Molten rock that lies beneath the Earths crust is called magma. Once that molten material reaches the surface and contacts air or ground it is called lava. Lava as it hardens has a multitude of colors, shapes and textures and forms new land mass.
Pahoehoe lava flows (1,100 to 1,200 c) are a very dense fluid core with a congealing surface. They can flow uphill or downhill and will flow around obstacles and barriers. Over flat even ground the lava forms a flat pancake surface, if there are obstacles the form will be bumpy, undulating or even rope like. Pahoehoe can be compared to a pan of soft brownie mix
A’ a lava flows (1,000 to 1,000 c) form a front and surface of clinkers that covers the molten core. Tumbling and falling at the front of the advancing flow these rough stoney pieces can pile up from a few feet to forty feet high or more. The loose jagged stones are light weight, spiny, sharp and erratically shaped. A’a lava is a loose surface treacherous to walk on and edges are abrasive or cut as easily as glass.