The two types of lavas in Hawaii are pahoehoe and a'a. Although these two lavas have the same chemistry, they are very different.
Pahoehoe lava has a ropey, billowy look to it.
This is caused because it has a lower viscosity. That causes less cooling, so only the surface cools while the rest of the flow is still magma. This type of lava travels through lava tubes, like the Thurston Lava Tube we visited. Pahoehoe lava A'a Lava A'a lava has a spinier, pointier apperance. It dries while its flowing, causing it to tumble over the dry parts making it more fragmented and jagged.