14.2 Flashcards
what are the two classifications for volcanoes?
shape
type of eruption
lava plateaux/ fissure eruptions
shield volcanoes may erupt along lines of fissures rather than a central vent spilling liquid lava in successive layers
form broad plateaux such as the Colombia plateaux - often cut by deep canyons that expose the layers of rock - Grand Canyon
extensive lava flow are basaltic in nature so they can they can flow great distances
flat and featureless
macrofeature
basic/shield volcano
3-4 miles wide and 1500-2000m tall
eg Mauna Loa
built up slowly by accreation of thousands of flows of highly fluid basaltic
low silica so spreads over wide areas
cools as thins forming gently dipping sheets
lava erupts form rift vents along fractures that develops on the flanks of the cone
magma has low gas content and is low in silica allowing it to flow over wide distances
acid/ dome volcanoes
craggy, steep sloped convex sides covered with rock debris
typically found near large composite volcanoes
made of layers of lava
formed by repeated violent eruptions and slow moving lava flows which gives layered structure
magma is made of higher silica and high gas pressure making magma slow moving and explosive
eg Puy region of central france
ash-cinder cones
formed from ash, cinders and volcanic bombs ejected from crater
sides are steep and symmetrical
eg Patricutun, Mexico
may occur as single volcanoes or secondary volcanoes on the sides of stratovolcanoes or shield volcanoes
tephra ejected
lava cools and builds up around the vent forming crater
build up over time
composite volcano/ stratovolcano
tall and conical
built up from many layers of hardened lava, tephra, pumice and volcanic ash
steep profiles
periodically explosive and quiet eruptions
lava typically cools before spreading due to high viscocity
layered structure built up of sequential outpourings of eruptive materials
increase in temp causes dome to expand while its outer lava cools, causes newly hardened surface to splinter causing loose debris to fall from its sides
eg Mt Etna
caldera
bowl shaped depression formed when volcano collapses into void left by empty magma chamber
crater lake caldera
results from stratovolcano collapsing into its magma chamber during a violent eruption
basalstic caldera
concentric ring pattern resulting from a series of gradual collapses
often found at summit of shield volcanoes such as the craters at the top of Mauna Loa
resurgent calderas
largest volcanic structure
result from catastrophic eruptions that dwarf eruptions recorded by humans
Yellowstone Caldera
lava type explosive volcano
rhyolite anderite
lava type effusive volano
basalt
lava characteristics explosive
acid high % silica
high viscocity
lower temp @ eruption
lava characteristics effusive
low % silica
low viscocity
high temp @ eruption
style of eruption explosive
violent bursting of bubbles when magma reaches surfacr
style of eruption effusive
limited explosive force
materials erupted explosive
ash, dust, lava bombs, tephra
materials erupted effusive
gas, lava flows
frequency of eruption explosive
long periods with no acitivity
frequency of eruption effusive
more frequent
shape of volcano explosive
steep sided strato volcanoes
caldera
shape of volcano effusive
gently sloping sides
shield volcanoes
lava plataux
strato volcanoes
made up of layers of ash and acid lava
concave symmetrical profiles
complex internal networks of lava flows which form minor igneous features such as sills and dykes
caldera
volcanic craters
2km in diameter
eruption destroys cone and underlying magma chamber is emptied - sides collapse
eg Krakatoa
archipelago
closely grouped cluster of islands
Indonesia
icelandic lava eruptions
large persistent fissure eruption
large quantities of basaltic lava
hawaiian eruption
runny basaltic lava
travels down sides of volcano in lava flows
gases escape
strombolian eruption
frequent gas explosions
large quantities of pyroclastic rock thrown out
vulcanian eruption
blasts out of plugs fo sticky or cooled lava
fragments build up into cones of ash and pumice
viscous lava
large quantities of ash
vesuvian eruption
powerful blasts of gas pushing ash clouds high into the sky
violent
ash covers surrounding areas
plinian eruption
gas rushed up through sticky lava
ash and fragments
clouds of gas and volcanic debris - kilometres thick
lava plateaux
magma erupts from multiple fissures
vast areas covered by free flowing lava
- flood basalts
millions of years of denudation create varied relief
eg Columbia plateaux covers 130,000km2
shield volcanoes
effusive eruptions found at divergent plate boundaries
mostly occur at mid ocean ridges
successive flows accumulate forming huge volcanoes
eg Skjadbreidur, Iceland - example of above ground one
eruptions at hot spot
fixed area of volcanic activity where magma from a rising mantle plume reaches the Earth’s surface
magma rises and forms island arc, and as plates move, island moves further away from hotspot and new island forms above hotspot
creates chain of islands
eg Hawaiian chain, pacific plate moves NW
super volcanoes
volcano that erupts more than 1000km3 of material on a single eruption event
exist as giant calderas
eg Yellowstone last erupted 70,000 years ago
what two factors need to be considered when assessing volcanic acitivity?
magnitude - amount of material erupted
intensity- the speed at which material is erupted
Volcanic Explosivity Index
combines magnitude and intensity into a single number on a scale 0-8
not good for effusive
what factors are taken into consideration when assessing explosivity of the eruption?
volume of erupted material
height ejected material reaches
time duration
lava flows
PRIMARY
impacts dependent on type of lava
basaltic lava is free flowing and can cover significant distances
eg Hawaii 2015, covered 20km
acidic lava is thicker and bulldozes everything in its path
pycrolastic flows
PRIMARY
combination of hot gases (500+ degrees), ash and rock fragments travelling at high speeds 100km/h
follow contours of ground
inhaling these gases causes instant death
eg Pompeii
tephra
any material ejected from a volcano into the air
ranges in size from very fine- Pele’s hair, Pele’s tears to ballistic material - lava bombs, Lapilli
buries farmland in layers of ash
weight of accumulated ash causes buildings to collapse and people with respitory issues are at risk
eg, eruption of Eyjafjallajokul 2010 caused cancellation of 100,000 flights
toxic gases
PRIMARY
eruptions emit CO2, carbon monoxide and sulfur dioxide
deadly threat to human and livestock populations
can causes acid rain
also can cause limnic eruptions eg Lake Nyos killed over 1000 people
lahars
SECONDARY
mud flow with consistency of concrete
snow and ice melt and mix with mud and flow rapidly down cone
travel at 50km/h
bury and destroy everything in their path
eg Nevado de Ruiz, Columbia, 23,000 killed
floods
SECONDARY
eruptions beneath an ice field or glacier cause rapid melting
vast quantities of water accumulate until they find an exit from under the ice
aka jokulhlaup
tsunami
violent eruptions of island volcanoes can cause massive displacement of ocean water and waves travleling at 600km/h
eg Krakotoa, killed 36,000
