Hazards (Landforms)

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What are the features of Continental Crust?

Older, lighter, silicon, aluminium

What are the features of Oceanic Crust?

thicker, younger, heavier, basalt, magnesium

Define the features of Constructive plate margins

• Plates move away from each other.

• New lithosphere is created

• Produces Ocean Ridge Systems (over 90% of mountain ranges lie at an average depth of 2,500m underwater)

• e.g. the Mid Atlantic Ridge or the Galapagos Ridge

• Also produces Rift Valleys

• e.g. the Great Rift Valley of East Africa. Rising magma caused the whole region to be uplifted creating weaknesses in the crust. Low viscosity basalts emerged and flooded the area.

• As with oceanic ridge, partial collapse of the crust causes deep, steep sides rift valleys.

Outline Destructive (Convergent) plate margins

• When lithospheric plates move towards each other

• The nature of the boundary depends on the combination of plate types

Describe Ocean/Cont. convergence in the formation of Deep Sea Trenches

• Denser oceanic plate is forced under the lighter continental plate in the process of SUBDUCTION.

• The downward displacement (DOWNWARPING) of the oceanic plate forms a DEEP-SEA TRENCH that runs parallel to the plate boundary

• e.g. the Marianas Trench

Describe Ocean/Cont. convergence in the formation of Young Fold Mountains

• During subduction process, sediments process, sediments that have accumulated on the edge of the cont. plate are deformed by folding and faulting and then uplifted to form these landforms.

• e.g. the Andes

• These are parallel chains of high volcanic mountains.

Describe Ocean/Ocean convergence in the formation of Island Arcs

• The more dense oceanic crust subducts beneath the less dense oceanic crust generating these landforms.

• On the West side of Pacific: the Pacific Plate is being subducted beneath the Philippines Plate, a line of islands such as Guam and the Marianas are formed from magma upwelling from the Benioff Zone.

Describe the features of Cont./Cont. Convergence (Collision Boundary) in the formations of Young Fold Mountains

• If two low density cont. plates converge, there is NO subduction

• Sediments are forced upwards.

• e.g. Indo-Australian Plate is being forced northwards into the Eurasian Plate, forming the Himalayas.

Describe the Nature of Conservative (passive) plate margins

• when two plates pass each other, parallel to the plate margins, no subduction and therefore no volcanic activity.

• The movements of plates creates stresses between plate margins.

• Sudden movements of the plates trigger shallow focus earthquakes

• e.g. San Andreas, California

Explain the formation of Magma Plumes

• Volcanic activity away from a plate boundary

• Localised heating in the core/mantle caused a bubble of magma to rise and ‘eat’ through the crust called a HOT SPOT

• Where magma rose to the surface, active volcanoes were formed.

• As the tectonic plate continues to move away from the hotspot, it takes the formed volcanoes with it, where they cool and subside.

• Atoll, chain islands and seamounts can form.

• e.g. Hawaiian Hotspot