There are two types of lava most often seen on the Island of Hawaii, pahoehoe pronounced pa’ hoy hoy and ‘a’a pronounced ah ah.
Pahoehoe is a nice, soft, pillowy, brownie batter looking lava. There are some lumps, folds, and creases, but in general it takes on a smooth appearance.
Like a lazy river, it slowly meanders through the landscape. The flow front will often cool and stop only to have a small toe or lobe break out at a weak point in the crust up-slope, fill in what the initial flow missed, and continue on. A pahoehoe flow that was initially 50 meters wide can balloon to ten times that or more as a result of this stopping and starting. The slow and steady behavior is the result of a constant well insulated lava supply. While some molten rock appears on the surface, most of it is being channeled through a series of tubes to wherever the lava is pushing into new terrain. This type of flow can take years to play out.
‘a’a lava is very jagged and inhospitable looking. When a lot of lava is discharged in a short period of time, generally ‘a’a lava is formed.
Often ‘a’a lava will not move for days as it builds up pressure at the front, then blast forward all at once. Traveling on the surface, the ‘a’a lava cools quicker. This results in a dense, jagged crust resistant to flowing and causes the lava to build up pressure for the next big surge.
What type of lava is the June 27th lava flow sending towards Pahoa?
Slow moving and smooth.
Toe like breakouts upslope from the flow front.
I would say pahoehoe.
How do you tell what type of lava you are looking at? Walk across it barefoot. If you scream ahhh ahh! Then it is most likely ‘a’a. If it only causes mild discomfort then you are probably walking on pahoehoe. For an explanation from the experts, check out the Hawaiian Volcano Observatory’s Post from 1999.