 The lithosphere is broken up into what are called tectonic plates. In the case of Earth, there are currently eight major and many minor plates  Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along plate boundaries.  The lithospheric plates ride on the asthenosphere. These plates move in relation to one another at one of three types of plate boundaries: Plate Tectonics

Video – Plate Tectonics

1. Divergent Plate Boundaries  Almost all the Earth’s new crust forms at divergent boundaries, but most are not well known because they lie deep beneath the oceans. These are zones where two plates move away from each other, allowing magma from the mantle to rise up and solidify as new crust.  Ex. Currently in the Atlantic Ocean.

2. Convergent plate boundaries  Subduction - one plate is pulled beneath another forming a deep trench.  The fate of the colliding plates depends mostly on the density of the interacting plates, as the denser will sink.  This forms a subduction zone above the sunken lithosphere: This forms volcanoes, mountain ranges, and islands.

 Transform Plate Boundaries  At transform plate boundaries plates grind past each other side by side. This type of boundary separates the North American plate from the Pacific plate along the San Andreas fault, a famous transform plate boundary that’s responsible for many of California’s earthquakes.  Sudden movements in the fault cause EARTHQUAKES!