Plate Tectonics 2

Question 1

Give two types of divergence at constructive plates

Answer 1

Seafloor spreading

Rift Valley

Question 2

What type of lava is found at constructive late margins

Answer 2

Basaltic Lava (runny) - low silica content

Question 3

Give two examples of constructive margins

Answer 3

Mid Atlantic Ridge

African Rift Valley

Question 4

Is old or young rock found at constructive margins

Answer 4

Young - New crust is being formed as the gap created by the spreading plates is filled by the magma rising from the asthenosphere.

As the magma cools it solidifies to form new rock

Question 5

Describe the characteristics of Ocean ridges

Answer 5

Can rise up to 4000m above the ocean floor - middle of the ridges are marked by deep rift valleys

Over centuries the rift valleys are widend by magma rising from the asthenosphere, which cools and solifies to form new crust

Volcanic eruptions along the ridges can build submarine volcanes - which may eventually grow to rise above sea level creating volcanic islands

Question 6

Can constructive plate bpundires (ocean ridges) cause earthquakes

Answer 6

Yes

Regular breaks (transform faults) cut across ridges at right angles to the plate boundary - seperating sections of the ridge

They may widen at different rates which leads to frictiona stesses huilding up - shallow focus earthquakes

Question 7

Describe the location of the Mid-Atlantic Ridge

Answer 7

Submerged mountain range

15,000km through Atlantic Ocean from iceland to a point 7,200km east of Argentina

Question 8

Giev some of the volcanic islands formed by the Mid-Atlantic Ridge

Answer 8

Iceland

Tristan du Cunha

Question 9

How fast is the Mid Atlantic Ridge widening

Answer 9

3cm per year

Question 10

Explain sea floor spreading

Answer 10

Hot buoyant mantle rises up a mid-ocean ridge, causing the ridge to rise upward.

The hot magma at the ridge erupts as lava that forms new seafloor.

When the lava cools, the magnetite crystals take on the current magnetic polarity and as more lava erupts, it pushes the seafloor horizontally away from ridge axis.

The magnetic stripes continue across the seafloor. As oceanic crust forms and spreads, moving away from the ridge crest, it pushes the oceanic lithosphere away from the ridge axis.

Question 11

What is a rift valley

Answer 11

Continental divergence

Lithosphere streches, causing it to fracture into sets of parallel faults.

The land between these faults collpases into deep, wide valleys that are seperated by upriht blocks of land called horsts

Minor earthquakes + risingmagma forming shield volcanoes (Mt Killimangaro)

Question 12

How do rift valleys form a new sea

Answer 12

The deep valleys fall bellow sea level so a linear sea starts to form. As the plates continue to split this will become a new ocean

Question 13

At destructive plate bounders, if both are oceanic plates ten which one will subduct

Answer 13

Same density so the one with the largest mass (pacific plate)

Question 14

What landfroms are created at destructiove margins

Answer 14

Composite cone volcanoes (oceainic continental + oceanic - oceanic)

Fold mountains (continental - continental)

Question 15

Is old or young rock created at destructieb boudnies

Answer 15

At subductive (oceainic continental + oceanic - oceanic) young rock will be created. Subduction esnures mantel material rises above the plate surface and cools to form new rock

At fold mountians, old rock will be formed as their is nto vlcanic activity (magma not present)

Question 16

What is the type/charatristic of lava found at destructive

Answer 16

Viscious, high levels of ash/silica, explosive (andesitic)

Question 17

Why is destruictive lava explosive

Answer 17

Sea water dragged into mantle

creates steam and makes lava more acidic

Question 18

Give an example of an oceanic - continental destructive margin

Answer 18

Nazca - South American plate

Question 19

Give an example of an oceanic - oceanic destructive margin

Answer 19

Carabein - South American

Question 20

Give an example of an continental - continental destructive margin

Answer 20

Indian - Eurasian

Question 21

Explain the surface proccesses occuring at oceanic - cointinetal destructive plate margin

Answer 21

Oceanic lithospher subducts beneath the continetal plate beacuse it is denser

The exact point of collsiion is marked by bending of the oceanic plate to form a deep ocean trench such as the Peru-Chilie trench

