Chapter 5: Volcanoes Flashcards
What are volcanoes?
Hill or mountain that forms around a vent where lava or pyroclastic materials are ejected
What is volcanism?
The processes related to rise and discharge of magma
Ex. Fissure eruptions
What are Volcanic gases?
Small part of magma that are primarily water. Do not harm humans
What are the different kinds of lava flows?
Aa lava: angular blocks and fragments
Pahoehoe: smooth rooy surface
Columnar joints: form when lava flows, cools, and contracts
What are the pyroclastic materials?
Solid magma fragments that are explosively ejected by volcanoes
Ash<2mm diameter (small sand grains)
Lipilli 2-64mm
Bombs: partially molten, >64mm
Blocks: solid, >64mm
What is ash falls?
Settles out of the atmosphere
Turbulent clouds of ash and gas that travel close to the surface during pyroclastic materials
Draw what a conduit, crater, caldera are.
Conduit is the chamber leading to the top of the volcano
Crater is the depression at the summit
Caldera is a large depression that forms when the summit collapses into the magma chamber following an eruption
What are some characteristics of a shield volcano?
Gentle slope
Largely composed of basalt with some mafic proclastsb
Usually non explosive
ex. Hawaii
What are some characteristics of a cinder come volcano?
Consists of cinders and other pyroclastic materials
Accumulate as steep-slope cones that rarely exceed 400 m High
ex. Wizard island inside of crater lake
What are some characteristics of a composite (stratavolcano)?
Composed of layers of lava flows, pyroclastic debris and volcanic mud flows
Explosive
Most have intermediate compositions
ex. Mt. St. Helens
What are some characteristics of lava domes?
Form when viscous, usually felsic or intermediate, lavas are forced up through the conduits of some volcanoes.
Can erupt explosively and commonly eject núee ardentes (hot clouds of pyroclastic materials)
What are super volcanoes?
Erupt hundreds of square km of material and produce huge calderas
Non have erupted in recorded history
3 have erupted in Yellowstone in the past 3 million years
Possibly caused my a mantle plume
What is a basalt plateau?
Fluid mafic lava erupts from long fissures (not vents)
Made up of numerous overlapping basalt- lava flows
ex. Columbia river
What are pyroclastic sheet deposits?
Huge sheet-like eruptions of pyroclastic materials, especially ash
Cover large areas when erupted from fissures during caldera formation
What are the zones of volcanoes
Circum-pacific belt “ring of fire”
60% of volcanoes
Mediterranean belt
20%
Mid-ocean ridges
Explain Alaska’s volcanoes
Stretch from the mainland to the Aleutian Islands
Mostly composite
Some with huge calderas
Extremely active with huge explosions
Explain the cascade range
Mostly composite
Has 2 shield and lots of cinder cones
Result from the subduction of the Juan de Fuca
Explain volcanic activity at divergent plate boundaries
Volcanic activity near or at mid-ocean ridges is mainly submarine
In a few places such as island, occurs above sea level
Form mafic shield volcanoes
Explain volcanic activity at convergent plate boundaries
The volcanism in the circum pacific and Mediterranean belts results from subduction
Magmas are produced by the partial melting of subducted plate
How large is an eruption and how long do they last?
Volcanic explosivity index (VEI)
Eruption size indicator
Ranges from 0-8
Measures the explosive intensity of an eruption using: volume of material erupted, eruption cloud height
Eruption duration varies
Is it possible to forecast eruption?
Monitoring volcanoes helps geologists to forecast imminent eruptions:
Recording and analyzing both physical and chemical changes at volcanoes
Tiltmeters and geometers are used to detect change of slope, elevation, and shape of the volcanoes
Monitoring involves recording and analyzing both physical and chemical changes at volcanoes
Siesmeters detect harmonic tremors
