To VolcanoWorld
This lava is called toothpaste lava and it is kind of a transitional form between pahoehoe and 'a'a. It develops when the lava has cooled enough to have a high viscosity but when it is only flowing slowly. The ridges are formed because the orifice through which the lava issued had irregularities. The bulges are formed when the lava comes out in pulses rather than at a constant rate. (January 1984)
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