Both volcanoes and earthquakes occur due to movement of the Earth’s tectonic plates. They are both caused by the heat and energy releasing from the Earth’s core. Earthquakes can trigger volcanic eruptions through severe movement of tectonic plates.
The outer layer of the Earth is made up of solid rock, called lithosphere. The lithosphere is broken up into 17 major separate pieces that fit together like a bad jigsaw puzzle. A piece of the puzzle is called a tectonic plate. The plates are horribly placed, with overlapping pieces, gaps, and are forced to fit with each other even when they don’t. Because the tectonic plates don’t go well together, it creates earthquakes and volcanic activity when two plates collide, diverge or slide past each other.
Both volcanoes and earthquakes are caused along the boundaries of tectonic plates due to their movements and interactions.
How many deaths there are and how severe a natural disaster is depends on the interactions we have as humans with our environment. A strong earthquake can be completely overlooked if it happens in the middle of land where hardly any people live in, for example in December 2003, when a 6.5 magnitude earthquake in Central California killed two people. Consequently, a similar earthquake in a densely populated metropolitan area can cause many deaths, injuries and destruction of property, for example, a 6.6 magnitude earthquake in Bam, Iran killing 30,000 people, injuring 30,000 more and destroying 85% of property.
The same goes for volcanic eruptions, if an underwater volcano erupted in the middle of the ocean, it would have little impact to humans living far inland. However, if the volcano had been dormant for a significant amount of time and humans started populating the land close to the base of a volcano it would be devastating should it ever erupt. Further, indirect consequences of a volcanic eruption can have a greater impact than the eruption itself. For example, volcanic ash can induce climate change that have serious agricultural, economic, and sociological impacts on people’s lives.
Tsunamis are giant waves that occur when a large volume of water is displaced. The most common causes of underwater disturbances that lead to tsunamis are earthquakes and volcanic eruptions, especially because most volcanoes are underwater. Although tsunamis can also be caused by landslides, meteorite impacts and underwater explosions. Tsunami waves travel extremely fast, with wave speeds reaching up to 900 km/h in deep water. The waves get taller the closer they reach the shoreline because of rapidly decreasing depth of the sea floor, and slow down to 20 – 50 km/h.
The bulk of this explanatory text came from the Australian Museum.