Answer
Tectonic plates are parts of the earth's crust. There are cracks in these plates that allow magma to seep through and build-up which creates volcanic eruptions. Volcanos themselves are created by the earth's plates pushing against each other and slowly, over time, rising to create these large raises in the crust. Earthquakes are caused by these plates creating friction against one another until they forcefully overlap or rip apart, hence the shaking effect during an earthquake.
