This was taken in Jaggar Museum. This is a diagram of how a Lava Tree Mold forms. A real tree mold. There are two major types of Hawaiian Lava. Theses are Pahoehoe, and A'a lava.
Pahoehoe lava is very smooth and ropey type of lava.
Pahoehoe lava forms and travels through a lava channel. It tends to have a low eruption rate and cools slowly which means it has a low viscosity. A'a lava is very spikey and it is very rough. You probably wouldn't want to walk on this type of lava barefooted. A'a lava flows through lava channels.