Plate Tectonics (Types and landforms) KQ1&2

Question 1

Define Natural Hazard

Answer 1

Naturally occurring event that threatens human lives and causes damage to property

Tectonic hazard: caused by plate movement

Climate-related: caused by severe/extreme weather and climate conditions

Question 2

What is the internal structure of the earth?

Answer 2

1. Crust
   - Oceanic: Denser Basalt, 5-8km,
   - Continental: Lighter Granite, 30-70km
2. (Upper and lower) Mantle
   -800-3000c
   -Solid rocks flowing under high temp and pressure
   -2900km
3. Outer Core
   -3000-5000c
   -Liquid metals (iron/nickel),
   -2100km
4. Inner Core
   -3000-5000c
   -Solid Metals (iron/nickel),
   -1400km

Question 3

Convection currents (5)

Answer 3

1) Core heats mantle
2) Magma expands, rises and spreads out beneath plates
3) Spreading under crust = divergent movement
4) Cool and sinking magma = dragging crust = convergent movement
5) Mantle material heated up by core again and process is repeated

Question 4

Slab-Pull force (2)

Answer 4

1) Denser subducting plates pull rest of plate behind it
2) Upward rising convection currents push plate along while downward sinking currents drag plate down.

Question 5

O-O Plates Divergence

Answer 5

1) Magma flows through C&F and solidifies, forming new seafloor (seafloor spreading)
2) Magma accumulates higher, MOR and undersea volcanoes formed
3) MOR accumulates above MSL, volcanic island (belt) formed

Question 6

O-O divergence examples

Answer 6

MOR
-Mid-Atlantic ridge
-North-American plate and Eurasian Plate

Undersea Volcanoes
-Azores, mid Atlantic Ocean

Question 7

C-C plate divergence

Answer 7

1) Crust pulled apart,
2) Fractures formed
3) Central blocks sink and linear depression formed
4) Rift valley and block mountains w/ volcanoes and EQs

Question 8

C-C divergence examples

Answer 8

East African Rift Valley System
- African plates: Nubian plate boundary, somalian plate boundary
-30-60km long
-EQ and volcanoes

Question 9

O-O convergent plates

Answer 9

1) Denser subducts under less dense
2) Folds less dense crust downwards, forming oceanic trench
3) Subducted crust melts, forming magma
4) Magma rises through C&F, undersea vocanoes
5) repeated eruptions = accumulation of magma = rise above sea level forming volcanic islands

Question 10

O-O convergence examples

Answer 10

Mariana trench and islands
-Pacific plate subducting under philipines plate (Mariana trench)
- Magma rises to overlying philipines plate (Mariana islands)

Question 11

C-C plate convergence

Answer 11

1) resists subduction
2) Plates compressed, buckle and fold, creating fold mountains

• No volcanoes formed, plates too thick for magma to exploit

Question 12

C-C plate convergence example

Answer 12

Himalayas
-Indian and Eurasian plate

Question 13

O-C plate convergence

Answer 13

1) oceanic plate subducts under continental plate
2) Oceanic trench formed at subduction zone
3) Fold mountains formed on continental plate
4) Magma rises through C&F fold mountains become volcanoes
5) EQs

Question 14

O-C plate convergence examples

Answer 14

Sunda Trench and Barisan Mountains
-Australian plate and Eurasian plate

Question 15

Transform plate boundaries

Answer 15

1) Plates slide past each other (same or op direction)
2) Form faultlines = stress = EQs

Question 16

Transform plate boundary examples

Answer 16

San Andreas Fault
- Pacific and North American Plate
-1906 EQ, plates displaced 2-5m in 1min

Question 17

Fold Mountains

Answer 17

1) Converging plates collide
2) Compressional forces buckle and fold rocks (Upfold: Anticline, downfold: Syncline)
3) C&F formed, exploited by magma, volcanoes formed
4) Limb ride over each other, stack and increase in height and length
5) Prevalent in flexible sedimentary rocks (Igneous and metamorphic not flexible)

Question 18

Fold Mountains Example

Answer 18

1) Himalayas
-Eurasian and Indian Plate (C-C)

2) Rocky Mountains
- Juan De Fuca and NA plate (O-C)

Question 19

Rift valleys and block mountains

Answer 19

1) Diverging plates create faultlines (somewhat // to each other)
2) Tensional forces cause faulting, displacing central block (btwn // faultlines)
3) Gravity subsides central block (rift valley) , remaining highlands called block mountains

Question 20

RV and BM examples

Answer 20

East African Rift Valley
- Somalian and Nubian plate boundary (African plate)

Question 21

Volcanoes

Answer 21

1) Forms at all plate boundaries where subduction occurs
2) At subduction zone, mantle material melts,
3) Magma rises through C&F, accumulates in enclosed cracks, forming magma chambers
4) Pressure causes Magma in magma chamber to rise to surface through vents as lava
5) Lava cools and solidifies, forming volcanic cone
6) New eruptions build up volcano
7) Summit may be blown off, crater collapses, forming caldera
8) Vents may be obstructed, lava forced through other C&F, forming secondary volcanoes.

Question 22

Low Silica Lava

Answer 22

-Low viscosity
-Allows gases to escape easily = less pressure = less explosive
-Flows through vent easily, quickly and silently

Question 23

High Silica Lava

Answer 23

-High Viscosity
- Traps gases easily = High pressure = more explosive
- Ejects Pyroclast

Question 24

Shield Volcanoes

Answer 24

• Lows Silica
• High temp lava
• Gentle grad.
• Wide Base
• Only primary cone
• Less explosive
• Divergent boundaries

-e.g. Mount Washington, USA

Question 25

Stratovolcanoes

Answer 25

• High Silica
• Lower Temp
• Steeper grad.
• Narrower base
• Primary and Secondary Cones
• Explosive
• Convergent plates

e.g. Mount Pinatubo, philipines, 1991
- 10mil tonnes lava
- 20 mil tonnes SO2
- 30km ash into air

Question 26

Types of pyroclast

Answer 26

1) Pyroclast (volcanic rock frags and heated gases)

2) Pyroclast + Superheated gases = Pyroclastic Flow
- 200m/s

3) Pyroclast + Water = Lahars
- Fast flowing mudflows
- 40m/s

Question 27

Earthquakes

Answer 27

1) Plates move = friction generated (all plate boundaries)
2) Energy accumulated in crust on either side of fault
3) When rocks no longer able to resist stress, they slip, causing SUDDEN RELEASE OF STORED ENERGY (seismic s/p waves) VIBRATING EARTH´S CRUST (def)
4) Aftershocks can occur for several months after initial EQ

Question 28

What constitutes an “oceanic-plate”

Answer 28

A plate with at least 50% submerged under ocean bodies.

Question 29

What constitutes a “continental plate”

Answer 29

A plate with at least 50% exposed to earths surface

Question 30

Which plates compose the pacific ring of fire

Answer 30

Pacific, Juan de Fuca, Cocos,
Indian-Australian, Nazca, North American, and Philippine Plates (7)