lecture 9 pt 2

Question 1

strombolian type eruptions

Answer 1

medium viscosity basaltic to andesitic magmas TRAP MORE of the GAS BUBBLES, producing mildly explosive eruptions as at stromboli italy

Question 2

scoria cones

Answer 2

strombolian type eruptions: repeated eruptions produce mounds of volcanic rock fragments piled up next to a volcanic vent. Summit crater may hold a lava lake during eruption
BC: stikine volcanic belt and Wells gray-clearwater volcanic field

Question 3

vulcanian type eruptions

Answer 3

medium to high viscosity magmas, typically andesitic in composition
- magma is sufficiently viscous that explosive eruptions send rock and ash into atmosphere forming a plume

Question 4

frequency of eruption occurances

Answer 4

strombonian–> occur pretty much daily, 100s a year
plinian: more violent and high visocsity so 1/200 years
ultra plinian: every few millions

Question 5

stratovolcanoes

Answer 5

vulcanian type eruptions: tall steep sided symmetrical peaks built of alternating ash and viscous magma flows

Question 6

plinian type eruptions

Answer 6

high viscosity rhyolitic magmas trap gas bubles most effectively producing a violent plinian type eruptions (ex. omunt st helens 1980)

Question 7

caldera

Answer 7

plinian type eruptions–> associated w/stratovolcanoes but empty magma chamber can lead to collapse of volcanic cone forming caldera
- mountains break apart

Question 8

pliny the younger

Answer 8

erupted in 79CE, roman city was buried in pyroclastic flow

Question 9

ultra plinican type eruptions

Answer 9

sixth class of volcanic eruption accounts for largest eruptions of all defined by > 25km high plumes and >10km volumes
- 630ka yellowstone: caldera 75 x 45 km volume = 1000km

Question 10

what is special about yellow stone supervolcano

Answer 10

occupies a continental hot spot, magma is rhytolitic since it must rise through thick continental crust

Question 11

volcanic explosivity index (VEI)

Answer 11

classifies volcanic eruptions based on

1. volume of material erupted
2. height of eruption column
3. duration fo major eruptive blast

Question 12

viscosity/volatiles/volume of eruption types

Answer 12

icelandic: basalt, low viscosity, low volatiles, large volume, flood basalt
hawaiin: basalt, low viscosity, low volatiles, large volume, shield volcano
strombolian: basalt/andesite, low/medium viscosity, medium volatiles, small volume and scoria cones
vulcanian: basalt (rhyolite), medium/high viscosity, medium/high volatiles, large volume, stratovolcanoes
plinian: adnesite (rhyolite), high viscosity, high volaties, very large volume and calderas

Question 13

glass

Answer 13

obsidian: produced when lava comes in contact with cool air or water and can be quenched solidifying so quickly that crystalizzation cannot happen

Question 14

pumice

Answer 14

gas escapes quickly from lava producing frothy glass

can comprise 90% holes

Question 15

tephra or pyroclasts

Answer 15

explosive eruptions blast out chunks of magma and surrounding rock

Question 16

ash fall and pyroclastic flow

Answer 16

pyroclasts can fall from volcanic plume as ash fall(sorted into layers of grain size) or if too dense to be carried into plume - entrained in denser gravity current known as pyroclastic flow (more chaotic, no sorting)

Question 17

elements in volcanic gases

Answer 17

H, O, C, S, Cl, N

CO2, Co, CH4, N, SO2, H2S, H2 HCl

Question 18

fatal attractions

Answer 18

people live near volcano because soils are particulalry fertile
Mg, Fe/ Al, Ca, K, Na