crust from the underlying mantle

Moment Magnitude

a more precise measure of earthquake magnitude than the richter scale derived from the displacement that happens along the fault line. can also be calculated from seismograms looking through long period of earthquakes.

P and S

Body waves

P wave shadow zones

exist due to the refraction of the waves band all the way around the world. refracted when they go from solid to liquid

primary (P) waves

known as a p wave or a compressional wave, it reaches the objects first because it moves the fastest and has a push pull motion. It moves things parallel to the focus and can travel through a solid, liquid, or gas.

Richter scale

1935 uses seismic records to find the approximate size of earthquakes. based on the amplitude (height) of the earthquake

S-P lag time

aka lapse time; difference in arrival time between the P and S waves

San Andreas fault

the fault between the North American and Pacific plates that causes major earthquakes in CA

secondary (S) waves

known as an s wave or shear wave, it arrives after the p wave because it moves slightly slower. It moves from side to side and is perpendicular to the focus. It can only travel through solids

seismic gap

An area along a fault where there has not been any earthquake activity for a long period of time

seismogram

the documented seismic data on paper (or digitally).

seismograph

the device used to detect the shaking of Earth's crust. records amplitude vs. time.

seismology

study of earthquake waves

Shadow Zone

Area where waves aren't received from earthquake; P waves get refracted through the core; S waves don't travel through outer or inner core

Subsidence

a geological phenomenon in which the ground in an area sinks

Surface waves

up and down motion, love and Rayleigh - types of surface wave, slowest of all waves, most dangerous

tsunami

"harbor wave" and is created when the seafloor quickly deforms and displaces overlying waves

aa

A lava flow of basaltic lava that forms rough, jagged blocks. It forms when the lava has cooled down, thus increasing the viscosity.

andesitic (intermediate)

Igneous rocks with a composition between granitic and basaltic rocks. Associated with volcanic activity.

ash

Tephra less than 2mm in diameter

assimilation

The process where magma incorporates some of the surrounding rock as it migrates upward.

basaltic (mafic)

Igneous rocks with a substantial amount of dark-colored minerals (basaltic composition)

block

Tephra that is bigger than 64mm, solid piece of side of volcano

Bombs

Ejected from a volcano while molten or semi-molten

Bowen's reaction series

The arrangement of minerals that shows at what temperatures they solidify at. Discovered at the beginning of the 12th century. Olivine is first to cool and quartz is last.

Caldera

a large crater caused by the violent explosion of a volcano that collapses into a depression

cinder cone

Volcanos built from ejected lava fragments (pyroclastic material). A product of relatively gas-rich mafic magma. They are very steep, have deep craters, and do not usually eject lava. 1000-1500 ft (small), mild eruptions, example : Paricutin, Mexico

Clinkers

broken lava blocks that fall down the from of an Aa flow

Composite (Strato) Volcano

classic volcanic shape, taller than wide, layers, Made from felsic magma, high in quartz, high in viscosity, high in gas content, violent eruptions, Example: Mt. St. Helens, Fuji, Tambora

crater

A steep-walled depression on the summit of many volcanoes. They are formed when ejected fragments of the volcano collect around the vent.

crystal settling

A process that occurs when the earlier-formed minerals are denser than the liquid portion and sink to the bottom of the magma chamber.

crystallization

The process by which magma cools and solidifies. This may occur beneath the surface or after a volcanic eruption. The slower the process, the larger the crystals.

decompression melting

melting due to a drop in confining pressure that occurs as rock rises closer to the surface

extrusive (volcanic) igneous rock

rocks that form when molten rock solidify at the surface,

felsic

light in color, high in quartz and feldspar, generated by partial melting at subduction boundaries

Fissure eruption

the eruption of magma out of a crack in the lithosphere, rather than from a single pipe or vent

Geothermal Gradient

the gradual increase in temperature with depth in the crust.

granitic composition

igneous rocks composed of light colored silicates, also known as felsic

Harry Truman

Man who refuses to leave before Mt. St. Helen's eruption. he dies in his home by Spirit Lake and a song is made for him.

hornito

A spatter cone that forms on the surface of a lava flow and looks like a big drip-castle. It develops when lava accumulates around a vent in the ground. They typically have steep sides and form pinnacles.

Hot Spot

an area where material from deep within the mantle rises and then melts, forming magma

igneous rock

the rock resulting from the cooling and crystallized magma or lava

inclusion

the other name for the xenolith, when a different type of rock is incorporated into another plutonic rock

intrusive

igneous rocks that form at depth that are only exposed through uplifting.

Kipuka

A small piece of land that is completely surrounded by lava flows

lahar

Large composite cones generate this type of mudflow, which is saturated volcanic debris that moves down the steep volcano slopes. They can form in hard rainfall or when the volcano erupts and melts snow

lapilli

Tephra between 2mm-64mm in diameter and is vesicular

lava

hot molten (or semi molten) rock that has reached the surface. Most of the gasses have escaped

lava bench

A platform created by more recent lava flows that extend over the old shoreline. They often conceal loose material and are hazardous.

lava trees

Lava surrounds the tree but does not destroy it (leaves a column of rock.)

Lava tubes

A natural conduit where lava travels under the surface of a lava flow. The tubes form by the crusting over of lava channels. (generally pahoehoe lava)

mafic

igneous rocks high in Mg and Fe, dark colored, prevalent in ocean crust

magma

hot , molten rock located under ground made of a liquid (melt), solid portion (minerals)

magmatic differentiation

The formation of one or more secondary magmas from a single parent magmas.

melt

The liquid portion of the magma body. As this hardens, it forms crystals.

mush

the crystallized rock that is on the verge of being solid

Nuee Ardente

french word for pyroclastic flow means glowing cloud

Pahoehoe

a hot, fast-moving type of lava that hardens to form smooth, ropelike coils

Partial melting

The process by which most igneous rocks melt. Since individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results.

Pele

Hawaiian goddess of the Volcanoes

Pele's Hair

A naturally spun volcanic glass thats blown away from lava formations, lava falls, or turbulent flows. Generally gold in color

pele's tears

molten lava spews up and as it falls down, it's elongated

pillow basalt

round blobs of basalt cooled in water

Pyroclastic flow

a ground- hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the Mt. 100-400 mph, deadliest aspect of a volcanic eruption and can reach temperatures of 600-800 degrees

rift eruption

a divergent boundary on land

Ring of Fire

A narrow zone that rims the Pacific Ocean and contains most of the active continental volcanoes (composite cones.)

shield volcanoes

Broad, slightly domed volcanoes. They are formed by fluid basaltic lavas and are frown up from the ocean floor to form islands or seamounts. (An example is the Hawaiian chain.)

skylight

an opening in the roof of a lava tube

Strato Volcano

Another name fore Composite volcanoes

tephra

A general term for fragments of volcanic rock and lava that are blasted into the air (solid.)

Tree molds

Type of lava formation that is formed when lava surounds a tree, clings against it and drains away

Tsunami

Japanese word for "harbor wave", a volcanic eruptions abruptly displaces ocean water by either an explosion or landslide, Example : Krakatoa

vent

the surface opening at the top of a pipe

viscosity

a magmas resistance to flow, factors including temp and magmas chemical composition

Volatiles

gaseous components of magma dissolved in the melt. They will readily vaporize at surface pressures

Volcano

an opening in the earth's crust through which magma reaches the surface

xenolith

when a different type of rock is incorporated into another plutonic rock