Cold air IS less dense, sinks, holds less vapor
The Volga river is the largest river in Europe, so that should be the answer.
it gives you a certain direction, north, south,east,west, and in-between!
Convection is a process which transfers the heat between the temperatures when fluid (i.e. liquid or gas) is in motion. Due to the presence of heat source, water temperature increases and also it will become less dense and rise. Hot air is less dense than cold. When air rises higher in the atmosphere its pressure gets down and it becomes colder.
