a) Earthquakes are measured using magnitude, which is a measure of the ground motion. (3) Earthquakes and volcanoes are usually formed along boundaries of plate tectonics. Most of the time, they are formed where the plates experience subduction, when a plate is pushed beneath another one.
b) Under the outer crust of the Earth (where we live) is the Earth's mantle. The mantle is very thick and extremely hot, but for the most part, it doesn't melt because the pressure inside Earth is too great for it to melt. Sometimes it does melt though, forming magma. This magma is described as a "liquid, molten rock." It is a unique substance, because it is part gas, part solid, and part liquid. Plate Tectonics are located under the crust and include a bit of the mantle. They are basically right above the mantle, and thus, the magma. Depending on how the plates come into contact with each other. If the plates move away from each other, the mantle is pushed up to fill the gap. Being that the pressure is not as great, the mantle melts into magma, and it hardens, forming more crust. If plates move towards each other, one can be pushed under the other, causing a trench where the water comes into contact with the mantle, which then melts into magma. This is called subduction zone volcanism. (1)
http://www.ruf.rice.edu/~leeman/islandarc2.jpg c) When volcanoes erupt, they eject lots of different things into the atmosphere, including sulfer, ash, and carbon dioxide. This can do a lot of damage to the earth, its creatures, and the atmosphere. This can result in numerous atmospheric reactions, including a reduction in solar radiation (because it forms clouds that both absorb and scatter the radiaton), lowering trophespheric temperatures (because the eruption can cause the lower stratosphere to consume more heat, leaving less for the tropesphere), and changes in the circluation patterns of the atmosphere.
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhO9K7efxjOITvnmYvoEgqcJ2k-UiDa0lIKAaD7xZj5X-3hKNylL1SM11hLkfv-hEU7fN32ctxHRESce9bVDnxrdLzCCQtKaroHUJhMOJZRnscmidl8mrY5X-cWrl8jp4djY4SB9CDy-bQ/s1600/VolcanicEruption%5B1%5D.jpgBibliography:
1. http://science.howstuffworks.com/nature/natural-disasters/volcano1.htm; How Volcanoes Work; HowStuffWorks Inc.; 2011
2. http://earthobservatory.nasa.gov/Features/Volcano/; Volcanoes and Climate Change; Jason Wolfe; 2000
3. http://earthquake.usgs.gov/learn/topics/measure.php; Measuring the Size of an Earthquake; EHP Web Team; 2009
4. (first picture) http://media.web.britannica.com/eb-media/53/4953-004-9D51CA25.jpg
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