By mapping population density, the concentration of rivers, and the gradient of streams using gis, geographers were able to

Magma is outside the volcano  and lava is inside the volcano. 

So  if  the sum of the enthalpies of the reactants is greater than the products, the  reaction  will be  exothermic.  if  the products side has a larger enthalpy, the  reaction  is  endothermic. you may wonder why  endothermic reactions, which soak up energy or enthalpy from the environment, even happen

Ido believe it is b