Ya it actually takes lava a couple weeks to cool depending upon how big the flow is. It would have to be linked to the current mark number. The more marks the eruption lasts, the longer it takes the lava to cool. Since there is a day/night cycle, it would be really interesting to add this taking into account the number of days. Basalt lava is the hardest there is. It has a high melting point and is usually impregnated with gasses from the mantle. Most pillow lavas are basalt. The gasses contained in the lava makes it thick and frothy. Flows of basalt are usually very dense, slow moving and slow to cool. For a basalt flow that lasted a week (5 day/night cycles in game) would take 1.5 times as long to completely cool. That means about 8 day/night cycles. This would mean that a moderate eruption would take very long to cool in terms of marks. (Eventually I will time a day/night cycle and see how many marks it is)
The first level of the Plymouth campaign takes only 1 day/night cycle to fill the map with lava. So for a feature like this to work, some parameters would have to be outlined to set the min and max duration of an eruption so that the time it takes to cool isnt so long that the lava never cools before the game is over. Having volcanoes erupt multiple times at random intervals would be interesting. You could set different volcanoes to erupt different kinds of lava. Basalt being the slowest to flow and longest to cool. Others would flow faster but cool quicker. I really like this idea.
