Biophysical Interactions

The Lithosphere

The lithosphere (from the Greek for "rocky" sphere) is the ‘solid’ part of the Earth and is made up of the top of the upper mantle and the continental (under the continents) and oceanic (under the ocean) crust.  The lithosphere is approximately 100km thick and the thickness is an indication of its age.  This means that the thicker sections are older than the thinner sections.  Oceanic crust is only about 5km thick but made of very dense material whereas the continental crust can be up to 65km thick but is made of less dense material.  The continental crust is older than the oceanic crust.

Figure 1:  A Cross-Section of the Lithosphere
(Source: originally from Glencoe text, Earth Science.)

The cross-section above shows the layers of the lithosphere.  As you can see the oceanic crust (the Earths crust that is under the ocean) is much thinner than the continental crust (the crust under the dry land surfaces).  The oceanic crust is thinner because as the tectonic plates (the plates that move like lily pads on the less solid part of the mantle) move and collide, they stretch the oceanic crust and produce new crust along the boundary lines such as the mid-Atlantic ridge.  Subduction zones are located at tectonic plate boundaries where oceanic crust is pulled (subducted) underneath either continental or oceanic crust where it is subjected to enormous temperatures and pressures and becomes part of the mantle again.  Oceanic ridges (such as the mid-Atlantic Ridge) are basically underwater volcanic ridges which provide a way for the mantle the ‘resurface’ and form new oceanic crust.  The diagram below shows you how this occurs.  

Figure 2: A Cross-Section Showing an Ocean-Continent Subduction Zone

The cross-section above shows how an oceanic plate moves under a continental plate.  An example of where this occurs is in the Peru-Chile trench off the west coast of South America (see map below).  You can see that as one plate moves under the other it slowly becomes part of the material in the mantle (the Asthenosphere) underneath.  The continental crust remains relatively unchanged except for the formation of what are known as ‘volcanic arcs’ which are what forms high mountains ranges such as the Andes and the Himalayas.  The continental lithosphere/crust is thicker under these mountain ranges to support their immense weight.  A trench usually forms near the boundary between the continental and oceanic crust

Figure 3:   A Cross-Section Showing an Ocean-Ocean Subduction Zone

The cross-section above shows how an oceanic plate moves underneath another oceanic plate.  An example of where this occurs is Marianas Trench south-east of Japan (see map below).  Again as one plate moves below the other it slowly becomes part of the material in the mantle below (the Asthenosphere).  In this case ‘island arcs’ are formed which is how islands such as Hawaii, Tonga and Fiji were formed and continue to change and grow.  A trench still forms in this scenario and can be found on whichever side of the island arc that is closest to the plate that is being subducted.

Figure 4:  A Cross-Section Showing a Continent-Continent Subduction Zone

The cross-section above shows how a continental plate moves underneath another continental plate.  An example of where this occurs is between the Indian-Australian Plate and the Eurasian Plate which is located where India/Nepal meets China.  This is how the Himalayas and the Tibetan Plateau were formed and continue to grow and change.  A trench does not form in this scenario instead a high plateau forms next to the mountain range on the plate which is not being subducted.  The lithosphere is thicker under the maintain range in order to support the massive weight.  This is known as the mountain root.

The map below shows the location of what is known as “The Ring of Fire”.  The ‘Ring of Fire’ describes a number of locations around the Pacific Ocean where frequent earthquakes (approximately 90% of all the earthquakes in the world) and volcanic eruptions take place.  The ‘Ring of Fire’ has formed due to the locations of tectonic plate boundaries which is where tectonic plates ‘bump’ into one another.  It should be noted that as Australia currently (this was not always the case) sits close to the middle of the Indo-Australian Plate we do not experience the major earthquakes or volcanic eruptions that our neighbour New Zealand does (see locations of the world tectonic plates on the map below).  The deepest place on Earth is located in the Marianas Trench and is 11km deep.

Figure 5:  The Ring of Fire – The Locations of Some Subduction Zones

The map below shows the locations of all of the major tectonic plates of the world.  By comparing this map to the one before you can see that where these plates meet is also where subduction zones tend to occur.  The small red arrows indicate in which direction each plate is moving in relation to the one next to it.  Arrows pointing towards one another means there is a subduction zone and one plate is moving under the other and two arrows pointing away from one another means the plates are moving apart which causes rifts or fracturing of the crust which often results in earthquakes.

Figure 6:   Tectonic Plates of the World

Students learn about the nature and functioning of the four components: the atmosphere, hydrosphere, lithosphere and biosphere in a specific biophysical environment including:
  • Atmospheric processes, climatic components, climatic variation
  • Operation of the water cycle and the role of water in geomorphological processes
  • Parent material, slope processes, weathering, mass movements, erosion, transport and deposition, and the fluvial, Aeolian and/ or coastal geomorphological processes
  • The variety and distribution of plants and animals and soil formation– cave environments
Students learn about the interactions between and the impacts on the functioning of the atmosphere, hydrosphere, lithosphere and biosphere.