Earth Mat Flashcards - Ch 9
Lava commonly erupts from a _________ located in a crater near the summit of the volcano.
central vent
Low discharge flank eruptions produce smaller _________ along the summit, side or base of larger volcanoes.
parasitic volcanoes
Mauna Kea has _____ parasitic cones
100
are large, generally circular to oval depressions caused by subsidence of Earth’s surface. in the context of volcanism
Calderas
Magma Loss in caldera formation can be caused by two things
subsurface withdrawal of magma from a shallow chamber as magma migrates to another location,
cataclysmic eruptions that empty the shallow magma chamber.
is an intrusive igneous body that is circular, oval or arcuate in plan view and has steep contact
A ring dike or ring dyke
, are the product of massive outpourings of low viscosity basaltic lava that envelop hundreds of thousands of square kilometers.
Flood basalts , also known as large igneous provinces (LIP)
Mantle Hotspot related LIP
Ontong Plateau, W. Pacific
Kerguelen Plateau, Indian Ocean
Continental Flood Plateau
Deccan Traps, India
Siberian Flood Basalts
Karoo, E. Africa
Columbia River/Snake River Plain, N. America
Marine and continental
Records break up of pangea
Central Atlantic Magmatic Province (CAMP)
consist of a 65,000 km long global network of submarine rift mountains
Ocean ridges
Rare examples of surface exposed ocean ridges
Iceland, Galapagos Is., Azores Is.
As hot (1100 – 1300 ° C) basaltic magma rises upward and reacts with cold seawater, spheroidal ____________ develop
pillow lavas
Ocean ridges also contain _________ that emit lower temperature (100 – 300 ° C) solutions that precipitate light - colored minerals such as calcite, gypsum, barite and quartz.
white smokers
are broad, sloping edifices that cover hundreds to thousands of square kilometers with shapes that resemble the defensive shields of ancient warriors.
Shield volcanoes
5 Shield volcanoes of the Big Island of Hawaii
Kilauea
Mauna Loa
Mauna Kea
Hualalai
Kohala
The Hawaiian eruptions that produce shield volcanoes also generate fiery basaltic___________ several hundred feet high
lava fountains
Airborne blobs of liquid lava emitted by fountains are referred to as
spatter
Spatter that solidifies at the base of the lava fountains is referred to as
welded spatter or agglutinate deposits
Lava fountains that erupt via fissures produce linear ridges called ____________ on either side of the fissure
spatter ramparts
are elevated lateral banks that contain the lava flow within stream-like channel.
Lava levees
are shallow subterranean tunnels channelling lava beneath thin, solidifi ed basaltic roofs.
Lava tubes
lava consists of low viscosity, “ runny ” basaltic lava which produces thin flows with a billowing, rippled and/or ropey surface
Pahoehoe lava
More viscous aa lava tends to produce thicker, slower moving lava flows with angular, jagged, fractured surfaces
Aa lava
are steep - sided (~30 – 35° ) conical features composed of tephra.
Pyroclastic cones
Tephra consists
of volcanic rock fragments of various sizes and compositions emitted during explosive eruptions.
Pyroclastic cones composed predominantly of vesicular basaltic material.
Scoria cones
Pyroclastic cones consisting of ash, lapilli and bomb - sized particles of various compositions that accumulate as circular to oval - shaped conical volcanoes
Cinder cones
are majestic cone - shaped mountains encompassing tens to hundreds of square kilometers in area with slopes ranging from 10 ° to 30°
Composite volcanoes
consists of smooth - sided blocks up to several meters in diameter that tumble downslope
lithifies as volcanic breccia deposits
Block lava
develop when a solidified magma plug is pushed up through the conduit, forming a vertical column on Earth ’ s surface.
Spines
are steep - sided, blister - like forms that occur within volcanic craters
Domes
Explosive volcanic eruptions produce a vertical plume or eruption column that can be divided into three distinct parts
lower gas thrust
Upper convectice thrust
Umbrella Region
region in the eruption column where
material thrust from the vent
100 to 600 m/s
Lower Gas Thrust
region in the eruption column where
convective rise of heated atmospheric gases and fragments
Upper convective thrust region
region in the eruption column where
vertrical plume begins to spread laterally as the result of temperature inversions
Umbrella region
Two modes of eruptive column behavior ______________ result in two kinds of deposits: pyroclastic fall (air fall) deposits and pyroclastic fl ow deposits.
