1.4 Tectonic processes at diff plate boundaries

Question 1

Divergent plate boundaries

Answer 1

• as plates move apart from each other, they form mid-oceanic ridges, volcanoes and volcanic islands, rift systems and earthquakes
  1. Oceanic-Oceanic Divergent plate boundaries
  2. Continental-Continental divergent plate boundaries

Question 2

Oceanic-oceanic divergent plate boundaries

Answer 2

1. 2 oceanic plate move apart
2. Decrease in overlying pressure causes parts of the underlying mantle to melt, forming magma
3. Magma rises through weak areas in the crust to the Earth’s surface, and fill gaps caused by the spreading plates
4. Lava cools and solidifies and accumulates to form basaltic rocks—forming new oceanic crusts
5. extensive underwater mountain chain — mid-oceanic ridge forms

Example: Mid-(A)tlantic Ridge (NEA)
- formed from divergence of the Oceanic (N)orth American Plate and Oceanic (E)urasian Plate
- decrease in pressure in underlying mantle causes it to melt, forming magma
- magma rises through the weak areas in the crust to the earth’s surface, forming submarine volcanoes
- after many eruptions, volcanoes break the surface of the ocean to form volcanic islands
- earthquakes also occur here due to stress and tension released when plates move

Question 3

Continental-continental divergent plate boundaries

Answer 3

1. 2 continental plates move apart
2. rocks eventually fracture to form parallel faults
3. rocks between faults collapses to form a deep rift valley with steep sides
4. as plates move apart, decrease in overlying pressure causes parts of the underlying mantle to melt, forming magma. magma rises through weak areas in crusts to earth’s surface, forming volcanoes
5. earthquakes occur as stress and tension are released when plates move.

Example: The Great (A)frican Rift Valley (NAS)
- (N)ubian plate pulling apart from (S)omalian plate (both plates are part of African plate)
- Volcanoes formed: Mount (K)enya & Mount (K)ilimanjaro (KK)

Question 4

Convergent plate boundaries

Answer 4

• plates moving towards each other, resulting in fold mountains, volcanoes, oceanic trenches and earthquakes
  1. Oceanic - Oceanic
  2. Continental - Continental
  3. Oceanic - continental

Question 5

Oceanic-Oceanic convergent plate boundaries

Answer 5

1. convergence of 2 oceanic plates
2. denser plate subducts beneath the less dense plate
3. forms deep depression known as the oceanic trench
4. subducting plate sinks into mantle, high-pressure forces water out of its oceanic crust. Water lower melting point of overlying mantle, causing it to melt, forming magma
5. magma rises through weak areas in the crust to the earth’s surface
6. forms a chain of volcanoes known as a volcanic island
7. friction along subducting plate and less dense plate causes earthquakes

Example: Marina Trench (PAP MM)
- oceanic (pa)cific plate subducts beneath oceanic (p)hilippine plate
- forms the (m)ariana trench, as well as volcanic islands known as (m)ariana islands
- Guam, an island near the Mariana trench, commonly experiences earthquakes

Question 6

Continental-continental convergent plate boundaries

Answer 6

1. 2 continental plates collide
2. subduction does not take place because continental plates are too buoyant to subduct
3. Enormous pressure causes rocks to be uplifted and buckled to form fold mountains
4. Friction along subducting oceanic plate causes earthquakes
5. magma does not rise to the surface, hence no volcanoes are formed

Example: Himalayan Mountain Range (HEI)
- continental (I)ndo-Australian Plate converses with the continental (E)urasian Plate
- forms the (H)imalayan Mountain Range
- this area experiences a lot of earthquakes such as the devastating 2015 Nepal Earthquake

Question 7

Oceanic - continental convergent plate boundaries

Answer 7

1. Oceanic plate collides with a continental plate
2. the denser oceanic plate subducts beneath the continental plate
3. forms an oceanic trench in the subduction zone
4. as subducting plate sinks into the mantle, high pressure forces water out of the oceanic crust, lowering the melting point of the overlying mantle. Mantle melts, forming magma
5. magma rises through weak areas in the crust to the earth’s surface, forming volcanoes on the continental plate
6. enormous pressure at the plate boundary causes rocks on the continental plate to be uplifted and buckled, forming fold mountains
7. friction along subducting oceanic plate causes earthquakes

Example: Andes Fold Mountain Range (NANAP)
- oceanic (N)azca Plate Converges with the continental South (A)merican Plate
- denser Nazca plate subducts beneath the South American plate forming the (A)ndes Fold Mountain Range, (P)eru-Chile Trench & (N)evado del Ruiz volcano
- earthquakes are also common here, such as the 2010 Chile earthquake

Question 8

Transform Plate Booundaries

Answer 8

• plates slide past each other
• no crust is created nor destroyed
• stress caused by the plate movement produces a fault (zone of fractures)

Example: **Andes Fold Mountain Range (NAPS)
- (P)acific plate sliding past (N)orth (A)merican Plate
- forms (S)an Andreas Fault in California, USA
- earthquakes are common here, such as the 1989 Loma Preita earthquake in california