Lecture 7: Volcanoes

Question 1

mamga

Answer 1

• liquid ricks vary in their chemical composition ability to flow easily, their gas content and their volume
• these variation govern whether eruptions are peaceful or explosive
• liquid = molten rock
• solids = minerals incorporated in the melt
• volatiles = gases dissolved in the melt
• igneous rocks: form from cooling and solidification from hot molten rock material

Question 2

lava

Answer 2

• magma that reaches the surface

Question 3

intrusive igneous rocks

Answer 3

• cooling at depth: intrusive igneous rocks
• slow cooling
• large grains

Question 4

extrusive igneous rocks

Answer 4

• cooling at the surface: extrusive igneous rocks
• fast cooling
• small grains
• contact with the atmosphere or water

Question 5

viscosity

Answer 5

• internal resistance of a liquid to flow
• the less viscous a fluid, the faster it flows

Question 6

what controls magma viscosity

Answer 6

• % SiO2 (more SiO2 = higher viscosity)
• magma with high SiO2 has more silicate chains, sheets and 3D structures
• more bounds between atoms increases viscosity
• temperature: atoms vibrate more vigorously at high temperatures. bounds between atoms tend to break, decreasing viscosity
• amount of solids in the melt: more solids = higher viscosity

Question 7

low viscosity magma

Answer 7

• tends to reach the earths surface
• erupts peacefully
• basaltic magma
• high temperature
• low volatile content

Question 8

high viscosity magma

Answer 8

• tends to form intrusive bodies
• when reaching the surface, erupts explosively
• andesitic and rhyolitic magma
• low temperature
• high volatile content

Question 9

ejecta

Answer 9

• volcanic materials extruded into the earth;-‘s surface and into the atmosphere

Question 10

pyroclastic material

Answer 10

formed by volcanic explosion or aerial expulsion from a volcanic vent

Question 11

volatiles

Answer 11

• mainly H2O, CO2 and SO2

Question 12

volcanic glass

Answer 12

• fast-cooling lava produces volcanic glass
• atoms did not have enough time to develop an orderly structure

Question 13

viscous lava

Answer 13

• high SiO2
• flows slowly

Question 14

fluid lava

Answer 14

• low % SiO2
• flows quickly over large distances
• pahoehoe: flow wrinkles

Question 15

pyroclastic material

Answer 15

• classified according to particle size:
• ash (<2mm)
  lapilli (2-64 mm)
  scoria (>64mm)

Question 16

bombs

Answer 16

ejected as incandescent lava fragments with were semi-molten when airborn

Question 17

volcanoes at divergent zones

Answer 17

• very large volume of magma extruded at mid-ocean ridges
• volcanic activity below sea level
• formation of new oceanic crust
• peaceful eruptions: low pressure, rock melts partially, magma rises and flows easily
• ex. Iceland volcanoes

Question 18

volcanoes at subduction zones

Answer 18

• H2O from subducting plate lowers the melting point of rock
• partial melting is induced in the overriding plate
• magma rises and erupts
• potentially explosive eruptions
• low temp and high SiO2 + high viscosity
• at ocean- ocean boundary there is less SiO2
• at ocean - continent boundary there is more SiO2 (et mont st helens)

Question 19

hot spots

Answer 19

• long-lived (100 Ma)
• chains of volcanoes (oldest = smallest)
• peaceful eruptions: rising magma does not ix with thin oceanic crust
• low viscosity and low volatile content; low SiO2