Answer: elevation
, The boundaries of a watershed are determined by topography, which is the shape or the physical features of the land's surface. If the highest points of land surrounding a river were connected (like “connect-the-dots”), this line would form the watershed boundary.
Think of dirt and rocks . Common as they are they do mix and they are great examples of a outside mixture. This could give u the perfect idea or picture of what u need.
The energy produced by burning : -32.92 kJ
<h3>Further explanation</h3>
Delta H reaction (ΔH) is the amount of heat change between the system and its environment
(ΔH) can be positive (endothermic = requires heat) or negative (exothermic = releasing heat)
The enthalpy and heat(energy) can be formulated :

The enthalpy of combustion of naphthalene (MW = 128.17 g/mol) is -5139.6 kJ/mol.
The energy released for 0.8210 g of naphthalene :

A tornado! I think or it could be rain