What causes earthquakes and volcanic eruptions to happen in certain places and not others?

Some places have boundaries and some do not have them

It depends if you're on a vault or hotplate. Just off the Oregon coast, there is a large hot plate, putting them at risk of an earth quake. It made their ocean floor drop 4 feet, which is a sign a large earthquake will hit.

Amath expression is a collection of one or more terms, which are separated by the signs ( + , - , x , / ).example :   8+b8+b  or  a−3a−3in algebra, an equation is a mathematical statement with two expressions where, each expression is separated by an equal (=) sign. variables can be present on both the sides of the equality (=) sign and we use letters to denote such variables.example 1:   x=4+2x=4+2  , [here, we can observe that the variable is present only on one side of the equation].example 2:   2x+3=x+42x+3=x+4  , [here, we can observe that the variables are present on both side of the equation].