As the two plates converge, the continetal land mass is uplifted, compressed, buckled and folded into chains of fold mountains (Andes)

Question 22

Explain the melting proccesses occuring at oceanic - cointinetal destructive plate margin

Answer 22

The descending oceanic plate starts to melt at depths iof 100Km +. The zone of melthing is caused the Benioff zone. Melting is caused by increased heat and friction

This friction may also lead to tension building up, which may lead to deep focus earthquakes

The melted oceanic plate creates magma which is less dense tahn the sorrounding asthenosphere ans, thereofre rises in great plumes

Passes through faults in buckled continetal plate, magma edventially reaches the sufcae to form explosive eruptions

Question 23

Explain the proccess occuirng at Oceanic- oceanic destructive plate margins

Answer 23

The oceanic plate with a higher mass or speed subducts beneath the other leading to the formation of a deep oceanic trench and melting

Resulting rising magma from the benioff zone forms crescents of submarine volcanoes along the plate margin which may grow to form island arcs

Continued subduction of the oceanic plate brings sea water, locked in the oceans crust deep into the mantle. Explosive andesite lava formed

Question 24

What are island arcs

Answer 24

Long chains of volcanic islands - typically formed where oceanic crust meets oceanic rust at destructive margins

Question 25

Explain the formation of island arcs

Answer 25

From subduction - hot magma leaks out of fractures in the crust- cuaisnga. series of volcnoes to form an island arc

Magma plumesm, an upswelling of abnormally hot rock within the mantle can also form island arcs through hotspot actvity. The plate passes over the magma plume ans weaknesses in the crust allow it to excape onto the surface as an active volcano

Question 26

Decribe the charaticristcs of anesitic lava

Answer 26

Less dense than the sorrounding mterial and can have a tempature of 1000ºC

Viscious, trpaping gas inside at it rises. This water and gas accounts ofr its exploive activity

Question 27

Explain continetal continetal destructive plate margins

Answer 27

Continental plates have a much lower density than the asthesnopsher beneath them so subduction does not occur

They become uplifted, and buckle to form high fold mountains (Himmilayas)

Volcanci activity does not occur an there is no subduction, but shallow focused earhquakes can be triggered

Question 28

Himmilayas still rising by more than…cm per year as India continues to move north into Eurasia

Why then are the Himmilayas not rising

Answer 28

1

FOrces of weatehringa nd erosion are lowerig the Himmilayas at about the smae rate

Question 29

What proccess occurs at conservatiev plate

Answer 29

Smae directions t different speeds

or oppositie directions

Question 30

Give an example of a conservative plate

Answer 30

Pacific - North America (San Andres Fault)

Question 31

Conservative plate margins are also known as………………

Answer 31

trasnform faults

Question 32

Describe conservative margins

Answer 32

Mainly found ont eh ocean floor where they offset mid ocean ridges and enable the ocean to spread at different rates

Relative movemnt is horizontal

Lithosphereis neither crated or subducted

No volcanic activity or formation of new crust

Site of extensive shallow earthquakes

Question 33

Why is the relative movemnt of the North AMerican Plate to the SE

Answer 33

Although both plates move West, the Pacific plate is moving faster that the N.A plate (6cm per year comapred with 3cm) so the relatiev movemnt = South East

Question 34

Exlain Conservative margins

Answer 34

Friction between the plates stop them moving. Fores build up to overcome the friction. Pressure suddenley relaeased casuing plates to jolt past each other

Cause shallow focus earthquakes - exacerbating the impact felt

Question 35

How do magma plumes form

Answer 35

Radioactive decay in the Earth’s core generates hot tempatures.
If the decay is concentrated, hots;ots will form aroudn the core

Heat the lower mantle creating localised thermal currents where magam plumes rise vertically

Burn throught eh lithospehere to create volcanic activity on the surface

Question 36

How don hotspots create islands arcs

Answer 36

Hotspot remains staionary, the movement of the overlying plate reults in formation of a chain of active volcanoes. Hawii

As oceanic lithosphere oves away, volcanic activity ceases, cools and becomes an island

Question 37

Dexcirbe Hawwi’s volcanoes

Answer 37

Often very wide, shied volcanoes

Basaltic lava flows

Mauna Loa