lecture 9

Question 1

volcano

Answer 1

opening in earths crust through which molten rock, hot rock fragments and gases escape in a volcanic eruption

Question 2

lava

Answer 2

molten rock at earths surface erupted from volcano that can take different forms: bombs, flows and ash fall

Question 3

magma

Answer 3

molten rock situated within the earth within a magma chamber or conduit

Question 4

4 steps of volcanic eruptions

Answer 4

1. eruption starts with magma at depth, gases are kept dissolved in solution by high pressure
2. as magma rises, pressure is reduced. Gases come out of solution (exsolution) to form bubbles and decompression melting may occur. Surrounding bedrock can also melt and mix with magma
3. bubbles propel the magma upwards, bubble volume may overwhelm the magma fragmenting it into pieces and explloding as a gas jet
4. gas jet draws in surrounding air forming a bouyant plume

Question 5

volcanic rocks

Answer 5

formed from lava that solidified above the surface (extrusive)

Question 6

plutonic rocks

Answer 6

formed from magma that solidifed below the surface (intrusive)

Question 7

what happens when lava or magma cools

Answer 7

solidifies and atoms arrange themselves into crystals

Question 8

viscosity- magma characteristics

Answer 8

measure of internal resistance to flow, low viscosity flows easily and high viscosity flow slowly

1. higher temperature = lower viscosity
2. higher crystal content = higher viscosity
3. higher siica content = higher viscosity

Question 9

how does oceanic crust from at mid ocean ridges

Answer 9

new oceanic crust forms by decompression melting of asthenosphere. Magma at high temp, low H20 content, low SiO2 content and therefore low viscsoity

Question 10

what forms a pillow shape of lava

Answer 10

when basalt erupts underwater, contact w/ cold water quenches the surface and the lava forms a distinctive pillow shape

Question 11

icelandic type eruptions

Answer 11

iceland sits on a mid-ocean ridge that is above sea level. Because of the low viscosity, gas bubbles can escape and eruptions are peaceful

Question 12

flood basalts- icelandic type eruptions

Answer 12

low viscosity basalt spreads out into a horizontal layer and over time stacks up to form flood basalts

Question 13

what happens to magma at oceanic hot spots

Answer 13

hihg temperature, low H20 and low SiO2 so low viscosity, gas bubbles can escape and eruptions are peaceful

Question 14

hawaiian type eruptions

Answer 14

basaltic lava spills out of fissures as lava fountains and flows downhill as lava rivers

Question 15

shield volcano- hawaiin type eruptions

Answer 15

magma erupted in hawaii is more viscious than in iceland so builds giant shield volcano (Mauna Loa) By volume, largest sub-aerial volcano on Earth

Question 16

what happens to magma at volcanic arcs

Answer 16

addition of water to the mantle from the cold slab lowers solidus, which touches geotherm. Basaltic magma is lower temp with higher H20 content than at mid ocean ridges
- magma has to pass through arc crust which increases SiO and raises viscosity

Question 17

3 types of magma in volcanic arc

Answer 17

basaltic- H20 released from slab melts asthenosphere
andesitic- heat melts continental crust to mix with basalt
rhyolitic - furthur melting and mixing of continental crust

Question 18

3 types of arc volcano eruption styles

Answer 18

pliny, stomboli and vulcano