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fragments of rock that have fallen from a cliff or steep slope and accumulated at its base.

Variables that underpin landslide classification.

mechanism of movement, type of material, amount of H2O, and rate of movement


free fall and bounding of rock/blocks of sediment from the face of a cliff


downslope movement of a coherent block of rock/sediment along a failure plane


type of slide where the failure plane is curved


slow to rapid downslope movement of sediment


a very slow flow


a German term for deep-seated rock creep


pivoting of a rock mass about a point

subaqueous landslides

landslide that occurs on the floor of a lake or sea

shear strength

it resistance to failure by sliding or flow along potential slip planes

factor of safety (FS)

resisting forces/driving forces, <1=unstable slope

driving and resisting forces are determined by:

type of material; slope angle and topography; climate; vegetation; water; time

rotational slides

blocks of sediment/weak rock move along a curved rupture surface

translational slides

blocks of strong rock move along a weak plane

reasons vegetation is a factor

reduces the impact of falling rain; plant roots add strength and cohesion to slope materials; adds weight to a slope which can increase failure likelihood

reasons water is a factor

many landslides occur when slope materials become saturated; other landslides develop months/years after deep infiltration of water into a slope; erosion of the toe of a slope by a stream reduces the slopes stability.

factors that increase incidence of landslides

urbanization in landslide-prone areas; clear cutting; changing global climate increases precipitation in some areas

landslide triggers

intense rainfall, rapid snowmelt, water-level change, volcanic eruption, seismic loading, rapid erosion

indications of potentially unstable slopes

crescent shaped cracks or terraces on a hillside; a recessed crest of a valley wall; tongue-shaped area of bare soil/rock on a hillside, large piles of talus at the base of a cliff, tilted tress, pistol butt trees, exposed bedrock, tongue-shaped masses of sediment at base of a slope, hummocky land surface at the base of a slope

landslide prevention techniques

drainage control, grading, slope supports

cloud-to-cloud lightning

occurs when the voltage gradient within a cloud or between clouds overcomes the electrical resistance of the air.

sheet lightning

cloud-to-cloud lightning that is obscured by the cloud itself

cloud-to-ground lightning

occurs when the negative charges accumulate in the lower portions of the cloud and because there is a charge difference between the cloud and the ground there's lightning

runaway breakdown

occurs when a large number of fast-moving electrons accumulate in a small volume and the release energy

stepped leader

a channel of ionized air that approaches teh ground in a series of nearly invisible bursts

strokes/return stronkes

downward flow of electrons during a cloud-to-ground lightning discharge

dart leader

forms from the leftover negatively charged ions near the base of the cloud that are not neutralized by the first stroke

positive lightning stroke

winds can carry positive charges ahead of the storm, these positive charges induce negative charges at the surface resulting in lighting, very dangerous

ball lightning

appears as a round glowing mass of electrified air that seems to roll through the air or along the surface for around 15 seconds.

St. Elmo's fire

ionization in the air can cause tall objects to glow as they emit a continuous barrage of sparks


very large and short lived electrical bursts that rise from cloud tops

blue jets

upward-moving electrical ejections from the tops of the most active regions of thunderstorms


caused by the large increase in temperature during a lightning stroke which leads to the air expanding explosively and producing a noise

heat lightning

lightning that seems to occur without thunder

air mass thunderstorm stages:

cumulus stage; mature stage; dissipative stage

air mass thunderstorm

short-lived storms that stop themselves by creating downdrafts that cut off the supply of mositure into the clouds

severe thunderstorms

occur when the downdrafts actually intensify the storms

cumulus stage

unstable air begins to rise, the rising air cools to form cumulus clouds, these clouds move water vapor the the middle troposphere, the atmosphere becomes humid enough that the clouds grow vertically

mature stage

precipitation begins to fall, downdrafts form in areas of intense precipitation, precipitation lightning and thunder are most intense

dissipative stage

when downdrafts occupy the entire base the supply of water vapor is cut off, precipitation diminishes, sky begins to clear

mesoscale convective systems

clusters of thunderstorms that form from common origin

squall lines

a linear band of thunderstorms

mesoscale convective complexes

oval clusters of thunderstorms


intensely powerful storm that has a single updraft zone

conditions necessary for a severe thunderstorm

wind shear, high water vapor content in lower troposphere, trigger uplift, potential instability

outflow boundary

line seperating an air mass cooled by a thunderstorm and the surrounding air.

