Home » Earth Science » Earth’s layered structure » Action at plate boundaries

Action at plate boundaries

Content objective:

What are we learning and why are we learning this? Content, procedures, or skills.

Vocabulary objective

Tier II: High frequency words used across content areas. Key to understanding directions & relationships, and for making inferences.

Tier III: Low frequency, domain specific terms.

Building on what we already know

Make connections to prior knowledge. This is where we build from.


Convergent boundary:

actively deforming region where 2 (or more) tectonic plates toward one another.

As a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent boundaries.

When plates move towards one another, they form either a subduction zone, or a continental collision.

In a subduction zone, the subducting plate, normally a plate with oceanic crust, moves beneath the other plate (either oceanic or continental crust.)

During collisions between two continental plates, large mountain ranges, such as the Himalayas are formed.

{ adapted from Wikipedia, Convergent boundary }

convergent plate

What happens when two continental plates converge? Mountain building
{ http://geologycafe.com/class/chapter3.html }

When continents collide mountains belts form. Examples:
* Himalayas
* Alps
* ancient Appalachian Mountains (northeastern USA)


Divergent boundary is when two of the Earth’s plates move apart

Most are located on the crests of the mid-ocean ridges.
Divergent boundary in the ocean
New oceanic lithosphere is created here. Rock added to the ocean floor.

When this happens on a continent, it is called “rifting”, and can literally split a continent apart.

divergent plate boundary

Divergent boundary in Iceland

divergent boundary_iceland

Transform boundaries

are where 2 plates grind past each other.
No new lithosphere is formed.

When plates slide past each other creating fault systems along plate margins. Examples:
* San Andreas Fault
* Pakistan
* Turkey
* Jordan River/Dead Sea
Transform plate boundary California

Three types of change

Divergent convergent Transform plate boundaries

continental rifting

Graben and rift formation


Isostasy (Greek ísos “equal”, stásis “standstill”) is the state of gravitational equilibrium between Earth’s crust (or lithosphere) and mantle such that the crust “floats” at an elevation that depends on its thickness and density.

{ http://geologycafe.com/images/crustal_thickening.jpg }

The state of balance, or equilibrium, which sections of the earth’s lithosphere (whether continental or oceanic crust) are thought ultimately to achieve when the vertical forces upon them remain unchanged. The lithosphere floats upon the semifluid asthenosphere below. If a section of lithosphere is loaded, as by ice, it will slowly subside to a new equilibrium position; if a section of lithosphere is reduced in mass, as by erosion, it will slowly rise to a new equilibrium position.


isotacy crustal_thickening

%d bloggers like this: