Week 3 - Initial Landscapes

Question 1

What are Volcanic Processes/Initial Landforms?

Answer 1

The extrusion of magma (molten rock) at the Earths surface produces a variety of different landforms

*The size and shape of these landforms reflects the composition and properties of the magma

Question 2

What are volcanoes made of?

Answer 2

Dome shaped, made up of

Question 3

What are the form main types of Volcanoes and what landscapes do they produce?

Answer 3

1. Shield Volcanoes - Broad mountains with gentle slopes, mostly made of lava which are able to travel great distances.
   *very fluid basalt lavas with little contained gases.
   Often located within plate interiors and associated with hotspots.
2. Scoria (cinder) cones - small steep sided, made of basalt blocks and fragments, from short lived mildly explosive eruptions
3. Stratovolcanoes (classic) - conical shaped with steep slopes, often large mountains. called composite because they are made of alternating layers of lava & tephra, magma of andesite composition, more gas rich so explosive eruptions, associated with subduction and convergent boundaries.
   * pyroclastic flow - full of ash and steam wiping out all in its path
4. Calderas - large collapse craters up to 30km long, formed by the most violent super volcano eruptions, highly explosive, gas-rich rhyolite magma
   * roof of the magma chamber collapses after a violent ash flow leaving roof unsupported

Question 4

Local Volcanic Features

Answer 4

Fence lines
Bluestone Buildings
Alluvial terraces

Question 5

Describe 2 types of Tectonic processes

Answer 5

FOLDING

• plate convergence compresses the crust and folds rock strata
• they can be synclines, where the limbs turn upwards or anticlines where the limbs fold downwards
• produces fold belts where the land surface is buckled into linear anticlinal ridges

FAULTING

• tectonic forces can cause rocks to break
• fractures in rocks across which rocks on each side have been displaced
• can be NORMAL under extension (block drops down, no overhang) or REVERSE under compression (block pushes up, overhang)
• other faults can be strike-slip, where the two sides laterally pass each other
• fault movements cause earthquakes

Question 6

Discuss Faults

Answer 6

Normal faults normally occur in parallel arrays
Uplifted ‘horsts’ alternate with downdropped ‘garbens’
Complex large scale faults are rifts valleys and block mountains

Question 7

What are Rift Valleys?

Answer 7

Are large complex linear depressions controlled by extensive normal faulting.
Produced by extension and accompanied by volcanic activity
*magma rising up to the surface due to thinning of the crust
*may develop into divergent plate boundary

Question 8

What are Block Mountains?

Answer 8

Often formed by many large fault blocks rotating during extension
Each ‘tilt block’ forms a separate range