Physical Geography

Theory of Plate Tectonics
Earth is divided into several plates which glide on top of the mantle.
Convection is believed to be what causes these tectonic plates to move.
Evidence of Plate Tectonics
– Fossil comparisons found along edges of continents.
– Ridges
– Glacial Striations, scratches bedrock and show us direction of ice
– Volcanic eruptions along conjectured plate boundaries.
– Shapes of continent would fit like a puzzle if pushed together.
Types of plate margins?
Subduction zones
Subduction zone?
When two plates collide and one slides under the other.
Divergent Margins?
Two plates spread apart, allowing magma to reach earths surface.
Transform Margin?
When plates glide past eachother
What is a volcano?
A conical hill or mountain formed by material of the many,e being forced through an opening in the earths crust.
3 types of volcanoes?
1. Composite
2. Shield
3. Dome
Composite Volcano?
– explosive
– steep sided
– eg. Mount Juji, Japan
Shield Volcano?
– non-explosive
– fast flow
– gently sloped sides
– eg. Newberry
Dome Volcano?
– thick lava
– slow flow
– eg. Puy de Dome, France
Define magma
Molten rock beneath earths surface
Define lava
Magma which has reached the earths surface
Define pyroclastics
Mixture of ash, dirt, dust and steam
I due for big earthquake in San Andreas Fault. Last one was 150 years ago. Due for one every 74-144 years.
Types of Mountain building
1. Folding
2. Faulting
3. Volcanic
When one plates slides under the other and some rocks are forced down and become part of the magma; others are forced up and are bent
When rocks crack and two sections move. Some move sideways and some move vertically and produce mountain valleys.
Magma rises from mantle and puts pressure on the surface rocks. When the volcano does not erupt the surface is pushed up to form dome mountains
What is weathering?
Refers to the mechanical, chemical and biotic breakdown of rock material
Weathering of rocks will depend upon varying factors such as:
– climatic conditions
– topography
– nature and structure of rock material
– vegetate cover
3 types of weathering are:
1. Mechanical
2. Chemical
3. Biotic
Examples of Chemical weathering
Eg of mechanical weathering
Frost shattering
Frost heaving
Salt crystal expansion
Eg of biotic weathering
Humid Acid
Mechanical wearing is
Breakdown of rock by physical stresses and strains
Chemical weathering is
Gradual decomposition of rock as the minerals react to atmospheric substances
Biotic weathering is
Breakup of rock matter due to vegetation
Chemical Oxidation is
Reaction of rock minerals with oxygen; changing mineral composition of the rock
Chemical Solution is
Removal of rock by acidic rainwater
Biotic geotropism is
Plants growing through fractures of rock caused by gravity
Mechanical frost shattering is
When temperatures are around freezing point and water enters fractures in rock during day and freezes over night
Mechanical exfoliation
Rock breaks off into curved sheets caused by cracks in the rock
What is mass wasting?
The downslope movement of weathered material under the largely unaided urging of gravity
2 types of mass wasting
1. Fast
2. Slow
Examples of fast mass wasting:
– mudflows
– rock falls
– landslides
Examples of slow mass wasting:
– earth flows
– soil creeps
– slumping
– solifluction
Slow solifouction
The continuous freeze and thaw cycles slowly moving weathered particles downslope
Slow earthflow
Stream of soil and rock material, saturated with water, flowing downslope under the pull of gravity
Fast mudflow
Rapid flow of debris that has become partially or fully liquified
Fast rockfall
Fragment of rock detached by sliding, toppling or falling along a vertical cliff
Erosion is
The movement of weathered material from one place to another by wind, water, ice or gravity
Deposition is
The process by which eroded materials are added to a new landform
Agents of erosion:
– water
– wind
– ice
– gravity
Examples of erosion
– Caves by waves over 1000’s of years.
– Coastal erosion by water entering cracks causing rocks to wash away
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