– convective thrust and gravitational collapse–
occurs when the thrust region plume exhibits buoyancy
Convective thrust
_of the plume occurs due to negative buoyancy
initiation of pyroclastic flows
Gravitational collapse
deposits are produced by airborne pyroclasts propelled upward in an eruption column
Pyroclastic fall (air fall)
lateral sequence of air fall particales from nearest to farthest
Bombs and breccia settle first and closest, smaller particles slow and farthest
Solidifies deposits grades upward from brccias to lapili tufts and lastly fiend tuffs
Distal ash - sized particles are deposited and later compacted and cemented together as ash fall tuffs
deposits generally lack stratification and are poorly sorted
chaotic mixtures of clast sizes are deposited rapidly.
pyroclastic flow
Three major types of pyroclastic flows are recognized:
Pyroclastic Surges
Pumice Flows
Nuee Ardentes
Pyroclastic flow
very low density, extremely hot, gaseous flows
ash - to lapilli - size particles; 100 km/h
Low densities allow surges to defy gravity and climb upwards
Pyroclastic surges
Pyroclastic flow
low to moderate density, hot vesiculated flows
Siliceous pumice flows produce light - colored, vesicular ignimbrites
Andesitic to basaltic flows produce vesicular scoria flow.
Pumice flows
Pyroclastic flow
fluidized mixtures of hot, incandescent rock fragments and gases
1000C at 150 km/h
High density, vesicle - poor block and ash pyroclastic flow deposits are generated
Nuées ardentes (French for “ fiery clouds ”)
Siliceous pumice flows produce light - colored, vesicular _________
ignimbrites
are volcanic mudflows up to tens of meters thick with the consistency of wet cement.
Lahars
Lahars can form at three different times:
Synchronous with volcanism (syn-eruption lahars) and active pyroclastic flow.
After volcanism has ceased (early post - eruption lahars)
slopes of dormant or inactive volcanoes (late post - eruption lahars)
The 1991 Mt Pinatubo (Philippines) eruption involved both ________ and _______ lahars
syn-eruption and post -eruption
are large volcanic features that lack the typical, highly elevated landform associated with most volcanoes.
Rhyolite caldera complexes
Rhyolite calderas are known as __________; since low depression calderas are the signature aspect,
inverse volcanoes
After eruption of rhyolite calderas, they can emit smaller scale eruptions over long time intervals and experience regional uplift, referred to as
“resurgence”
eruption involving both magma and heated groundwater
magma below water table
Phreatomagmatic eruptions
Volcanic features produced by phreatomagmatic eruptions include
tuff rings, tuff cones (both positive) and maars (negative).
gently sloping, circular structures composed of stratified, glassy volcanic debris and scoria
explosive eruption of basalt in a lake, beach or wetland environment.
Reworked shallow water cinder cones
Tuff rings
circular volcanic cones formed by the eruption of basalt in water
smaller and steeper features
Less explosive eruption, short durations
Tuff cones
low relief volcanic craters that form by shallow explosive phreatomag matic eruptions
volcanic crater filled with water to create either a freshwater or saline lake
Maars
The eruption of heated water and steam without magma, characterizes phreatic eruptions
Phreatic eruptions
groundwater heated by proximity to magma
Hot springs
eruptive hot springs that eject fountains of heated water periodically
Geysers
Eruptions begin as fissures, evolving to central vent flows and the generation of large shield volcanoes.
Fiery basaltic lava fountain eruptions, quiet lava flows, and cinder cones are also generated.
Hawaiian
Persistent fissure eruption of low viscosity basaltic lava flows.
Prolonged quiet eruptions may generate lava plateaus and flood basalts.
Icelandic
Explosive, steam-blast eruptions with lava flows and pyroclastic debris.
Surtseyan
(phreatomagmatic)
Surtseyan eruptions are named after the volcanic island of _____, which rose above sea level on November 14, 1963.
Surtsey
Periodic bursts (“burps”) of moderately explosive eruptions (less than 5 km high).
These eruptions contain great concentrations of pyroclastic fragments and incandescent basaltic lava flows.
Strombolian
Explosive eruptions of basaltic to rhyolitic viscous lava.
Large volumes of volcanic ash plumes (less than 25 km high) and pyroclastic debris.
Vulcanian
Violent eruptions of volcanic debris ejected, scattering ash over thousands of square kilometers
Vesuvian
Tephra eruptions emit immense ash clouds over 11 km in height into the stratosphere.
Plinian
Violent tephra eruptions with volumes greater than 1 km³ and ash cloud heights ranging from 25 to 55 km
Ultraplinian
