Earthquakes are caused by energy released from tectonic plates shifting beneath the earth's surface, while volcanoes are mountains that trap gas and vapor underground until intense pressure forces an eruption. Earthquakes can cause the ground to shake violently, creating hazards, such as rockslides, falling objects and collapsed buildings. Active volcanoes become dangerous when they cause avalanches or eject lava and ash, burning nearby cities or terrain and polluting the air.
Earthquakes and volcanoes often occur near plate boundaries and fault planes, so they commonly affect the same geographic regions. Earth is made up of large blocks, or tectonic plates, that continually move and slide past one another. These plates build up energy as they move, and their roughened edges, known as boundaries, can accidentally become jammed against other plates, producing a fault plane. As the body of each plate continues to move, the plate edges are wrenched free and the surrounding earth experiences a "quaking" vibration.
Tectonic plate activity can also trigger volcano formation when sections of the earth's crust shift apart or push together. When plates slide away from each other, the heat and pressure from the earth's core can force magma up through the gaps. When plates collide, they can produce strong impact that causes pieces of the Earth's crust to collapse inward. The caved-in crust becomes overheated and pushed upward by the Earth's interior heat. In both scenarios, the unstable plate activity creates hotspots in the Earth where gas and magma continually collect and add more layers of rock to the volcano after each eruption.