Plate boundary

The lithosphere

The lithosphere is broken up into large sections called plates.

There are 7 major plates and several minor plates.

theory of continental drift

according to the theory of continental drift

plate tectonic occur due to forceful convection currents within the earth’s mantle heated by the earth’s core.

constructive plate boundaries (divergent plate boundaries)

regions where plate tectonics move away from one another.

This separation results in

• volcanic activity

• the formation of new crust

• geological features such as mid ocean ridges and rift valleys.

Rift valleys - Continental Crust

when a constructive boundary forms on a continental plate, the thick crust stretches and thins as it is pulled apart.

The separation causes the crust to sink, forming a rift valley, a steep sidded depression.

E.g East African Rift valley

East African Rift Valley

runs through Eastern Africa and is one of the most active continental rifts in the world.

formed as the african plate and the smaller Somali plate pull away from each other.

Over time this region may expand if the rifting process continues. This could result in the formation of a new ocean.

East African Rift Valley is an example

how constructive plate boundaries can affect continental landmasses.

It also shows the long term impact of tectonic activity on the Earth’s landscape.

In this region volcanic activity and earthquakes are common as the crust adjusts to the tectonic forces

Mid ocean Ridges on oceanic crust

Oceanic crust is thinner than continental crust meaning the separation of the plates can cause a gap called a fissure to appear.

This fissure allows magma from the mantle to rise to the ocean floor.

Mid ocean ridge when it reaches the surface

as the magma reaches the surface, it cools and solidifies forming basaltic rock.

Over time this continuous process results in a mid ocean ridge, a long elevated feature on the ocean floor formed by the collection of cooled magma.

exaple of mid ocean ridge

Mid Atlantic Ridge, stretches 16,000 kilometress along the bed of the Atlantic ocean.
This ridge marks the boundary between the

• Eurasian and North american plates in the north

• South American and African plates in the south

when these plates pull apart, magma rises to fill the gap and creates a long mountain range on the earth.

In some places the peaks emerge above sea level.

Volcanic activity

Magma rises to the surface at constructive plate boundaries and forms volcanic mountains along mid ocean ridges.

if the volcanic activity is intense enough to reach above the ocean’s surface, it can create new island, e.g Iceland.

sea floor spreading

Active volcanoes along constructive boundaries result from high pressure and heat in the mantle, pushing magma through the fissure.

This process contributes to sea floor spreading

new oceanic crust is formed and slowly pushed away from the ridge as more magma solidifies at the plate boundary.