Distribution & Characteristics of Plate Boundaries
Plate tectonics
- The Earth's crust is broken into 15 large tectonic plates and a number of smaller ones
- The place where the plates meet is called a plate boundary
Tectonic plates
Types of plate boundary
- Volcanic eruptions and earthquakes most commonly occur at or near plate boundaries
- There are three main types of plate boundaries:
- Divergent
- Convergent
- Conservative
Divergent plate boundary
- At a divergent boundary the plates are moving apart
- The Mid Atlantic Ridge is an example of a divergent plate boundary
- Both volcanic eruptions and earthquakes can occur at this type of plate boundary
Divergent plate boundary
Convergent plate boundary
- At a convergent plate boundary the plates are moving together
- The denser, heavier oceanic plate subducts under the lighter, less dense continental plate
- The boundary between the Nazca plate and the South American plate is one example
- Both volcanic eruptions and earthquakes occur at this type of plate boundary
Collision Zone
- When two continental plates collide the rock which makes up the land is folded forming fold mountains
- An example of a collision zone is where the Eurasian and Indo-Australian plates meet forming the Himalayas
Convergent plate boundary
Conservative boundary
- At a conservative boundary the plates move passed each other in opposite directions or in the same direction at different speeds
- An example of this type of boundary would be the San Andreas Fault, California
- Earthquakes are the only hazard at this type of boundary
Conservative plate boundary
Hot spots
- At a hot spot the tectonic plate passes over a plume of magma:
- The magma rises to the surface through cracks in the crust
- As the tectonic plate moves slowly over the magma plume a line of islands may form e.g. Hawaii
Hot spot
Worked example
Study Figure 1 which shows a plate boundary along the west coast of South America.
Identify the type of plate tectonic feature shown.
(1 mark)
A. A divergent boundary | |
B. A hotspot | |
C. A convergent boundary | |
D. A conservative boundary |
Answer:
- C - A convergent boundary (where a dense oceanic plate converges with a less dense continental plate)
Earthquake distribution
- Earthquakes occur at all types of plate boundaries
- Most occur along the Pacific 'Ring of Fire' (approximately 90%)
Global earthquake distribution
Volcano distribution
- Most volcanoes occur at constructive and destructive plate boundaries
- The majority of active volcanoes (approximately 75%) are located around the rim of the Pacific Ocean called the 'Ring of Fire'
- Hotspots occur away from plate boundaries and are plumes/columns of magma which escape through the Earth's crust
Active volcano distribution
Exam Tip
When describing the distribution of hazards from a map ask yourself the following questions:
- What is the general pattern?
- Does the pattern relate to anything else for example the location of plate boundaries?
- Are they close to the equator or further away?
- Are they inland or coastal?
Use map features to help with your description: place names, compass rose, latitude and longitude.