Text Ch.5

Question 1

lahars

Answer 1

damaging flows of volcanic debris and water

Question 2

Mount Unzen volcano occurred when and where?

Answer 2

Japan, has erupted twice in last 200 years and has caused huge loss of life and damage from pyroclastic flows and lahars

Question 3

_______ and _______ zones are sites where molten rock, or magma reaches the surface and erupts as lava

Answer 3

Mid-ocean riges and subduction zones

Question 4

most magmas come from the _______, where rock is close to its melting temp

Answer 4

astenosphere

Question 5

Three main ways in which silicate rocks can melt and become magma:

Answer 5

1. ) Decompression melting
   - occurs when the pressure exerted on hot rock within the asthenosphere is reduced
   - temperature and pressure increase with depth so rocks remain solid beyond their melting temp because of the increased pressure from overlying weight of rocks
   - occurs at divergent plate boundaries, continental rifts, and hot spots
   - essentially finds weakened parts of lithosphere because of decompression of lithosphere
2. )Addition of Volatiles(dissolved gas)
   - lowers the melting temperature of rock by helping to break chemical bonds within silicate minerals
   - volatiles are chemical compounds that exist in a gaseous state at earths surface and evaporate easily
   - are found within oceanic lithosphere and are released when that is subducted
   - magma created in this way erupts at earths surface at subduction zone volcanoes
3. ) Addition of Heat
   - can induce melting if the temperature of the rocks eceeds the melting temperature of silicate rocks at that depth
   - as magma rises from the aestenosphere it transfers heat to the surrounding rocks
   - these new rocks can change the composition of the magma

Question 6

Magma Properties

Answer 6

1. Composition
   - magma is composed of melted silicate minerals and dissolved gases
   - main elements in magma are oxygen and silicon, silica when combined
2. Viscosity
   - a fluids resistance to flow
   - Silica rich magma, like molasses, does not flow easily and has high viscosity
   - low silica magma

Question 7

Basalt

Andesite

Dacite

Rhyolite

Answer 7

.most common volcanic rock on earth
-45-52% silicate

52-63% silicate and is not as common

63-68% silicate-even more uncommon

> 68%- most uncommon