Theory/Basics

• There are three types of volcanic eruption: effusive (lava flows slowly), explosive (violent ejection of ash and rock fragments), and phreatomagmatic (explosion of water mixed with lava).
• Earth is divided into 7 major tectonic plates (or 8 if Indo-Australian plate is considered as two separate plates) (+20mil km2 area), 10 minor plates (1-20 km2 area) and 50microplates.  
• The Asthenosphere: a low-viscosity, plastic, partially molten layer on which lithospheric plates can slide  
• Seismic waves: vibrations generated by earthquakes or other disturbances that travel through the earth at different speeds depending on their type.
• P wave: primary seismic wave; travels fastest and causes compression and expansion of rocks it passes through.
• S wave: secondary seismic wave; slower than P waves but faster than L waves; causes shearing motion between layers of rock.
• L wave: longitudinal seismic wave; slowest to travel; causes horizontal movement of particles within the ground.