INFLATION FEATURES ASSOCIATED WITH THE MCCARTYS LAVA FLOW, ZBVF, NM
Crack depths suggest a minimum of several months for the emplacement of the flow, but depending on the whether the whole flow was one more or less continuous flow or a series of discreet pulses or eruptive phases, the actual duration of the emplacement may have been much longer. This raises an important issue regarding the origin of terracing within pahoehoe flow fields. Are the plateaus, the result of successive flows stacking on top of one another in a “layer cake” fashion? Are they the result of a single sheet-like lobe with differential inflation occuring due to the development of preferred lava emplacement? Or is the construction process more complicated, with initial lobes helping to confine subsequent flows that in turn invert the topography through inflation and create new barriers for later flows? Mapping of flow units exposed in the Lava Falls area provides evidence in support of the latter scenario, with at least 10 phases of lava emplacement that can be distinguished on the basis of cross-cutting relationships, crack patterns, and surface textures. The later phases of lava emplacement produced small flows and lobes that originated from different levels within the extensive plateaus implying a complex emplacement and cooling history of the overall flow. This implies that partial burial of plateaus margins by younger breakouts may obscure the true thickness of the each plateau and that the overall duration of emplacement was much longer than the crack depths at any one location would suggest.