geology mid-term 2

chapter 5, chapter 8, interlude d, chapter 9, chapter 12, chapter 10, interlude e, chapter 11, interlude f, chapter 13

eruption

the release of lava and/or pyroclastic debris from a volcanic vent

volcano

(1) a vent from which melt from inside the Earth spews out onto the planet's surface; (2) a mountain formed by the accumulation of extrusive volcanic rock

lava flow

sheets or mounds of lava that flow onto the ground surface or sea floor in molten form and then solidify

lava tube

the empty space left when a lava tunnel drains; this happens when the surface of a lava flow solidifies while the inner part of the flow continues to stream downslope

pahoehoe

a lava flow with a surface texture of smooth, glassy ropelike ridges

a’

a lava flow with a rubbly surface

pillow basalt

glass-encrusted basalt blobs that form when magma extrudes on the seafloor and cools very quickly

columnar jointing

a type of fracturing that yields roughly hexagonal columns of basalt; columnar joints form when a dike, sill, or lava flows cools

aerosol

tiny solid particles or liquid droplets that remain suspended in the atmosphere for a long time

vesicle

open holes in igneous rock formed by the preservation of bubbles in magma as the magma cools into solid rock

tephra

unconsolidated accumulation of pyroclastic grains

pyroclastic debris

fragmented material that sprayed out of a volcano and landed on the ground or sea floor in solid form

lava fountain

an eruption of lava at a volcano, during which lava spurts into the air while sill molten

lapilli

any pyroclastic particle that is 2 to 64 mm in diameter (i.e., marble-sized); the particles can consist of frozen lava clots, pumice fragments, or ash clumps

bomb

a stream-lined block of rock ejected by a volcano while still hot; it gets shaped as it flies through the air

block

large, angular pyroclastic fragments consisting of volcanic rock, broken up during the eruption

pyroclastic flow

a fast-moving avalanche that occurs when hot volcanic ash and debris mix with air and flow down the side of a volcano

tuff

a pyroclastic igneous rock composed of volcanic ash and fragmented pumice, formed when accumulations of the debris cement together

lahar

a thick slurry formed when volcanic ash and debris mix with water, either in rivers or from rain or melting snow and ice on the flank of a volcano

magma chamber

a space below ground filled with magma

fissure

a conduit in a magma chamber in the shape of a long crack through which magma rises and erupts at the surface

crater

(1) a circular depression at the top of a volcanic mound; (2) a depression formed by the impact of a meteorite

caldera

a large circular depression with steep walls and a fairly-flat floor, formed after an eruption as the center of the volcano collapses into the drained magma chamber below

shield volcano

a subaerial volcano with a broad, gentle dome, formed either from low-viscosity basaltic lava or from large pyroclastic sheets

cinder cone

a subaerial volcano consisting of a cone-shaped pile of tephra whose slope approaches the angle of repose for tephra

stratovolcano

a large, cone-shaped subaerial volcano consisting of alternating layers of lava and tephra

effusive eruption

an eruption that yields mostly lava, not ash

explosive eruption

violent volcanic eruptions that produce clouds and avalanches or pyroclastic debris

supervolcano

a volcano that erupts a vast amount (more than 1,000 cubic km) of volcanic material during a single event; none have erupted during recorded human history

flood basalt

vast sheets of basalt that spread from a volcanic vent over an extensive surface of land; they may form where a rift develops above a continental hot spot, and where lava is particularly hot and has low viscosity

large igneous province (LIP)

a region in which huge volumes of lava and/or ash erupted over a relatively short interval of geologic time

active volcano

a volcano that has erupted within the past few centuries and will likely erupt again

dormant volcano

a volcano that hasn’t erupted for hundreds to thousands of years but does have the potential to erupt again in the future

extinct volcano

a volcano that was active in the past but has now shut off entirely and will not erupt in the future

mare

the broad, darker areas on the Moon's surface; they consist of flood basalts that erupted over 3 billion years ago and spread out across the Moon's lowlands

fault

a fracture on which one body of rock slides past another

earthquake

a vibration caused by the sudden breaking or frictional sliding of rock in the earth

seismologist

a scientist who specializes in the study of earthquakes, or in the study of how seismic waves characterize the interior of the earth

seismicity

earthquake activity

seismic waves

waves of energy emitted at the focus of an earthquake

displacement

the amount of movement of slip across a fault plane

fault scarp

a small step on the ground surface where one side of a fault has moved vertically with respect to the other

stress

the push, pull, or shear that a material feels when subjected to a force; formally, the force applied per unite area over which the force acts

elastic behavior

a response of a material to stress, during which the material changes shape. the amount of change depends on the magnitude of stress, and the change disappears when stress is removed. the behavior occurs when chemical bonds bend or stretch, but do not break

friction

resistance to sliding on a surface

elastic-rebound theory

the concept that earthquakes happen because stress builds up, causing rock adjacent to a fault to bend elastically until breaking and slip on a fault occurs; the slip relaxes the elastic bending and decreases stress

stick-slip behavior

stop-start movement along a fault plane caused by friction, which prevents movement until stress builds up sufficiently

mainshock

the largest earthquake during a succession of related earthquakes; foreshocks, which precede the mainshock, and aftershocks that come after the mainshock, all release much less energy than the mainshock

foreshock

the series of smaller earthquakes that precede a major earthquake

aftershock

the series of smaller earthquakes that follow a major earthquake

focus

the location where a fault slips during an earthquake (hypocenter)

