Plate Tectonics (Types and landforms) KQ1&2 Flashcards
Define Natural Hazard
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
What is the internal structure of the earth?
- Crust
- Oceanic: Denser Basalt, 5-8km,
- Continental: Lighter Granite, 30-70km - (Upper and lower) Mantle
-800-3000c
-Solid rocks flowing under high temp and pressure
-2900km - Outer Core
-3000-5000c
-Liquid metals (iron/nickel),
-2100km - Inner Core
-3000-5000c
-Solid Metals (iron/nickel),
-1400km
Convection currents (5)
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
Slab-Pull force (2)
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.
O-O Plates Divergence
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
O-O divergence examples
MOR
-Mid-Atlantic ridge
-North-American plate and Eurasian Plate
Undersea Volcanoes
-Azores, mid Atlantic Ocean
C-C plate divergence
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
C-C divergence examples
East African Rift Valley System
- African plates: Nubian plate boundary, somalian plate boundary
-30-60km long
-EQ and volcanoes
O-O convergent plates
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
O-O convergence examples
Mariana trench and islands
-Pacific plate subducting under philipines plate (Mariana trench)
- Magma rises to overlying philipines plate (Mariana islands)
C-C plate convergence
1) resists subduction
2) Plates compressed, buckle and fold, creating fold mountains
- No volcanoes formed, plates too thick for magma to exploit
C-C plate convergence example
Himalayas
-Indian and Eurasian plate
O-C plate convergence
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
O-C plate convergence examples
Sunda Trench and Barisan Mountains
-Australian plate and Eurasian plate
Transform plate boundaries
1) Plates slide past each other (same or op direction)
2) Form faultlines = stress = EQs
Transform plate boundary examples
San Andreas Fault
- Pacific and North American Plate
-1906 EQ, plates displaced 2-5m in 1min
Fold Mountains
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)
Fold Mountains Example
1) Himalayas
-Eurasian and Indian Plate (C-C)
2) Rocky Mountains
- Juan De Fuca and NA plate (O-C)
Rift valleys and block mountains
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
RV and BM examples
East African Rift Valley
- Somalian and Nubian plate boundary (African plate)
Volcanoes
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.
Low Silica Lava
-Low viscosity
-Allows gases to escape easily = less pressure = less explosive
-Flows through vent easily, quickly and silently
High Silica Lava
-High Viscosity
- Traps gases easily = High pressure = more explosive
- Ejects Pyroclast
Shield Volcanoes
- Lows Silica
- High temp lava
- Gentle grad.
- Wide Base
- Only primary cone
- Less explosive
- Divergent boundaries
-e.g. Mount Washington, USA
Stratovolcanoes
- 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
Types of pyroclast
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
Earthquakes
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
What constitutes an “oceanic-plate”
A plate with at least 50% submerged under ocean bodies.
What constitutes a “continental plate”
A plate with at least 50% exposed to earths surface
Which plates compose the pacific ring of fire
Pacific, Juan de Fuca, Cocos,
Indian-Australian, Nazca, North American, and Philippine Plates (7)
