03-12-2014, 06:15 AM
The difference between pahoehoe and a'a is based almost entirely on the relationship between shear forces and the viscosity of the lava. You will tend to see more a'a on steeper slopes since that increases the shear force beyond the ability of the viscosity to remain fluid - kind of like when you stretch silly putty too fast - the shear force overcomes the viscosity of the silly putty and it snaps. Stretch it slower and it remains more liquid. I'm not entirely sure that Carey is correct that a'a is slower as it is the faster pace on steeper slopes that cause it to become 'chunky', but I'm sure someone (possibly even Carey) will correct me if I'm wrong.
Source: http://volcano.oregonstate.edu/what-are-...-they-form
Source: http://volcano.oregonstate.edu/what-are-...-they-form
Me ka ha`aha`a,
Mike
Mike