Lava flows are the most common volcanic formation on earth. Lava flows cover 70% of the earth's surface.
Lava is a non-Newtonian fluid. The behaviour of a lava flow is reproduced by a two-dimensional model of a Bingham liquid (plastic) flowing down a uniform slope. (Dragoni 1989).
Aa lava
Solidified clinkery lava. The surface is sharp and broken into many pieces. Walking over this surface can be dangerous because it is like broken glass. May be described as cauliflower or rubbly.
Blocky Lava
Lava which has broken segments a metre or more across. The surface is smooth and planar.
Pahoehoe Lava
Smooth lava flows. May be described as entrail, ropy, shelly, or slab.
Toothpaste Lava
Viscous lava which is squeezed through a gap in the lava flow crust.