'a'a and pahoehoe

Here you can see the two kinds of lava, 'a'a, a rough, gravelly rocky lava (the kind you put in your gas grill), and pahoehoe or rope lava, which is smooth and solid. Pahoehoe is fairly easy to walk on, although very uneven. 'A'a is very difficult to walk across, so the trail only crosses a field of it in the narrowest places.