You're likely thinking of pyroclastic flow - which is actually hot ash and gases rather than lava. Wikipedia has an article if you're interested. see related link.
Pyroclastic flow
It is forced to flow downhill by the Earth's gravity.
downhill
Downhill.
Gravity ! The source (or start) of a river is (usually) high up in a mountain or hill. As the water travels downhill, it combines with others - gradually widening and gathering pace.
downstream Resources: research and I'm smart as hell :P
Water flows downhill, and the topography of that region just happens to be downhill to the east.
Water flowing downhill as a thin sheet is called sheet flow
As with all rivers the Nile cannot defy gravity and therefore flows 'downhill'.
Rivers can flow in any compass direction, a river will always flow downhill.
They are wetThey flow downhill
Gravity, rivers flow downhill