epicenter

the point on the surface of the earth directly above the focus of an earthquake

body wave

seismic waves that pass through the interior of the earth

surface wave

seismic waves that travel along the earth’s surface

compressional wave

waves in which particles of material move back and forth parallel to the direction in which the wave itself moves

shear wave

seismic waves in which particles of material move back and forth perpendicular to the direction in which the wave itself moves

seismograph

an instrument that can record the ground motion from an earthquake

seismogram

the record of an earthquake produced by a seismometer

travel-time curve

a graph that plots the time since an earthquake began on the vertical axis and the distance to the epicenter on the horizontal axis

earthquake intensity

a representation of the strength of an earthquake, based on the amount of damage due to the event and on people's perception of ground shaking during the event; intensity is measured with the Mercalli scale; intensity decreases with increasing distance from the epicenter

modified mercalli intensity (MMI) scale

an earthquake characterization scale based on the amount of damage that the earthquake causes

earthquake magnitude

a representation of the energy released by an earthquake, as indicated by the amplitude of specific seismic waves as they would be recorded by a seismometer at a set distance from the epicenter

richter scale

a scale that defines earthquakes on the basis of the amplitude of the largest ground motion recorded on a seismogram

moment magnitude

a modern scale for measuring the relative size of earthquakes that involves studying the amplitude of waves on a seismograph, along with other parameter

seismic belt

the relatively narrow strips of crust on the earth under which most earthquakes occur

seismic zone

a region in which earthquakes happen fairly frequently; a seismic belt is an elongate seismic zone

megathrust earthquakes

the largest type of earthquake, which occurs when a large area of the boundary between the overriding plate and the downgoing plate slips during a single event, and which can trigger large tsunamis

wadati-benioff zone

a sloping band of seismicity defined by intermediate- and deep-focus earthquakes that occur in the downgoing slab of a convergent plate boundary

intraplate earthquakes

earthquakes that occur away from plate boundaries

landslide

a sudden movement of rock and debris down a non-vertical slope

sediment liquefaction

when pressure in the water in the pores push sediment grains apart so that they become surrounded by water and no longer rest against each other, and the sediment becomes able to flow like a liquid

tsunami

a large wave along the sea surface trigged by and earthquake of large submarine slump

recurrence interval

the average time between events of a given size or magnitude; the term is commonly used to give a sense of the frequency of earthquakes or of flooding

earthquake early warning system

a communications network that provides an alert within microseconds after the first earthquake waves arrive at a seismograph near the epicenter, but before damaging vibrations reach population centers

geophysics

the subdiscipline of geology focused on the quantitative analysis and modeling of physical characteristics of the earth; it includes the study of earthquakes, gravity, and magnetism

seismic ray

the changing position of an imaginary point on a wave front as the front moves through rock

travel time

the time that it takes for a seismic wave to travel from the focus of an earthquake to a seismometer along a given ray path

reflection

what happens when energy bounces off a boundary; when this happens, the incoming angle and outgoing angle are equal

refraction

the bending of a ray as it passes through a boundary between two different materials

moho

the seismic-velocity discontinuity that defines the boundary between the earth’s crust and mantle

low-velocity zone (LVZ)

the asthenosphere underlying oceanic lithosphere in which seismic waves travel more slowly, probably because rock had partially melted

seismic-velocity discontinuity

a boundary in the earth at which seismic velocity changes abruptly

upper mantle

the uppermost section of the mantle, reaching down to a depth of 400 km

lower mantle

the deepest section of the mantle, stretching from 670 km down to the core-mantle boundary

transition zone

the middle portion of the mantle, from 400-670 km deep, in which there are several jumps in seismic velocity

p-wave shadow zone

a band between 103° and 143° from an earthquake epicenter, as measured along the circumference of the earth, inside which p-waves do not arrive at seismograph stations

core-mantle boundary

an interface 2,900 km below the earth’s surface separating the mantle and core

s-wave shadow zone

a band between 103° and 180° from the epicenter of an earthquake inside which s-waves do not arrive at seismograph stations

seismic tomography

analysis by sophisticated computers of global seismic data in order to create a three-dimensional image of variations in seismic-wave velocities within the earth

EarthScope

A study, funded by the US National Science Foundation and conducted between about 2004 and 2019, that involved the installation of large arrays of seismometers and other instruments to study the internal structure of the Earth and, in places, deformation of the land surface of the United States

seismic-reflection profile

a cross-sectional view of the crust made by measuring the reflection of artificial seismic waves off boundaries between different layers of rock in the crust

equipotential surface

in the context of discussing groundwater, an imaginary surface to which groundwater will rise in a stand pipe

geoid

a reference surface representing the elevations, worldwide, at which gravitational potential energy is the same

gravity anomaly

a value of gravitational pull that is greater than or lesser than the pull predicted by the geoid

isostasy

the condition that exists when the buoyancy force pushing lithosphere up equals the gravitational force pulling lithosphere down

archimedes’ principle

the mass of the water displaces by a block of material equals the mass of the whole block of material

dynamo

a power plant generator in which water or wind power spins an electrical conductor around a permanent magnet

magnetic anomaly

the difference between the expected strength of the earth's magnetic field at a certain location and the actual measured strength of the field at that location

mountain belt

an elongate band of mountains, formed as the result of an orogeny

orogen

a linear range of mountains