They don't, they just get out of the way.
firefighters
firefighters or rain
Firefighters are able to stop a muck fire when the rain comes. The rain seeps into the ground to put out the fire. Or the fire runs into a lake.
Different methods have been used including: breaching the sides of a lava tube or channel, diverting the flow, constructing barriers, and bombing the lava flow. Another way to stop a lava flow is to increase the lava flow's viscosity by spraying it with water, increasing the rate at which gas escapes from the flow, stirring the flow, or seeding the flow with foreign nuclei .In Italy, engineers have installed retaining walls to try and slow down lava flows coming down the side of Mount Etna, on the island of Sicily. These walls did slow down the lava flows enough that they didn't reach inhabited land. In Hawaii, engineers bombed narrow lava tubes, forcing the lava to lose energy. And in Iceland, firefighters sprayed water on lava flows for nearly 5 months, cooling it so that it solidified early and didn't block an important port.
It is not possible to completely stop lava flow using barriers. However, barriers can be used to redirect the flow or slow it down by creating obstacles in its path. Cooling the lava with water or earth-moving equipment can also help in managing lava flows.
Generally, no. In unusual circumstances, possibly. If there were only a tiny bit of lava flowing at a very slow pace, then it would be conceivable that an average sort of tree could stop the lava.
Lava flows can be stopped or deflected by ridges, valleys and depressions in the ground.
Firefighters, fire & or park rangers, volunteers if they are able to, etc.
Put a block of anything into the hole that the lava is coming out of and it will stop. Works with water falls also.
There is no standard collective noun for firefighters, in which case a noun that suits the situation can be used; for example a crew of firefighters, a squadron of firefighters, a team of firefighters, etc.
The possessive form for the plural noun firefighters is firefighters'.
In many cases suburban firefighters will make larger salaries then big city firefighters for several reason.