Study Note - The Restless Earth – Plate Tectonics

Plate tectonics is the theory that underpins all of modern geology – it informs our understanding of earthquakes and volcanoes. The theory states that there are tectonic plates – large segments moving around the Earth being created and destroyed at their margins. The plates are part of the lithosphere, which literally means ‘rock layer’.

The lithosphere is made up of the Earth’s crust and upper mantle, averaging about 100km in thickness. There are two types of lithosphere, which can exist on the same plate: continental and oceanic. Both types have their own set of unique features and characteristics, but the continental lithosphere is often much thicker than 100km.

There are three types of plate margin, each of which produces different landforms or natural hazards.

Constructive plate margins are also known as divergent margins, and both words describe what is going on at the margin well. At a mid-ocean ridge, where constructive margins are found, magma wells up as the two plates spread apart, creating new oceanic lithosphere. A destructive plate margin is also called a subduction zone, as it is where one plate is forced beneath another, destroying it.

There are three types of destructive plate margin, which will be elaborated upon in a more detailed study note. The last, and easiest to understand, plate margin is the conservative plate margin, which is where two plate margins move alongside each other, often in a strike-slip sequence, causing many earthquakes. The San Andreas fault in California is probably the most famous conservative margin.

WATCH THIS:

The United States Geological Service (USGS) have put together a beautiful, hour-long film about geological processes all over the globe. If you can get past the cheesy voiceover, watch the whole thing here: http://media.wr.usgs.gov/movies/index.html?id=living_rock

They begin talking about plate tectonics about 4 minutes in.