What is the main cause of earthquakes and volcanic eruptions?

Answer 1

Volcanoes are formed by increased tectonic plate pressures which force molten rock (at that stage known as Magma) up through weak points in the Earth's outer crust and mantle. Magma usually builds up inside a Magma chamber, which is a fancy name for a big cave underground. At a certain point, pressure will build inside the magma chamber to such a level that the magma will force itself upward through the Earth's crust, causing an eruption. When the magma erupts and begins flowing at the surface, it is then referred to as Lava.

If the magma chamber is close enough to the surface, it will actually raise the surface of the crust to either modest or high altitudes, and the eruption and subsequent lava flow over the resulting ground deformation begins a volcanic mountain.

Repeated eruptions over thousands and millions of years, and repeated lava flows are what create Volcanic mountains that are so familiar. After the eruption subsides (as the magma chamber empties to the surface and the pressure is released) the cycle begins again. At the surface over time, the Volcano's crater will sometimes fill in, or in many cases fill with water, creating a lake. Over time though, the magma chamber will fill again, and the pressure will increase. Occasionally, earthquakes caused by tectonic plates sliding will ease pressure in the magma chamber and extend the eruption cycle. But eventually with most established volcanoes, eruption is a certainty at some point, and more lava flows will increase the height of the mountain.

Occasionally, the eruption is so violent that it will literally blow off the top of the volcano's mountain that has built up over many years. Mount St. Helens was such an eruption, as was Krakatoa in the 1800's, and Vesuvius near Naples in Italy. One famous eruption in the Mediterranean is the island of Santorini, which in 1630 BC was so violent it destroyed much of the island itself.

Super Volcanoes are the most destructive - we have not seen one during the period of human existence (which by historical Earth standards hasn't been that long). The most notable is Yellowstone Park - the caldera (the center inside the cone where the magma bursts through) is literally miles across, as is the magma chamber. Such an eruption will be an ELE, or Extinction Level Event, due to the amount of ash and rock it will eject into the atmosphere.

Answer 2

when earths plates collide they go up causing earthquakes ad volcanoes are when a build up of magma and rock builds up under the earths crust when it gets so powerful the magma breaks through the crust and goes up in to the volcano then it erupts