gust front

leading edge of strong and variable surface winds produced by downdraft

shelf cloud

caused by a gust front lifting warm air, formed above the gust front and ahead of the main portion of thunderstorm

roll cloud

caused by horizontally rotating air beneath the leading edge of the gust front

doppler radar

emits electromagnetic waves to detect the velocity of precipitation that is falling toward/away from the receiver


appear as a mall appendage attached to the body of the storm on a radar image, usually indicate tornado formation is imminent


the zone with no radar return is where the inflow of warm surface air enters the supercell


described as a boundary seperating air masses based on moisture content


a localized area of strong winds in a downdraft beneath a thunderstorm


powerful horizontal winds produced by strong downdrafts associated MCSs


downbursts with diameters <4km, dangerous for airplanes


a violently rotating funnel-shaped column of air extending downward from a severe thunderstorm to the ground

tornados spin

counterclockwise in the Northern Hemisphere (cyclonically)

tornadoes result from

large differences in atmospheric pressure over short distances


an area on the flank of a supercell storm characterized by rotating clouds, precede tornado formation

wall cloud

a localized wall of condensed water vapor at the base of a severe thunderstorm, commonly associated with tornadoes

funnel cloud

forms when a narrow rapidly rotating vortex emerges from the base of the wall cloud, tornado that hasn't touched the ground

suction vortices

small, intense, rotating wind cells that are responsible for much of the damage done by a tornado

Fujita scale

describes the intensity of a tornado

severe storm and tornado watches

an alert that weather conditions are favorable for such events; continue on life as normal while keeping an eye out

severe storm and tornado warnings

an alert that a severe thunderstorm has already developed; take immediate safety precautions

tornado outbreak

an event in which a single weather system produces at least 6 tornadoes


a rapidly rotating column of air extending down from a thunderstorm to a body of water


damaging flows of volcanic debris and water


molten rock formed deep within the Earth's crust or mantle

shield volcanoes

gently sloping, broad, convex volcano consisting of basalt lava flows


basaltic magma that erupts from volcanos


fragmented volcanic material blown out of a volcano

pyroclastic deposits

accumulations of tephra

stratovolcano/composite volcano

steep-sided, explosive volcano formed of pyroclastic deposits and lava flows

volcanic domes

volcano formed from viscous magma with a high silica content, generally explosive

cinder cones

conical volcano consisting of pyroclastic deposits, usually only erupt once or twice


a flat-bottomed, roughly circular volcanic crater produced by a single explosive eruption, commonly filled with water


huge outburst floods that are caused when subglacial volcanoes erupt and melt large quantities of ice


depressions at the tops of volcanoes that form by explosion or collapse of the summit area


steep-sided, flat toppoed volcanoes associated with glaciers


a large crater produced by a violent volcanic eruoption or the collapse of the summit area of a volcano after an eruption

volcanic vents

openings through which lava and pyroclastic debris erupt

lava flows

molten rock that flows downslope from a volcanic vent, cools, and solidifies


basaltic lava flow with a ropy surface texture


basaltic lava flow with a broken, blocky surface texture

pyroclastic flows

dense avalanches of hot gas, ash, and volcanic rock that cascade down the slopes of a volcano during an explosive eruption

pyroclastic surges

dense clouds of hot gas and rock debris produced by explosive interaction of water and magma

lateral blasts

gas, ash, and rock fragments blown horizontally from the side of the mountain at the start of an eruption; very fast and destructive

ash fall

deposition of a layer of fine air-borne rock and glass that have been erupted from a volcano


a tropical cyclone with sustained winds of at least 118km/h


a region of relatively clear skies, slowly descending air, and light winds

eye wall

the portion of a hurricane bordering the eye; it is the region with the highest winds and heaviest rainfalls

double eye walls

the presence of two eye walls; usually indicates a hurricane is achieving maximum strength

hot towers

localized portions of the eye walls that rise to greater heights than the rest of the eye wall; indicates a greater likelihood that the hurricane will intensify

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