Most people think that lava flows simply ooze forward and cool in place. But there is more going on than this simple version. Yes, flows ooze forward, but much of the mass of a lava flow arrives later, the flow can inflate to many times the volume as more lava arrives and lifts the crust from underneath.
A very close view of advancing pāhoehoe lavaHow many of us have played with molten wax from a candle, or perhaps simply watched a thick syrup or honey flow over a pancake? An observant person watches things like this and learns how materials behave. The problem is that these lessons, while valuable, sometimes do not translate well to all cases. Lava is a good example, it behaves much differently than many would expect.
